MANUAL OF BOTANY ANATOMICAL AND PHYSIOLOGICAL FOR THE USE OF STUDENTS BY .ROBERT BROWN Honorary ^ofetary, and formerly President, of the Royal Physical Society ; Vice-Pr6Sqent of the Botanical Society of Edinburgh ; Comman- der anjd Government Agent of the Vancouver Exploring "-Ekpedition ; Botanist of the British Columbia Ex- pedition ; Botanist of the '67 Greenland M.A. Ph.Dr. F.L.S. F.R.G.S. Expedition, &c. &c. LECTURER ON BOTANY, EDINBURGH WILLIAM BLACKWOOD AND SONS EDINBURGH AND LONDON MDCCCLXXIV All Rights rescrvi'il PRINTED BY WILLIAM BLACKWOOD AND SONS, EDINBURGH. TO JOSEPH DALTON HOOKER, C.B. M.D. LL.D. D.C.L. V.P.L.S. DIRECTOK OF THE ROYAL GARDENS, KEW ; PRESIDENT OF THE ROYAL SOCIETY OF LONDON ; ETC. ETC. ♦ DEAR DR HOOKER, I know that the age of Dedications — wheji Dedi- cations simply 7neant fulsome flattery — is gotte by. But I trust that the respectful gratitude which a pupil owes to a master, and to one whose bright example and kindly words have stimulated him under 7nany discouragements —afid it may be with little success and 7nuch faint-heartedness — to tread the same path in 'life, never grows old. May I therefore be permitted to embrace the opportunity which the publication of the very modest task embraced in these pages presents, to express my sense of the value of your labours in the cause of botanical science, and of the many kindnesses you have ever shown me. '* Sic redit ad doviimim, quod fuit ante suum." With great respect, allow me to remain, DEAR DR HOOKER, Your faithful friend. ROB. BROWN. Digitized by tlie internet Archive in 2015 Iittps://arcliive.org/details/b21931902 PREFACE. If any apology is necessary for adding one more to the already existing text-books of Botany, it would be found in the ever-changing state of the science, in the new aspects it has assumed by the discoveries of the last few years, and by the ever-accumulating pile of materials which the industry of the busy workers in the French and German laboratories — for vegetable physiology is almost dead in Britain — are continu- ally pouring forth. The task I have laid out for myself in this Manual has been to digest, for the use of the student, this mass of material as perfectly as the natural difficulties and intricacy of the subject will admit of; to present in one view, within a moderate compass, an outline of the chief facts and researches scattered through hundreds of memoirs, brochures, volumes, transactions of learned societies, and journals in nearly every European language ; and, without overlaying the line of argument and reasoning, where such exists, with too great a multiplicity of facts and examples, to present, in a form fit to be assimilated by the really earnest worker, a compre- hensive view of the anatomy and physiology of flowering plants, as elucidated by the best teachers of our day. Whether I have succeeded in this laborious though unpre- tentious task, it is not for me to say. I can only hope that I have; for in order to do so, no labour has been spared. Upwards of twelve hundred separate papers and treatises, in German, French) English, and to a less extent in Danish, Swedish, Dutch, Spanish, and Italian, have been consulted vi PREFACE. —often without a greater reward than to obtain a single fact, which the exigencies of space have compelled to be rele- gated to a footnote or a parenthesis. To mention every datum discovered by the hundreds of workers in our science during the last forty or fifty years, even had this been advis- able, would have been impossible. I trust, however, that few facts of importance have been omitted, or the more important labours of any of my confreres passed over. To have thus un- intentionally done injustice to any one would be a sincere cause of regret to me. So rapid is, however, the advance of the science, that while these pages were passing through the press, interesting observations were being published which might have found a place in the body of the book under their proper headings. Such, for instance, not to enumerate foreign researches, are the observations of Professors M'Nab and Thisleton - Dyer on the Perigynium or Utricle of the genus Carex (Journ. Linn. Soc. Bot., xiv. 152, 154) — clearly proving from its development that it cannot be looked upon as peri- anthal or staminal (as Bentham ^ believed), but as bracteal, or " equivalent to the sheath of the foliage leaf; " and the addi- tional observations of Professor Dickie on the buds of Malaxis in the same journal (p. 180), confirming his former results, which I have noted in this text-book (p. 369). Every text-book must necessarily be more or less a compila- tion ; for the science of Botany has been built up by the com- bined labours of many workers, whose researches it ought to be a digest of. To make it anything else would be simply to convert an impartial resume of the state of the science into a one-sided view of the author's crotchets, regarding the value and truth of which he is the worst possible judge. I may, however, be allowed to mention, that in many cases I have delayed giving an account of any observations which seemed improbable, until by personal examination I had satisfied myself of their truth or erroneousness. This course, while in various cases helping to weed the pages of some useless matter, bulks little from any other point of view, and has delayed the 1 Nature, March 13, 1873. PREFACE. publiaation of the book considerably. In the plan of it, I have followed what experience has told most teachers to be the best way of introducing a student to the science, though I have avoided what in some eyes may be looked upon as a fault — the elaborate account of the development of plants, as usually given in German text-books. To have done so would have taken up much space both in text and woodcuts, without a corresponding advantage ; for without going over the work himself, it would have been impossible for the student to have followed it. I have, however, given the result of these obser- vations, which is the main thing. In a text-book, it is not only necessary to give the newest researches — for the newest and the truest are not always synonymous — but to give the views generally taught and believed' in. This repeated visits to all the chief botanical schools of Europe and America have enabled nae to do. Illustrations are supplied wherever absolutely necessary. Too many illustrations often not only confuse the student, take up space where it might be better employed, but take him from nature itself. Ten minutes' examination of the most common plant will teach more than an atlas of the best figures ever can. Those inserted here are, by arrangement with the publishers, chiefly from the excellent ' Elements de Botanique ' of M. le Professeur Duchartre, drawn by the Chevalier Rio- creux, and M. Germain de St Pierre's ' Nouveau Dictionnaire de Botanique,' to both of which works I have necessarily been much indebted. Others are supplied from the various sources noted. Some are original ; and for a few I am indebted to the accomplished pencil of Mr Roger Kennedy, Lecturer on Botany in the Andersonian University, Glasgow. As half the student's education is to know familiarly the names of the workers in his science, and to be enabled to ex- tend his knowledge by perusal of memoirs treating of special subjects more fully than the limited space of a text-book can, I have given a bibliography of each subject as fully as neces- sary. In every case I have scrupulously endeavoured to verify the refereaces ; and where I have not been able to do this, VIU PREFACE. the authorities are given for them. If accidentally I have omitted to give my authority for any fact, I must beforehand apologise to the unknown author, and plead that, as the book was originally to a great extent prepared as lectures for my own students, I might have neglected at the time to note the exact reference, and when too late was unable to do so. In two respects I have departed from the time-honoured conventionality prevailing in text-books. The science has got now so extensive, that if the student is to get in a "manual" of this nature anything better than a mere smattering of the well-worn facts of the science, so interlarded, as to be most repulsive, with technical names — in use, obsolete, or which ought to be abolished, or rather never to have seen the light of print — it is impossible to cram into one moderately-sized volume anatomy, physiology, classification of the natural orders, palseo-phytology, and phyto-geography. Either the volume must become inconveniently bulky, or the outline given be so meagre as to be next to useless. I have there- fore adopted the method now very generally coming into use both in lectures and text-books — viz., to divide the two de- partments of the science. Accordingly, in this volume only the anatomy and physiology of flowering plants are treated of. In another, the history of the science, the description of the natural orders, with the economic and medicinal plants, the extinct species, the method of studying the science, and the laws regulating the distribution of plants Over the world, ac- cording to the latest views, will be given. Both volumes, though complementary to each other, will be entirely separate treatises, each complete in itself. The description of the physiology of - the cryptogamia or flowerless plants I have not mixed up with that of the flowering ones. My own experience as a student and teacher of Botany, now extending to upwards of twenty years, as well as that of others with an infinitely wider knowledge of the requirements of the young botanist, has taught me that to do otherwise only embarrasses and confuses the student. The modes of reproduction in the lower orders of plants are so intricate and varied that they are PREFACE. IX better studied each under the head of the natural order to which it belongs. Accordingly, in the ' Manual of Botany, Systematic and Geographical,' the anatomy and physiology of the cryptogamia will be fully described. Microscopists are now so generally adopting the millimetre as the standard of measurement, that whenever I have occa- sion to notice observations in which the measurements are in this unit, I have not reduced them to the English standard. To enable the student imperfectly acquainted with the convenient decimal standard to do so, there is appended a table (p. xii.) of English and French lineal measures, as well as one show- ing the different thermometrical scales. The Index and Glos- sary will contain an explanation of almost every word in use not explained in the body of the book. Those who desire a fuller vocabulary will find it in the late Professor Henslow or Mr Cooke's excellent dictionaries of botanical terms (to both of which I have been often indebted), or in M. Plee's ' Gloss- ologie Botanique.' Coiners of botanical terms seem, however, too often to have forgotten that the names are for the science, not the science for the names. Every assistance rendered me I have carefully acknowledged ; but in writing the chapter on "The Ultimate Constituents of the Plant," my gratitude is especially due to Professor Johnson of Yale's works, and to my friend Mr J. Falconer-King, City Analyst of Edinburgh, for timely hints and assistance. Lastly, though in drawing up this resume of vegetable anatomy and physiology the writer has experienced what all compilers of such books must ever do — the accumulation of material beyond the power to make use of it — he trusts that throughout he has ever remembered John Dryden's advice, — " not to write all he can, but all he ought." R. Br., Cajtipst* Botanical Laboratory, School of Arts, Edinburgh, May 1874. " At the suggestion of M. Alphonse de Candolle, I have adopted the affix CampUerianus, to distinguish me— a not very difficult matter— from the late illustrious botanist of the same name. Table I.— For Converting Millimeters into English Inches and Decimals. A millimetre equals 0.03937079 English inch. Milli- metres. Inclies. Milli- metres. Inches. Milli- metres. lllCflCS. Milli- metres. Inches. Milli- metres. Inches. 661 26. 024 687 27. 048 / D 28. 071 / jy 29.095 30.119 662 26. 063 688 27. 087 714 28. Ill 74.0 29.134 766 30.158 663 26. 103 689 27. 126 7IS / A J 28. 150 74 I 29.174 30- 197 664 26. 142 690 27. 166 716 28. 189 29.213 768 30.237 665 26. 182 691 27. 205 717 28. 229 29.252 30.276 666 26. 221 692 27. 245 718 28. 268 744 / IT 29.292 770 30-316 667 26. 260 693 27. 284 7IQ 28. 308 74^ 29-331 771 30-355 668 26. 300 694 27. 323 720 28. 347 / 29.371 772 30-394 669 26. 339 695 27. 363 721 28. 386 74.7 /'+/ 29.410 77^ 30.434 670 26. 378 696 27. 402 722 28. 426 748 29.449 774. 30 473 671 26. 418 697 27. 441 723 28. 465 740 29 489 77 K /ID 30.512 672 26.457 869 27. 481 724 28. 504 7^0 29.528 776 30-552 673 26. 497 6qq 27. 520 725 28. 544 / 29.567 777 / / / 30-591 674 26.536 700 27. 560 726 28.583 29.607 778 30.630 67s 26. 575 701 27- 599 727 28. 623 753 29. 646 779 30. 670 676 26.615 702 27. 638 728 28. 662 754 29.686 780 30.709 677 26. 654 703 27. 678 729 28. 701 755 29.725 781 30-749 678 26. 704 27.717 730 28. 741 756 29.764 782 30.700 679 26. 733 705 27. 756 731 28. 780 757 29. 804 783 30.827 680 26. 772 706 27. 796 732 28.819 758 29.843 784 30.867 681 26. 812 707 27. 83s 733 28. 859 759 29.882 785 30. 906 682 26. 851 708 27- 875 734 28. 898 760 29. 922 786 30.945 683 26. 890 709 27- 914 735 28. 938 761 29.961 787 30.985 684 26. 930 710 27- 953 736 28. 977 762 30.001 788 31.024 685 26. 969 711 27. 993 737 29.016 763 30.040 789 31.064 686 27. 008 28. 032 738 29. 056 • 764 30.079 790 31. 103 Tenths of a Millimetre in the Decimal of an Inch. I 2 3 4 5 6 7 8 0. 004 0.008 0.012 0,016 0.020 0.024 0.028 0.031 XI Table II. — Comparison of the Centigrade Thermometer with Fahrenheit's and Reaumur's, giving the corresponding Values for each Degree, from + 50° to —41° Centigrade. Cent. Fahr. Keau. 1 , Cent. Falir. Reau. Cent. Falir. Reau. Cent. Falir. Eeau. 40.0 27 80.6 21 6 4 39' 2 3- 2 19 2. 2 15.2 4y 39.2 26 78.8 20, 8 3 37' 4 2.4 4.0 118.4 78 A JO. 4 77.0 35-^ 1.6 5.0 — 16.8 47 116. 6 37*^ 24 75' 2 19.2 33.0 0.8 — 7.0 17. 6 114.8 •j6 8 23 73' 4 18.4 32.0 — 23 — 9-4 ig,^ 45 ii3»o 36.0 22 71.6 30.2 — 0. 0 — 24 — 11. 2 — 19. 2 44 35-2 21 □9' 0 ID.O — 2 20.4 I. 0 —25 — 13.0 — 20.0 43 109.4 34-4 20 Do. 0 16.0 — 3 oA A 20. 0 — 2.4 20 — 14.0 ZO. 0 33*^ 19 66.2 15. 2 4 24. 0 — 3-2 —27 tA ID. 0 A T ICC 8 18 04.4 14.4 — 5 23.0 — 4.0 20 ^10.4 ~~22. 4 AO 104.0 32.0 17 62.6 13.6 5 — 4.8 29 20. 2 23.2 39 102.2 16 • 60.8 12 8 7 TO A 5.0 3° 38 100.4 30.4 15 59- 0 12.0 — 8 17.6 - 6.4 ~3i —23.8 — 24.8 37 98.6 29.6 14 S7-2 II.2 — 9 15-8 — 7.2 —32 —23. 6 — 25.6 36 96.8 28.8 13 55- 4 10.4 — 10 14.0 — 8.0 —33 —27.4 — 26.4 35 95-0 28.0 12 53-6 9.6 — 11 12.2 — 8.8 —34 — 29.2 27.2 34 93-2 27 2 11 51.8 8.8 — 12 10.4 -9.6 —35 —31.0 —28 0 33 91.4 26.4 10 50.0 8.0 —13 8.6 — 10.4 -36 —32.8 —28.8 32 89.6 25.6 9 48.2 7.2 —14 6.8 — 11.2 —37 —34-6 29.6 31 87.8 24.8 8 46.4 6.4 —IS S.o — 12.0 -38 -36.4 —30-4 30 86.0 24.0 7 44.6 5-6 —16 3-2 —12.8 —39 —38.2 — 31-2 29 84.2 23.2 6 42.8 4.8 —17 1.4 — r3 6 —40 — 40.0 —32.0 28 82.4 22.4 5 41.0 4.0 —18 —0.4 —14.4 —41 —41.8 —32.8 Comparison of the Scales for each Teftih of a Degree. Cent. Fahr. Reau. Fahr. Cent. Reau. Reau. Fahr. Cent. 0. 1 0.2 0.3 0.4 o-S 0.6 0.7 0.8 0 9 I.O 0.18 0.36 054 0.72 0.9 1.08 1.26 1.44 i.r2 1.8 0.08 0.16 , 0.24 0.32 0.4 0.48 0.56 0.64 0.73 0.8 0,1 0.2 0.3 0.4 o-S 0 6 0.7 0.8 0.9 1.0 0.06 O.ll 0. 17 0.22 0.28 0-33 0 39 0.44 0.5 0 56 0.04 0.09 0.13 0.18 0.22 0.27 0.31 0. 36 0.4 0.44 0. 1 0.2 0-3 0.4 O'S 06 0.7 0.8 O.Q 10 0.22 0-4S 0.67 0.9 1. 12 I-3S 1-57 1.80 2.02 2.25 0. 12 0.25 0.37 o-S 0. 62 0.7s 0.87 1. 00 1. 12 I 25 CONTENTS. INTRODUCTION. What Botany is — Distinctions between plants and animals— Divisions of botanical study, ........ 1-6 SECTION I.— General Anatomy or Histology of the Elementary Tissues. CHAPTER I. CELLULAR TISSUE OR PARENCHYMA. Forms of cells — Single-celled plants — Intercellular canals — Intercel- lular substance — Nature of the cell-wall — Markings on the cell- wall — Contents of cells — Lacunae in cellular tissue — Development and increase of cellular tissues — Original cell-formation — Cell- multiplication — Transference of fluid from cell to cell, . 9-37 CHAPTER II. WOODY AND VASCULAR TISSUES. Woody fibre — Punctations — Bast- tissue — Vascular tissue — Laticifer- ous or simple- walled vessels — Tracheary vessels — Punctated and barred vessels — Vascular bundles, ..... 38-50 CHAPTER III. EPIDERMIS AND APPENDAGES. Epidermis— Stomata — Lenticels—Haire— Glands— Recapitulation, 5 1-67 CONTENTS. SECTION II.— Nutrition. CHAPTER I. THE STEM, Stem — Division according to structure — Stem of Dicotyledons — Buds — Ramification — Twining stems — Fleshy stems — Cladodia — vStruc- ture of the stem — Development — Structure of the stem of annual Dicotyledons — Uses of the stem — Stem of Monocotyledons — Structure and grovcth of palms — Theoretical structure of the stem of Dicotyledons — Stem of Acotyledons — Ferns — Equisetacese, Lyco- podiaceze — Subterranean stems — Rhizome — Tuber — Coi-m — Ter- restrio-aerial stems — Stolon — Sucker — Runner — Bulbs — Bulb- lets — Uses of bulbs — Spines, tendrils, &c. — Anomalous stems — Exogenous stems — Cy cadacese — Coniferse — Gnetacese — Sapin- daceae — Bignoniaceas — Malpighiacese — Menispermacefe — Aristo- lochiacese — Bauhinia — Eijdogenous stems — Teratology of the stem — Different forms and technical teiTns applied to the stem — Direction — Ramification — Consistence — Form — Form and elas- ticity— Structure and Covering — Summary, . . . 71 CHAPTER II. THE ROOT. The root — General characteristics — Development — Development of the roots of Monocotyledons — Elongation of the root — Rhizotaxis — Structure of the root — of Dicotyledons— Monocotyledons — Aco- tyledons— Adventitious roots— Deciduous roots — Functions of roots — As an organ of fixation — Absorption— Respiration — The root as a magazine of nourishment — As a floating organ— Excre- tion of roots— Antipathies and sympathies of plants— Different forms of roots, and terms used in describing them— Duration — Situation — Direction— Division— Form— Surface— Consistence — Summary 124 CHAPTER III. THE LEAF. General remarks— General structure— Acessory or modified parts- Stipules— Phyllodia— Microscopic anatomy— Normal histology of a leaf— Deviations from the normal structure— Development of leaves— Leaf-buds— Prsefoliation— Folded leaves— Rolled leaves- Straight leaves— Conduplicate leaves— Venation— Forms of leaves —Margin— Compound leaves — Pinnate leaves— Palmate leaves— xiv CONTENTS. Succession of compound and simple leaves — Variability of leaves — Phyllomoi-phosis — Anomalous forms of leaves — Unsymmetrical leaves— "Vertical and equitant leaves — Leaves as spines — Pitcher- plants — Eryophyllum — Phyllotaxis— Alternate leaves— Opposite leaves — Verticillate leaves— Fascicled leaves — Abnormal arrange- ments—Recapitulation of Phyllotaxis— Uses of the leaf— Dura- tion—Fall and death of the leaf— Autumnal colour of leaves — In-egularity in appearance of the leaves — Teratology of the leaf — Modifications of the leaf, and technical terms used in describing it — Situation — Attachment — Configuration — Direction — Sur- face— Coloration— Duration — Nervation — Divisions of the mar- gin— Composition — Substance, 146-208 CHAPTER IV. THE ULTIMATE CONSTITUENTS OF PLANTS. Volatile parts of plants — Carbon— Oxygen — Niti-ogen — Hydrogen — Sulphur — Phosphorus — Vegetable organic compounds or proxi- mate principles — Water — Cellulose group, or amyloids — Pectose group — Vegetable acids — Fats and oils — Albuminoid or proteine bodies — Chlorophyll — Glucosides — Tannin — Alkaloids — Ingredi- ents of the ash and non-volatile sub-ingredients — Non-metallic substances — Metals — Salts of metals found in the ash — Car- bonates— Sulphates — Phosphates — Nitrates — Vaiying proportion of ash — Uses of mineral ingredients — Absorption of excess of ash ingredients by plants — Composition of the plant in successive stages of growth — Soils and rotation of crops, . . . 209-237 CHAPTER V. THE FUNCTION OF NUTRITION. General nature— Absorption of the nutritive fluid — Circulation — Ascent of the crude sap — Respiration — Transpiration — Circula- tion— Descending sap — Secretion and excretion — Assimilation — Increase of the plant, . 238-276 SECTION III— Reproduction. CHAPTER I. GENERAL REMARKS ON THE FLOWER AND FLOWERING. General observations— Peduncle and bracts— Flowering, . . 279-29S CONTENTS. XV CHAPTER II. THE PERIANTH, OR FLORAL ENVELOPES. Calyx — Form and nervation of sepals — Pappus or aigrette — Morpho- logical nature of sepals — Duration of calyx — Calyx regular or irregular — Calyx dialysepalous and gamosepalous — Regular or irregular dialysepalous calyx — Regular or irregular gamosepalous calyx — Colour of calyx — Peculiar calyces — Absence or presence — Corolla — Petals — Corolla dialypetalous and gamopetalous — Dialypetalous corolla — Gamopetalous corolla — Other appendages of corolla — Colour of corolla — Duration of corolla — Use of corolla — Perianth of Monocotyledons, .... 299-318 CHAPTER III. THE ANDRCECIUM, OR STAMINAL WHORL. Stamens — Number — Relative lengths — Situation in regard to petals and sepals — Filament — Anthers — Structure of the stamen in general — Attachment of the filament to the anther — Insertion of the stamens — Relation of the number of the stamens to the number of petals^ — Staminodia — Morphology of the stamen — Pollen — Shape — Size — Structure — Development of the anther and pollen — Compound pollen-grains — Solid pollen — Colour, 319-347 CHAPTER IV. THE GYNCECIUM, OR PISTILLINE WHORL. General remarks— Ovary — Placenta and placentation— Style— Stigma — Structure and formation of carpels — Ovule — Development and structure — Relation of the poles of the ovule to each other — Position of the ovules in the ovary — Exceptional structure of the ovule — Variation in the number of the integuments and the form of the ovules— Naked ovules— Morphology of the petal, . 348-370 CHAPTER V. DEVELOPMENT, PRiEFLORATION, SYMMETRY, AND METAMAPHOSIS. Development or organogeny— Calyx— Corolla and androecium— Prte- floration of the floral envelopes — Of each piece of the ver- ticil in particular — Relation of the pieces of the verticil to those of the verticil more interior — Prcefloration of stamens and I pistil— Symmetry of the flower— Variation and alterations in the symmetry— Primitive regularity of the flower— Relation of the floral whorls to the axis— Metamorphosis of flowers— Tran- sition from leaves to petals and sepals— Formation of stamens and carpels, 371-387 xvi CONTENTS. CHAPTER Vr, DISC AND NECTARIES. Disc— Position— Position in reference to the pistils or carpels— Effect of the disc on the symmetry— Nectaries 388-390 CHAPTER VII. INFLORESCENCE OR ANTHOTAXIS. General division of inflorescences — Indeterminate inflorescences — Flowers on the primary axes — Flowers on secondary axes — Flowers on tertiary axes or their ramifications — Determinate in- florescences— Mixed inflorescences— Anomalous inflorescences, 391-405 CHAPTER VIII. FERTILISATION OF THE OVULE : ORTHOGAMY. Preparatory phenomena— Essential process — Length of time taken to fertilise ovules — Rate of growth of pollen-tubes — The embryo-sac — Origin of the embryo — Germinal vesicle — Consecutive phenomena, ......... 406-417 CHAPTER IX. FERTILISATION : HETEROGAMY. Hybridity — Degrees of hybridity — Laws governing the sterility of first crosses and of hybrids — Uses of hybridism — Origin and causes of the sterility of first crosses and hybrids — Good effects of inter- crossing— Fertility of varieties when crossed, and of their mongrel offspring — Dimorphism and trimorphism — Dichogamy — Fer- tilisation by means of insects — Fertilisation of orchids and Ascle- piadaceee — Stnicture of orchids — The wind as a fertilising agent — Fertilisation of grasses — Fertilisation of winter-flowering plants — Cleistogenous flowers — Fertilisation of water-plants — Partheno- genesis—Summary, 418-463 CHAPTER X. THE FRUIT. General remarks — Parts of the flower adherent to the fi-uit — Ripening of the fruit — Changes in the tissues — Changes in substance — Changes in green fruits when cooked — Production of sugar during CONTENTS. XVU ripening— Changes from bletting to rotting — Period required for ripening of the fruit — Structure of the pericarp — Epicarp— Endo- carp Mesocarp — Loculaments and dissepiments — Dehiscence of the fruit — Porous dehiscence— Valvular dehiscence — Circum- cissal dehiscence — Dehiscence of unilocular fruits — Elastic dehiscence— Classification of fniits, 464-495 CHAPTER XI. THE SEED. General remarks — Structure of the seed — Integuments— Nucleus — Naked seeds — Character of the embryo in Dicotyledons and Monocotyledons — Growth of the seed, .... 496-521 CHAPTER XII. GERMINATION. Duration of vitality of seeds — Results of the use of long-kept seeds — Unripe seeds — Dwarfed or light seeds — Value of seed as regards density — The act of germination — Conditions necessary to ger- mination— Period of time required for germination — Proper depth for sowing seed — Chemical physiology of germination — Teratology of the seed, ....... 522-543 CHAPTER XIII. GRAFTING : LONGEVITY OF PLANTS, ETC. General remarks on grafting — Advantages of grafting — Physiological conditions necessary to grafting — Longevity of plants — Death of the plant, • . . 544-553 SECTION IV.— General Phenomena connected with Plant-life. CHAPTER I. HOMOPLASMY : MOVEMENTS AND SPECIAL DIRECTIONS IN PLANTS. General remarks on homoplasmy or mimicry — Free movements of plants— Reproductive organs and spores of ci7ptogamia — Hedy- XVUl CONTENTS. sarum— Labellum of orchids — The Compass plant— Return of leaves — Heliotropic plants— Movement of leaves of Colocasia esculentea — Movements of leaves in water — Special directions of root, stem, &c., 557-565 CHAPTER II. OPENING AND CLOSING OF FLOWERS : SLEEP OF PLANTS. General remarks — Hygrometric plants — Different periods of flowering — Sleep of plants, ........ 566-570 CHAPTER III. VEGETABLE IRRITABILITY, AND MOVEMENTS OF CLIMBING PLANTS. Mimosa — Diontea — Drosera — Other plants with irritable leaves — Irritability in the stamens and stigmas of plants — Movements of climbing plants — Spirally twining plants — Leaf climbers — Ten- dril-bearing plants — Root climbers — What is vegetable irrita- biUty? 571-585 CHAPTER IV. ODOURS, COLOURS, LUMINOSITY, TEMPERATURE, AND NOSOLOGY OF PLANTS. Odours — Classification of odours — Colours of plants — Classification of colours — Dickie's researches — Luminosity of plants — Lumin- osity of roots, &c. — Luminosity of flowers — Luminosity of fungi — Luminosity of sap — Temperature of plants — Vegetable nosology, 586-600 Index and Glossary, . 601-614 ERRATA. Page 49, line 45, "Tyloses" read ""t.y\osi%," and add reference, "Thisle- ton-Dyer, Journ. of Bot., Nov. 1872; Caird.Trans. Bot. See. Edin., 496." Page 128, line 16, for " petiole forming " read "result being." ,, 164, ,, i8,yor " LeniceraceEe" r^a^^ "Loniceraceas." ,, 218, ,, 40, 44,/or " Aleurine" rtfflrf "Aleurone." ,, 288, ,, ^6, for " Periclenium " read " Periclinium." ,, 407, ,, 43, ybr " erepos, crooked, " rtarf "'Exepos," other. ,, 494, ,, 25, " Glabulus" rca^^ " Galbulus." .1 398, 9, "And the so-called panicle." 468, fig. 3ii,_/yr "Anassa" read "Ananassa." „ 491, line 6, for " Sphacerocaqjium " read "Sphalerocarpium." MANUAL OF BOTANY. INTRODUCTION. Botany,^ or Phytology^ is that department of biological science which treats of the nature, functions, and classification of plants, and of the relation of these plants one to another, to the animal kingdom, and to the forces of inanimate nature — in a word, it is to the vegetable kingdom what Zoology is to the animal — the history, in the broadest sense, of the beings composing it. If the relative importance of the subject of which any science treats is to be taken as a criterion of the interest or importance of that science, then the one to an exposition of which the following pages are to be devoted ranks high in the list. Without plants the earth would be a dreary uninhabitable desert throughout a vast portion of its extent, and man reduced to a, condition somewhat similar to that of the Eskimo— tribes of miserable fishers and maritime hunters. It is even questionable if he could exist ; for many of the marine animals, and all of the terrestrial ones, are in- directly or directly dependent for their subsistence on the vegetable kingdom. Plants furnish the food of herbivo^oys animals, and the animals in their turn give nourishmeijit to vast tribes of other beings called carnivorous— including man himself. The vegetable kingdom also furnishes a great portion of the food of the human family, as well as its clothing, medicine, fuel, and the material for its dwellings, and implements of domestic economy, of the arts and manufactures, of war and peace. The earth owes her beauty to the flowers and green leaves of plants ; and the very air we breathe, the water we drink, and the food which nourishes us, are alike de- pendent on the vegetable kingdom. The plant could do without man, as in ages past it did— the flower could bloom in the lonely desert or umbrageous forest, as it still does over regions of the 1 Boraio), a plant. 2 a plant ; Xoyd?, a discourse. A 2 INTRODUCTION. earth undisturbed by the human race ; but man could not subsist, except in the lowest condition of savagedom, without its aid. In- dependently, however, of the mere economic importance of plants, they afford an insight into many interesting and complicated phenomena of nature, both past and present, and present a field for study so extensive, that Botany might in any of its various departments furnish a field wide enough for the industry of a lifetime. At the very outset of our study we are met by the question, What distinguishes plants from animals ? When we look at the oak and the elephant, the question might seem an idle one ; and it is only when we approach the confines of the two animated kingdoms that we see how difficult it is to draw a line between the lower members of each, or to say where the plant ends and the animal begins, though between the mineral and the animated kingdoms there is a hard and fast line of demarcation — viz., the possession of the vital principle, in addition to many others sub- ordinate to and dependent on this. Chief among these are the powers of nutrition or self-support, by which all organised beings can assimilate within their constitution the particles of other bodies, by which each iridividual member increases in size, and so grows and maintains life ; and secondly, the power of reproduction, by which each individual member can produce others resem- bling itself, and so increase and perpetuate its kind. Unorganised substances can do neither. Such being the ground common to plants and animals, we next come to consider what is the distifiction between them ; and here we are at fault. Motion, we shall find, is a characteristic not peculiar to the animal kingdom, but is found throughout life in some of the lower members of the vegetable kingdom ; and equally we shall have occasion to discuss, in the course of our study, a certain irritability, and even instinct, which it is almost impossible, without drawing an arbitrary distinction, to character- ise as very different from that found in some of the lower animals. Even in composition some animals do not differ from plants ; the presence of the substance called "cellulose" (p. 17) — once sup- posed to be a constant element found in the latter only — having been discovered to a large extent in some of theascidian molluscs, and even in the low forms of animal life called coccospheres. The difficulty of drawing a distinction between plants and animals is, however, one more of words than reality ; for, as we have said, it is only when we approach the shadowy boundaries of the two kingdoms that we find any difficulty in seeing the respective lines which divide the regions of the botanist and zoologist. The fol- lowing characteristics may therefore, in the present state of our knowledge, be accepted as true : (i.) Plants alone can subsist INTRODUCTION. 3 directly on the mineral king-dom, and on the surrounding air and moisture, and assimilate these elements into organised structure. (2.) The permanent fabric of plants is composed of ternary com- pounds— i.e.y substances composed of three elements, these being carbon, hydrogen, and oxygen. The tissues of animals contain, in addition, nitrogen, and so are composed of quaternary com- pounds. Contrary to what is commonly stated in some works, the student ought to bear in mind that it is only in the proportion which these elements bear to each other that the members of one kingdom differ from the other, both containing nitrogenous and non-nitrogenous elements, though in those substances in plants (legumen and gluten) which contain nitrogen, it is found in com- paratively small quantities. Cellulose, again, with the exception named, is only found in plants ; and though chlorophyll, or the green colouring substance of plants (p. 23), has been discovered in some members of the animal kingdom {e.g., Stentor, the trumpet animalcule, and Hydra, the fresh-water polype), its presence is, as a rule, strong presumptive evidence of the vegetable nature of the organism. (3.) Plants, as a rule, decompose carbonic acid and exhale oxygen — an exception being found in some of the fungi. Some of the last-named plants also require the aid of organised matter for their support. It necessarily follows that a science so extensive, and taking cognisance of so many points of study, must be divided into sub- ordinate departments for the more convenient acquisition of knowledge, and for the classification of the knowledge so obtained. Looking at any common flowering plant, we see that it is com- posed of root, leaf, flower, and so on, but these compound organs are in their turn composed of substances which cannot be ex- amined by the naked eye. Hence this leads us at an early stage of our studies to examine the General Anatomy or Histology'^ of plants. Having proceeded thus far, we next come to consider the different organs made up of these minute ones common to all — viz., the cells and vessels, and their structure and arrangement in reference to one another ; this constitutes Organography.'^ Furthermore, we shall find, if we examine the relations and de- velopments of the organs of the plant, that these organs are not each formed on a distinct plan, but are only modifications of one type, that type being the leaf; we shall see that the leaves are arranged in whorls along the stem, and that even the component parts of the flower, though generally close together, alternate with one another, and are only modifications of the leaf— this modifica- tion being gradual, from the typical leaf to the bracts, sepals, petals, stamens, and pistil. This constitutes the philosophical or 'loTos, a web ; Aoyds, a discourse. 2 "Opyavov, organ ; ypaijiaj, I write. 4 INTRODUCTION. transcendental view of organography, or Morphology} and is to botany wliat comparative anatomy is to Zoology and Zootomy. The special study of the developments of organs has been called Organogenesis? completing, as it does with organography, Phytotomy? or Vegetable Anatomy. All these organs, though modifications of one type, have, however, special and distinct functions to perform — e.g., the root to absorb nutriment, the stem to convey it throughout the plant, the leaves to elaborate it, the flower and its part to form the seed, which in its turn per- petuates the species, the acme of organic existence. The study of this constitutes Physiological'^ Botany. If we investigate the composition of the substances composing the plant, and their re- actions one with another, we enter on the study of Vegetable Chemistry. Like all organisms, these functions of the plant are apt to get into an abnormal state, the result being disease, the study of which constitutes vegetable pathology or TVi^Wogj/^ or there may be congenital or other abnormalities in the forms of organs, which enable the anatomist often to get an insight into the plan of structure, by, as it were, a lifting up of nature's veil ; the study of these is Teratology.^ Hitherto we have been only looking at the plant as an abstrac- tion, a typical phyton, which possibly may not in all its details exist in nature. Plants, however, as the student need not be told, are found in apparently endless forms, all modifications of the typical phyton or model plant, but seemingly with such wide divergences from it that it would be almost hopeless to work all the forms into this type. However, on studying the multiplicity of species scattered over the earth, we shall find that they may be reduced to about three great types of structure, and that each of these in its turn will be found to embrace a number of secondary classes, the members of which have their forms modified on one plan. Each of these classes, again, contains numerous orders embi'acing plants different one from another, but yet having a gen- eral likeness ; while each of these is composed of a greater or less number of genera, 7^ the species of each genus having a close likeness, showing that, though now different, they may have originally sprung from the same ancestor, or have been formed on the same plan ; lastly, each of these species is the type of an 1 Mop), the earth. 8 IIoAaibs, ancient ; ovra, being. 6 INTRODUCTION — DIVISION OF SUBJECT. departments mentioned will probably embrace the chief sub- divisions of the science. Luckily, however, for the student, he is not at the outset of his botanical studies called upon to examine plants from any of these points of view exclusively. He must first gain an acquaintance with the general elements of plant history ; and in so doing, many, if not all, of these departments will get absorbed under other more general heads, which we shall now proceed to discuss in a systematic manner. Unfortunately (or fortunately), not more in a text-book than in nature is it possible to give what has been called a perfectly " natural classi- fication " of the subjects of study. For instance, though it is necessary for the tyro to know the minute structure of plants be- fore he proceeds to the study of the organs which are composed of these minute structures, yet he will not fully understand the first before he has some acquaintance with the second, and so with all the other departments. From time to time, therefore, he will find it advisable to revise his earlier studies in the light of his more recent ones. Laying aside for the present the division of Botanical science sketched in the foregoing paragraphs, let us consider the biography of the plant under the following headings : — L Histological or General Anatomy. — The history of cells, vessels, &c., their origin and multiplication, and other minute organs common to all parts of the plant. IL Nutrition. — The organs ministering to the nourishment of the plant, their structure and function. IIL Reproduction. — The description of the flower and its modifications and development, the structure and development of the fruit and seed, the methods of impregnation necessary to produce the latter, &c. IV. Cryptogamia, or the structure and functions of flowerless plants, the previous sections relating only to Phanerogamous or flowering plants. V. General Phenomena of Plant Life. — In this section will be con- sidered the subjects of irritability, temperature, colour, luminosity, &c. — in a word, subjects which cannot, without breaking the thread of argument, be introduced under any of the foregoing headings. VI. Taxonomy, or classification and the method of studying and describing species. VII. Phyto-geography, or botanical geography. VIII. Pal^eo-phytology, or fossil botany — a description of the gradual appearance of plants on the earth up to the present day, and their connection with the present flora, either by descent or consanguinity. SECTION I. i i I GENERAL ANATOMY OR HISTOLOGY OF THE ELEMENTARY TISSUES. In the preceding pages we have glanced at the plant from a general point of view, and have seen that its organs — leaves, stem, root, flower, &c. — are all varied to subserve certain purposes, though composed of materials seemingly much the same. If we go deeper into the examination of the substance composing these organs, we find that the microscope reveals that the plant, no matter how diversified may be its appearance, size, or habits, is composed of the following elementary tissues : i. Cells, or little bladders, with thin transparent walls, very minute and variable in form, being sometimes regular, at other times irregular in shape; 2. Short tubes, attenuated at either end; 3. Vessels, cylin- drical or angular, and either scattered through the plant singly, or united in bundles. These three in composition get the names of cellular tissue, woody or ligneous tissue, and vascular tissjie. Again, though seemingly different, they are only modifications of one and the same thing — viz., the vegetable cell. From this are formed, by various modifications, all the organs of the plant ; the simplest, as well as the most complex, alike owe their structure to the primary cell. This being so, it becomes important, before we proceed one step further in the examination of the structure and functions of the complex organs, to examine more minutely the elementary tissues of which they are built up. These we shall con- sider under the heads of cellular, woody, and vascular tissues. CHAPTER 1. CELLULAR TISSUE OR PARENCHYMA. Cellular tissue ^ is the fundamental organisation of the plant. It is composed of little cells, utricles, or bladders, with very thin walls, firmly united together, and appearing to form a continuous mass. The uniting material of the cells appears to be the inter- cellular stibstance, which, if the cellular tissue is boiled in water or nitric acid, dissolves out and leaves the disunited cells in their proper form. Form of Cells. — In shape the cells vary very much. Some are polyhedral, commonly dodecahedral, or in the form of prisms with four, five, or six faces. Sometimes in the same tissue the contiguous cells will vary in shape, as is well shown in fig. i of cel- lular tissue from the pith of the vine. At first they are almost spherical, especially when they remain isolated. However, in course of time, owing to pressure of the neighbouring cells, mul- tiplication, and other causes, this primi- tive form becomes much modified. Then they will become more or less angular or polyhedral. In most cases the cell is dodecahedral, so that a section of such a tissue looks at a glance not unlike a section of a honeycomb. Fig. I. — Portion of the cellular tissue which forms the pith of the vine, seen in longitudinal section. Here are exhibited cells with six unequal sides, others with five The form is, sides, while others have only however, rarely perfectly regular, and either unpunctated or very little then only when the cell has been subject ^o. to perhaps equal pressure on all sides. More frequently the cells are irregularly hexagonal, one or more of the faces having devel- ^ ria^jevxvfio, substance of organs (tTapa., through ; and ivxioi, I infuse). " Also called Parenchymatous, areolar, utricular, or vesicular tissue. Hayne (Flora, 1827, ii. 601), Meyen (Phytotomie, 57 ; Physiologic, i. 12), and Morren (Bulletin de I'Acad. de Bruxelles, v. No. 3), have all proposed names for the varieties of this tissue. The nomenclature proposed by Hayne attracted little attention ; while those of Meyen and Morren have been adopted by a few writers, ROUNDED AND POLYHEDRAL PARENCHYMA. oped at the expense of the others.^ So marked is often this irregularity, that it is difficult to reduce the shape to the hexa- gonal form at all. Under the influence of this pressure, not unrarely we find the cell losing one or other of its sides, and becoming pentagonal or even quadrilat- eral (fig. 4). Lastly, there are the anomalous cells known as stomata. Some microscopists, and particularly Charles Morren, have applied particular names to each of these tissues, in accordance with the form of the cells composing it The chief of these are : — I. Rounded Parenchyma"^ (fig, 2), com- posed of an aggregation of globular or ellipsoidal cells. It is common in young plants or young organs, and in the soft fleshy parts of plants and fruits. 2. Polyhedral Parenchyina (fig. 3). — This is the most com- mon form of cellular tissue — in fact, is that to which the name parenchyma in general refers. The form usually, though not but in most cases of little weight. Both, especially that of Morren, have only served to confuse an already burdensome terminology, and are worthy of the neglect with which they have been treated of late by the best authors. No ex- act subdivision, such as Morren gave, can be adopted, "because no exact con- nection exists between the form and function, and frequently enough the same organ is formed of cells differing considerably in form in two closely alUed plants." I have given the chief of these names in footnotes, so as to obviate as far as possible the mischief done in some recent books by their injudicious adoption. 1 No doubt, theoretically, when the cells get collected in masses, as in the pith, &c., each cell being surrounded on all sides by other cells, the form of each individual cell ought to be that of a rhombic dodecahedron, since this form encloses the greatest space within the smallest limits. However, it would be vain to seek for this actually in nature, since the contiguous cells are too unequal in size for them to become moulded into regular mathematical forms by their reciprocal pressure. — Kieser, Grundz. d. Anat. der Pflanzen, § 127 ; Mohl's Anat. and Phys. of Veg. Cell., Engl. Trans., 6 (an admirable work, which the student should make himself master of, as soon after he has acquired some elementary knowledge as possible. He must, however, remem- ber that much in it has been shown to be erroneous, and that it is to a great extent a defence of many crotchets held by no observer but himself). 2 Mercnchyma of Meyer (nTjpuoi, I revolve), and Sphccrcnchyma {alpa, a sphere), applied to spheroidal cells, ovcnchyma {iiov, an egg), to oval cells, &c. , are just modifications of this. These and other terms of a similar nature, applied to modifications of cellular tissue owing to the form of the cells— these modifications often differing very little from each other— are not in general use by the best descriptive writers. Fig. 2. — Fragment of cellu- lar tissue from the fleshy stem of Rhipsalis salicornioides. Haw. 711 711 Intercellular pas- sages, almost all triangular, but of which one, much larger, is quandrangular ; a A cell surrounded by six others. MURIFORM AND TABULAR PARENCHYMA. 1 1 invariably taken, is the hexagonal ; hence the various names applied to it.^ I ^1 JL Fig. 3. — Cellular tissue of the bulb of Lili wn snperbuiii, L. ccc Cells viewed on hexa- gonal section ; Intercellular passages ap- pearing triangular ; a Continuous membrane, which forms the common wall of two adja- cent cells. Fig. 4. — Muriform parenchyma, taken from the stem of Anstolochia Sipho, L'Herit. Longitudinal section. 3. Miiriform Parettchy7na (fig. 4). — This tissue is commonly found in the medullary rays of dicotyledonous trees, and derives its name from its cells appearing like bricks in a wall. 4. Tabular Parenchyma'^ (fig. 5) is seen in the epidermis of plants, particularly in that of ferns. It de- rives its name from the fact that it gains in breadth without a corresponding increase in thickness, on account of the pressure of the tissues which it covers ; and hence each long thin cell looks like a table without the legs. In the four different forms of cells which we have noted, there is no thickening of the cell-walls at their junction. In those, the description of which follows, the con- trary is the case. Hence the intercellular passages, which will be presently noticed, Fig. 5.— Tabular par- are increased, and the air has freer access '^^J^^^tX^C. to the surface of the cells. The paren- (Aspidium FUix-mas, chyma formed by such cells, as would natu- ^^"'^ rally follow, is also always looser and more spongy than that composed of cells more intimately united to each other, as in the four preceding types. 1 Hexagonal parenchyma, hexagonal cellular tissue, &c. ; or shortly, hexa- gonienchyma (efaywuoT, six-angled). The Prisinenchyina (npCaixa, prism) is only a slight modification of it. Pinatchy^na of some authors (jrii/of , a table). 12 BRANCHED AND STELLATE PARENCHYMA. S. Branched Parenchyma}-lr, this case the cells are distin- guished by irregular and little marked prominences uniting with the neighbouring cells, and leaving lacunar between them; hence It is sometimes called lacunary tissue. This kind of tissue is com- monly found in the layer of parenchyma nearest to the under surface of leaves (fig. 6), or in branched hairs. 6. Stellate parenchyma} — When the prominences on the cells assume a more marked character, the cells appear in the form of asterisks, with five or six rays, giving th-e tissue under the micro- scope a very characteristic aspect. In this case the intercellular passages are very large. Such a tissue is markedly seen in the stem of aquatic and other plants {Sagittaria, Juncus, Musa, seed- Fig. 6. — Transverse section of a leaf of Pelargottinin iiiquiii- aiis, Ait., showing branched par- enchyma, with lacunae, pr" pr' , of which it is chiefly composed ; "Pallisaded," or upper layer of oblong or ovoid cells ; ip, dp. Epidermis. The cells are filled with chlorophyll. Fig. 7. — Stellate parenchyma, from the stem of Juncns effusns, L. a Point of union of the ex- tremities of two adjacent cells. coat of the privet, " white " of the rind of the orange, &c.) In these cases the air gets freer access through the whole interior of the stem, giving plants made up of such tissues a lightness necessary to their mode of existence. In this stellate parenchyma the rays of the cells are unbi-anched' — one or two of the rays being directed downward, the others upwards, to join their neighbours, as in fig. 7. M. Duchartre has very aptly remarked that the organs of plants in the course of their development present in general two successive periods. In the first, the cells, in forming the substance of the plant, multiply without cessation ; in the second case, they do not increase, but elongate, following the elongation of the organ in which they are found. In this last-mentioned 1 Cladenchyma (xAo«09, a branch). * Actinenchyma (oktiv, a ray). ELONGATED AND FUSIFORM CELLS. 13 period, the forms of each are notably modified, and the modifica- tion operates in different manners, so that we can distinguish two categories of elongated cells. 7. Elongated cylindrical cells. — In this case the cells are formed in horizontal lines, which end by forming a cylinder more or less narrow in diameter, and terminating in abrupt or moderately in- clined points, as in Chara> Caspary, finding these elongated cells in the essential parts of the architecture of plants, and in their interior nitrogenous matter, thinks that they perform an important function in the life of the plant — namely, that they convey the nutritious fluids. Hence he called them cellulce conducirices? 8. Fusifortn cells, fibres or prosenchyma"^ (fig. 8). — In this kind of elongated cells each terminates in points which insert themselves between the cells of the same kind lying above and below them — in a word, they are spindle-shaped ; hence the name {fuseau, Fr. a spindle). For the same reason Dutrochet called them Clostres^ These fusiform cells, when thickened by internal deposits, form the fibrous or resisting portion of wood and bark, and are often called simply fib^-es. It is impossible to give in to the idea of Adrian de Jussieu, and a few other botanists, that pros- enchyma is a tissue different altogether from cellular tissue. All transitions from the one to the other can be traced, showing that the fibres commence with cells becoming closed. The following table, after Duchartre, shows at a glance the characteristics of the eight dif- ferent tissues which we have been describing. Some authors whose delight is more in nomen- clature than real science have distinguished others, but we cannot see that they are marked by any characteristics sufficiently salient to cause us to enlarge our already too extended catalogue by their mention. Fig. 8. — An isolat- ed fusiform cell of the prosenchyma of Bra- gantia tomentosa, Bl. punctations. 1 Sometimes this kind of cellular tissue is called Cylindrenchyma ((cvAtfSpor, a cylinder) by some authors. * Leitzellen in German. 3 npos, and ivy^yim, strong substance ; or Airacteiichyma (arpoKTos, a spindle). •* KAwoTTjp, KXajoTiipos, spindle. 14 CLASSIFICATION OF TISSUES— SINGLE-CELLED PLANTS. -I " I " ft -O 4-. .ti o CELLS. TISSUES. Globular or ovoid cells, showing in ) section a rounded or oval aspect, . I bounded parenchyma. Polyhedral cells, showing a hexagonal 1 Ordinary or polyhedral section, . . . ,j parenchyma. Parallelopiped, showing a rectangular ) section j ^^uriform parenchyma. Cells in a tabular form, showing •) at least a rectangular elongated J> Tabular parenchyma, section, 6 o u. P. V Elongated Cells. < Branched cells, or with short angular ) Branched or lacunary prominences, . . .J parenchyma. ' Rayed cells, with prominences generally long and more regularly disposed Istellate parenchyma, than in the former, . . J Cylindrical cells, with base abrupt or little pointed. {Cdlulce conductrices, Casp. ) Fusiform cells (Cte, Dutr.. /^m ^ p^^^^^^^ of other authors), . . . ) ' Single-celled Plants. — The majority of the higher plants are composed of numerous cells of one or more of the kinds just de- scribed. Others, such as fungi, algae, lichens, &c., are composed of simple cells alone, and are hence known as cellular plants; while other plants lower down in the scale of existence consist of simply a single cell — the organs of life being here reduced to its simplest element, viz., the cell. And tjiis cell performs all the functions which it is intended to fulfil just as well as in species more com- plexly organised. We find such in the red snow plant {Haina- tococais nivalis of C. A. Agardh), which covers considerable tracts of the snow of the Alps and the Arctic regions. So rapidly does it increase, that in one night in the month of March the red snow plant covered a bank of snow to a considerable thickness. Each of these plants consists of a minute globule, distinct and separate, composed of a thin membrane perfectly closed in all its parts, colourless, but containing in the interior a red liquid. By- and-by granules appear in this red liquid, which grow and soon tear the envelope, and after a time give birth to other globular vesicles exactly resembling the mother cells. The same mode of growth can be seen in another species {H. crice?iius), which covers with crimson stains the north side of damp walls. Oscillatoria, a minute plant which sometimes stains lakes of a greenish hue, is only an elongated single cell. Again Vauchcria, a fresh-water Alga, and Bryopsis, a marine one, are only single cells more or less branched. The "Zoospores" of all algae, &c., are of this nature. The spores of Equisetaceee are also single cells surrounded by INTERCELLULAR CANALS AND SUBSTANCE. IS curious bodies called Elaters (fig. 9). In Botrydmm we see a cell branched, with some of the branches performing the function of a root to fix the minute plant in the mud. Here we see a tendency to a higher growth, where, as in moulds, the plant is composed of a series of cells— until we get on in the higher sea- weeds to a plant composed of layers of cells, then to cells thickened in various ways to surrounded by sen^e the purposes of hard tissue, until finally we see them altered to woody tissue, and vessels as in the higher plants. Intercellular Canals. — Though most cells are united to the contiguous ones so closely as to leave no appreciable space be- tween,^ yet in various plants the cells only touch each other at one or two points, leaving, as in the green pulpy parenchyma, spaces between them, known as mtercellular canals? In some species of plants these are well marked, while in others they are so indis- tinct as to have led some authors to deny their existence. In shape they also vary much. Kieser and De Candolle look upon them as intended to contain sap, and even make them out to be true sap -vessels. The probability is, however, that they principally contain air. In the stems and leaves of most aquatic plants, such as rushes, Nymphseaceas, &c., the intercellular canals are filled with air. In some cases, by the absorption of the cells which bound them, these canals can be increased in size. This is seen in the culm of grasses and in the stem of orchids. Intercellular Substance. — The myriads of minute cells which in combination make up the parenchyma of the plant, are cemented together by a substance apparently secreted by them, and known as the intercellular substance? Ordinarily it is found in a very thin layer between the cells, but in some cases where large intercellular canals are found, it exists in considerable quantity ; and in Nostoc, and other low forms of Algae, it exists as a jelly, in the midst of which the cells are found in the form of little strings. In Chordaria scorpioides and in Fuc7is vesiculosus (the bladder-wrack), two species of marine Algas, Schacht found that the intercellular substance was the product of the decomposition of the walls of the cells. The cuticle of Algae is of the same origin. In the cellular tissue of Helleborus foetidus (fetid hellebore) and Dipsacus fullonum (fullers' teasel), it completely fills up the intervals between the cells, except the central part, which is sometimes ^ The " perfect parenchyma " of Schleiden. ^ Meatus interccllulares ; hence called by Schleiden "imperfect paren- chyma." ' " Intercellular substanz" of Mohl, who so named it in 1836. i6 INTERCELLULAR SUBSTANCE — CELL-WALL. occupied by a bubble of air. Iodine and sulphuric acid colour the walls of the cells blue, whilst the intercellular substance remains uncoloured ; on heating the preparation in a solution of potash, the walls, composed of cellulose, swell up, while the inter- cellular substaHce does not : finally, while the cell-walls are rapidly destroyed by sulphuric acid, the intercellular substance resists that agent, though, according to Schultz, it disappears more quickly under maceration than the cell-wall. The intercellular substance is common to the two cells, which it unites ; and so firmly does it cement them together, that the cell will tear before the intercellular substance will give way. It follows that, though we portray on paper the cells as being separated from each other by well-marked lines, these lines are to a great extent fictitious. For instance, in fig. 3, a a, the intercellular membrane is shown as interposed between double lines, the walls of two contiguous cells. In nature, however, the cells seem as if soldered together — as will be apparent from what we have said regarding the inti- mate union effected between them by means of this intercellular substance.^ Schacht, Wiegand, and others, seem to consider that the cuticle is simply the intercellular substance formed on the free surface of cells ; but others are inclined to doubt the existence of the intercellular substance altogether, or its identity with cuticle. Relying on the behaviour of cellular tissue when coloured with carmine, Dr W. R. M'Nab believes that the "so-called inter- cellular substance is in reality the primary or cell wall — that as the growth goes on, this primary cell-wall becomes thickened by the addition of numerous more or less marked layers on the inside."^ The subject is one of interest, but we cannot think, for many reasons, that the question is yet definitely settled. Nature of the Cell-Wall. — We now come to consider what is the nature of the membrane which forms the walls of the cell. In its original form the membrane is thin, transparent, and colourless, with a pearly lustre ; and if the tissue into which it enters is coloured, the colour is due to particles inside the cell, and not to the cell-wall. If the cells communicate with each other it must be by exosmose and endosmose, or by means of minute pores which we have not yet been able to detect, though such have been seen by some observers. In one cell from a Euphorbia (Spurgewort), Miilder and Harting saw forty-five ex- ceedingly minute openings, though the whole transverse diameter of the cell was only 0.03777 of a millimetre. Chemically considered, the cellular membrane is composed of 1 Hartig appears to have mistaken this for a third coat of the cell-wall, common to two contiguous cells. He calls it Eustathe. « Trans. Bot. Soc. Edin., x. 73, 315. MARKINGS ON CELL-WALL. 17 a substance which dissolves in sulphuric acid and swells in a solu- tion of caustic potash. To the substance characterised by these reactions has been given the name of Cellulose (CsHioOg). It is isomeric with starch and dextrine, and contains no nitrogen.^ Pringsheim considered it a secretion of the protoplasm, or liquid which it envelops. Markings on the Cell- Wall— Up to a certain stage the cell- wall thickens hiterstitially by the incorporation of new matter into its substance, and then remains stationary— either thin or thick, according to its nature. Often, however, the cell-wall is thickened by deposits, which circumscribe the space inside into very small dimensions (figs. 10 and 1 1). In the stones of fruit, the Fig. 10. — Section of some cells with thickened walls taken from an exotic Aristolochia {A. cymbi- /era, Mart.) The concentric lines (a d) seen in the walls indi- cate the superimposed layers of thickening matter; p' p" Hollow canaliculae in the walls. Towards the left the same cells are seen {lb lb) in transverse section. Fig. II. — Transverse section of thickened cells from the pulp of the pear. wo cells re- shells of the Cocoa-nut, and suchlike structures, the whole interior is filled up with a hard deposit called lignine or sclerogen,^ which is only a modification of cellulose. In others it is only deposited to a slight extent and re- mains soft. This thickening (or " secondary deposit ") is due to the deposition of material, at first liquid, on the interior of the cell-wall,^ in successive layers, so that a transverse sec- _ ,. . , .■ ic 7j J \ 1 1 c gularly and distinctly tion (fig. 10, lb, and fig. 11) shows a number of marked with little poly- superimposed deposits firmly united together. reticulations, from - '. ^ , ■' r , 'he endosperm of the seed It sometimes, however, happens, that after the oi Aristolochia clematis, first layer has been deposited, the second ^• layer does not cover it, but is deposited in detached patches over it ; the successive layers which follow take the same dis- ^ See Ultimate Constituents of the Plant, Chap. iv. Sect, ii., for the Chemistry of Cellulose. * Lignum, wood ; (rKXr)p(5?, hard ; and yewoetv, to generate. ' Mohl and the greater number of observers believe this, but Hartig, Hart- ing, and others, teach that the cell-wall is thickened by layers from without inwards, and hence this has been called the "centrifugal theory. " t8 THICKENED CELLS. position —SO that, on looking at the cell, it seems as if covered over with punctations or slits, these apparent punctations being the im- perfect deposits inside ; and the slit-like appearances, longitudinal bars of a similar nature appearing through the still transparent cell-wall. The cell-wall is never perforated unless accidentally ; such an appearance is only an optical illusion. We have spoken of these markings as " deposits." The student ought, however, to bear in mind that these are not due to a mechanical but to a vital process— in fact, that the process is a physiological one. To be brief— it seems that certain parts of the cell-membrane have the power of assimilating the nutritive material in its interior, and so thickening it, and that other portions have not this power, and accordingly remain in the primitive condition of the transparent membrane. Sometimes this deposit takes a spiral form, and these forms of deposit on the interior of the cell-walls are characteristic of particular tissues in particular orders or species of plants, which can be readily recognised by this means. The modifications of the cell-wall are, then, as follows : — 1. Simple (fig. 2) : those transparent and without markings of any sort. 2. Thickened {^gs. 10 and 11) : concentric layers deposited in the interior, and united one to another (as seen in the stones of fruit, &c.) 3. Punctated, or dotted and disked (figs. 8 and i). The first form is seen in the elder, plane, gourd, wheat, and other plants. The pits of contiguous cells exactly correspond. Though not previously pits, they often become so with age "by the destruction of the pri- mary membrane after the cell has lost its vitality." Their use may be to convey sap from cell to cell, when the thickening of the walls might prevent this by the ordinary " endosmose " and " ex- osmose." The second kind of marking (viz., the disc) is found on firs, pines, and all the trees of that order, as well as on the winter bark (Drymis), Magnolia, &c. The regularity of the discs in the coniferte is especially remarked — the markings on two contiguous cells being uniform ; so that the disciform mark- ings are in lines transversely and perpendicularly in the tissue. The nature of these areolse has been studied with great care by Schacht,^ Mohl,^ Sanio, Dippel,^ and others, with different results. In general terms it may be affirmed that what looks like dottings in this tissue is, in many cases, formed simply by crescen- tic depressions in the sides of two contiguous cells or vessels, the two in apposition forming between them a lenticular cavity, in the centre of which is a canal — frequently funnel-shaped — which, 1 Botanische Zeitung, 1859, 283; De Maculis, &c., i860; and in Ann. Sc. Nat., i860. 2 Die vegetabilische Zelle, 1851 (also English Trans, by Henfrey, 1852). a Bot. Zeit., i860. THICKENED CELLS ; CONTENTS OF CELLS. 19 owing to the thinness of the contiguous tube, gives the appearance of a second circle inside of it. 4. Reticulated (fig. 12), in which the markings form a more or less re<^ular reticulation, as in the wing of the seed of Swietenia (maho- gany), seed-vessel of Picridiuvi tingitanum (a Tangiers plant be- longing to the order Compositje, common in our gardens), pith oiRu- busodoratus (an American bramble cultivated in this country), &c. 5. Annular or ringed, as in Opuntia. 6. Transversely barred— m short, incomplete bars ; hence called " scaliform," or barred like the rungs of a ladder (elder, &c.) 7. Spirally marked, composed of one or more bands or fila- ments rolled in a spiral manner, as in the leaves of various Orchids {Oncidiiim, Pletiro- thallis), also in Balsam, XtzS. q{ Sphagtmm. (moss), &c., and in the spore-cases of various Crypto- gams. Further examples are afforded by the spirally-lined hairs which cover the coats of the seeds and seed-like fruits oi Acanthodiuin spica- tutn, Sphenogyjie speciosa, and species of Collo- mia, Gilia, Senecio (groundsel), Crocidiuni, Sal- via (sage), &c., the filaments from which exhibit movements when placed in water, probably only due simply to elasticity from the absorption of ed^i™UiesT!wo fluid. When the wall is very thin, then the spiral imperfect tracheary marking is apt to be left as a separate thread by orthe^ garden balsam the obliteration at maturity of the wall. This, (^'^^•^^"^p'^) IppUed as Gray has remarked, occurs in the tissue that against each 'other, lines the walls of the anther ; and the spirally- marked tubes {Elaters) of the spore-cases of Hepaticce (fig. 9) are converted by this means into elastic spiral threads. The reticulated, annular, and spiral cells are often called " fibrous cells," ^ forming as they do the woody or fibrous tissue. The different tissues formed from these cells, or fibre-cells, will be considered when we come to speak of vascular tissue. Contents of Cells. — Many cells, such as those of the epidermis, pith, bark, &c., are often empty or filled with air, but all true living cells are filled with liquid and other contents. These contents may be divided into — i. Gaseous; 2. Liquid; 3. Solid. Under these heads we shall therefore consider them. I. The Gaseous Contents are chiefly air, more or less altered. 2. The Liquids contained in cells are somewhat more complex. First in importance ought to be mentioned the protoplasm, a ^ Or in mass " fibrocellular tissue," or Inenchyma, (im, fibres). See Pur- kinje, "De Cellulis antherarum fibrosis" (1830), in which memoir attention was first called to them ; and the subsequent papers of Slack (Ann. des Sc. Nat., i. 19s); Schleiden and Horkel (ibid., 1839), Mirbel, &c. 2 0 GYRATION OF THE LIQUID CONTENTS OF CELLS. granular viscid substance, composed of proteine and rich in nitro- gen, and surrounding the fiucleus. It chiefly occupies the interior of young cells, which it often fills entirely. Tht primordial vesicle, an extremely fine membrane, separates this protoplasm from the other liquids contained in the cell. Gyration in Cells. — In some plants the granules of the proto- plasm keep up a gyratory motion within its containing membrane — e.g.^ in the cells of Chara, Cauliiiia, Nitella, Naias, Anacharis, Hydrocharis, Vallisneria, the hairs and stamens of Tradescantia} in the hairs of the Cucu7-bita, Galeopsis, Borage, nettle, plantain — indeed nearly all hairs, the cells of the cotyledons of the seed of the common walnut, &c. This is called Rotation or Gyration, and was described in 1774 by Bonaventura Corti of Modena, though since that time the phenomenon has been the subject of numerous memoirs by Treviranus, Schultze, Amici, Poiseuille, Donnd, Dutrochet, Slack, Branson, &c. It can be seen, in the hairs of Tradescantia (the Virginian spider-liiy), in thread-like currents traversing the cell in various indeterminate directions. In the bristles on the ovaiy of Circcea, the current flows regu- larly up one side of the cell, round the top, and down the other side. In Chara and Nitella the circulation is also seen with lower power (50-100 diameters) of the microscope. In Vallis- neria spiralis, as seen with from 2-400 diameters, it describes a com- plete course round the cell, often carrying granules of chlorophyll with it, and even setting free the nucleus in its course. It is retarded by cold and accelerated by moderate warmth, though heat above 150° Fahr. stops it ; a current of electricity also stops it ; but no sooner is the current shut off than it recommences. Any mechan- ical irritation, such as jolting, pricking, &c., also stops it. Putting Vallisneria in milk or a thin solution of gum accelerates the gyration in that plant. The circulation in one cell is independent of that in the others, even contiguous cells. Speed of the Currents. — The speed of these currents has been calculated by Mohl at tbVt of a line per second in the hairs of the cucumber ; of a line in the hair of the nettle ; ^hs of a line in the Tradescantia virginica; and tss of a line in the leaves of Vallisneria spiralis?- However, in the latter plant the current has been observed to describe the circuit of the cell in less than 20 seconds, and in the bristles of the ovary of Circaa, which are half a line long, Mr H. J. Clark has seen the revolution completed in a minute. Cause of the Gyration. — This is very unsatisfactorily known. Cohn, Unger, and more recently Max Schulze,^ have expressed a belief that it is due to vital contractility— the idea that it is effected 1 Wenham in Quart. Journ. Mic. Sc., iv. 44. - Bot. Zeit., 1846, Col. 92. 3 Das Protoplasma der Rhizopodcn und d. Pflanzen— Zellen, 1863. GYRATION OF THE LIQUID CONTENTS OF CELLS. 21 by " cilia," or minute lashes attached to the sides of the cells, being discarded as originating in an optical illusion.^ It has been sup- posed by some physiologists that they have detected on the inner wall of the cell a series of exceedingly minute anastomosing vessels in which the gyration is performed ; and Slack ^ has described the existence of a second cell within the first, and attached here and there to it, but leaving a narrow space between the two, in which the gyra- tion goes on. Dr J. Bell Pettigrew considered that he had proved, by his producing these gyra- tory movements artificially by means of an in- genious apparatus, that they were chiefly caused " by absorption on one hand, resulting in endos- mosis and exosmosis ; and evaporation on the other."^ This idea is not improbable; and pos- sibly the effect of lead, opium, corrosive subli- mate, prussic acid, alcohol, &c., in stopping the gyration, may be due to the well-known fact that all acids, alkalies, soluble salts, alcohol, &c., on account of their liability to enter into com- bination with the permeable organic membrane, destroy endosmosis. We should, however, re- member, that gyration in cells is not a general phenomenon in plants, as we should expect to find it if this explanation of the able and justly eminent physiologist quoted was correct. It is not unlikely that gyration may be a much more universal phenomenon, especially in early cell-life, than we have hitherto sup- posed. Max Schulze observed in the pseudo- podia of Amoeba porrecta, a protozoan animal, a similar current to that in the cells of the cotyledons of the walnut. Lastly, Professor J. B. Schnetzler records some observations on the motions of the fluid in the leaves of the common water-weed Anacharis alsinastrum, introduced from Ame- rica some fifteen years since, and now known in this country as a great pest in our canals and rivers, which the great transparency of the leaves renders peculiarly favourable for examination. These rotatory motions of the protoplasm have, in addition to the explana- tions mentioned above as being proposed, been attributed by some to successive contractions of the exterior layer of the cells, by others ^ Branson in Quart. Joiim. Mic. Sc., ii. (1854) 131. " Ann. des Sc. Nat., 2d ser., i. 193. ^ Lectures on the Circulation: Edin. Med. Journ., 1872, 98. Fig. 14. — A few cells of the leaf of Naias Jlexilis, highly magni- fied, showing the inter- cellular circulation, the direction of the cur- rents indicated by ar- row-heads (after Gray. ) 22 CELL-CONTENTS — SOLID MATERIALS, to successive displacements produced by purely mechanical action. Neither of these explanations, Professor Schnetzler points out, goes to the root of the matter; and he believes that he has detected their ultimate cause in the chemical action of oxygen, which passes through the wall of the cells, and of which a portion is probably transformed into ozone under the influence of light, assisted by currents of electricity passing between the surface of the leaf and the contents of the cell. A similar conversion of oxygen into ozone is said to take place in the globules of the blood of animals. From the point of view of the mechanical theory, we have here evidently an example of the transformation of light and of heat into motion.^- The question as to how these strange gyratory movements in the cells of plants are caused is therefore still sub judice. The cell-liquid proper is a juice rarely altogether colourless, the colour being probably derived from the solid cell-contents, of which we have to speak presently. Sometimes the place of the water is taken by oils secreted by the cell ; it disappears in old wood-cells, and air takes its place in cork. It is capable of holding in solution very different and varied substances, such as gums and sugars. 3. Solid Materials. — These are very important and numerous, and play an important part in the nutrition of the plant. They are chiefly the tiucletis, chlorophyll, starch, and crystals. (a) The Nucleus. — We always find in the interior of young cells a lenticular or irregularly globose body, applied to a point on their sides in the midst of the protoplasm, to which the name of nucleus or kernel has been given. Schleiden, on account of the belief common among many physiologists that it plays an import- ant part in the production of young cells, has called it the cyto- blast, and describes it as composed of a number of extremely little corpuscles of indeterminate form. These he calls fmcleoli, and according to this celebrated observer each nucleolus is a rudi- mentary cell. The nucleus, Schleiden affirms, is found in all young cells ; it gets atrophied during the progress of growth, and in a number of cells is wanting altogether. On the contrary, Un- ger^ and Richard^ believe that the nucleus does not exist in very young cells, and that it only commences to show itself at a late period of the cell's existence. In orchids, in which order Robert Brown showed it for the first time, the nucleus is very well seen ; and in the leaves of Oroniium japonicum it is suffi- cient to cause elevated markings on the epidermis, each subjacent cell having a well-marked nucleus. It can be easily seen, espe- cially if a little iodine is applied. In that case it takes a marked brown colour, and shows distinctly that it is composed of irregu- 1 The Academy, 1869, 47. Ann, des Sc. Nat., xvii. 232. 3 Noveaux Elements de Botanique, loth ed. 9. CELL-CONTENTS — CHLOROPHYLL. 23 larly round transparent globules, though we do not yet know whether they are really globules or little cells— solid or empty. Dujardin ^ has put forth another opinion on the origin and func- tions of the nucleus, different from that of Schleiden. Accoi'ding to him, this body results from the condensation of the protoplasm, which fills the interior of the cells, and does not serve the import- ant purposes that many phytotomists would ascribe to it — in a word, he holds that there is no reason to believethat it is concerned in the formation of new cells. This doctrine, though held by some physiologists, is scarcely consistent with observed facts. (/3) Chlorophyll.'^— This peculiar substance is found in all parts of the cellular tissue having a green colour — the green colour of the tissue being due to the fact that the colour of the granules can be seen through the thin transparent cell-wall. It especially abounds in leaves,^ and has been shown by Mohl to be present in two forms — viz., round or ovoid grains or granules, and in a gela- tinous shapeless mass, in which are scattered granules of starch. The granules or masses float loose in the cell or are united to the sides. Some observers consider that the granules are colourless in themselves, but get coloured by a semi-liquid substance de- posited on their surfaces. Alcohol decolourises chlorophyll by dissolving the resinous matter ; hence flowers and leaves, if plunged into alcohol, are quickly blanched. Amorphous chloro- phyll is usually found in the shape of little gelatinous or flocculent masses, or of filaments adhering to the sides of cells ; but in some of the simpler Algae, Mongeotia genufiexa, Conferva zonata, Zyg- neina, &c., it is found in bands or lines of a remarkable character. In the last-mentioned genus it is in the form of a spiral against the wall of the cylindrical cell. Chlorophyll, however, generally exists in cells in the granular form. These granules are very small — from tss to itt of a milli- metre in diameter,* and often hexagonal from mutual pressure. The external layer of these granules is not, however, a special membrane, and has nothing of the nature of a true vesicle,^ though a contrary opinion has been held by some botanists of eminence," who even went so far as to consider the chlorophyll granules destined to develop true cells. On the whole, after sift- 1 Observations au microscope, 202; cited by Richard, op. cit., 9. - Chromule of De Candolle (from xp"^"». colour). •■' Hence the somewhat inappropriate but familiar name Chlorophyll (x^«pos. green ; and ^hXav, leaf), given in 1818 by Pelletier and Caventon to this sub- stance. Mohl in Ann. des. Sc. Nat., 1838, 1855 ; Boehm in Sitzungsberichte derAkad. Wien, &c., 1857; Berzelius, Ann. des Sc. Nat., 1850. ' Morren, Dissert, sur les feuilles vertes et col., i8<;8 ; Gris in Ann. des Sc. Nat., 1857. ^ * Turpin (1828), Raspail (1837), Meyen (1830, though in 1837 he abandoned that doctrine), Mirbel (1831), NaegH, Trecul (1858), and others. 24 CELL-CONTENTS — CHLOROPHYLL. ing the various contradictory opinions evolved in the voluminous literature of which chlorophyll has been the theme, we are inclined to agree with the opinion of M. Duchartre that it " affects a series of states connected with and passing into each other," and that " the jelly-like condition of the granular form can change into the amorphous by the granules acquiring a greater consistence and being confined within a false envelope." The chemical characters of chlorophyll will-be given when treating of the chemical consti- tuents of plants. Sachs has shown ^ that the intensity of the colour of chlorophyll diminishes under the direct influence of the sun's rays ; but by the researches of Famintzin,^ Borodin,^ Prilleux,^ and Roze," it has been shown that this change of colour is only apparent, and results from certain movements performed by the granules in the interior of the cell. During the day the granules group themselves in the cells along the horizontal walls or those parallel to the surface ; but during the night they execute a movement of retreat and place themBelves along the walls perpendicular to the surface. Light, and not heat, is the cause of this phenomenon. The most refrangible rays alone have the power of drawing the chlorophyll towards the surface, the most luminous rays producing the same effect as complete darkness. These movements must necessarily, from the anatomical rela- tions of the different parts ,of the cell, be accompanied by a dis- placement of the whele protoplasmic mass. Frank,® from observatiens made on Sagittaria sagittifolia and Mnium ro&tratum (Schiyasgf.)i came to the conclusion that chlo- rophyll, in addition to the properties described, has a "tendency to move in the interior of the cell to the side which is most illu- minated, exactly as zoospores (or the free-moving seed-like bodies of certain algae) do when piaced in a plate near a window." Though the position, orientation, or direction of the cells has no influence on this phejiomenon — it being as well manifested in diffused ligbt as in the sun's rays^" in a. general way diminution of the intensity of the iight -renders the piienomenon less striking and sometijnies irregular ; it is, hewever, always manifested, what- ever may be the .colour of Ihe Jjumi-nous rays." It is probably associated with peculiar protoplasmic intracellular currents. It has now been shown thatswe must greatly modify our old belief in the most luminous rays of the epectrum alone acting in the phenomena of assimilation. This is a subject so important that even In elementary studies some knowledge of the recent 1 Physiologie Vy^g^tale (Fr. Trana.), 1.6. 3 Pringsheim's Jahrbuch fiirwiss Bolanilc, v, 49, M(51anges Biologiques tirds de I'Acad. Imp. de St Petersburg, vii. (1869), 505 and Bot. Zeit., 1869, No. 38. 4 Comptes rendus, 1870, Ixx. * Ibid. « Bot. Zeit., 1871, No, 14. CELL-CONTENTS — STARCH. 25 researches in regard to it ougiit to be acquired by the student. Gregor Krauss/ Prilleux,^ and Baranetzky,^ particularly the latter, have made investigations in regard to this question, and the state of knowledge regarding it may be summed up as follows, viz., that — (a) The decomposition of carbonic acid (CO2) or as- similation, the formation of chlorophyll, and the destruction of the colouring principle, are phenomena solely dependent on the degree of luminous intensity; 0) " heliotropic curvatures" — i.e., the movements which certain plants, like the sun-flower, perform under the influence of the sun — the periodical movements of organs, the currents of protoplasm, and the changes of place of the grains of chlorophyll, are executed only under the influence of the most refrangible rays. From the observations of Mr H. L. Smith there seem some grounds for believing that the endochrome of the microscopic aquatic plants known as " diatoms " is identical with chlorophyll. Lastly, chlorophyll is not confined to the vegetable kingdom ; a green colouring matter closely allied to, if not identical with it, may be detected in many animals belonging to the sub-kingdom Protozoa, &c. Its origin has been the subject of careful research by Quekett,* Mohl,^ Gris,^ and Trecul,^ but it is still more a matter of specu- lation than of ascertained fact, the general belief being that it is either derived from the nucleus in a manner analogous to that in which starch is, or that it is a transformation of the protoplasm — the last view being that of Mohl and Trecul, while Quekett and Gris are the authorities for the former opinion. (y) Starch? — Fecula or starch is one of the most important and generally diff"used of cell-contents, and one which renders plants so valuable as the food of many animals. In a dry state, it presents itself in the form of a white powder composed of little grains, set free by the rupture of the membrane of the cell containing them. It is found in a variety of plants. In the records of economic botany are enumerated many such — more or less familiar in domestic or commercial economy. Among seeds abounding in starch may be mentioned the whole order of the Graminese or grasses, more especially those species known as cereals: such as wheat, barley, r)'e, oats, maize or Indian corn {Zea Mays, L.), x\c^{Oryza sativa,!.^; various cereals of Africa, such as "teff" {Poa abyssinica, Jacq.), "dourra" {Sorghum), the "toucusso" ^ Pringsheim's Jahrb., vii. 511. * Comptes rendus, 1870, Ixx. 521 ; Ann. des Sc. Nat. se s6r. x. * Bot. Zeit., 1871, No. 13. 4 Annals of Nat. Hist. 1846. ' Vegetable Cell, &c. ' Ann. des Sc. Nat. 1857, cited in Bull. Bot. Soc. Fr. 1857, 154-156. ^ Ann. des Sc. Nat. 1858. 8 Cells containing it in tissue received the name of Perenchyma (mipa, a sac) from Charles Morren. 26 CELL-CONTENTS — STARCH. {Eleusine Tocusso, Fres.) ; the Natchanee or Murooa of the Hindoos {Eleusine coracana, Gsert.), millet, Bujera or Bujra of the Hindoos {Penicellaria spicata W.), &c. Starch is also found in the following plants cultivated for their edible seeds : Buckwheat {Fagopyrum esculenteum, Maench, and F. tartaricujn, Gasrt.), quinoa {Chenopodium Quinoa, L.), and two or three Amaranths very little known {Amarantus frumentaceus, Buchan. ; A. farinaceus, Roxb. ; A. Anardhaiia, Royle). It is the starch which gives the value to the seeds of various leguminous plants, such as haricots iPhaseolus), peas {Pisiim sativum, L.), lentils {Ervum Lens, L.), beans {Faba vulgaris, Meench), chick ^e.2i(jCicer arietinu7it),Dolichos, &c. ; also the chestnut {Casianed) and various other trees. It ought also to be mentioned that in most of these plants, and especially among the cereals, the starch is mixed with nitrogenous matter, which renders them more nutritious than they would other- wise be. The fruit of the banana {Musa) contains, before being ripe, starch, which is replaced at that period by sugar. In the stems of some plants starch accumulates, especially towards the centre. For instance, sago is obtained from the pith of the sago-palm {Metroxylon Rumphii and M. Iceve) of the Malay Islands, — a single tree of which will sometimes yield 800 pounds ; Caryota urens, L., Cyas revoluta, Thim., and C. circinalis, L. : little of the sago de- rived from the three latter ever comes to this country, being mostly consumed on the spot. In the parts of plants which are situated beneath the surface of the ground starch also accumulates, for the nutrition of the plant. Among such plants we have to enumerate the well-known potato {Solamun tuberosum, L.) ; the sweet-potato {Batatas edulis, Choisy) ; yams {Dioscorea alata, L. ; D. Batatas, Dene., &c.) ; colocasia or kuchoo of the Hindoos {Colocasia antiquorum, Schott) ; taro or tara of the Polynesians {Colocasia esculentea, Schott) ; Pia {Tacca pinnatifida, Forst.) ; Manioc {Manihot Aipi, Pohl. ; M. utilissiina, Pohl.) This latter species furnishes tapioca, while M. arundinacea, and M. ramocissiina, L., West Indian species, furnishes the chief portion of the arrowroot of commerce.'^ " Tous les mois " is got from the tuber of a species of Canna, — probably C. edulis. Finally, we may mention that starch is not confined to the vege- table kingdom, being, at all events, found in the lowly-organised animals known as the Radiolaria."^ In form starch-grains are well marked, consisting of a dot or hilum, generally near the smaller end, with concentric lines drawn around it. The shape of the grain differs in every different species 1 Julius Munter showed (Bot. Zeit., 1845, No. 12) that under the common name of " arrowroot " are imported the starch of at least three species of plants, each easily distinguished by the characteristic form of their grains. 2 Haeckel— "Beitrage zur Plastiden Theorie"— Jenaische Zeitschrift, v. CELL-CONTENTS— STARCH. 27 of plant in which it is found. The grains are generally rounded or oval, but sometimes angular from mutual pressure. In the tissues starch is rarely found in an amorphous state, but generally in the form of separate grains, each possessing the characters above men- tioned. The starch-grains and their mode of formation have, since the days of Leeuwenhoek down to our own, been a fertile subject of observation and opinio,n, — more frequently of opinion without obser- vation at all. Notwithstanding that microscopists of the eminence of Raspail, Payen, and Trecul, in France ; Busk, Allman, Cruger, Grunde, Henfrey, and Rainy, in England ; and Fritzche, Schleiden, (above all) Naegli and Munter, in Germany, — have given their attention to it, we are yet far from having very clear ideas in regard to the subject. Our space forbids to enter upon this discussion, nor will the student lose much by the omission. One fact tolerably well established regarding starch is — that its presence is a criterion of the age of the plant, the vital activity of the cell being at an end after this substance is developed. Regarding the mode in which starch is produced in the interior Fig. 15. — Two cells of a potato-tuber, con- taining starch-grains. Fig. 16. — A grain of starch from the potato ; h Central point or iiiluni ; a b The two extremi- ties of the granule, the last of which (i) is very excentric. Fig. 17. — Acciden- tal form of starch- grains in the potato. Here three simple grains are united in- to one. of the vegetable cell, Trecul and Gris have made researches, — the result of which is that it seems to be ex- creted by the protoplasmic material con- tained in the cells— either by the primordial utricle, by the filaments of protoplasm, or directly or indirectly by the cell-nucleus. The lines shown on the surface of a grain of starch are evid- ently marks of the deposition of layers around a central nucleus (the "dot" or hilum), which is usually very excentric • ^'s- 'S.— Section of cellular 4.11 ' tissue containing starch-grams owing to the deposits being thicker on (from the seed of maize or one side than on the other. Indian corn). It appears that before starch can be fitted for the nutrition of the plant, it must be converted through the agency of diastase 28 CELL-CONTENTS — : FORMS OF STARCH-GRAINS. into dextrine, as it cannot dissolve in cold water, and hence not in the juices of the plant. A chemical test for starch is its giving a beautiful blue or purple colour when acted on with iodine. The shape of the starch-grains, we have already mentioned, varies much. The following table, compiled from Duchartre,^ shows the chief forms of the starch-grain, which it is all-essential for the botanical student to be acquainted with, so that he may recognise them under the microscope : — a. S 'Eo [/I C ■3 1-1 O X) c o 1 O O ^ u S o U O 1- a bo Without visible nucleus. Nucleus small and rounded. Nucleus elongat- ed and branched Angular or polyhedral. Without visible nucleus. With a visible nucleus. f Very small, rounded. Ex. Throughout nearly I all plants, but especially in wood in winter. ( Large, ovoid, generally rather straight towards \ the tip. Ex. Potato (fig. 16). J Small or large, oval, a little depressed. Ex. \ Haricot, Pea, Bean. /Polyhedral, more or less rounded on one side. I Ex. Maize (fig. 18). j Very small, polyhedral, with marked ridges. Ex. \ Rice. Formed of two to four elementary grains with a { ( Formed of many elementary grains disposed \ round a greater. Ex. Sago. small rounded nucleus. Ex. Tapioca. In size starch-grains also differ much, and, as might be expected, often differ much in the same plant. Payen has given a table of the sizes of the starch-grains of various plants, from which the following are selected : — Various kinds of potato from .185 — .140th of a millimetre. Arrowroot of Maranta aruiidinacea Various sagos Large garden-bean Lentil Haricot Seed of Maize Seed of Millet 2 Seed of Beet » Seed of Quinoa* .140 .070— .045 • 075 .067 .063 .030 .010 .004 .002 Imiline and Aleurone are only other forms of starch, and will be noted more particularly when we speak of the "Ultimate Consti- tuents of Plants." To recapitulate — the contents of the cells may be put in tabu- lar form as follows, classifying them according to their chemical ^ See also the researches of Rivot and Moitessier in Annales de physique et de chemie, 36 sdrie, l.xvii. ; and M^m. de I'Academie de Montpellier, \A. 336. 2 Panicum miliaceiim. ' Beta vulgaris, var. rapacca. 4 C/ienopodium Ouinoa. CELL-CONTENTS — CRYSTALS. 29 constitution, though for convenience' sake we have considered thenn in the foregoing pages according to their physical character : — /Neutral . . . Starch, inuline, gums, sugars, &c. J Oxygenised . . Vegetable acids, pectinc, and pectose. j Hydrogenised . Oils, resins, wax, &c. g) ; 5 5) I Hydrocarbons . Essential oils of turpentine, orange, citron, &c. i S j Neutral . . . Aleurone, albumen, legumine, glutine, fibrine. •- c 1 Non-neutral . Alkaloids, chlorophyll, colouring materials. ^ Si ^ .- 3 s % o { Salts (dissolved . . f Carbonates, oxalates, chlorates, malates, tart- or crystallised) . . \ rates, &c., of lime, potash, &c. ba (. Acids Silicic, oxalic, carbonic, &c.i In the progress of growth the contents change, one substance disappearing and another taking its place ; again, during the ger- mination of the seed changes take place, oxygen being absorbed, and the insoluble starch and oil passing in a state of solution to serve as food for the young plant. (S) Crystals. — In the interior of the cells are also found crystals of a perfect and determinate form, sometimes isolated, at other times united in masses of greater or less size. They are found in the shape of rhomboids, cubes, octohedrons, or prisms. Sometimes the cells which contain them do not differ from the rest of the parenchyma; at other times they are manifestly larger. They are found in more or less abundance in all plants, but are more plen- tiful in the cells of the leaves and bark, and in the wood and pith of herbaceous plants. In an old stem of the " old-man cactus" {Cactus senilis), according to Gray, 80 per cent of the solid matter was found to consist of crystals, rendering it almost as brittle as glass: and in the inner layer of the Ipcust-bark each cell con- tains a single crystal. The late Professor Bailey, of the U.S. Military Academy at West Point, calculated that " in a square inch of a piece of the locust-bark, no thicker than ordinaiy writing- paper, there are more than a million of these ciystals." (i.) One form common in plants belonging, to various orders is that known under the name of Raphides (D.C.) ^ They consist of sharp needle-shaped bundles of prisms, commonly of oxalate of lime, though carbonate, sulphate, or phosphate of lime not unfrequently enters into their composition, terminating each in a fine pyramidal point^ — one cell often containing them in consid- erable numbers (fig. 19.) The cells in which these crystals are found are very often without chlorophyll or starch. They may be seen to the extent of from 301040 per cent in the cells of the stalk ^ For further information on these cell-contents not already described, see Chap. iv. Sect. ii. * 'Pou(>is, a needle. ' Kieser, Organ, des Plant., 94, 122. Kieser was the first to point out their crystalline nature. 3° CELL-CONTENTS — CRYSTALS, Fig. ig. — Raphides in a cell of Co- locasia aiitiqiw-nim. A cell, a, made larger than those which surround it, of the rhubarb (giving sign of their presence by gritliness of the tissue when cut through), the Calla, &c. (2.) In the screw-pine {Pandanus- iitilis), the stem of which is remark- able on account of containing vessels belonging to the scalariform type, though otherwise resembling that of the palm, in addition to raphides in the cells of the cortex, &c., crystals of a peculiar type are found in connec- tion with the fibro-vascular bundles. These crystals are contained each in a square-shaped cell, forming part of a string or chain. A number of these chains or strings are distributed round the circumference of each fibro- vascular bundle ; they are especially abundant in its cortical continuation, containing these rafihides or crystals as they do not Suffer a degradation of oxalate of lime (1!'). ' . , . ° , proportionate to that of the other constituent tissues. Mr Thissleton Dyer, to whom we are in- debted for this curious observation, thinks that this arrangement of crystal-bearing cells is probably unique. The crystals are four- sided prisms with pyramidal apices. They are almost certainly composed of oxalate of lime, though they are too minute, and isolated with too much difficulty, to allow of their satisfactory examination.^ (3.) In fig. 20 is portrayed another group of crystals, common enough in various plants. Weddell has -applied the name of cystolithes^ to these curious crystalline bodies generally found in the superficial cells of nettles and some other species of the order Urticacece and various genera of Acanthacece. Since they were first discovered (in Ficus elastica, Rox.) by Meyen in 1827, they have given rise to some difference of opinion regarding their nature.^ They are globular or club-shaped bodies, or of various other forms, " usually hang- ing by a short stalk in an enlarged cell ; their principal mass is found to be cellulose, but their surface is studded with crystalline points of carbonate of lime." Not only are the crystalline con- tents of cells enclosed by the general cell-wall, but they are covered by an extremely delicate organic covering closely applied to every part. 1 Dyer in Report Brit. Assoc. (Trans, of Sect.), 1871, 128. 3 Kvcrris, bladder ; and ViSos, stone. 3 Besides their original describer Meyen, Payen, Schleiden, Weddell, Gottsche, and Schacht have all prominently shared in the controversy. CELL-CONTENTS — CRYSTALS j LACUNA. 31 It only now remains for us to note the remarkable excretions (?) of carbonate of lime which form on the leaves of Saxifraga Aizoon, L., the silex in the stems of various species of plants, the tabascheer or deposit of silex in the hol- low stem of the bamboo, &c. These can, however, be scarcely classed as cell-contents, and are noticed more in detail in their proper place. It may be asked- — how do these crystals form in " the interior of cells? In reply to this question, Fig. 20.— A cell, it may in the first place be pointed out, that acids /^^/„vi sipho, con- of various kinds are formed in the plant, and that taining a mass, cr, , , , , . , . . of united crystals bases are taken up by the roots in the nutritive or cystoiithes, only juices derived from the earth, and that the reaction showing their free ■' . extremities. of the one upon the other might produce such crys- tals of insoluble salts (carbonate and oxalate of lime). In proof of the probable truth of this explanation it may be pointed out that the late Prof. Quekett artificially produced raphides within the cells of rice-paper (pith oiAralia papyrifera) by first filling them with lime- water and then placing, the paper in weak solutions of phosphoric and oxalic acids — the artificial crystal agreeing in crystalline form with the natural one of the same chemical composition, those of phosphate of lime being rhomboidal, while oxalate of lime crystal- lised into stellate forms. Allowing, then, that this is the source of these crystals, where does the thin organic envelope which covers them in the cell come from ? In default of a better explanation Richard's may be received. He thinks that after the crystal has formed in the midst of the nutritive fluid of the cell, little by little a deposit of organic matter is applied to its surface until it is entirely covered. No other explanation can account for the ex- istence of such a delicate membrane covering in such a close manner so many crystals as are found in the -interior of a cell. Lacunse in Cellular Tissue.— In the cellular tissue are often found a number of lacunae or cavities formed by the separation of cells, and the tearing, absorption, or partial destruction of the tissue. The most familiar examples of such lacunae are afforded by the hollow stems of grasses and other plants, the pith of the walnut and other trees in which the tissue is found in the form of disciform transverse partitions, and in the floating leaves of water- plants. Sometimes these lacunae are regular, at other times very irregular in form, and though generally filled with air, sometimes resin occupies their interior. To lacunae, produced simply by the amplification of the intercellular spaces and the separation of the cells without tearing, Meyen and Leitgib ^ have applied the name of Air-bearing Canals? They are so common, and occupy such a portion of the mass of the leaves of aquatic plants, that, ac- ^ Sitzungsberichte, &c., 1856. 2 Luftgcenge in German. 32 LACUNiE IN CELLULAR TISSUE ; CYTOGENESIS. cording to Unger, there are 713 parts of air in volume in 1000 of the substance of Phtia Texensis. They are also very regular in shape— passing continuously in a longitudinal direction through the substance of the leaf, as in fig. 21, showing a number of these Fig. 21. — Transverse section of a portion of the leaf of Zostera marina, L., showing the range of air-bearing lacunse. / / / / Separated by partitions, cl, formed of a single tier of cells ; « Nerves ; e'p Epidermis ; fl fl Jl Bundles of very long cells. in a transverse section of the common sea-grass [Zostera marina), a marine flov^ering plant, or in Cymodocea aguorea. They in- crease with the increase in length of the leaf. To the spaces produced by the tearing, absorption, and destruc- tion of tissue, the authors named have applied the special designa- tion of Air-bearing lacunce} Unlike the air-bearing canals, these lacuncE do not appear in the early stages of the plant, and increase with the growth of the surrounding parts, or indeed are subject to any special laws of growth. In a word, they may be said to be accide7ital. They are seen in the stems of gramineas, reeds, and similar plants. The leaves of many bulbous plants are also, apparently for the sake of lightness, full of such cavities — e.g., those of the hyacinth. Leitgib has even divided these "air-bearing lacunse " into two subdivisions : (a) Canaliform lacuncE, when they are somewhat long and continuous, and give passage to air ; and (/3) Lacunae, properly so called, when perfectly isolated in the middle of the tissue, and often superimposed in lines or separated one from the other by transverse partitions. These distinctions cannot, however, be precisely applied to organs so variable. In the genus Jussicea, particularly in y. repens, the lacunae are very well marked in the roots, which here subserve the purposes of floats. In these species, Martins and Moitessier state the compo- sition of the contained air to be 7 to 14 per cent of oxygen, and 86 to 93 per cent of nitrogen — a composition different from that of atmospheric air (nitrogen 79, oxygen 21 per cent). ^ I.uftlucken in German. CELLULAR TISSUE. 33 DEVELOPMENT AND INCREASE OF CELLULAR TISSUE (CYTOGENESIS).I Having sketched out the character of the parenchyma formed by the union of cells, the student is now better able to understand the current doctrines regarding the development and increase of cells resulting in the formation of this tissue. That these cells are very minute he will have already under- stood. In size, however, they vary much, even in the same organ, their ordinary diameter being between ^xtt and x-sVo of an inch, though those of the gourd are of an inch in diameter, those of the lemon more than ^ an inch in length, and those of the shad- dock much larger.^ Canlerpa prolifera, a marine Alga, though often a foot in length and branched into what look like leaves and roots, is in reality only a single cell ; while in Vaucheria, Bryopsis, and Chara, the cells of the stem attain the length of several inches and a diameter of one-third of a line or more. The hairs which constitute " cotton " are single filamentous cells one to two inches in length. Again, the spores or dust-like seed-bodies of fungi are much smaller than any of those we have mentioned — the smallest of them allowing as many as 1728 millions within the compass of a cubic inch, each being not more than 5^ of an inch in diameter. That the rate of the production of cells is inconceivably rapid may be imagined from the fact that the flower-stalks oi Agave or Century plant are said to increase in the humid tropics at the rate of about two feet per day. Mushrooms of gigantic size will spring up in a single night: the large puff-ball {Bovista gigantea) is calculated to develop at the rate of three or four hundred million cells per hour, though it ought to be remembered that the rapid increase of this plant is owing chiefly to the expansion of cells already formed. The cell is in reality a complete living organism, capable of per- forming all the functions of life within itself; and the plant is either composed of one (p. 14) or of many such organisms in combination. We have already seen what the cell, in general terms, consists of. Looking at it from an anatomical point of view, we see that in a state of vitality it consists of — i. The cell-wall, already described (p. 16) ; 2. The primordial vesicle^ {jitricle of Mohl), a delicate mucilaginous film lining the wall ; 3. The nucleus (or cytoblast*); also described (p. 22) ; and 4. The protoplasmic fluid^ (p. 20), which ^ KuTo?, a cell ; ycVeo-i?, origin. Quekett's Lectures on Histology, 18. ^ In German, Primordial-Schlauch — the utricle protoplasmiqiie of Trecul. ■* KuTos, a cell ; /SAoorb?, a germ. npwTo?, first ; and n\ke with a plain outline. By this means the presence of one or other fibre in a fabric can be instantly detected. For instance, by this test the cloth wrapped round the Egyptian mummies was shown to be linen, and that around the Peruvian ones to be cotton. VASCULAR TISSUE : LATICIFEROUS VESSELS. 4I VASCULAR TISSUE.^ We have seen in the preceding pages the cell either performing all the functions of the plant, or multiplying to form celhilar tissue —a mass of united cells ; or, secondly, these cells may elongate, and, with their cell-walls thickened by internal deposits, form ivoody tissue. In neither of these cases are there any true con- ducting vessels formed. We now come to the last modification of cells,— viz., that in which they form vessels by being placed end to end, and the transverse partitions getting absorbed— just as a number of casks, if placed end to end, one above another, would form hollow cylinders if the contiguous tops and bottoms fell out. It must therefore follow, if this is the mode in which vessels are formed from cells, that these vessels, as in the woody tissue, must partake of all the character- istics of the individual cells of which they are composed. Tubes or vessels are conse- quently divided, according to the markings on the cells of which they are compos- ed, into — I. Simple-walled or laticiferous vessels ; 2. Trach- eary vessels; 3. Punctated and barred vessels. These three great divisions have some mi- nor modifications, which we shall consider under the differ- ent headings mentioned. Laticiferous or Simple- walled Vessels.^ — These re- marVahlp vp^spI-? wprp fir=;t Fig. 25.— Fragment of a Liaciierous vessel marKaOie vessels were nrst from the cultivated fig (i^zc/«<;«r/cri, L.) The fully called attention to in 1836 globules of latex can be seen, owing to its K,r r TJ C^kiiU, "Roi-lJti 3 transparency. The vessels in the figure ap- Dy K^. n. SCnUltZ 01 iSeiim, pear wider (a) or narrower («' «') at certain and were again the subject of points, owing to the knife, in making the sec- 1 , . . 1 T-~. . tion, having let out some of the globules. elaborate memoirs by Dip- pel and Hanstein in 1863. Nevertheless, their nature, contents, 1 Angienchyma (ayyos, a vessel). The words "duct" and "vessel" are generally used synonymously, though attempts have been made to reserve the former name for vessels proper, the latter for wood-cells. * Lebetusaftgefcesse (vessels of the vital sap), Milchsaftgefcssse (vessels of the milky sap), vaisseaux propres (proper vessels), &c., of various German and French authors ; the Ciuenchyma {kLvsm, I move — from the movements of the latex under them) of Morren. * Die Natur der lebenden Pflanze (1823-28) ; Sur la circulation et sur les vaisseaux laticiferes dans les Plantes (1839) ; Die Cyclose des Lebenssaftes (1841). 42 LATICIFEROUS VESSELS. and uses are far from being thoroughly known. The following facts in regard to them may, however, be accepted by the student as resting on a tolerably sure foundation. Their walls are generally thin, deprived of any markings ; more or less winding in their course through the tissues, unequal in their diameter at different points ; and, above all, they are frequently branched, different tubes anastamosing to form a sort of open net- work in the tissue. Minor characteristics may be noted in that they are opaque-walled, and in that their contents are opaque, white, or coloured. In shape they are more or less cylindrical when they are isolated, and prismatic or angular when they are united, on account of the mutual pressure which they exert on one another. Their average diameter is about rrinr of an inch. They exist in most dicotyledonous and monocotyle- donous plants, and Schultz has even found them in some acotyledonous orders. In these divisions they, however, occupy different places. In Di- Fig 26 —Globules ^^ty^^dons and Monocotyledons they are con- of latex from Ficus stantly found in the vascular bundles of the magnified.'"'' leaves which are known as nerves. In the stem of Dicotyledons they are seen in the bark ; in other instances they are found in the pith. In the stem of Mon- ocotyledons, on the contrary, they are found in each of the woody bundles scattered through the cellular tissue of the stem. In some plants — e.g., the hedge-maple — they are confined to the young shoots. Regarding the origin of the laticiferous vessels, the student ought to know that though they are generally believed to be formed like other vessels, by the union of lines of cells, this opinion is not universally held by botanists. On the contrary, it is stoutly maintained by some physiologists of great eminence that they are simply intercellular canals, enlarged by the accumulation of the latex (p. 43) in their cavity, and around which the liquid secreted forms little by little, by a simple deposition, the walls of the canal. This latter opinion is adopted by Mohl, Schleiden, and others; while for the former, which is more generally adopted, the names of Unger,^ Schacht,^ Dippel and Hanstein,^ Vogel, Trecul, &c., stand sponsors. Unger, indeed, describes and figures the laticiferous vessels in the root and stem of Chelidonium majus (common celandine) as formed of cells easily distinguished the one from the other ; and Schacht, in terms equally explicit, de- scribes them as formed of several cells fused into one.* 1 Grand, der Anat. u. Phys. der Gewachse, s. 159. 2 Die Milchsaftgeffisse d. Carica, 1857. 3 Comptes rendus, Ix. (1865) 78, 522. * The truth probably is, that in some cases they are simply intercellular LATICI FERGUS VESSELS : LATEX. 43 Laticiferous vessels may be divided into two categories : (i.) Those in which the tubes branch but do not unite with the neigh- bouring- tubes, and accordingly form no network, and are all, in all stages of their growth, inclined to be semi-articulated — i.e., composed of cells which, on maceration, separate easily (Ex. Cheli- donium majus, EnpJiorbias, Vhtca minor, Chicory, &c.) ; and (2.) Those in which they form a network, and show no signs of articulation. In 1853, Th. Hartig discovered, between the liber and the cambium, elongated thin-walled cells, generally cylindrical, super- imposed in rows, and remarkable in so far that they present either on the diaphragm formed by their superposition, or upon their lateral walls, minute punctations, so that they resemble little sieves. Hence they were called cribriform tubes?- It has been supposed by some that these are the cells which unite to form the laticiferous vessels, and it is pointed out that they replace in milky-juiced plants those sieve-like cells which are found in the liber of other flowering plants. Latex. — We now come to speak of the latex ox milky juice found in the interior of these vessels. This and the containing vessels are found in a great number of plants familiarly known as possess- ing milky juices, such as the spurges {EupJwrbid), figs, dandelion, lettuce, &c. This juice is generally opaque, white, or more rarely coloured : for instance, in Chelidonium majus it is yellow, orange in the artichoke, greenish in the periwinkle {Vinca minor), &c. It is generally found disseminated in greater or less quantities through every organ of the plants in which it is found. Microscopically (fig. 26), the Iktex is shown to be formed of an enormous quantity of very minute globules floating in a liquid to which they give the opacity or coloration : it is generally bitter and acrid in taste. Chetnically, we find that this latex contains materials which give many plants in which it is found a high commercial value — caoutchouc and analogous materials being forms of it. For example, caoutchouc or India-rubber is derived from vari-. ous species of trees — viz., Ficus elastica and Castilloa elastica of the order Artocarpeaceas, and Urceola elastica, belonging to the Apocynaceas. The India-rubber of Brazil is furnished by Sipho- nia brasiliensis, and that of Guiana by Hewaa guyanensis, both canals, as may be seen in Alisma Plantago, and other monocotyledons ; as also in Rhus, Nvild angelica, and the Umbelliferse generally, and, according to W. R. M'Nab, in the young stem of the ivy (Trans. Bot. Soc, ix. 316). These canals are different from the resin canals of the Coniferee in wanting the delicate lining. 1 Siebrmhrcn in German. Mohl, in 1855, called them Giitcrzdlat, or cellulcB clathrata (Bot. Zeit., 1855, §§ 873, 889). He has also called them, as found in the isolated vascular bundles of the monocotyledons, vasa propria ; in French, cellules treiblisdes, or grillagics, &c. 44 LATEX AND ITS VARIETIES. Euphoi-bacious trees. One of the Sapotaceae {Iso?iandra guttd) of the Malay Islands furnishes in its latex the familiar gutta- percha. The latex, again, of Antiaris toxicaria (Artocarpeaceai), furnishes the celebrated poison of the Javanese, known as Upas antiar, and the origin of the fabled " upas-tree " invented by the " Puck of commentators," George Steevens, and perpet- uated by Erasmus Darwin. Karsten, however, found that when standing under one of these milky-juiced trees in Brazil, for the purpose of collecting some of the latex, his skin got seriously blistered, owing to the poisonous emanation from the fluid. It may be also noted that several species of Rhus found in America {R. toxicodendron, &c.) are popularly known as " poison oaks," from their blistering the skin coming in contact with their foliage. It is said that so sensitive are some people to the poison, that they will be affected by the smoke from a fire composed of these bushes blowing over them."^ By contrast, some other trees of the same order, Galactodendron utile and Ficus brasiliensis, have a latex rich in sugar and alb umen ; and that of TaberncEmontana utilis or Hya — Hya of Guiana — is even used as vegetable milk ; while a close ally in the same natural order, Tanghinia venenifera, furnishes in its latex a violent poison. Galactodendron utile, from the use made of its milky juice, is well known under the Spanish name of Palo de vaca, or cow-tree of the English. Two opinions are held regarding the uses of the latex : one is that it plays an important part in nutrition, and is the elabor- ated juice after descending from the leaves ; the other belief, much more generally adopted, and more in accordance with reason and facts, is that it is simply a material secreted by the living plant, and plays but a feeble part in nutrition. Schultz, Schleiden, and others, described a regular circulation (" cyclosis ") of the latex in various plants ; but of late, Amici, Treviranus, Dutrochet, and Mohl,^ have denied the existence of this — asserting that if any . such movement exists, it is merely mechanical from one part to another w^hen the plant is injured, and the juice is allowed to escape. We are, however, of opinion that these eminent micro- scopists are wrong, and that the prior view is the correct one. If the under side of the leaf of Chelidoniuni niaj'us, Taraxicum 1 R. Brown (Campst.), Trans. Bot. Soc, Edin., ix. 399. 2 Bot. Zeit., 1843, s. 563. The student, however, in weighing the argument which Mohl and Schleiden brought against Schultz's theory of the milk-sap, must take into account the violent antipathy which both, especially the late eminent Tubingen Professor, appear to have entertained to anything emanating from their scarcely less distinguished Berlin rival — an antipathy often expressed in language which, however it might be considered suitable for a botanical con- troversy in Germany, would, in our more westerly longitude, be deemed de- cidedly unparliamentary. TRACHEARY VESSELS. 45 officinale, the bracts of the common bindweed, the lower surface of the split stipules of the India-rubber plant, or any such milky- juiced plant, is put under the microscope, and a strong- reflected sunlight be thrown on it, a distinct movement can be seen — sometimes very rapid, at other times slower; and what is more curious, the direction of the circulation can be changed at will by the interception of the sunlight. It is not the result of evapora- tion.^ Amici also noticed the eflfect of the sunlight in reversing the current in the leaves of Tragopogon, but believes that the motion of the sap was produced by mechanical causes. Tracheary Vessels.^ — Under this name we include all vessels in which the thickening on the interior of the cell-wall assumes a more or less spiral arrangement. When the thread inside is closely coiled with the different spirals firmly united together, it is almost impossible to detect any membranous tube-wall at all; and the presence of this has in these cases been even doubted, or it has been asserted that at most it did no more than simply solder the different turns of the coil together. The tube-wall membrane, however, exists in all cases, but is very thin, transparent, and very little resistant or elastic, tearing with the utmost facility. It was long believed that this spiral thread was solid ; but it has been shown by the researches of Hedwig, Mustel, Link, Visiani, and lastly by Trecul,^ that it is in reality hollow, and filled with a gelatinous material of a colour different from that of the tube-wall, Fig. 27.— Longitudinal section of a portion of the stem of the garden balsam (Balsam- i>tahorte>ists,T)csp.) We see, ist, An annular vessel, 2d, A spiro-annular vessel v' ; 3d, Three tracheary or spiral vessels v" v'" v"" ; 4th, A large reticulated vessel, v""'. and of a variable consistency. It is generally simple and undivided, but at other times becomes bifurcated in a dichotomous manner. ^ Dr H. C. Perkins in American Naturalist, 1870, 318. " Trachenchyma of Morren ; trachea, the windpipe— which is, again, from ffo-yy^, rough— and Ivxvm, I infuse— a barbarous union of Greek and Latin. The tissue into which it enters is also called fibro-vascular tissue, just as cellular tissue composed of cells which contain a spiral in their interior, is called fibro- cellular. •' ' Ann, des Sc. Nat., 1854. ] 46 TRACHEARY VESSELS. In this case, if we unroll each trachea, we find it composed of two, three, four, five, or often of a great number of threads, united to form a ribbon-like structure.^ This is frequently seen in mono- cotyledons, particularly in the banana. In the immense majority of cases, however, the spiral thread is simple, non-bifurcating. In many plants there are two, or even three threads, each turning in an opposite course within the vessel. De Candolle counted as many as seven in the tracheary vessels of the banana, and in one vessel of the same plant La Chesnaye affirmed that he saw as many as twenty-two spirals. In diameter the spiral thread varies from ^-j^ to xoTinr of an inch. The nature of vessels is well shown by the mode of termination and commencement of these trachea or spiral threads. Each ends in a cone more or less elongated at its extremity, and another commences by being applied against the first by a similar termi- nation— in such a manner that it appears to be continuous. They are rarely longer than half an inch. In the stem of dicotyle- dons, tracheary vessels are found surrounding the pith, and form what is known as the "medullary sheath." In monocoty- ledons they are found in all the wood bundles scattered through the cellular tissue which forms the mass of the trunk. They are also found in the nerves of leaves, and in the petals of the flower, which, we shall find by-and-by, are only modified leaves. Lastly, we observe them in the radicles, especially of monocotyledons. The spiral thread can be seen on breaking the leaf-stalk of almost any plant (the hyacinth, for example) and gently drawing the ends asunder, when the thread appears in the form of a fine cobweb. In the banana the threads are united in the band-like form described, and are even used in manufactures. For instance, in Musa texiilis of Manilla these fine cobweb-like threads are extracted and largely used in the production of delicate textile fabrics. The spiral thread is not found in all tracheary vessels in a con- tinual coil, but is more or less broken ; hence these vessels may be classified into several subdivisions, distinguished by the more or less continuous nature of this spiral thread, though there is eveiy gradation uniting all the forms together. Instances are seen in which the spiral will commence in detached rings or trachese and end in a spiral.^ Hence these have been called spiro-annular vessels. Schleiden^ considers that the various forms of tracheary vessels are only modifications of one another — a view which is now gene- 1 Which, the student will be pleased to learn, has been called by some nomenclators a Pleiotrachea {nKeCwv, more). a Moldenhawer in Anat. des Plantes, i. fig. 3 ; Slack in Ann. dcs Sc. Nat., s6t., i. pi. 7, fig. 20, 21 ; and Richard, /. c, 34. 3 Ann. des Sc. Nat., 2° ser., xiii. 364. PUNCTATED AND BARRED VESSELS. 47 rally adopted ; though Mohl,^ on the contrary, maintains that they " present the same structure at every epoch of their existence." Adopting the former view, the modifications of the tracheary vessels are then as follow:— - (a) The spiral vessel, which we have already described as the type of the division. 0) The annular vessel, in which the spiral thread seems only to form detached rings. (y) The reticulated vessel, in which it branches and anastomoses, forming a network. Reticulated and annular vessels (sometimes called "false tracheary vessels ") abound most in herbaceous plants ; but in the stem of Polyg07ium orientate, and other plants, almost every form and gradation occurs. The use of the tracheary vessels is probably to convey air; though in the younger states of the plant, or during the season when the whole stem is gorged with sap, they may also assist in conveying that. Punctated and Barred Vessels.— In this division the deposit inside the cells forming the tube takes the form of little dots or '"t"-^ ilia 'i5i:-;i^;\ Fig. 28. — Longitudinal section of portion of the stem of Arisiolochia Sipho, L'Herit., in which are seen two large punctated vessels, — the one to the right entire, with constric- tions, a a, which indicate the point of reunion of two primitive cells ; the other to the left, cut longitudinally, to show its interior, a a Two annular markings, the remains of two horizontal divisions ; b b A section of the walls in which punctation forms a little recess. more or less perfect transverse bars — these forms, however, dove- tailing into one another by numerous modifi^cations, which show them to be only forms of one and the same organism. They have, however, received separate names, and have even been classed as ^ Ann. des Sc. Nat., 20 sdr,, xix. 242. 48 PUNCTATED VESSELS. distinct tissues; so that in order to simplify the subject, we shall arrange them as subdivisions under the names most commonly- applied to them by descriptive histologists : — (a) Dotted vessels} — This is the simplest modification. Here the thickening deposit appears through the transparent wall in the form of little dots. They often exhibit constrictions, which point out their origin to be in a row of cells, placed end to end, and becoming a tube by the absorption of the partitions between them. This form of vessels Richard ^ divides into two classes, which it may be convenient to adopt. The first are simple dotted vessels, in which the tube is cylindrical or a little compressed, having a considerable diameter. Their walls show the puncta- tions, generally very small, sometimes even granular, and rarely equal in size, and sometimes irregular in distribution. In general, however, these dots are disposed in perfectly horizontal lines. They are chiefly seen in the woody bundles of the stem of monocotyle- dons (fig. 29). They exist, however, also in the woody layers of dicotyledonous stems. The se- cond class are the areolar dotted vessels, in which there is in gene- ral a circular areola surrounding the punctation like a circular cushion. This appearance is pro- bably owing to air in the cavities between contiguous vessels. A curious fact has been observed in these dotted vessels, and that is, that they will often differ in the same part, or even in the same cell. Thus Moldenhawer observed that in a tube of Tilia one side was dotted, and the other had imper- fectly-barred markings. Again, in Coniferas the side of the dotted vessels facing the medullaiy rays shows areolar punctations, while the other side has only plain dots. In general terms, it may be affirmed that the structure of dotted vessels is affected by the tissue with which they are in contact. All the walls of vessels united with other vessels of the same nature present areolar punctations. But if the organs which touch them are of a different nature, the points in contact may show simple punctations,' horizontal or oblique bars, or even spiral markings, according to the nature of the contiguous vessel. 1 Bothrcnchyma (^oflpos. a pit) or Taphrcnchyma (Tapoi) of Morren ; pitted or vasifonn tissue ; porous vessels. 2 Richard, /. c, 28. Fig. 29. — Longitudinal section of cylin- drical cells, with walls moderately thicken- ed and abundantly punctated, from .5m- gantia Wiillachii,V<. Br., an e.xotic shrub. The punctations are seen both in a front (/ /) and in a profile (/'), or longitudinal sectional, view. BARRED VESSELS. 49 These clotted vessels are often of considerable length, and are of greater calibre than any other in the wood (in which part of the vegetable structure they chiefly abound), and accordingly they show markedly on transverse section. The "pores," conspicuous to the naked eye on the transverse sections of coarse-grained wood, like oak, chestnut, mahogany, as well as the longitudinal channel seen on longitudinal section, are these dotted vessels. In the plane they are particularly well marked.^ 0) Imperfectly-barred vessels? — Here we find the markings extended transversely, or more rarely obliquely, in the form of broken bars — unequal, or almost equal, among themselves. Sometimes these markings are very linear, at other times broader and rounded at both extremities. This kind of tissue is very generally found in the wood of dicotyledonous plants, or com- posing part of the bundles of monocotyledonous stems. In these vessels there are often seen slight constrictions, or remains of transverse partitions, pointing to their being originally formed of superimposed cells. (y) Scalariforin vessels. — From the imperfectly to the perfectly barred vessel there is a regular gradation. In this kind of tissue the vessels are usually prismatic from mutual pressure. The markings are in the form of transverse lines closely united to- gether, but with regular and uniform distances between them, stretching nearly right across each face of the prismatic tube ; hence, from their resemblance to the bars of a ladder (scald), they have received their distinctive name (fig. 30). This tissue is very characteristic of both the aerial and underground stems of ferns. The markings are often spiral in their arrangement, and can be unrolled, or rather torn out, in spiral ribbons, for in them the fila- ment, instead of being only in apposition, as in the true spiral vessels, is soldered to the tube; hence such vessels are called closed ducts. We have thus seen that all vessels are modi- fications of each other, just as the original cells out of which they were formed were all modifica- tions of one simple cell. Though it has been necessary to arrange the different forms which they eventually take into classes, yet these classes of^sSform [issu" are to a great extent artificial — the one graduating hora AspidiuufiUx into the other. A vessel will even in different parts of its course have different characters, and be successively imperfectly barred, punctated, scalariform, reticulated, &c. ; so ^ Vaissaux rayh of French botanists. 2 Punctated vessels occasionally get filled up with cellular tissue. Tyloses is the name which has been applied to this peculiarity. D 5° VASCULAR BUNDLES. that Mirbel's class of " mixed vessels " is perfectly unnecessary and inadmissible. To sum up — we see that the different appearance which the same tube may present at different points of its course may be due to : ist, The original structure of the cells of which it is composed, which structure may be different in each cell out of which it is made ; 2d, The influence which the neigh- bouring tissues invariably exercise on the vessels with which they come in contact. Vascular Bundles. — Vessels by their union form vascular bun- dles, often called fibres, though this name is equally applied to the woody tissue, which, in conjunction with the vascular, makes up all the parts of the plant which are not composed of cel- lular tissue or parenchyma. In cellular plants like fungi, algs, lichens, and mosses, there are no true vessels ; and hence these plants are composed simply of cellular tissue. When we examine a vascular plant at the earliest stage of growth, we equally find that it is entirely made up of cells. After a while the vessels appear, being formed, as we explained at the beginning of this section, by the absorption of the tops and bottoms of contiguous cells — a discovery great in its very simplicity, and for which we ar.e indebted to Treviranus and Mirbel. In fig. 28 this is shown. In this longitudinal section of a portion of the stem of Aristolochia Sipho, L'Herit., we see two great dotted vessels, the one to the right entire, with two constrictions, a a, which indicate two points of union of two primitive cells; the other to the left, with the interior exposed in order to show at a a two annular pads, remains of the two horizontal partitions ; a.t d d, the section of its walls shows each punctation, as a sort of little recess. Vessels are generally of great length, but it is very difficult to follow them up ; so that on this point our information is as yet somewhat imperfect. Transitory vessels. — In general, vessels when once formed remain during the life of the plant. Before, however, dismissing the subject, a curious exception to the rule ought to be noticed. In certain aquatic plants, generally supposed to be entirely cellular in their structure, Robert Caspary of Konigsberg discovered that in early life they possessed a tracheary vessel, which in the pro- cess of growth gets absorbed, leaving only a longitudinal canal. The cells and vessels are united together by the intercel- lular substance to form the body of the plant. We now come to consider the organs which these in combination form; but first we must describe a structure which is common to all the organs, besides being the simplest modification of the paren- chyma— viz., the general integument or Epidermis. ' CHAPTER III. EPIDERMIS AND APPENDAGES. The Epidermis ^ is a thin, transparent, but firm cellular mem- brane covering all the parts of the plant exposed to the action of the atmospheric air (except the stigma), and is not, as frequently described, formed of the superficial layer of the cells of the part which it covers, but is a distinct structure, composed of two parts : (i.) The cuticle, a thin homogeneous external part, without any appearance of organisation ; and (2.) The derma, a more interior cellular structure. These two membranes are placed one over the other, and intimately united together (fig. 31). They are pierced by a great number of little openings called stoinata. The appendages of the epidermis are hairs, scales, and their modifica- tions, glands and lenticels, each of which structures we shall consider somewhat more in detail. Cuticle.'^ — It exists on the epider- mis of leaves as well as on that of the stem, and, as proved by the re- searches of Bdn^dict de Saussure, Hedwig, and particularly of Brong- ti^^^^^lt^.'^'-''' Fig. 31. — Longitudinal section of a fragment of the leaf of a hyacinth, passing through the middle of a stoma, cells of distinct which surround the stoma ; ch The air- chamber, situated beneath the stoma ; /> Interior parenchyma of the leaf, in exists alone on the '^^ cells are filled with chloro- phyll-grams. mart, is a structure quite from the layer on which it is super- imposed. It parts of plants which are completely immersed in water {Potamogetons, for example). In these plg.nts the cellular derma is entirely wanting. In ordinary terrestrial plants it can be peeled off by maceration in water. Its existence can also be demonstrated by a chemical test. If we treat a trans- verse section of the epidermis with iodine, the cellular derma will 1 'Eirl, upon ; and Sepm"*, skin. I prefer to retain the term epidermis for the general integument as a whole, and the terms cuticle and derma for its com- ponent parts, confusion arising from using the same term (epidermis) in a general and in a special sense, as is often done. Superficial pellicle. 52 EPIDERMIS. remain colourless, while the cuticle will turn to a deep yellow, or even brown colour. If the section of epidermis thus treated is placed in sulphuric acid, the derma, which has remained uncoloured, dissolves, and takes in most cases a beautiful indigo hue ; while the cuticle keeps its yellow colour, and is not affected by the acid. The cuticle is one of the most constant parts of plants, existing on all organs and in all stages of their growth ; so that it cannot be, as Treviranus and others thought, a mere secretion deposited by the epidermal cells. Moreover, it has a different chemi- Fi "32 Z.y\evf composition from the rest of the epidermis, being of the tabular represented, according to Garreau,^ who obtained, dermis.^ '^^ by a very delicate process, enough for analysis, by the formula Ci7H3.205' — a formula analogous to that of caoutchouc ; while the derma is represented by C24H40O10. It has no appreciable organisation, though Brongniart^ some- times recognised the existence of granulations, disposed in par- allel and spiral series; or now and then, according to Mohl, in branching lines. These facts are true of a vast number of plants. However, it ought to be noted that, in fungi, lichens, and algas, there is no true epidermis, the tissues being all composed of the same kind of cells. Schacht has observed that in some plants the cuticle even is wanting. For instance, he found none on any of the orchids which he examined. On the other hand, on the leaves of Cycas revohita the cuticle forms a thick layer. Bar- thdlmy^ considers that, in the interchange of gaseous molecules between the plant and the atmosphere, the oxygen and carbonic acid pass especially through the cuticle, while the nitrogen makes a way for itself through the stomata. Der7tia. — This is the cellular portion of the epidermis under- lying and united with the cuticle. It is composed of one layer of cells in thick-leaved plants, or of two, three, or four layers lying one over the other. The cells composing this layer are firmly united together; and when the firm attachment of this layer to the cuticle above is added, a considerable strength is given to the whole epidermis. Nearly always flattened in shape, the cells of the derma differ widely in form from those of the rest of the tissues lying immediately under it. When the plant on which the epidermis exists spreads out laterally, the outline of the cells is generally wavy and irregular ; * but if it increases more in length than breadth, these are regular and elongated, and generally in longitudinal lines. The cells of the epidermis are generally without chlorophyll, though now and then instances occur in 1 Comptes rendus, xxxi. (Sept. 2, 1830). ^ Ann. des Sc. Nat., Feb. 1834. 3 Ibid., 5°. sdr., ix, 287. * Forming Morren's Colpcnchyma (koAttos, a fold). EPIDERMIS. 53 which a few grains of that substance can be seen. The walls of the cells are usually somewhat thick, though in most cases simple, and instances are not wanting in which transparent punctations are seen. , n i. ■ 4. The epidermis often contains, as we shall have occasion to notice in another place, a considerable quantity of silex, which substance impreg- nates the cells of the structure. On the inside of the epidermis are seen a number of lines forming an irregular network, or meshes almost equal, which Hedwig. Kieser. Amici. and others, have considered as, and called the ctdiailar ves- sels. On the epidermis of flowers are a number of papilla, which assist in giving the velvety appearance to certain flowers. Schleiden considered that he could see certain modifications in the structure of the epidermis on diff"erent parts which would allow it being divided into— I. Epithelium, 2. Epiblema, and 3. True Epidermis, But Fig. 33. — Fragment of the epidermis of a petal of a pansy, magnified to show the papilla upon it. Fig. 34.— Epider- mis from the hya- cinth - leaf (Hyacitt- tkns orieninlis, L.), showing the cells of the epidermis with a rectangular, straight, and elongated con- tour. The stomata are arranged in longi- tudinal rows. ^^S- 3S- — Pcronospora in/esians, Casp., a fungus sending its mycelium into the parenchyma of a potato- leaf through one of the stomata (after De Barry). this subdivision is generally acknowledged by the best micro- scopisls to be unnecessary. 54 STOMATA. Stomata.1 — These openings pierce the epidermis in great num- bers. They are in general formed by two crescent-shaped cells,^ united at their e.xtremities, and forming between them a longitu- dinal opening or mouth {ostiole), surrounded by two lips, somewhat like the two sides and centre of the letter O (fig. 36). They communicate with the intercellular passage of the infrajacent tissues, and assist in the transpira- tion and respiration of the plant. They are found on leaves, principally on their inferior aspect, on herbaceous stems, bracts, calyx, &c., and are ordi- narily wanting on roots, submerged leaves, non- foliaceous petioles, petals in general, the epidermis of old stems, that of fleshy fruits, seeds, &c. There are, however, exceptions to this rule, as the student can discover for himself by examining the epider- mis of the berry of the common holly. A curious form of stoma may also be seen in the epidermis Fig. 36.— Astoma ^ gourd. Some leaves have them only on one from the leaf of a side (^.-f^., pear-tree, olive, svringa, &c., which have hyacmth, with part v > i ^-i ■ ■ c ■ r \ .-i *u of the cells which them Only on their mfenor surface), while the surround it— seen g-reater number have them on both sides, though from above. , . ^ . ^ . , i ■ , , the inferior surface is the part on which the great- est number are found. Their arrangement on the surface of leaves is due in all cases to the arrangement and form of the cells which compose the epidermis. In those cases in which these cells are irregular, the stomata are scattered over the surface without order ; but when the contrary is the case, and the cells of the epidermis are disposed in an almost equal series, the stomata are arranged regularly. This latter disposition is more often seen in Dicotyledons than in Monocotyledons. On the aclcular leaves of pines and other Coniferte, they are arranged in lines. On some plants {e. g., Saxifraga sarinentosa), the cells among which the stomata occur are very small, are arranged in clusters, and sur- i-ounded by the larger ordinary cells of the epidermis. In the 1 Srofia, a mouth— so named by Link in 1819. He makes the plural slotnatia, though nowadays most authors write stomata. They are the spaltdffiiungen of German botanists. Before their exact use was known, various names, in accordance with the theoretical ideas of the authors of these names, were given to them — e.g., A'liliaty glands (Guetard), Epidcrmoidal (Lam^therie), Cortical glands (Saussure), Evaprafhig pores (Hedw'xg), Elongated or Great Pores (Mirbel), Cortical Pores (De Candolle). As late as 1837-39, Meyen called them Hautdrusen^ or epidermal glands. 2 Sometimes two, three, four (Yucca), or even more ; or the cells may be united in a continuous margin. In the liverwort {Marchantia), the stoma is most complicated, being built of a tier of rings each composed of four or five cells. — (Carpenter's Microscope, § 23). The stomata of Ancima fraxinofolia are also curiously modified. STOMATA. 55 Nerium Oleander (rose laurel), and various species of Dryandra and Banksia, there is a remarkable arrangement of the stomata. On the under surface of the leaf are a great number of cavities, each with a straight opening, lined by long hairs. At the bottom of these cavities the stomata, v^^hich are veiy small, exist in great numbers. Stomata are also either found solitary or in united groups. They are usually developed in a cell of the epidermis by the Ibrmation of a partition, which, splitting in two, constitutes the two sides of the opening.^ We have already noted, in general terms, where the stomata are absent or present. Schleiden and Fournier have found them in the cavity of that part of the flower which afterwards becomes the fruit, in at least the orders CruciflorcB and Passiflorce, the latter author observing them also in Reseda (mignonette). The general law that they are not found on those parts of plants which are buried in the earth or float in water has one or two exceptions. They exist, according to Duchartre, on the inferior surface of the leaves oi Hydrocharis Morsus-rancE, L.,and in considerablygreater numbers on those of Limnocharis Humboldtii, Rich. ,2 two water- plants; and they are also found on the scale-like leaves oi Lath- rcea clatidestina, L., a singular subterranean parasite. That submerged plants should want stomata is natural, and suited to their mode of existence ; but still it must be noted that when a plant such as Hyacinth, which has stomata, is compelled for a number of years to develop its leaves in water, this change of habit has no effect on either the epidermis or its stomata. They are only found on the upper surface of floating plants {e.g., Nym- phcEa, Marsilea, Nuphar, &c.) ; but on the upper surface of the leaves of these plants they are about three times as many in number as on the upper surface of aerial leaves. In some cases the opening of the stoma is surrounded by a raised border {Pro- teacecE and Cycadacece), though in other cases the opening is below the level of the surface of the epidermis (Gasteria, Aloe, Phormium &c.) In Himantoglossum and Helleborus the stoma is exactly on a level with the surface. Schacht found that the stomata of all the plants studied by him {Aloe, Phormium, Rusais, Dipsacus, Arbutus, Ilex, &c.) were coloured, by the action of iodine and sulphuric acid, of a violet or blue colour; so that the two cells which form the stoma must always be composed of cellulose. The number of the stomata on the leaves of different plants varies greatly, from only a few up to 160,000 on a square inch ; ^ Mohl in Ann. des Sc. Nat., xix. 201 ; Weiss in Verhand des Zoolog- bot. Vereins in Wien., 1857, &c. ^ The leaves, however, of these plants are not really floating, but more or less upright. 56 STOMATA, or 708,750 on an entire leaf of the lilac, and 1,053,000 on an entire leaf of the lime-tree. The subject has been investij^ated with patient labour by the two Krokers, Thompson, Lindley, Unger, and, above all, by Edouard Morren ^ and Duchartre,^ the result of whose researches may be summed \ip as follows : i. With a few exceptions, woody plants are richer in stomata than her- baceous plants. 2. Among trees and shrubs it is on those having leathery leaves that the greatest number is found. 3. Fleshy leaves have fewest. 4. Those which have few or none on their upper surface, have them more numerous on the inferior surface than those which are not so deprived. 5. Among plants which have sto- mata both on the upper and under surface of the leaves, some have more on the upper than the under side, and others have an equal number on both aspects of the leaf. 6. They are fewer on those plants which are exposed to the sun than on others belonging to damp and shaded situations. 7. In general, the stomata are smaller in size when they are found in less numbers. It ought also to be noted that the greater or less vigour of the plant, and, above all, the different ages of the leaves, will modify these gen- eralisations. The following table gives some of the data for these conclusions as regards very common wild or garden plants, in reference to the number of stomata in a square millimetre on each side of the leaf, and the length of the stomata in each species in fractions of a millimetre. The table is made up from the measure- ments given by the authors mentioned. ( i I. . t I. Terrestrial Plants. , . . ..5 A. Herbs and under-shrubs with their leaves-. . UPPER UNDER ■ {-ENGTH, IN FRACTIONS SURFACE. surface: i OF A MILLIMETRE. Lolium perenne, L., 65 40 ;o40 to .050 Hordeum murinum, L. , 40 45 •037 •043 Polygonatum vulgare, Derf., 0 65 .030 •033 Echium vulgare, L., 190 190 .026 .030 Chenopodium vulvaria, L., . 65 85 .023 Tagetes patula, L., 43 70 .036 •050 Impatiens Balsamina, 55 95 .030 .030 Pulmonaria angustifolia, L., 25 85 •033 .040 Euphorbia helioscopia, L., . very rare 50 .027 .030 Mercurialis annua, L., 0 65 .027 Parietaria officinalis, L., 0 100 .027 •Hypericum perforatum, L., . 0 165 .023 Teucriuni Chamaedrys, L., . 0 225 .026 .026 Scorodonia, L., 0 150 .020 Fragariavirginiana, L., 0 110 .020 .023 Calystegia sepium, R. Br., very rare 50 .030 •033 Helianthemum vulgare, Ga3rtn. , 30-40 85-100 .026 .036 1 Bulletin de 1' Academic royale de Belgique, ■2" sdr., .wi. ^ Op. cit., 106-109. STOMATA. 57 B. Herbs with fleshy leaves. V'VVB.V. UNDER LENGTH IN FRACTIONS SURFACE. SURFACE. OF A MILLIMETRE. Portulaca oleracea, . . " 45 20 .046 .050 Sedum reflexum, ... 75 (all round) o (towards the summit) .043 C. Shrubs and trees. JEsc\x\ms Hippocastanum, L., 0 175 .023 Bu.xus sempervirens, L., 0 140 • 033 Castanea 0 17s .030 Cerasus Mahaleb, Mill., 0 170 • ^^5 ,04.0 Fraxinus excelsior, L. , . 0 165 .027 Legustrum vulgare, L. , 0 95 .030 Lonicera pereclynium, L., 0 65 OQO Olea europcea, L. , . . . 0 215 • O16 • 020 Quercus pedunculata, Ehrh., 0 250 Syringa vulgaris, L. , 0 175. .027 ■033 Tilia platyphyllos, Scop., 0 150 .027 Vitis vinifera, L., 0 125 .030 Protea' cynaroides, L., . 25-30 25-30 .020 D. Resinous trees ( Conifem). Pinus Pinaster, Soland., 50 (all round the leaf). II. Aquatic Plants. Nymphcea alba, L. , 255 0 .027 Limnocharis Humboldtii, Rich., 125 75 •037 Hydrocharis Morsus-ranoe, L., 60 rare .040 The use of the stomata was long a subject of lively controversy — Malpighii regarding them as analogous to glands, and Grew^ that they were either for the admission of air or outlets for super- fluous fluid. Up to within the last thirty or forty years the glandular nature of the stomata was maintained by botanists so illustrious as Meyen and Robert Brown, neither of them believing that the stomata were furnished with a central opening. Sir Joseph Banks and Moldenhavver assisted in the discovery of their true nature ; but it is to Mohl^ that we are chiefly indebted for the complete demonstration of their function in the vegetable economy : and, wonderful to relate, all physiologists are at one on this point — viz., that their function is to give passage to air to serve the purposes of inspiration and expiration. Exhalation also takes place through them when, the epidermis is too thick to pre- vent the escape of much moisture by direct transudation. From ^ Opera omnia (1687), 142. 2 Anatomy of Plants (1682), 153. Botanische Zeitung, 1856, 967, and trans, loc. cit. ; and in Amer. Journal of Science, March 1857. 58 LENTICELS. the section of one given in fig, 31, it will be seen that they open directly into the air-cavities,^ which pervade the parenchyma, and thus keep up free communication with the external air and the sub- stance of the leaf (or other organ). The cells which form the lips of the stoma are contractile, and open and close according as the leaf is subjected to wetness or dryness ; so that the evaporation of the plant is regulated according to the supply of sap it may have. It is probably owing to this fact that the stomata do not act well in direct sunshine, and that most of them are on the under side of the leaf. Lenticels. — On young branches the surface of the epidermis is often marked by little elongated, oval or elliptical, brown, cellular rugosities, the greatest length being usually in the direction of the branch in young branches, but in old ones without any particular direction. These Guettard called " lenticular glands," and De Candolle, simply lenticels? No traces of them are found in Monocotyledons or Acotyledons, and they are also wanting in the greater number of herbaceous Dicotyledons. They can be seen in willows, and are particularly well marked in Etionymus verru- cosus, L. De Candolle considered that they were a sort of buds to give rise to adventitious roots ; but, thanks to the researches of MohP and Unger,* we know that in this idea he was mistaken. They are formed by the development of sub-epidermal cellular tissue, which causes the epidermis to tear to give passage to them. They are situated on the periderm, and have no com- munication with the interior of the bark or the wood. They exist on the potato-tubercles, and are sometimes so well developed as to appear like buds scattered over the surface. Their nature is that of local developments of cork. For instance, on the birch they grow under the glands which secrete resin. In a branch of more than one year, the glands disappear, and are replaced by lenticels or tubercles of cork, which increase with the growth of the limb, and form those brown lines observed on old bark. In a word, Mohl considered that the " lenticels are analogous to cork, and are the result of a hypertrophy of the mesophloeum." Unger and St 1 By funnel-shaped openings called cistomas (fcumj, crro/ia) by Gasparrini. For those remarks on the stomata see Prasitt Die Ergebnisse der neueren unter- suchungen iiber die spaltoffnungen, " Flora," 1872, which I have only seen in abstract in the Swedish " Botaniska Notiser," 1872, s. 141-148. VM£ also E. Pfitzer Ebenda, vii. (1870) s. 532 ; Ranter, Mitth. ber naturw. vereins of Steiermark, 1870, ii. Heft II. ; Borodin Bot. Zeitung, 1870, s. 841 ; Hilde- brand Einige Beob. aus dem Gebiete der Pflanzenantomie (1861), &c. 2 "Little lentils." 3 Ann. des Sc. Nat., x. 33 (trans.) * Ann. Sc. Nat., x. 46. He was certainly, however, in error when he con- sidered them as in some way connected with respiration, even as obliterated respiratory organs. HAIRS. 59 Pierre^ have arrived at very similar conclusions ; but their use, if any, simple as they seem, has yet to be satisfactorily determined. HAIRS. {yUli, pili-) This name is applied to those appendages of the epidermis which resemble in external appearance, but not in Fig. 37. — A unicellular stellate hair from the inferior surface of the leaf of Fig. 38. — Hair from the leaf of Alyssjim saxatile, L. — viewed from Hipfiophde rhamtioides — seen from below. above. Structure, development, or nature, the hairs of animals. They are composed of one long cell, or of several superimposed cells. They Fig. 39.— Two branching hairs from the leafolArali'a papyri/era. are present in nearly all parts of the plant at one stage or another of its existence, from merely a few scattered ones to a vast number, 1 Diet, de Botanique, 830-833. 6o HAIRS. Fig. 40. — ^The same seen in profile, with the cells of the epidermis on which it is carried. giving the plant a villous aspect. Sometimes the hairs are simu- lated by other parts of the plant, such as the pappus of the seeds of many of the Compositse, &c. ; but, as we shall see by-and-by, these hair-like organs are of an entirely different nature. They may be divided into — i. Ojie-celled Hairs ; 2. Uniserial Hairs; 3. Pluriserial Hairs; 4. Glandular Hairs. I. The first, as the name implies, are formed of a single cell, simple or branched (figs. 37, 42, 44, 46).! 2. Uniserial Hairs are made up of several superimposed cells, ar- ranged in a single series or line (fig. 41). After the cell of the epi- dermis which gives birth to this kind of hair has attained a certain stage, a transverse partition forms, and divides the cell into two equal parts. As the growth goes on, this forming of transverse partitions continues, until the hair consists of a number of cells placed end on end. Hence De CandoUe called these hairs " parti- tioned hairs." This kind of hair can also branch, as in fig. 39 of a two- branched and stellate hair from the leaf of the Chinese rice-paper plant {Aralia papyri/era). Some uniserial hairs (e. g., from the thistle and groundsel) have the last cell deve- loped into a long thread-like lash. 3. In Pluriserial Hairs there is a more complex structure — the cells forming several threads placed in juxtaposition and parallel (figs. 38, 40). In the figures, a front and profile view of the sea-buckthorn {Hippophde rhanmoides) are given. From this it will be seen that the hair, which is in the form of a circular disc, is supported on a short column formed of cells of the epidermis. In this cate- gory of hairs, which are not only pluricellular hut pluriserial, may be classed prickles (aculei), which are really only thickened hairs, and are distinguished from thorns by being attached, not to the wood, but simply to the epidermis — off which (as in the Rose and ^ By an absurd hair-splitting refinement of nomenclature, these one-celled hairs liave been classed as a particular type of cellular tissue, under the name of Concnchyma (kSivo^, a cone). Fig. 41. — Pluricellular, uniserial hair from Pelargonium iiiguinaiis, Ait., with a subulate point, a The epidermic cell, which forms its base : ep The other epidermic cells in the immediate neighbourhood, with their contours feebly sinuate. GLANDULAR HAIRS. 6i many other plants) they can be pulled without injuring the struc- ture of the plant. The brown scurfy scales of the stem of ferns may also be classed as pluriserial hairs. 4. Glandular hairs are perhaps the most important of the whole four classes. This name was applied by De Candolle to all hairs possessing glands, wher- ever placed or of whatever nature. They ap- pear on the surface of the epidermis in the form of cellular bodies, more or less round- ed, and either resting immediately on the epi- dermis or raised on a very short support, as in Robinia viscosa. De Candolle further divides glandular hairs into— (a) Glandulifer- ons hairs, in which the gland is borne on the summit of the hair; and 0) Excretory glandular hairs, in which the gland is at the base of the hair, which in this case may be regarded as the duct by which the material secreted by the gland finds its way outwards. An excellent example of the first class is afforded by glan- duliferous hair from the leaf of Pelargonium inqninans, Ait. (fig. 43). Again, on the chick- pea {Czcer arietinum, L.), there are hairs of this nature which secrete an acid liquid, considered by some chemists as oxalic, and by others — such as Vanquelin — as a mix- ture of malic, oxalic, and acetic acids. In the sundew {Drosera), the hairs secrete a sticky fluid, which stands on their tips. Hairs with glan- dular tips are also found on the sepals of the common flowering currant {Ribes san- guineum) of our shrubberies. In the tobacco-plant there are hairs with a double gland at the top, which secrete the nicotine, or active principle of the plant. In hop the bitter substance is called lupuline, and is developed by little glanduliferous bo- dies, called by St Pierre Lnpulins (fig. 45). On Geum there is also a double gland. In the yellow snap-dragon there is a conical terminal gland with spiral markings, and in the common verbena the gland is rosette-shaped. In the common lavender the peculiar "bloom-like" appearance of the surface of the leaf Fig. 43. — Glandu- liferous hair from the leaf of Pelargoniu7n iiiquitiMis, Ait., of our gardens. Fig. 42. — Stinging hair of the nettle {Urtica ureus, L.) b b \5 the unicellular hair itself, the base of which is swollen into an ampulla, which occupied the greater portion of the cellular support, a b. At the side of the figure is shown the summit of the hair more highly magnified. 62 GLANDULAR HAIRS. is caused by much-branched hairs covering other short glandu- hferous ones, which secrete and contain the perfume. In the 6 c Fig. 44. — Hairs (c) and glands (a b) of Rottlern tinctoria, one of the Euphorbiaceae. The hairs and glands cover the plant, and especially the front, with a red or reddish pow- dery substance, which in India and China is used as a dye and a taenifuge. interior of the hairs of Drosera (sundew) and other plants there are spiral filaments. An example of the second class is afforded by the fraxinella {Dictamnus albus, L.), the hairs of which secrete a volatile inflammable oil. Hence, if, when the flowers are fading in the autumn, a light be applied, they are surrounded by a sort of luminous " atmosphere, " caused by the ignition of this volatile oil, a fact dis- covered long ago by the daughter of Linneeus, but only recently confirmed and its cause discovered through the obsei-vation of Dr Hahn. Perhaps, however, the most familiar example of the excretory hair is af- forded by the nettle, the type of hair to which it belongs being sometimes described as "stinging" or " urticant" hairs. It has been often described in text-books, though frequently very erro- neously. Our figure (42) will explain the structure as seen in the ordinary stinging nettle {Urtica nrens, L.) It is formed of a single cell, b b, which swells out inferiorly into an oval ampulla, and which, decreasing in diameter little by little, terminates in a small round knob-like point, turned slightly to one side. The base of this hair terminates in a cylindrical simple column (fig. Fig. 45. — Development of the little glandulifef- ous organs called Lnpulins which supply, the bitter oleo-resinous extract called Lupttline; char- acteristic of hops, a Lupulin commencing to form ; b Lupulin composed of two cells ; c Pedi- culated lupulin ; d Lupulin in the form of a striated cup ; e Lupulin completely developed. GLANDULAR HAIRS. 63 42, a b), which, in order to receive the bulbous extremity of the hair {l>), is hollowed at its superior extremity into a cuplike depres- Fig. 46. — Hairs [c] and glands {a b) of another closely-allied but distinct species oi Rottlera. sion. The column, in order to form this cup, reduces its tissue from two to finally one row of cells. Meyen and most other botanists after him consider that the pedicel is the organ which secretes the stinging liquid of the hair. The hair proper is then no more than a simple reservoir for the juice secreted by the basal gland. When this structure is understood, it is easy to see how the nettle stings ; the very delicate transparent point of the hair is ruptured, and allows the irritating juice to escape on the part in contact with it. In Urtica ferox, Forst., the glandular pedicel is much longer than the hair proper. Though the acrid juice secreted by our native nettles is sufficiently disagreeable in its action, in stinging powers they are far eclipsed by some of their congeners in tropical countries. Thus Urtica cretiulata, Roxb., stings so fiercely that it is to be avoided at all times, but especially in the autumn. Leschenault mentions that having been stung on three fingers of the hand by this species in the Calcutta Botanic Garden, the pain during two days was intense, and accompanied by tetanic symptoms ; nor did he get clear of the effects until the ninth day. Urtica ferox, Forst., of New Zealand, will cause its stinging hairs to be held in doleful remembrance for three or four days ; and Blume tells us that one species, Urtica ure/itissima, is known to 64 CLASSIFICATION OF HAIRS. the natives of Java as the Daoun setaii, or "Devil's leaf," from the effect of its sting lasting for years, especially during moist weather. It is said to have even occasioned tetanus and death. Curious stinging hairs, often called the Malpighinn hairs, are found in the leaves of Malpighia. Each is in the form of a shield, and is inserted by its middle on a mass of a glandular appear- ance, which secretes the stinging liquid. In some hairs {e.g., from flowers of the dead nettle, lobelia, pansy, verbena, &c.) there are curious protuberances or knobs along the surface. These exist in a much exaggerated form on the hairs of the pod of the cowitch {Macuna pruriens), causing great irritation when the hairs come in contact with the skin. To recapitulate in a synoptical form the chief forms of hairs, they may be classified as follows : — I. Simple or Lymphatic. ("Simple. I. Unicellular, \ Bi-trifurcate. Branched and stellate. Uniserial {IraJdied. r i-Simple and smooth. ^, . „ , . . , j Cylindrical, J Dentate or barbed. 2. Pluncellular. Plunserial, . i (Peltate or shield-shaped. V Flat, . . Scurfy. II. Glandular Hairs. ( (Capitate. 1. Glanduliferous, or with a terminal glands ^^P^^' tcupulate. V Branched, . With many heads. I" Inoffensive. 2. Excretory, or with a basilar gland, . S c-.- • I Needle-shaped. I Stinging. i Peltate. 1 The following technical terms are often met with in describing hairs. They are given without reference to the foregoing classification, simply because the same term is often used to describe the external appearance of a hair, without resrard to its internal structure or functions — on which two characters the above classification is based : — I. Stellate, when in a star-shaped form (Deutzia scabra). 2. Moniliform or beaded (Lychnis chalcedonica). 3. Lepidote or scaly (Elceagnus). 4. Ra- 7na?ieta or rametaceous hairs, as in the scales on the lower part of the stem of ferns. 5. Reticulate Hairs or Mattulla, on palms, 6. Prickles or aculei. 7. Setm or Stiff Hairs. 8. Clavate or club-shaped. 9. Capitate, a dis- tinct rounded head. 10. Scabrous, with slight projecting surface, giving a roughness on drawing the leaf or other organ over the skin. 11. Uncinaied or hooked. 12. Glochidiate or barbed, with one or more points round the apex! 13. Peltate or shield-shaped (Malpighia, various Cruciferse). The descriptive names applied to organs from the presence or 1 Duchartre, op. cit., loi. GLANDS. 65 absence of hairs, or from their situation, are chiefly connected with the leaf, and will be given when we come to enumerate the tech- nical terms used in describing that structure. GLANDS. To pass from glands to glandular hairs, or vice versd, as we have for the sake of convenience done, is a natural transition. A gland, the advanced student scarcely requires to be told, is a secret- ing organ formed of cells, and situated in various portions of the plant, in order to perform certain functions more or less essential to the life of the plant. The pedicellated glands, or glandular hairs, we have already described. The other and more typical ones are situated sessile on the surface of the epidermis. They generally contain oil or colourless resinous substances. These glands often appear on lea\-es like transparent punctations, as on the leaves of St John's wort {Hyperinim perforatjcni), rue, orange, &c. They secrete many of the distinguishing products of different plants — e.g., honey, as in the " nectariferous " glands at the base of the petals of many flowers, which are, properly speaking, cavities surrounded by secreting cells ; the " ice " of the ice-plant {M esevibryanthemum crystallinuni), so called from the presence of drops of fluid on the leaves, as if they were covered with minute frozen dewdrops. In Rochea falcata, the surface of the ordinary cuticle is nearly covered with a layer of large prominent isolated cells, which have probably a secreting power of a similar nature to that of the plant just mentioned. Glands are composed of a group of cells, which sometimes leaves between a space where the liquid gathers. In shape they are oval, round, flattened, &c., and are found in great numbers in plants— the same plant often containing several different forms. They have been particularly studied by Guettard,i Meyen,^ and Mirbel,3 to whose elaborate researches the student is referred for longer details. The latter botanist divides them into two classes : vascular glands, into the composition of which cells and vessel unite ; and cellular glands, formed of cellular tissue alone. In at least three species of the Ericaceous genus Ganltheria {G. procumbens, G. Shallon, G. ovalifolia), George Lawson has de- scribed * (and the observation has been confirmed by myself several 1 Observations sur les plantes (1847) ; and M^m. de I'Acad^mie des Sciences de Paris, 1847. ^ Uber die Secretions— Organe der Pflanzen, 1837. ! Annai. du museum d'liist. nat., ix. 455 ; and Mdm. de I'lnstit., 1808, 344. Trans. Bot. Soc. Edin., xi. 166. E 66 GLANDS : RECAPITULATION. years ag-o) long terete brown glandular processes, each arising from a larg-er iDase on the teeth of the leaves ; and in the case of G. Shallon and ovalifolia on the under surface of the leaf also, though in a less marked manner. RECAPITULATION. The tabular views g-iven at the end of the various chapters of this section (I.) render any recapitulation, beyond a few words, to link the leading ideas together, unnecessary, i. We have seen that the primary organic elernent of all plants is the cell — this cell being normally globular in shape, but in general more or less angular, from the pressure of the other cells. 2. Its component parts are the nucleus and nucleolus swimming in a protoplasmic fluid, and the primordial utricle lining the interior of the cell-wall. 3. In addition, the cell contains chlorophyll, starch; crystals, sugars, gums, oil — in a word, the various products for which plants are distinguished. 4. By the iiTegular deposition of the encrusting materials inside the cell-wall — cellulose, lignine, &c.- — the cell re- ceives various markings — dots, bars, spirals, &c. — which dis- tinguish cells into different classes. 5. By increase and union, cellular tissue is formed. 6. The original cell is formed as follows, our knowledge on the subject of which may be summed up in Unger's words : (a) The young cells develop freely in the interior of the mother cell without the intervention of the cellular mem- brane. A solid body — the cytoblast or nucleus — appears in the protoplasmic fluid. This nucleus gathers round it, by the con- densation of the exterior of its substance, the primordial utricle — which in its turn forms round it the cell-wall proper, composed of cellulose — the fluid now interposing between the nucleus and the primordial utricle, which acts as a lining to the cell-wall. (3) The cells are formed by the segmentation of the mother cell, which is accomplished in three distinct processes : a, The new membranes develop themselves from the interior of the generative membrane ; The mother membrane forms folds stretching into the interior ; c. The mother cell separates itself by constriction. 7. Lacunje are sometimes formed in the midst of cellular tissue. 8. Communica- tion between cell and cell is accomplished by endosmose and ex- osmose, or perhaps by minute openings. The thinner unthickened portions of the cell-wall also assist in this transmission of fluid. 9. When the cells elongate, get thickened with lignine, and splice over each other as in the chief mass of wood, &c., they form woody or ligneous tissue. This woody tissue is also distinguished by vari- ous markings, especially by the discs found so invariably in Coni- ferae and certain other trees. They are not, however, true vessels. RECAPITULATION. 67 10. Vessels are formed by the union of rows of cells, the partitions between which have been absorbed, so that a continuous tube re- mains— this tube from its origin being naturally characterised by all the markings found in the particular kind of cells out of which it has been formed. li. Vessels also, by their union, assist in form- ing woody bundles. 12. The epidermis is a semi-compound organ, the simplest product of the union of cells. It covers every portion of the plant exposed to the external air (except the stigma), and even some organs not so exposed. It is composed of a structureless cuticle or pellicle, and a derma composed of one or more layers of cells lying immediately under this. 13. The appendages of the Epidermis are : (a) The stomata, opening in the surface for the ad- mission of air and other uses, which will be particularly considered while discussing the function of the leaf ; (/3) Hairs of various shapes formed of one or more cells ; (y) Glands ; and (S) Lenticels, little cellular rugosities, the nature of which is but imperfectly known. It thus appears that the cell is a perfect organism in itself, and that from its modification or union all the complicated organs of the plant are formed. To borrow the illustration of Schleiden, what in vegetable anatomy appears progress is in reality nothing more than development in the true sense t)f the word — a division, or analysis simply into a greater number of the parts composing the whole. The number 100 is a simple number ; in its develop- ment it is possible to describe it as 99 -f- i ; 3 X 33 + i ; 3 X (32 + i) + I ; 3 X [ (4 times 8) + i] + i, &c. We are able to analyse the proportions which it contains, and in place of 100 united, to establish a most complicated calculus, the final product of which will be always 100. The same is true of all nature. j j I i I I I I SECTION II.' NUTRITION. We now come to consider the compound organs and their func- tions. "We have seen that a cell is a life in itself, performing every function of a perfect plant — nutrition and reproduction. We shall now see that in the highest plants these two functions require a more complicated series of organs. First, therefore, it behoves to consider the organs of Nutrition. These are the root, stem, and leaf. It will therefore be necessary to describe them before discussing the food of plants, and the method by which this food reaches the different parts of the plant and gets assimilated within its structure. Perhaps it may be more convenient to commence our description with the stem. CHAPTER I. THE STEM. The stem (caulis), or ascending axis, is that portion of the plant which rises above the medium from which the root — its continua- tion, and, in some respects, its subterranean counterpart — ab- sorbs the nutriment ; and as the rootlets spread through the soil from the main axis of the root for this purpose, according to a fixed law of arrangement, in like manner the leaves borne on the stem or its ramifications, according to a similar mathematical law, expose themselves to the influence of the air and light, to absorb and elaborate certain other nutritive materials required for the life of the plant ; and finally, it bears the flowers, the perfection of which is essential to the reproduction of the plant. All these organs are more important to the life of the plant than the stem itself. The juices absorbed by the root are also con- veyed through the medium of the stem to the organs named. On this view Richard has called the united stem and root the axophyte J and certain other botanists — Nees, for example — have styled this, while in the embryo, by the very unnecessary term of blastema. This " axophyte " has certain appendicular organs, leaves, &c. ; but before considering them, we shall discuss the nature, structure, development, and modification of the stem. Absence or existence. — It is not always present in plants. For instance, in some low orders of cryptogams, such as lichens, fungi, &c., it is absent ; and even in mosses and some of the larger algae, though apparently present, it does not fulfil the same physiological purposes as in the higher plants. Stemless plants {e.g., dandelion) are called acaulescent (a, privative; Kavkos, stem), in contradistinction to the caulescent or stemmed plants. These terms, though often loosely applied, and not perhaps strictly cor- rect (for in descriptive botany a plant is often styled acaulescent which is not really so, but only with a very much shortened or indistinct stem), are sufficiently convenient to be preserved. If, as in all herbaceous plants, it is very short, and produces annually young branches, which live for a season and then perish, it is called the crown of the root. 72 SIZE AND CONSISTENCE OF THE STEM. Size. — The stem varies much in size, from a mere thread in some plants to from fifteen to thirty feet in diameter in the Sequoia gigatitea of California ; and from being so short that the leaves seem to spring from the head of the root, to a length of 330 feet in the gigantic tree just mentioned, and an almost equal height in some other conifers.^ Nor does the length invariably bear ai\y proportion to the thickness. The stem of Calajuus ruden- tum, L., is often 900 feet in length, creeping along the ground, and rarely attaining a thickness of more than lyi or 2 inches. Stems are often classed into three categories : i. The culm (culmus), herbaceous or woody, generally simple, with well- marked elongated nodes ; ex. grasses and sedges.^ 2. The trunk (truncus), characteristic of most of our ordinary dicoty- ledonous trees, such as the oak, chestnut, elm, poplar, &c. Here the stem is usually divided after a certain distance, and ramified into smaller subdivisions called h'auches, and these again into branchlets and twigs. 3. The stipe^ (stipes) or caudex, another kind of woody stem observed in the great division of plants called monocotyledons, and specially in the palms. Yucca. DraccBfia, Pan- danus, &c. The tree-ferns may also be said to have stipes. They are generally simple, cylindrical, often thicker at the summit than at the base, and in structure have the character of the monocotyle- donous or endogenous stem, which will be presently described. Consistence. — Taking the substance of the stem into considera- tion, it may be herbaceous, as in most plants familiarly called herbs ; ligneotcs, or woody, when woody fibre forms its greatest bulk, as in trees and shrubs ; a third class may be partly woody and partly herbaceous — i.e., the perennial stem maybe woody, but the branches which it puts out yearly, and which are only annual, are herbaceous. Such stems are called fructicose or semiligneous, and the plants themselves under-shrubs. This leads us to speak of certain terms applied to the plant in reference to its height or thickness. There are : i. Herbs (sing, herba), in which the stem is completely herbaceous ; 2. Under-shriibs (suffrutex), tit supi-aj 3. Shrubs (frutex), in whifch the stem is completely ligneous, is branched at the base, a little elongated, and less than five times the height of a man. Between shrubs and trees there are all gradations ; and if the shrub approaches to the size of a tree, it is 1 The writer has examined a felled tree oi Abies Douglasii in North- West America which measured 320 feet in length. 3 This can be well seen in the bamboo. Physicists have shown that in this hollow culm there is the greatest amount of strength combined with the smallest expenditure of material, and that the transverse diaphragms at the nodes add to the strength of this long slender stem. It is said that it was the study of this stem which suggested to Robert Stephenson the idea of tubular bridges, such as that which he afterwards threw over the Menai Strait. 3 Also applied to the stalk of an ovary. DIVISION OF STEMS ACCORDING TO STRUCTURE. 73 called arborescent, just as the under-shrubsare called suffrutesceiit, or suffruticose if less decidedly woody than ordinarily. 4. Trees (arbor), in which there is a true trunk not branched at the base, and which attains at least five times the height of a man. 5. Bushes may be defined as low, much-branched shrubs. Numerous other terms are used to express the form, composition, and direction of the stem. Division of stems according to stnictnre. — There are three great classes of stems corresponding to those three great classes into which plants have been divided. The first is the Dicotyledonous (fits, twice; and KOTvkr\blov, a seed- lobe} or exogenous stem, which shows on a transverse section con- centric layers of wood surrounding a pith, and the wood again surrounded by a detachable outside bark. The plants of which this stem is characteristic have also two lobes to the seed, which seed, on first sprouting, sends up two seed-leaves or cotyledons above ground — hence the name of the class — and have, in nearly every case, their leaves reticulated or netted-veined. From in- creasing in thickness by additions of layers of wood — one being yearly superimposed above that of the previous year — they are called Exogenous or outside growers (e^w, without ; and yivofiai, to grow). All our British and temperate forest- trees have stems of this type. 2. The second class is the Mojiocotyledonojis (fiovos, one ; and kotv\t]§wv) or endogenous stem, in which there are no concentric layers of wood, no pith, and no detachable bark, and in which the embryo has only one seed-lobe, and the leaves are parallel- veined. This stem increases in thickness by deposition of wood- bundles from within outwards, and hence has been called Endo- genous {fubov, within; and ybo^ai). The palm-tree stem is a typical example of this description of stem. 3. The remaining division of stems is the Acotyledonotis (a, pri- vative ; and KOTvkr]hhv) ox Acrogenous {oKpos, summit; and yivoixai) stem, in which the young plant springs from a spore, and has no true seed-leaves, in which the stem or stipe increases in thickness by the union of the bases of the leaves or fronds, and in which the venation is forked. The tree-ferns have stems of this kind. This classification is not an artificial one, but is founded on nature — each stem, as we have seen, finding corresponding differences in other portions of the structure, and in the development of the three great classes of plants to which it belongs. To recapitulate in tabular form, the three kinds of stems are as follows : — 1. Dicotyledonous or Exogenous = two cotyledons, — netted- veined leaves - increase from without inwards. 2. Monocotyledonous or Endogenous = one cotyledon, — parallel-veined leaves = increase from within outwards. 74 STEM OF DICOTYLEDONS : BUDS. 3. Acotyledonous or Acrogenous = no cotyledons, — forked- veined leaves = increase at the summit by the remains of bases of the leaves. STEM OF DICOTYLEDONS. In the embryo (or plant as it exists in the seed) the future stem is represented by the part between the attachment of the two cotyledons superiorly, and the radicle inferiorly— the first of these two points being known as a node, the next as the collian, and the interspace between them the interiiode?- These parts are more marked in the developed plant, and go under the same names, the nodes giving attachment to the leaves, and the stem increasing by the development of these internodes, each internode represent- ing a year's growth. Buds. — The Geminule {^\\xrcvvi\t. Link'-'), or young bud {gemma), which terminates the young stem, is therefore the growing or vege- tative point.^ This vegetative point develops successively a series of internodes, each terminated by one or more leaves. In the terminal buds at the end of the stem — often the whole element of next year's growth — leaves and nodes can be seen, only requiring the elongation of the internodes to fully expand, as is shown in figs. 47, 48, 49, 50. A bud is therefore, in the language of Gray, "nothing more than the first stage in the development of a stem, with the axis still so short that the rudimentary leaves within successively cover each other, while the whole is covered and protected by the scales without. As the bud is well supplied with nourishment in spring by the stem on which it rests, its axis elongates rapidly ; and although the growth commences with the lowest internode, yet the second, third, and fourth internodes, &c., have all begun to lengthen long before the first has attained its full growth. The stem, thus continued from a terminal bud, is, if it survive, again terminated with a similar bud at the close of the season, which in its development repeats the same process." The rings (fig. 47, a) mark the limits of each year's growth, and are the scars left by the fall of the bud-scales. In trees with strong buds, like the horse-chestnut, they may be traced back for a number of years, until the distention of the stem and the weather have obliterated them. On the horse-chestnut, &c., can also be 1 Dupetit, Thomas, and others, have called this the merithallhnii (ftepls or (ie'pos, part ; and floAAbs, stem). Irmisch has also called the first internode, which terminates at the attachment of the cotyledons, the hypocotylonaxis. 2 Link has also given the Xsxmgemimtla to a form of leaf-bud ; and in addition, , Schleiden and Endlicher are almost alone in applying it to what is termed by nearly all botanists the ovule. Linnasus gave all buds the name of hybcrnacula, from their use in continuing the plant life through the winter. He divided them into— I. Buds proper, 2. Bulbs. The punctum vegetationis of G. Fr. Wolff. BUDS. 75 seen, after a long time, the scars left by the fall of the leaf, the "dots" marking the place where the woody bundles composing the petiole separated (figs. 47. So)- Buds vary considerably in their Fig. 47- 1. Diagram of the vertical section of a spring bud, such as that of the horse-chestnut. 2. The axis of the same developing, the elonga- tion beginning with the lowest intemode, soon followed by others in succession. 3. A year's growth of the horse-chestnut, crown- ed with a terminal bud. a Scars left by the bud- scales of the previous year ; b b Scars left by the fallen petioles or leaf-stalk ; c Axillary buds. 4. Branch and buds (all axillary) of the lilac (after Gray). Fig. 48. — Branch of cherry car- rying intermingled a number of buds, some for the flowers, b b b ; the others for the wood, b' b' b'. nature and size. In some plants they are covered by the bark until spring. In these cases the elements composing them are in their dormant condition, not very distinct. In many plants, as in herbs and very many tropical trees, and in some shrubs of temper- ate latitudes {R/iamnus frangiila. Viburnum lantana), they are 76 BUDS, naked, while in otliers they are covered with scales which envelop and protect the delicate structure from rain and sudden changes mit of which are found Fig. 50 — Extremity of a branch of the horse- two lateral buds. This chestnut (Ai:scitlus/Vijipoc(tsea)ua)i,h.) hearing branch, then, cannot be a large terminal bud, d, and two rather smaller prolonged in a direct lateral buds, b' b' ; a a a Cicatrices left by the course. fallen leaves. of temperature at a season when it can ill withstand such. In some the bud is covered with a gummy, waxy, or resinous exuda- tion, which wards off rain; while in a fourth kind of bud the interior IS lined with a non-conducting kind of down or wool, which serves the purpose of protecting the young leaves and other structures from cold during the winter season. The terminal bud (fig. 50), which many trees and shrubs habit- ually produce, is thus a direct continuation of the stem or branch ; but there are also latei-al buds produced in the axils of leaves, (figs. 47, 49, 50). Some trees and shrubs do not produce the ter- minal bud, and in this case their place is taken by lateral ones, unless as, for example, in the lilac (fig. 49), the axis is terminated by two opposite buds produced at its truncated extremity. On the other hand, palms and most monocotyledons produce no lateral buds, and the stem must be therefore continued upwards by the terminal bud. In general, each leaf of those shrubs and trees which produces axillary buds, produces but one in its axil ; and accordingly, the arrangement of the branches on the trunk and the twigs on the BUDS. 77 branches must be the same as the arrangement of the leaves — that is to say, the branches are opposite on plants with opposite leaves, alternate on plants with alternate leaves, and so on. There are a tew exceptions (as in certain species of Cuphea, in which the leaves are opposite or verticillate, but the ramifications alternate), but the main principle enunciated holds true in the great majority of plants. There are, however, certain natural orders (Scrophu- lariacece, Acanthaceas, Solanacese, Rubiaceas, &c.) which have habitually several buds in the axil of each leaf, all ranged longi- tudinally along the axis, the upper ones more advanced than the lower ones.^ In addition to the regular terminal and axillary buds, there occasionally appear adventitious ones on indetermi- nate parts of the stem, and even on leaves. These bud-scales (which Mirbel called as a vihoXe. perula) are again only modified leaves; they have the same structure and arrangement as the leaves proper of the plant, and graduate by insensible transi- tions to these in many plants. The turions or subterranean budding- shoots of many perennial herbs, and the unfolding buds of the lilac m3'^rtle {Vacciniimi myrtilhis), show every gradation between the bud-scales and the foliage— proving that there is no absolute line of demarcation between them, but that they are only modifications of the same organ to subserve different purposes. Such buds, only covered with the ordinary leaves remaining in an imperfectly-de- veloped state, are termed foliaceous buds. Again, the base of the petiole may be modified so as to serve the part of scales {petiolar buds), while the name of stipular buds is applied to those in which the stipules play that part {e.g., in various fruit-trees, beech, &c.) Lastly, in the roses, where the stipules are united to the sides of the petiole, both the petiole and stipules are thus conjoined in the office of protecting the young bud ; in these plants the scales may be distinguished as fulcrar'^ (Duchartre). Most fre- quently the terminal bud, which opens in spring, develops into a shoot bearing leaves alone, but in other cases it may bear flowers, while in a third case some plants are provided with buds which produce both flowers and leaves (the vine, for example). The first are accordingly called leafing or wood buds; the second, flower or fruit buds; while the name of mixed buds is applied to the last (fig. 48). It is not difficult to distinguish the flower and leaf buds. The first are large, swollen, ovoid, and more or less obtuse; while the second are straight and pointed, as shown in the apple, pear, or cheny (fig. 48). Though in their earliest stage they do not materially differ either internally or 1 Guillard, Bourgeois, and Damaskinos: Bull. Soc. bot. de Fr., iv. (1857) 957 et seq., and v. {1858) 598-610. " Under the name of fulcra, Linnaeus included stipules, bracts, spines, tendrils, and even hairs and glands. 78 RAMIFICATION : TWINING STEMS. externally, as a rule there is a determinate number of scales for the buds of each species of plant, and also an equal determinate number of leaves developed by the shoot.^ Lastly, it may be mentioned that though the buds of woody plants present the utmost variety, both in position and form, yet it is possible, even in the depth of winter, to recognise each species by its buds alone. This has actually been done.^ Ramification or Branching of Stems. — If the stem grows without branching, simply through one terminal bud, it is a simple stem. Short dicotyledonous stems, however, ramify into numerous subdivisions in the following manner : Each leaf, when it joins the stem, forms with the stem an angle more or less acute, which is the axil, just as the arm-pit is the axil at the union of the trunk and the arm. This axil has the power of form- ing axillary buds, which buds have all the characters of the ter- minal bud, and can continue the axis in the form of branches, just as the terminal bud can the main axis. This bud accord- ingly forms nodes and internodes in the manner already described, and it again is subdivided in the same way, until the branched character so familiar to us in ordinaiy trees like the oak or elm is given. The stem from which the first branches spring is, accordingly, the. primary axis, and the branches springing directly from it the secondajy axis, or the axis of the second degree ; and those from it again the tertiary axis, and so on ; or, in familiar lan- guage, the tree has a branched trunk, with branches, branchlets, and twigs. The extent and mode of ramification differs in differ- ent species of trees and other plants, giving to them their various habits and physiognomies.^ Twining Stems. — Many plants, particularlyof herbaceous species, have stems which support the plant in an erect position by twisting themselves around the stem of some stouter plant in its neighbour- hood ; and it is a most curious fact, which will be further touched on (Section IV.), that the direction in which they twine is always the same in each species, no matter under what conditions the species may be placed. For instance, the hop {Humuhis bipuhis, L.) and honeysuckle {Lofiicera) twist towards the left hand (standing in front of the plant), a direction expressed in systematic works by 1 Ohlert, Linn.Tea, 1837, 632-640. 2 Moritz Wilkomm, Deutschlands Laubhoelzer im Winter, 1859. 3 Humboldt on the physiognomy of plants in " Views of Nature " (Bohn's Trans.) p. 210. A most exhaustive treatise on the ramification of flowering, principally in relation to the division of the vegetative point, has been published by Dr Eugene Warming of Copenhagen, in the Transactions of the Danish Academy of Sciences (1872), entitled " Forgreningsforhold hos Fanerogamerne betragtede med scerligt Hensyn til klovning af Vaskstpunktet " (pp. 164, with risumi in French, 11 plates and 15 woodcuts), to which I can only refer the student. FLESHY STEMS : CLADODIA. 79 the sio-n ([ [sinistrorsiim volubilis). On the contrary, in the Chinese yam {Dioscorea Batatas, Dene.), the haricot {Phaseolus vulo-aris\ Dolichos, the great hedge bearbind {Calystegia septum, R. "Br.), &c., the twisting is towards the right, and is expressed by the sign ]) [dextrorsuvt volubilis). Fleshy Stems— The stems of some plants, particularly of the order Cactacca, are large and fleshy, taking the. most bizarre forms, and differing entirely in appearance from what is ordinarily under- stood as such in other dicotyledonous plants. For instance, in Echinocadus ottonis, Lehm. (fig. 51), the flower is absolutely Fig. 51. — Echinocadus ottonis, Lehm., entire plant longer than the stem is high. In Opiintia Dillenii, Haw. (fig. 52), the stem, which at first is almost cylindrical at the base, swells out into oval-flattened expansions, which look as if they were articu- lated one above another. Oladodia. — In the last-named species of cactus, the peculiar form of the stem approximates it to what Martius called a cladodiufn^ — a form of branch which simulates a leaf by reason of its abnormal form and green colour. The cladodium presents a certain analogy with the teratological phenomenon called " fasciation," with this difference, however, that the cladodium is normal, with rounded or even angular extremities, and that the form is regular and constant in the same species. A good 1 KA060S, branch. 8o CLADODIA : STEM-DEVELOPMENT. example of this form of branch is afforded by the common butcher's- broom {Ricscjis aculeatus) fig. 53, and in the genera Pkil/atiihux or Fig. 52.— Flowering branch of 0/z<«^/a on the median line, and on the Dillenii, Haw. upper aspect of the cladodium. Xyllophylla belonging to the order Euphorbiaceae. The thread-like branches of the common Asparagus {Asparagus officinalis') are also examples of cladodia. Vulgarly, these cladodia are looked upon as leaves, but in asparagus, as in butcher's-broom, the true leaves are in the form of minute scales ; and if we consider, as St Pierre does, the joint and stem of Optmtia Dille}ni {^g. 52) as also belong- ing to this type, we must look -for the leaves in the spines on the cladodia. Structure of the Stem: Development.— In the earliest state of the stem, its structure is extremely simple, being merely a mass of parenchyma, surrounded by a delicate epidermis — this parenchyma being divided into a central mass and a peripheral layer by the interposition of a layer of very minute cells. This central cellular mass, which is out of proportion to the diameter of the stem in its size, is the first trace of the pith. The peripheral layer is the first STEM — DEVELOPMENT. 8i stage of the bark, while the intermediate layer of delicate cellular tissue is the layer on which the future growth and increase of the woody zones and bark depend — in a word, that which goes under various names.^ but is most commonly known as the canibhim layer of the stem. Very soon after the stem has passed out of the embryo state, some of the cells begin to lengthen into tubes, and to become marked with transverse bars or spiral lines, and thus give rise to ducts or vessels; these form a small and definite number of bundles or threads, say four equidistant ones at first : surrounding these, other slender cells of small calibre, and destitute of markings, soon appear, and form the earliest woody tissue. As the rudiments of the next internode and its leaves develop, two or more additional threads of vascular tissue appear in the stem below in the paren- chyma, between the earliest-formed ones, and are equally surrounded with woody tissue. Thus, at an early stage, these bundles of woody tissue thus formed increase and en- large, and run together to make up a woody zone, which looks, on a transverse section, like a ring enclosing the central part of the parenchyma, and itself enclosed by the ex- ternal parenchyma, and so situated in the ori- ginal homogeneous cellular system as to divide it into two parts — namely, a central portion, which forms the pith, and an exterior /M' V / 1 °' Phylianihus (Xylo- portion, which belongs to the bark. The whole phylk) }nontn>tn, Sw., is invested by the epidermis or skin, which ^\'.kef 'wfth'^'patent covers the entire outer surface of the bark '^^'h, carrying little The woody masses or wedges are separated fe"^es) att flowe"' in from each other either by lines or bands of the ^" original cellular tissue, which pass from the pith to the bark, and which necessarily become narrower and more numerous as the woody bundles or wedges increase in size or number. These are the medullary rays ^ (fig. 55). 1 It is the Zone gdniratrice of Mirbel, the Bildungsschicht of Meyen, &c., coiiche sous-libcriinne or Endodcrm of Richards, and Verdicknngsring of Sschacht. Duhamel, to whom we are indebted for the term cambium, did not employ it in exactly the same signification as modern botanists ; but this is of no consequence. * Gray, Structural and Syst. Bot., 117. F 82 STRUCTURE OF THE STEM : PITH. F'S- SS- — Diagram of the first for- mation of an exogenous stem, a Pith ; 6 6 6 6 Bark ; c c c c Plates of cellular tissue (medullary rays) left between the woody bundles dddd^sSter Carpenter). The first yeai^s growth of the stem of a dicotyledonous plant consists accordingly of three principal parts : first, an interior cellular portion or pith j second, one zone of woodj third, an exterior cell- ular portion or bark (fig. 57). The mode of growth of these we have already explained. Making now a transverse section of a dicotyledonous plant, say at the age of four years, we would see the following structure from within out- ward : — 1. Pith or Medulla. 2. Medullary rays — radiating lines coming from the pith out to the bark. 3. Medullary sheath surrounding the pith. 4. Layers of woody substance in concentric arrangement. 5. Cambium layer, or Endophloeum. 6. Bark composed of the following layers : — a Liber or bast layer, with laticiferous tubes, &c. /3 Mesophloeum or green layer. 7 Epiphloeum, suberous, or corky layer. 8 Epidermis. Let us consider each of these separately. (i.) Pith.—ll\\& pith occu- pies the medullar}^ canal in the centre of the plant, and in the young plant is a con- tinuous mass of cellular tissue, the cells of which are filled with sap, and of a more or less intense green colour. When the plant gets older, the juices get absorbed by the plant, and the pith becomes dry and white, tearing with the utmost facility. In some plants, such as the Walnut and Jasmine {jfasminiuvi offi- cinale), the stem increases in its young state rapidly, so that the pith gets broken, and remains in the form of fragments, forming transverse partitions in the now hollow stem.^ In some 1 Hence, in this state, sometimes called disciform («io-icos, a disc). Fig. 56. — Transverse section of the trunk of an oak (Quercus Ro6ur, L.), aged 37 years. in Pith, with a pentagonal contour; Ig /g' Mass of wood formed by 37 annual zones ; through it traverse the medullary rays, distin- guished by the light lines ?-7n ; 6c Entire bark. li STRUCTURE OF THE STEM : MEDULLARY RAYS. 83 cases {e. g., most Umbelliferas) the pith is hollow or fistulose, and is interrupted at the nodes alone by transverse partitions. The rupture of the pith can also be seen in the clover-stalk, the rank pea-vine, and in a hollow potato-tuber. The cells of the pith are often of a perfectly regular hexagonal form. It is not uncom- mon, however, to find the pith pierced longitudinally by lati- ciferous bundles (p. 42), which have been called " Medullary ves- sels or fibres." These can be well seen in the Ferulas (fennels), Nyctora, Euphorbias, &c. These vascular bundles sometimes con- tain a few spiral vessels, which seem to have been detached from the medullary sheath. The cells on the periphery of the pith pre- sence their vitality longer than those in the centre. Hence, at the end of the second year of the life of the plant, Guillard distinguish- ed the annular and the ce7ttral ^\\.\\, and considered ;that in the former essentially vitality resided, the latter at that period being already dead. In the early state of the pith, especially when full of starch, it may perhaps assist in the nutrition of the young plant,^ but in the dry or disrupted state it can be of no use what- ever. Slices of the pith of Aralia papyri/era, Hook., form the rice- paper of the Chinese, just as the Papyrus of the Nile was employed for a similar purpose by the ancient Egyptians. In size and shape the medullary canal varies. It also decreases in diameter with the progress of vegetation. Though in general circular, it is sometimes elliptical, triangular, &c. Palissot de Beauvois^ thought that he had detected a connection between the shape of this canal and the petition of the leaves. For example, it is elliptical when the leaves are opposite, as in the ash ; triangular when they are in verticils of three [Nerium Oleander), &c. : but this law presents too many exceptions to be received as estab- lished. The pith can even be extracted without the plant suffering much, if any, injury. (2.) Medullary Rays (fig. 56, rm) are composed of muriform cell- ular tissue, elongated transversely (or in a direction opposite to that of the cellular tissue of the rest of the stem), rarely pointed at either extremity (fig. 4) ; they keep up the connection between the pith and the bai'k, as well as the rest of the stem, through which they probably distribute the sap. They penetrate in a stellate man- ner through the wood and cambium from the pith to the bark, and form the " silver grain " of the carpenter, which gives the glimmering lustre to many kinds of wood, such as maple, oak, ^ The chief part of the feculent substance of the tuber of the potato and sweet potato, and of many underground stems, is pith. The starch of the yams, manioc {Jatropha Manihot), and "arrowroot" (various species of Dioscorea, Marantacece, but particularly Maranta Indica), is also derived from the pith (p. 26). 2 M^m. de I'Instit., 1811. 84 STRUCTURE OF THE STEM : MEDULLARY SHEATH. &c., when cut so as to expose them. The medullary rays are wanting in some dicotyledons, such as the Crassulacese, Pisonia, LathrcBa Clajidestina, Melampyj-iiin, &c., and are very indistinct In others (Coniferas, &c.) (3.) Medullary Sheath (fig. 60, This layer scarcely deserves a separate name, as it is simply the first- formed layer of woody matter containing a number of spiral ducts— the only ones found in the wood— and surrounds the pith : hence the term applied to it. Fig. 57- C Fig. 59. Fig. 57- — Longitudinal and transverse section of a stem of the soft maple {Acer dasy- "j carpuin) at the close of the first year's growth (nat. size). I Fig. 58. — Portion of the same magnified, showing the cellular pith surrounded by ] the wood, and that enclosed by the bark. " | Fig. 59- — More magnified slice of the same, reaching from the bark to the pith, a Part of the pith ; i Vessels of the medullary sheath ; c The wood ; Dotted ducts in the wood ; e e Annular ducts ; / 'J'he liber, or inner fibrous bark ; g The cellular en- velope, green bark, or mesophla;um ; h The corky envelope, or epiphlceum ; i The epi- I dermis, or skin ; kOne. of the medullary rays, seen on the transverse section (after Gray), j If a young twig is broken through, after dividing the bark and most of the wood, the fibre coiled in the spiral ducts can be seen unrolled in the form of delicate gossamer threads. This medul- lary sheath is formed in the first year's growth, and is not repeated. STRUCTURE OF THE STEM : WOOD. 85 (4.) IVooi/ifigs. 56, 57, 58, 59, 60, 61).— The wood which forms the body of the stem is composed of woody tissue, with vascular intermingled, chiefly in the form of dotted ducts, or occasionally some annular ones. It is composed of circular layers, made up of these materials superimposed one above the other to an extent B C W Fig. 61. mr Fig. 60, portion of a transverse section, and fig. 61, a corresponding vertical section, magnified, reaching from the pith, /, to the epidermis, e, of Negtmdo aceroides, Mcench. (the American bo.\-elder), a year old. B The bark ; W The wood ; and C The cambium layer, as found in February, ms Medullary sheath ; iv iv Wood ; d d Dotted ducts ; cl Inner part of the cambium layer, which begins the new layer of wood ; / Liber — its bast- tissue, b, belongs to the woody system ; ge Green envelope, or mesophloeum ; ce Corky envelope, or epiphlceum ; vtr Medullary ray, seen on the vertical section, where it runs into the pith. In this tree we find a thick layer of parenchyma (/) inside of the bast- tissue, and therefore belonging to the liber. No bast-tissue is formed in it the second year. (After Gray.) practically indefinite. It will thus readily be seen that the outside layers are the youngest and the inside the oldest. Accordingly, if we examine the stem, say of an oak or walnut, we will find the wood in the interior of the stem denser and of a darker tint than the 86 STRUCTURE OF THE STEM : WOOD. outside layers. To the first has been given the name of Duramen or heartwood, and to the \2iiitr A Idurtittm or sapwood. Sometimes the difference between the colour is very marked, and the change from the one to the other is made sharply, without any intermediate shades, as in the ebony or in the Campeachy wood, in which the duramen is black or dark brown, while the alburnum is almost white. In most cases the duramen becomes brown. However, in the barberry it is yellow, in the red-cedar {Juniperus Virgini- ana) red, in the Judas-tree {Cercis) yellow, and in the Guaiacum greenish. Frequently, however, especially in white-wooded trees, Fig. 62. — Transverse section (much magnified) of a very small portion of the liber of Cinchona Calisaya. riii rin' Medullary rays entering the bark ; Jl' H' Cortical fibres ; cc cc Cellular tissue {Weddell, Qtiingtiinas, PI. II. fig. 33). there is no sensible difference in colour between the two kinds of wood, as in poplars, willows, &c. These colours appear in some cases to be due to special vegetable substances mingling with the incrusting lignine, and in other instances are owing to some peculiar effect of age on the lignine. The colour will be produced often rapidly, and bears no relation to the annual increase. Oc- casionally it will happen that one or more of the woody rings on one side of the stem will be coloured, while the remaining half of the same rings on the other side will have the hue of the alburnum. The duramen is always of more economic value than the alburnum. Physiologically, the effect of this hardening of the duramen is to STRUCTURE OF THE STEM : WOOD. 87 -Payen has shown that the base ll render it impervious to sap, so that the heart of the tree may be removed or injured by decay without its vigour being at all dis- turbed. Chemical Composition of Wood.- is cellulose, which is identical in composition with that which forms the other elementar>^ tis- sues of plants, but that this is changed in the course of growth by the deposition of four other substances having different pro- perties, and capable of being isolated one from the other by different chemical reagents. These substances are : (i.) lignose, insoluble in water, alco- hol, ether, or ammonia ; soluble in potash and soda: (2.) ligftone, insoluble in water, alcohol, and ether ; soluble in ammonia, potash, and soda : (3.) lignine, insoluble in water and in ether ; soluble in alcohol, ammonia, potash, and soda: and (4.) ligni- re'ose, soluble in alcohol, ether, ammonia, soda, and potash, and also to a slight degree in water. Formatioft of the Annual Zones of Wood. — As the cells of the cambium multiply, some lengthen vertically into woody tissue or prosenchyma ; some are transformed into ducts; while others, remaining as parenchyma, continue the medullary rings, or commence new ones. In this way a new layer of wood is formed above that of the former year.^ Next year the same process goes on, so that it will follow that the " rings " or concentric layers of wood displayed on making a transverse sec- tion of the stem will give the age of the tree, each layer repre- senting one year of growth, coincident with the growth in length by the development of the body, and "continuous with the woody layer of the new roots below, and of the leafy shoots of the season above." ^ This is not, however, exactly true; because, under certain exceptional circumstances, a second layer of wood 1 Hence Exogenous plants are sometimes called Cyclogens (kvkAos, a circle ; and yiVojiot). 2 Gray, lib. cit., p. 123. Fig. 63. — Longitudinal section of the liber of Cinchona Calisaya, parallel to the direc- tion of the medullary rays rvi. 88 STRUCTURE OF THE STEM : WOOD. may be formed ihe same year by the ascent of the sap during the autumn. In a chenopodiaceous plant — Phytolacca dioica — Martins counted seven layers formed in one year, probably by alter- nate stretches of cold or warm weather. In numerous instances, as in the arborescent species of cactus, Araucaria Brasiliensis, Cinchona succirubra, Coffea Arabica (coffee), Ardisia excelsa, Erica arborea, &c., the wood, owing to its growth going on all the year round, forms a uniform stratum, whatever be the age of the trunk; or, as we shall see in Cycas, where the layers are few, and do not correspond with the age of the trunk, other exceptional forms will be presently noticed. The annual layers are most distinct in trees of temperate climates, where there is a prolonged period of repose during the cold of winter. In tropical trees the layers of wood are rarely so well marked, though in these countries there is, during the dry and hot season, a marked annual suspension of vegetable life. In temperate countries, also, a cold or wet and warm season leaves its record in a narrower or broader ring of wood in the tree. Soft-wooded trees grow most rapidly ; and there is said to be a time in the life of trees when they grow more rapidly than at other times. For example, in the oak the period is be- tween the twentieth and thirtieth year of its age. The thickness of the woody layers also depends a good deal on ^ climate. Bravais and Mai^tins^ found in a Scotch fir, aged 150 years, in lat. 48° N. lat., the average thickness of the layers was 3 millimetres 42 ; in lat. 60° 40', the mean for a fir of the same age was i""™- 51 ; and that in 70° the thickness had decreased to oi"m- 84. They found also that the compactness of the wood increased in ah exact ratio to the distance north. Causes of the different qualities of Wood. — To sum up the causes of the differences of wood, Schacht shows that these differences must be referred to ; (i.) The existence of vessels which are want- ing in all true coniferse, but exist in " joint firs " {Ephedra, Gnetum, &c.), and in all foliaceous trees.* (2.) The disposition, length, and size of the medullary rays, which are scarcely visible in coniferae, being formed of only one row of cells, an arrange- ment also found in willows, poplars, elders, birches, hazels, horse- chestnuts, &c., while in others they are formed of several rows. Again, in most trees the rays are hardened, but in the trunks of various Cactacese — Mamillaria, Opuntia, and Encephalartos — this is not so. (3.) The presence or absence of cells or lacunas containing resin, found so abundantly in most coniferfe — lacuns being chiefly found in the firs, while cells containing this sub- stance are more characteristic of the cypresses and yews, neither the one nor the other being found in Abies pectinata or in Arau- caria. And (4.) the presence of a woody parenchyma, containing 1 Ann. des Sc. Nat., xix. 129 (1848). STRUCTURE OF THE STEM : CAMBIUM : BARK. 89 Starch or other analogous products. The hardness or the weight of wood depends on the structure and development of its tissues. The induration of the cells, the number of vessels, and the presence of woody parenchyma, also considerably assist in this. Some woods, such as Anojia (custard-apple), Erythrina (coral-tree), yEschynomefie palu 'dosa, Carica papaya (papaw-tree), poplars and willows, Thuja, &c., are very light ; others are so heavy as to sink in water — e.^., Brosimum Guyanense even when dried ; while Pmus potiderosa when full of sap will some- times have a specific gravity greater than that of water. Limitation of the Annual Layers. — In oak, chestnut, &c., the outer limit of each year's growth is sharply defined by the layers of large dotted ducts, the open mouths of which can be seen so easily on a transverse section. In other trees, such as maple, where they are not so large and are scattered, and in firs, &c., where there are no ducts at all, but only punctated tissue (p. 39) through- out, the limit of each year's growth is defined by the layers of more minute and laterally flattened wood-cells, which form as the vital efforts get feeble towards the end of the growing season, and the larger cells, which commence next year's layer when vital energy is active — the two thus forming a well-marked boundary. (5.) Cambium Layer} — If the bark is stripped off a tree in spring a slimy slippery substance is seen and felt. This is the Cambium layer — a delicate mucilaginous tissue, full of dextrine, protoplasm, and other organisable matters, and is particularly abundant in spring when growth commences. At that season it is charged with mucilaginous sap, and accordingly the bark is then more easily separated from the wood. In autumn the cells become indurated — in fact, liber and wood cells — so that to strip off the bark smoothly is a less easy task than in the spring. But still the tissue is or- ganically connected with both. The inner portion of the cambium layer is therefore young wood, the outer young bark. (6.) Bark (figs. 59, 60, 61, 62, 63, 64). — In early life the bark {cortex) is entirely cellular, like pith : but in a mature state it is composed of a cellular and a vascular system, in this respect agreeing with the wood ; the arrangement is, however, reversed, for in the bark the cellular portion is outside and of great thick- ness, while the vascular is inside and comparatively small. These discrepancies did not, however, prevent Dutrochet calling the middle layer of the bark (the mesophloeum) the "cortical med- ulla." The four layers of the bark we accordingly find are all cellular, with the exception of the inner one or liber. {a) This (figs. 62, 63) is often called the " bast layer," or Endo- phloeiim^ and derives its more familiar name of liber from the fibrous layers of which it is composed separating in many cases ^ Cambio, I change, 2 'Mvtov, within, and ^Aoios, bark. 90 STRUCTURE OF THE STEM : BARK. on account of the interposition of layers of cellular tissue, on maceration in water, into several leaf-like laminae like the leaves of a book, or rather like the rolls of an ancient manuscript (figs. 60, 61). It does not, however, in all cases, form a continuous envelope, but it is broken up by the passage of the medullary rays into wedge-shaped divisions. It is composed of bundles of fibrous duct-like elongated cells, anastomosing among them- selves, and forms a network the meshes of which are filled with cellular tissue. These fibrous bundles are formed of elongated cells, with very thick walls, and of small diameter, terminating in points or wedge-shaped extremities, and are known as bast-cells or bast-tissiie (p. 40). According to Gray, complete and well- developed liber, like that of Basswood or Linden {Tilia Etcropcea), consists of three elements — viz. (i.) Bast cells or fibres; (2.) large and more or less elongated cells, with the inner walls variously marked with transparent spots, appearing like' perforations, and usually traversed by an exceedingly minute network ; and (3.) cells of parenchyma. On the inner layer are usually found some laticiferous vessels. The second-named element, which would appear to be the proper cells of the liber. Fig. 64. — Transverse sec- tion (much magnified) of the very young bark of Cmchona ovata, intended to show the different layers which consti- tute the bark, before the pro- gress of vegetation has modi- fied it. ep Remains of the epidermis ; s The suberous layer (in which the resinous as they are seldom or cvcr absent, contains matter is contamed m the , , - ., ... cinchonas); cc' The cellular an abundance of mucilage and proteme, layer (mesophloeum) ; la Lacunae gorged with resinous matter ; I Liber ; 7?' Cortical fibres (after Weddell, Qnm- guinas, PI. IL fig. 42). and in all probability takes the principal part in the descending circulation of the plant — z. e., in conveying downward and distributing the rich sap which has been elaborated in the foliage. The bast-cells are not essential to the liber, being altogether wanting in the bark of some trees and other plants. The liber grows by annual additions from the cam- bium, and it has frequently as many distinct layfers as there are layers of wood, but in other cases there is not even a trace of such arrangement. In some plants, such as the vine and honey- suckle, the liber lives only one season, and is detached the follow- ing year, hanging " loose in papery layers or fibrous shreds." To- wards the inner side of the liber, laticiferous vessels are often found, but trachea; are markedly absent from every part of the bark. The liber of the lime-tree {Tilia Europcpd) forms Russia matting ; and that of the sack-tree of Coorg{Aniiaris saccidora)\s used to form mats, bags, &c. " Cuba bast " is the liber oi Paritiuvi datum (order I STRUCTURE OF THE STEM : BARK. pi ; Malvacece). In the lacebark-tree — Laghetta lititeria {ordtr Daphna- 1 cece) — it forms a somewhat regular network, on account of the med- 1 uUary rays interrupting the straight course of the fibres. The tough- ' ness of the fibres makes them of economic importance. Thus the I , liber of Linum usitatissimum forms "flax," \h2Xoi Cannabis sativa "hemp," that of^ciV/wi^r/^zw/wrt (Hook, and Arn) the "Chinagrass" I of commerce — nearly all the members of the order to which it be- I longs yielding fibre. The common nettle yields a strong \ fibre, which the North-West American Indians twist into string for i making nets. In a word, the liber forms the main source of the i fibres of commerce, no matter from what species of plants derived.^ {b) The Mesophlaiim " (fig. 64), or green layer, is that layer of the bark immediately outside of the liber. It is distinguished from the liber by being cellular, and from the superimposed layers by the , ' thin-walled globular or polyhedral cells, its greenish colour, and \ by the interspaces in it formed by the loose union of the cells. ' Richard has distinguished another layer between the mesophloeum I and the epiphloeum under the name of mesoderm (the collen- I chyma of other authors), distinguished by being composed of cells | rather elongated, unequal, thick-walled, and without green granula- j tion in their interior — sometimes, as in Acer psetcdoplatanus, the lilac, &c., forming a continuous layer, at other times showing a disposi- tion to form into distinct bundles separated by the Mesophloeum. In general appearance, it may be remarked, the mesoderm re- I sembles wax, and appears destined to moderate the superficial j evaporation of liquids going through the stem when the epi- ' dermis acts feebly as a protector. According to Schacht, it is I wanting in those stems where a layer of wax is developed in the epidermis of various large spurges — e.g., in Euphorbia canariensis, balsai?tifera, and piscatoria. To apply a separate name to this structure is perhaps, however, in common with some of the names which Mohl has applied to structures in the bark, an over-refine- | ment of nomenclature. The mesophloeum sometimes contains ' vessel-shaped lacunae containing resin — e.g., in pines, junipers, and various other coniferae. (c) The Epiphloeum? or suberous layer,* has no chlorophyll in i i Between the liber and the mesophloeum— in fact, forming the outer part of the Hber — is sometimes produced a layer of tubular cells, which, uniting to the mesophloeum, form those plates which detach from the bark of the "plane- tree " {Acer pseudoplatanus) yearly. To this layer Mohl has applied the names , Rytidotn, internal periderm, or false liber, and traces a correspondence be- tween it and the external periderm (p. 92). In the plane this layer is not de- veloped until the eighth year. 2 Metros, middle, and ^Xoio's. ' "El"', upon, and ^\oi.6%. Sometimes the term Exophlmtm {elKow<;,) is used. Stratum phlceum of Hugo v. MohX— periderm of Hanstein— a term which Mohl uses in a restricted sense. 92 STRUCTURE OF THE STEM : EPIDERMIS. the cellular tissue composing it. The cells are thin-walled, are placed close tog-ether, and are rectangular and elongated in a hori- zontal direction (figs. 60, 61, 64), being thus distinguished from those of the mesophloeum. It also is distinguished by remaining alive for a, short time only, in wanting sap, and in its cells containing air. Its chemical characteristics are that, unlike cellulose in a pure state, it does not turn blue under the action of iodine and of sulphuric acid, even after being boiled in potash. It resists the action of sulphuric acid, which dissolves it when in a state of cellulose ; finally, by boiling in nitric acid, it gives suberic acid. According to Mitscherlich, cork is composed of 65.73 carbon, 8.33 hydrogen, 24.54 oxygen, 1.50 nitrogen; while the cellular tissue of the tubercle of potatoes has the following composition: 62.3 carbon, 7.15 hydrogen, 27.57 oxygen, 3.03 nitrogen. It is often much developed, forming, in Quercus Suber, the well- known cork of commerce ; hence the name frequently applied to it — the suberous or corky layer. It is also largely developed in the bark of some other species of trees : for instance, on the stem of some AristolochiacecB, on the inferior portion of the stem of the curious Elephant's foot [Testudinaria elephantipes, Burch.), on the bark of a variety of elm {Ulmus campestris, L., var. suberosa), &c. When stripped off the cork-bearing tree, it can be renewed artifici- ally by a process of growth which space will only permit us to describe very briefly. It appears that the cork of commerce is not a true example of this suberous layer, but is an artificial product. In this operation the first thing done is to pull off the natural bark of the cork-oak, known as the " male cork " — this operation being known to the Algerian colonists under the name of " le ddmas- clage." The workman, in taking off the male cork, leaves on the trunk the mesophloeum and liber — these two layers being known to the colonist under the general name of " the mother." On a tree thus stripped, the cork of commerce (the " female cork " of the workmen) begins to form at a greater or less depth in the meso- phloeum and in the liber. The "male," or natural bark, is close in texture, and not elastic ; while the female, or " artificial," is, as every one knows, very elastic, being composed of elastic porous cells.^ (d) The Epidermis is the outside skin which covers the bark. It is composed of flattened cells, in which wax is sometimes develop- ed, giving it the familiar glistening appearance seen in many trees. It possesses stomata, scales, hairs, and other appendages, which we have already described (Sect. I.) On herbaceous plants, the epi- dermis remains unaltered ; but in perennial species it has to stretch to allow of the tree increasing in diameter, while in others it 1 Casimir de Candolle — De la Prcduction iiaturclle ct artificiellc dtt liege. Mdm. de la Soc. de Phys. at d'Mist. Nat. de Genfeve, t. xvi. STRUCTURE OF THE STEM OF ANNUAL DICOTYLEDONS. 93 cracks and falls off. The function of the epidermis then falls on the underlying epiphloeum, or rather of a particular portion — viz., what Mohl has called the Periderm. This is one or two rows of thickish-walled tubular cells, of a rather darker colour than the rest of the epiphloeum, and which mark the termination of each year's annual growth of cork. In plants in which the corky layer is feebly developed, \h\s peride7-m is most marked ; and it is to its coherent properties that the toughness of the bark of the canoe-birch {Beiiila papyracea, Wild.) is due. It is to this peri- derm, also, that is due the exfoliation in isolated plates of the bark of some trees, such as the planes, &c. Variations in Structure of the Bark. — The bark is more varied in structure and growth than the wood ; and, owing to distention by the growth of the wood, is liable to various abrasions and changes, as well as on account of its being exposed to all the influences of the elements without. Accordingly, in old trees it fissures and breaks off, so that its thickness in these trees never bears a regular pro- portion to the wood, even though the bark increases from within to the same annual amount as the wood. Hence a nail or other implement driven into the bark will, in due course, fall out; while, if put into the wood, it will get covered over by the annual in- crease.^ The different layers grow by additions of cells to their inner face. The green layer does not grow at all after the first year; the opaque corky layer soon excludes it from the light, and it gradually perishes, never to be renewed. The corky layer com- monly increases for a few years only by the formation of tubular cells.^ In some trees, such as Seqjioia gigantea, Abies Douglasii, the bark often attains a thickness of a foot or more. In others, by annual exfoliation, it is always about the same diameter. Structure of the Stem of Annual Dicotyledons. — In annual dicotyledons the structure of the stem is the same in general as we have described in the preceding pages, but with the fol- lowing differences : (i.) The bark is more simple in its structure, and the bundles forming the liber present these modifications, — {a) they form a continuous layer; {b) they are isolated and distinct in the middle of a herbaceous envelope; {c) they are placed immediately under the epidermis. (2.) The medullary rays are in general larger than in perennial plants. ^ Numerous such instances are on record, or continually being recorded in the journals of the day. — Vide several such in Histoire de TAcademie des Sciences, 177, cited in Bocquillon's La Vie des Plantes, 150. In some trees, which naturally branch from near the base, if growing in a dense forest or thicket where light cannot penetrate to the lower branches, these branches will often drop off at an early stage, and the scars left by their attachment get grown over by the bark, so that no visible trace remains to show that the trees were not originally unbranched from the trunk. * Gray, 1. c. 94 USES OF THE STEM : STEM OF MONOCOTYLEDONS. The Uses of the Stem will be duly considered when the function of nutrition comes to be discussed. In the mean time, dogmati- cally and in a few words, the functions of the various parts may be summed up as follows : (i.) The pith supplies nourishment to the young plant ; (2.) the medullary sheath keeps up the con- nection between the leaves and cortical parts of the stem by means of the spiral vessels which can be traced into the petiole of the leaf, and seem intended for the conveyance of air ; (3.) the medullary rays keep up a connection between the pith and the bark, and possibly help to produce leaf-buds ; (4.) the cambium forms the wood and bark ; (5.) the bark protects the tender wood, conveys the sap downward from the leaves after being elaborated, and contains many useful products (gum, tannin, turpentine) ; (6.) the woody portion conveys sap from the roots to the leaves — at one time all did this, but latterly only the open vessels, all the rest having got filled up by woody matter. STEM OF MONOCOTYLEDONS. To this type belong the stems of the palm-trees of tropical and subtropical countries, as well as many other trees and shrubs of those countries, and though in the north all of the arborescent species belong to the preceding class, we have many humble representatives of the Monocotyledonous, Endo- genous, or inside growers. The palms may, however, be now con- veniently taken as the representa- tives of this class of stems; their habit of growth — growing un- branched to the height of from 20 to 150 feet, with umbrella-like crowns of leaves — giving a strik- stem of 'a palm, Cortical zone ; aSDCCt tO the SCenery of the Internal portion, with woody bundles o i i • /c /- \ comparatively few, and not crowded countries thev are found m (ng. 67). together ; Peripheral portion of the structure.— The Structure of the wood to which the numerous firm fibro- tjux l*v/uliJ.v/• vascular bundles give considerable stem is widely different from that of dicotyledons (fig. 65). Instead of showing pith, concentric circles of wood, and a detachable bark with the intervening cambium layer, we find the woody bundles scattered irregularly through the stem from within out- ward ; the pith, as found in the dicotyledon, is absent ; there is no cambium layer ; and the bark can with difficulty be detached from the wood. Fig. 65. — Transverse section of the STRUCTURE OF THE ENDOGENOUS STEM. 95 Examining the structure of this kind of stem more minutely, we find that it is composed of woody bundles, or vascular fibres, scattered in the midst of cellular tissue, of which the greater mass of it is composed, without any appearance of superimposed layers. The woody mass of the stem is composed of thickened cellular tissue, in which the vascular bundles already mentioned are scat- tered, the one distinct from the other, but more numerous, closer together, and harder towards the exterior than towards the interior of the stem, contrary to what we find in dicotyledons. There is no medullary canal and no medullary rays. Each vascular bundle is composed of (i) spiral vessels, (2) fibrous vessels, (3) proper or laticiferous vessels, (4) cellular tissue. I. The spiral vessels (tracheae, or punctated vessels) occupy in general the centre of each bundle. 2. The laticiferous vessels are placed outside the spiral vessels. 3. The fibrous vessels are ordi- narily in two bundles, — the one external, which may be considered, according to Mohl, as corresponding to the liber of the dicoty- ledonous bark ; the other internal, placed on the interior side of the spiral vessel, may be compared to the woody body of the same stem. The cambium disappears after each bundle has completed its growth or become " definite ; " but it is present in the young state. ■ The bark is composed of (i) an epidermis, (2) cellular tissue, (3) bundles of fibrous vessels, which are sometimes wanting, but never forming, as in the liber of dicotyledons, leaf-like layers. In general, authors have described monocotyledons as having no true bark ; and it is to Richard ^ that we are indebted for showing the erroneousness of that idea. Schacht has even described the cambium layer as existing in the stipe of Draccena. In various palms and in grasses the bark is covered with a hard epidermis containing silicates. In various palms — Caladium, Phosnix, Chaincsdorea, Sabal, Raphis, &c. — we find, on the inside of the bark, bundles of fibrous tubes, isolated, but forming a some- what regular ring. The vascular bundles get indurated, by the deposition of lignine, in course of time. Their direction in the interior of the stem is always about the same. They may be usually traced from the base of the leaves down through the stem, " some of them to the roots in a young plant, while others, curving outward, lose themselves in the bark."- As new leaves are developed, new fibres descend into the interior of the trunk, and then, after descending so far, curve outwards towards the bark, with which they get incorporated, thus account- ing for the difficulty with which the bark is detached from the ^ Nouv. Eldm. de bot., 7" 6d. p. 132. 96 ENDOGENOUS STEM : GROWTH OF PALMS, Stem. This method of increase from within outwards will go on as often as new leaves are developed, until the bark will no longer distend, when the growth ceases (fig. 66). In Dracceiia, however, the bark remains soft through life. Hence some trees of this genus ■ — for ex- ample, the gigantic dragon-tree of Teneriffe, which, at the time of its death, was about twelve feet in dia- meter ten feet from the ground — will attain great dimensions. The bundles, however, through their whole length, have not the same organisation. At their inferior ex- tremity they are smaller in diameter, and are composed of fibrous tubes ; higher up they show laticiferous vessels, then spiral vessels ; still higher the false spiral vessels ; and lastly the true spiral vessels. From what we have said, it will be seen that the woody mass in the centre of the stem is the newest and the softest (hence sometimes called the "pith"), and the part outside the oldest and hardest. The wood of the lower part of the stem and the rind is also firm, from the greater number of woody fibres which terminate in them, and also from its proper induration in the former case. Growth of Palms.— Palms usu- ally grow from a terminal bud alone. Accordingly, if this bud is destroyed, the tree dies. However, on the Doum palm {Hyphccne Thcbaicd) of Egypt, and the Pa7idanus or screw-pine (be- longing to the order Patidanacecr, near allies of the palms), two or more buds are developed, which give rise to two or more trunks and branches ; and when, as in the asparagus, lateral buds are devel- oped, or, as in the bamboo, maize, &c., leaves are scattered along the stem and branches, these latter taper, just as in dicotyledons ; while in the case of the Doum palm, &c., the branches are cylin- drical like the stem. Fig. 66. — Diagram intended to show the course of the fibro-vascular bundles in the stem of a monocoty- ledon, bbbb Indicate the size of the stem ; « « Its median line. The bundles to the left, i 2 3 4 Si and those to the right, i' 2' 3' 4' 5', point to the leaves, newer or older, accord- ing to the same order of the numbers. STRUCTURE OF THE STEM OF MONOCOTYLEDONS. 97 Theoretical Structure of the Stem of Monocotyledons. — Com- paring the structure of an exogenous with an endogcnotis stem (to use the terms suggested by tlieir structure), we find that in the first the woody part consists of wedges of wood composed of layers formed by the inside cells of the cambium year after year, as long as the life of the plant extends, these wedges being separated one from the other by the interposition of the cellular medullary rays. In the endogenous stem we find no such arrangement of concen- Fig. f^l.—Meiroxylon Rumphii, one of the palms from the central portion of the stem ot which sago is extracted in Malacca ; a, b Fruit whole and in section. trie circles of wood forming wedges with the sharp end next the pith and the broad end next the cambium and liber. Neither exist. However, the two stems, if we examine them closely in a philoso- phical spirit, will be found not to be so entirely different from each other as might at first sight be imagined. An analogy can be traced between the parts of each. Each thread or fibrous bundle in the endogenous stem has all the elements found in the stem the Exogen, though sometimes irregularly mixed. This we nave already hinted at. A section of one of these threads shows G 98 STEM OF ACOTYLEDONS. woody fibre, and one or two spiral vessels on its inner border, corresponding to true wood ; and the thick-walled elongated cells on its outer border have been shown by MohP' — who originally pointed out these cor- respondences^— to be of the same nature as the bast-cells of Exogens. " Between the two is a structure of parenchymatous cells mixed with elongated and punctated cells, answer- ing to the proper cells of the inner part of the liber. The portion of each endogenous thread, therefore, which looks towards the centre of the trunk, answers to the wood, and its outer portion to the liber, or inner bark of the exogenous stem ; and the parenchyma through which the threads are interspersed answers to the medullary rays and pith to- gether. The main difference between the endogenous woody threads and the exogen- ous woody wedges is, that there is no cam- bium layer in the former between the liber and the wood, and therefore no provision for increase in diameter. The bundles are there- fore strictly limited, while those of Exogens are unlimited in growth. In Exogens the woody bundles or wedges, symmetrically arranged in a circle, become confluent in a zone in all woody and most herbaceous stems, which con- tinue to increase in thickness. In Endogens the woody bundles are unchanged in size after their formation ; but new and distinct ones are formed in the growing stem with each leaf it develops, and interspersed more or less irregularly among the older bun- dles "2 (fig. 67). STEM OF ACOTYLEDONS. The stipe, caiidex, or rachis of Acotyledonous plants, like ferns, &c., forms the type of stem which has been called the Acrogenous or summit grower. It differs from both the Dicotyledonous and Monocotyledonous stems in having neither concentric circles 1 Martius' Palmas (Intro.), 1824. His doctrine has been opposed by Mir- bel, Gaudichaud, and others, but still holds its ground. 2 Regarding the theory of stem-formations generally, Sehleiden holds some, very peculiar ideas, which those interested in the views of that botanist can. find in his paper, " Uber die Anatomisch-physiologischen Verschiedeiherten der Stengelgebilde, " in Wiegmann's Archiv., 1839, p. 219 ; or in various Eng- lish abstracts which the admirers of that style of botany have taken the trouble to make. They are not, I believe, usually given in modern text-books. Fig. 68. — Section of a woody bundle from an endogenous stem (a palm). Outside are thickened walled fibres, considered to be liberian. Immersed in a mass of parenchyma are seen the mouths of two large dotted vessels, while the three smaller openings are the mouths of spiral vessels. In the figure the laticiferous vessels do not appear ; they are usually immediately within the liber, like outer fibres. STEM OF ACOTYLEDONS : FERNS. 99 of woody matter nor woody bundles, being simply formed by the base of the leaves. In a tree-fern, for instance, the leaves • (orm a crown on the summat as in the palm. New leaves are formed year after year, one circle within those of the former year, -yvhich have died away, leaving their bases to increase the dia- nieter of the stem, which therefore decreases from the base up- wards. Examining its structure more intimately, we find that it is composed somewhat differently in the various acotyledonous orders, though the first we shall speak of may be taken as the type of them all. Ferns. — The woody stem is composed for the most part of cel- lular tissue and vascular bundles. The structure is best studied on a tree-fern, some of which reach 60 or 70 feet in height. On examining one of these, we find the external surface marked by the scars where leaves have been attached, and in these scars dots showing the openings of fibro-vascular bundles. This ex- ternal portion is a kind of bark, very dark brown and thin, but in which it is possible — according to MohU — to distinguish two concentric layers, the exterior of which is composed of polyhedric parenchyma, while the interior has no elongated cells or prosen- chyma. Within this bark, and separated from it by a thin zone of parenchyma, is seen a circle of large fibro-vascular bundles, unequal in size, and looking, on transverse section, each like a twisted band, single or double, with the corners outwards. These bundles are produced, not gradually, but simultaneously — being continuous with the vessels in the leaves. The vascular bundles are grouped and reunited in such a manner that they form very dark-coloured bands, stretching the whole length of the stipe, differently shaped in different species, but with a kind of regularity or symmetry in the same species. These vascular bands, in uniting, form the woody mass of the exterior of the stem. 'The interior, occupied by cellular tissue, is somewhat white. All the bands are fastened together through the whole length, except in one or two points. These bands ordinarily are united in twos, leaving between them a space filled with cellular tissue — giving to the transverse section of stem that peculiar figure-like marking which in the ordinary Pteris aquilina (bracken) has been compared to a two-headed eagle. They are formed of woody tissue, in which the fibrous tubes have thin walls, and are coloured by a brown substance. The tissue placed between these black perpendicular bands is composed of— (i .) scalariform vessels, very numerous, ended by cells short and very regular; (2.) of true vessels or cells, very long, unequal, and thin-walled. - The whole parenchymatous mass is formed of cellular tissue. It is thus seen that the stem of ferns differs from that of monocoty- ^ Martius' Icones plantarum Cryptogamicarum Brasiliae, 1833. lOO STEM OF ACOTYLEDONS: EQUISETACE^ — LYCOPODIACE>E. ledons in (i .) the woody bundles being less numerous, or by the form of the longitudinal bands; (2.) by the woody bundles in the fern anastomosing among themselves, so as to form a sort of sheath, which is not seen in the monocotyledons; (3.) by the ferns never containing in their adult state true spiral vessels. Of late years, however, Bert^ has shown that in ferns in a very young state these vessels are found, though they soon disappear, to give place to the scalariform vessels so characteristic of the order. In some of the larger species of tree-ferns adventitious roots come out, and in reaching the ground swell out the inferior portion of the stipe. They also have the power of growing for a long time in the direc- tion of their length, the other parts not taking any share in the increase. Equisetacese. — In the " horse-tails," or Equisetaceas, the aerial stem is annual, cylindrical, and hollow, though divided by parti- tions corresponding with the nodes where the branches are given off. The vascular system of the stem consists of a cylinder of distinct, very regular bundles, composed of annular or spiral ves- sels. The most internal of the vessels of each of these bundles have become absorbed,^ and in their place are regular and con- stant lacunas, which accompany towards the interior each of these bundles in the adult plant. The whole is surrounded by an epi- dermis, often hard from the deposition of silicious matter, and furnished with lines of stomata. This temporary existence of vessels to subserve a temporary purpose has been also noticed by Chatin and others in aquatic plants. The flinty matter in the epidermis — which has caused these plants to be used in commerce as polishing materials, and to have received the name of " Dutch rushes," on account of the Dutch housewives from time immemo- rial having used them to polish brasses — is considered by Douval- Jouve as a secretion of the external cells of the epidermis in con- tact with the air, and not as entering into even the constitution of their membranes. Lycopodiacese. — The stems of Club-mosses present an organisa- tion rather peculiar. The centre is occupied by a woody axis, composed of scalariform vessels analogous to those of ferns, and surrounded by a cellular zone, through which adventitious roots make their way outside, often extending to a great distance.^ It may, however, be noted, that in Psilotuin triquetrum the vascu- lar bundle is not all in the centre, but surrounds a mass of cellular tissue analogous to the pith. The structure of Lycopodiace^ is im- 1 Bert, Bull, de la Soc. Phil., 1859, p. 26; see also Mettenius, Uber d. Bau von Angeopteris, in Memoirs of the Royal Academy of Saxony, vi. (1863^ 501-570. 2 Douval-Jouve, Histoire naturelle des Equisetum de France, 1864. 3 Brongniart in Archives du Museum, i. pi. 32. STEM OF ACOTYLEDONS : LYCOPODIACE^. lOI portant in so far as they appear to be the true living- representatives of the extinct gigantic Lepidodettdrons of the Carboniferous era, which present, notwithstanding attempts have been lately made to prove that they are of a unique structure— exogenous among vas- cular cryptogams— a perfectly similar structure. In Lycopodmm Fig. 69. — Lycopodium clavatum, L., the common club-moss, with (a, h) the fruit (conceptacles) magnified. ChamceoparinuSy there is a cylinder of wood-cells surrounding the central cylinder of united fibro-vascular bundles. This cylinder of wood-cells represents, and is a mere modification of, the cel- lular tissue met with in the ordinary stems of lycopods. The central portion is not a pith, though analogous to it, but consists of the central group of the fibro-vascular bundles, and is not the homologue of the woody cylinder in Exogens.'^ In addition to the peculiarity of the structure of the stems in LycopodiacecE, there is a further peculiarity in their mode of elon- gation. Instead of terminating in one, they terminate in two col- lateral buds; so that, deprived of axillary buds, they lengthen by a curious dichotomous ramification (fig. 69). ^ See Sach's Lehrbuch (1873), s. 100, 107, &c. ; W. R. M'Nab, Nature, Aug. 31, 1871 (with the discussion by Williamson, Dyer, and others in subsequent numbers) ; and the papers of Williamson in the Phil. Trans., 1871 ; and M'Nab, Trans. Bot. Soc, 1872-73, 102 SUBTERRANEAN STEMS : RHT^OME OR ROOTSTOCK. Ferns, Club-mosses, and Equisetaceas are the only Acotyledon- ous or Cryptogamic plants which have true stems with vascular tissue, and hence they are called the vascular cryptogams. All the others — Algae, Mosses, Lichens— are cellular, and have no true stems. > SUBTERRANEAN STEMS. ^ Hitherto we have only spoken of aerial stems, which grow above ground, and are familiarly known as such. There is, however, a large and interesting class of stems which are concealed under- ground, and commonly classed as roots. Sometimes this sub- terranean stem is the only one which the plant possesses; at other times both an aerial and a subterranean stem are found on the same plant. They are distinguished from roots by producing re- gular buds, or " by being marked with scars which indicate the former insertion of leaves, or furnished with scales which are the rudiments or vestiges of leaves." In older botanical works, they may be usually found classed as roots ; and all the scaly roots of these writers are stems of this nature. What are commonly called Creeping roots are equally included in the underground stems of the botanist. In structure they do not materially differ from the aerial stems. The medullary canal is, however, frequent- ly absent in the underground stem of Dicotyledons. In like man- ner the underground stems of Monocotyledons do not differ in structure from the aerial one. The presence of unrollable tracheae distinguishes it from that of the former class. Let us consider a few of the principal forms of these. Rhizome, or Rootstock, is a general term applied to " peren- nial, horizontally elongated, more or less subterranean root-like forms of the stem, and more particularly to those which are con- siderably thickened by the accumulation of starch, or other forms of nutritive matter in their tissue." Examples are found in the Ginger, Iris, Calamus (fig. 70), and the ordinary underground " root " of the fern, which has two forms of stem, the aerial and the subterranean. They grow and branch in the same manner that ordinary stems do, and emit the true roots from the under side of their whole surface. In "Solomon's seal" {Polygoua- tum), the place where the last year's growth has terminated and the next year's commenced is marked by a circular scar shaped like a seal, hence the name ; and in the rhizomes of other plants by a contraction which gives the rhizome a somewhat knobbed appearance. The rhizome can be distinguished from the true root by the presence of one or more buds or scales. Rhizomes maybe divided into two categories — viz., I7idetermi7iaie Rhizomes, when the stem is terminated by a bud destined to prolong it directly (Ex. Butoinus nmbellatus, Triticuin rcpetis, couch-grass. .SUBtERRANEAN STEMS : TUBER. 103 &c.^ ; and Determinate Rhizomes, which, instead of the terminal bud, have lateral buds, as in the axil of a leaf, from which each year a branch issues (Ex. Polygonatiitn multijior- nm, and the greater number of underground stems of the rhizome type). It is also sometimes called a Sympo- dium}- Sobol: — This term is fre- quently applied to an under- ground stem, which, like the Cotich - grass, Carex arena- ria, &a, sends roots from one part and leaf-buds from an- other. Creeping stems of this nature are useful in bind- ing together drifting sands, and thereby preventing them drifting. Fig. 70 — Cnlaiitiis aroiiiaiicus, showing the rhizome [a). Fig. 71. — Transverse section (mag- nified) of the rhizome of a Smilax (order Smilacecr), which yields the Brazilian sarsaparilla. ^Bark; c Out- side harder portion of wood ; d In- terior portion, with e, woody bundles through it ; h Soft disrupted internal portion corresponding to the pith of dicotyledons. Tuber. — A " tuber " is that form of subterranean stem seen in the Jerusalem artichoke {Heliafit/uis tuber osus), and the ordinary ^ For an exhaustive account of rhizomes, &c., see Thilo Irmisch, Zuf mor- phologic d. Monok. Knollen-u. Zwiebelgewaschse, 1850 ; Clos in Ann. des. Sc. Nat., 1850, t. xiii. ; Fabre, ibid., 1855, t. iii. ; Duch. I.e.; and Turpin's Mems. (1. c.) ' - ' - ' 104 SUBTERRANEAN STEMS : TUBER. potato {Solatium iubc7-osujn). . It is usually caused by the enlarge- ment of the growing bud of a subterranean branch, and the de- Fig. 72 — Young plant of the potato {Solatium tuherosum) raised from seed, r r Root axis ; c Neck ; ct ct The two cotyledons expanded into httle germinal leaves — in their axils are two branches, swollen at their extremities into tubercles tbib; ec Little leaves or scales of the subterranean branches ; ^c' Scales of the tubercles, in the axes of which the buds br are found ; b b Branches equally subterraneous and tuberiferous arising from the axils of the inferior leaves ; h' A ramification of one of these ; r'r Adventitious roots aris- ing from the same branches ; /' Extremity of one of the branches, which, accidentally growing into the air, produces a tuft of leaves instead of a tuber; y" //Ordinary leaves situated on the part of the stem out of the earth (reduced after Turpin f). position of starch, &c., in its tissue (Gray), which deposit sen-es for the nutrition of the buds (eyes) which it evolves when they develop in the following year, corresponding in this respect somewhat to the bulbous roots of the turnip, &c. In other words, it is a stem with very much shortened internodes. In the 1 Mdm. sur I'organisation intdrieure et extdrieure de tubercules du Solanum tuberosum, &c.— Mdm. du Museum, xix. (1830) 1-36, pi. I-V. SUBTERRANEAN STEMS : TUBER. familiar example of the potato, we have a green leaf-bearing aerial stem, and an underground not green, and bearing leaves, if any, Fig. 73. — Tuber of potato which has grown out of the soil, and is prolonged upwards in a leafy stem t ; at a a we see the depressions on which the buds are fixed; at a' buds already developed into little leafy shoots. only in the form of scales. The buds which are present, however, in the form of " eyes," give rise to branches, which rise above ground, and bear leaves, flowers, and fruit. The stunted under- ground stem constitutes the " potato " of culinary fame. Some- times, however, under certain circumstances of light and nourishment, the aerial stem, instead of giving form to the ordi- nary branches, will bear tubers. The nature of these tubers is shown in the very instructive figures^ (71, 72) taken from actual ^ See also Gardeners' Chronicle, ii. 85, where such another specimen is figured and described. TERRESTRIO-AERIAL STEMS : STOLON. •I •specimens. Between the ordinary rhizome and the tuber 1 jthere are various gradations in the form of such tuber-like j masses, formed, as in the case of the Cyclamen cultivated in our j gardens, by a swelling, owing to the increase of cellular tissue in the i lower portion of the stem, and in the case of the carrot, radish, &c., ' by a similar enlargement of the root proper. Finally, in others, , as the beet {Beta vulgaris, L., var. rapacea), we see that the stem i and the root both take part in this swelling, forming tuberoid ' masses. In the mass commonly called "a beet," M. Decaisne j recognises two parts usually confounded together, — viz., an in- |i ferior portion, made up of the root ; and a superior, formed by the • part comprised between the base of the root and the attachment of the cotyledons (the " hypocotyle " of some authors). The last portion is genei'ally out of the ground, while the first is fixed in it. The pith, which occupies the centre of the first in the form of , an inverted cone, is surrounded by a medullary sheath with spiral vessels — wanting in the second, or at least existing only with reti- culated vessels : lastly, the nitrogenous materials are chiefly found , in the first portion, where at the same time a great number of -j little rhomboidal crystals are seen; while the second, or stem por- j tion of the beet, is particularly characterised by its richness in sugar.^ These facts, the reader can easily see, have an important practical bearing on the cultivation of beet.^ Corm. — We see this in Colchiciim, Crocus, Cuckoo-pint (Aricm maculaUim), Sno-wdiVO'^ {Galanlhus), Gladiolus, &c. It differs from * the bulb in being solid, and from the tuber by its rounded oval \ figure. Shortly, it may be described as a bulb in which the I scales are all solidified into one mass. It is usually the thickened ' end of the stem, and may bear 4eaf-buds at the summit or side, and may be regarded as "a much-shortened rhizome, consisting .! of a few undeveloped internddes." ., j TERRESTRIO-AERIAL STEMS. I There is another class of stems which, while perhaps more J aerial than terrestrial, partakes somewhat of both characters. ; These are the stems which creep along the ground. They have • -received various names, according to their character. ■ Stolon (offset or hybernaculum). — When a stem naturally falls to the ground, and, when favoured by light and shade, takes root, . 1 Duchartre, Elements, p. 267. ' \ . Tubercular structures, according to the theoretical ideas of the authors treating them, have been divided into various groups. Clos gives, for instance, ^ ceight kinds (Ann. Sc. Nat.,. 1850); but the student Ivill find the above quite j sufficient for his purpose, without further complicating if by details... TERRESTRIO-AERIAL" STEMS: SUCKER — RUNNER^BULBS. '107 and, ascending', forms an ordinary aerial stem capable of extracting moisture from the soil through means of the adventitious root? which it has given out, it is called a "stolon." Such a stolon can be separated from the mother plant, and lead an, independent existence, as the gardener is well aware when he grows the currant, gooseberry, &c., in this way, which he calls'" layering." Sucker (surculus). — The Rose, Raspberry, Asparagus, and Mint afford examples of this kind of stem. After running along the ground and emitting roots, it will rise into an ordinary aerial stem. When these branches or stems grow rapidly they are often called shoots. The gardener takes advantag^e of this tendency by cutting off the sucker's connection with the mother plant, and propagating it by " division " or " parting the roots." Runner is much the same as a suckef, only^, instead of the stem taking root at various portions of its course, the runner, is a slender branch given off from the base -of the plant, which, taking root, gives rise to a tuft of leaves, and if divided from the parent can give rise to an independent plant. The strawberry (fig. 74) is Fig. 74 — A strawberry plant [Fragaria vesca, I,., var. sem^er/lorens) out of flower, snowing the runner rooting, and giving origin to tufts of leaves at two successive nodes. an example of this. When, as in the case of the house-leek, a shoot presents a branch with a tuft- of .leaves at the end, which takes root while resting on the ground, it is called an offset. These offsets afterwards become independent plants. Bulbs.— A bulb is usually defined as " a permanently abbrevi- ated stem, mostly shorter than broad, ancl clothed with scales which are imperfett thickened leaves,; or' more commonly the thickened io8 TERRESTRIO-AERIAL STEMS : BULBS. and persistent bases of ordinary leaves." It may be distin- guislied into three parts : (i.) the stem which develops upwards, ' bearing stallc, foliage, flowers, and fruit; (2.) inferiorly, the true roots or radi- cles ; and (3.) the bud, in the shape of scales, in which nutritive matter is stor» , ed up (fig. 76). Of this form the hya.. \ cinth and onion are at once the most I familiar and best examples. What is i commonly thought to be the root of the hyacinth is in reality the " underground stem ; " and the true roots may be seen depending from it in the earth or in the ] water (when so grown) in the shape of ^ /•^ the radicles from its inferior surface. , A bulb is, however, in reality a fleshy : permanent bud, usually underground, Fig. 75- — Longitudinal section of the lower portion of an onion plant in flower. tl Bulb showing the differ- ent "scaly" layers or tunics ; r Base of the bulb ; / Flower- ing stem, of which the swollen portion commences at a ;_/' Lower leaf, almost reduced to its sheathing portion (va- gina) ; yy" The other leaves divided longitudinally, so as to show their interior cavity. Fig. 76. — Scaly bulb of the white lily {Lilium can* - diditm), with the tuft of leaves which it produces; i WThe bulb itself; dc Scales which it forms; // The] bottom of the bulb (not seen in the figure) ; / Le.iveS ! with well-developed blades ; r Roots depending from ' the base of the bulb (i nat. size). the scales being modified leaves; and the real stem, morphologi- TERRESTRIO-AERIAL stems: BULBLETS — USES OF BULBS. I09 cally considered, is the central cone, from the base of which the roots are attached. An examination of fig. 75 shows that the bulb-scales are a continuation of the leaves, and in fact are simply the expanded base of the petiole. Bulbs, like rhizomes proper, may be divided into two series — determinate and indeterminate. The first, like the onion and dahlia, vegetates, and gives origin to thin flowering stalks from its vegetative extremity, and accordingly perishes after once flower- ing; while the indeterminate bulbs, of which the hyacinth, ama- ryllis, and many others, are examples, flower by the development of lateral buds in the axil of their scales, below the summit of the axis, — in each year the terminal bud, always living, is able to pro- duce new leaves and to continue the axis ; while, on the other hand, new lateral buds are produced, and give forth new flowering branches. Hence such ijidetentiinate bulbs can live an i7idejinite number of years?- Bulblets are small bulbs produced in the axils of the leaves of several plants, which fall, take root, and develop into a plant exactly the counterpart of that which produced it. Such plants are called viviparous. Examples are afforded by the Lilium biilbiferuni. Allium carinatuni, Dioscorea batatas, D. bulbifera, &c., where they are often produced in the place of flower-buds — showing plainly the identity of bulbs with buds. Of a similar character are the little buds produced at the extremities of the branches of some aquatic plants — e.g., Aldrovandra vesiculosa, Sagittaria, &c. — which, during winter, fall to the bottom of the water — weighed down by the starch with which they are charged — and, taking root in the mud, rise to the surface in spring in the form of a new plant. Some such aquatic plants, rarely producing seed, propagate -themselves entirely in this manner. Properly speaking, all the forms of bulbs and bulblets ought to have been included under the head of buds, though, for the sake of con- venience, we have considered them while describing the allied terrestrio-aerial stems.^ The Uses of Bulbs to man are rather extensive. Among those used for food, or as condiments, may be mentioned the common onion {Alliujn cepa, L.), garlic {A. sativum, L.), shallot {A. asca- lonicum, L.), scallion {A.fistulostim, L.), chive {A. schcenoprasum, L.), leek {A. porrtitn, L.), rocambole {A. ophioscorodon, Don), &c.; while the Indians of North-West America use the bulbs of the blue-flowered Camassia esctilentea (Lind.) as winter stores of ^ Duchartre, Elements, p. 417. " The word scape, which the older botanists apply to the flower-bearing axis of a bulbous plant, provided it was deprived of leaves, had better be dropped out of use, since there exists every possible transition form between the axes which bear only flowers and those which bear leaves. I IP SPINES, TENDI^ILS, ETC, food ;i while Lilium tigrimhn, Gawl., L. Thunbergia7ium, Roem. el Schult., and L. Cainschatkense, L., are cultivated in the countries in which they are native as articles of diet. •i SPINES. TENDRILS, ETC. - Spines. — These must be classed as arrested or modified branches, differing from the thorns of the rose or other plants iij being connected with the wood and not with the epidermis, and accordingly cannot be deta*ched except by tearing the substance of the stem. They can further be proved to be branches by the fact that frequently (a^ in the hawthorn) they bear leaves and buds like true branches, and by their being placed in the axils of the leaves. Moreover, they show every gradation between a true branch and a pointed indurated spine. Sometimes, as in the Acacia, the. Echinopanax or prickly ash of America, &c., the stipules are de- veloped into spines. In Astragalus ti'agacantha and Volkatimia- aciileata, the persistent petioles get so altered ; and, as in Asparagus, horridits of Africa, and the Barberry even, the leaf itself gets so; transformed. When the spine springs, however, from the axil of a leaf, it must be looked on as a branch. In some plants, as in, the Honey-locust {Gleditschia),\\\& spines branch in a very compli- cated manner. Sometimes the spine will grow into a true branch if the bush or tree on which it grows is transplanted to good soil {e.g., in the sloe), or cultivated for some time. According to their, situation spines are, in descriptive language, caulinary when on* the stem {Cactus, Gleditschici) ; terminal when at the extremities- of the branches {Prunus spinosd) ; axillary when in the axils of. the leaves {Citrus inedicd) ; infra-axillary (common gooseberry,: Ribes grossularia), &c. These, and the terms simple, branched;. solitary, and fasciculated, explain themselves. ' Tendrils sometimes belong to leaves, as in the Pea, where they are pi-olongations of the leaf-stalk or midrib ; but they are more" commonly " thread - like leafless branches, capable of coiling spirally," in order to attach climbing-plants to other bodies for support. Some tendrils hook their tips round supporting objects,) while others expand their tips into a flat disc, which clings ta objects, and so enables the plant to climb up in much the same way as do the accessoiy rootlets of Ampelopsis, the Virginian' creeper. • 1 I have given a full account of this in " Plants used by the North-West A-merican Indians in Food, Medicine, and Domestic Economy."— Trans. Bot. Soc. Edin., vol. ix. -> ANOIilALOUS STEMS : EXOGENOUS, ETC. Ill ANOMALOUS STEMS. s Exogenous Stems. — Hitherto we have only spoken of the structure of the three great classes of stems as normally found in three great classes of plants. It has, however, been mentioned, when speaking of the formation of annual rings of wood in Dicotyledons, that in countries where there is no sensible inter- ruption of the growth of vegetation, the stem may show no mark of each year's growth, as in the ordinary concentric layers of wood of the Exogenous stem. / There are also known to exist various anomalous kinds of stem, (chit^y lianas or twining plants, which, while in no way altering ~the great facts already mentioned, deserve notice. Cycadaceae. — In these plants one annual layer of wood is not formed every year, but it takes several years to form one. Accord- ingly, even in old plants there are very few rings. The zones of wood are separated by a layer of cellular tissue, like that of the pith, and often as thick as the zones themselves, while the pith is filled with bundles of fibro-vascular tissue.^ Coniferse. — The stems of this great order are, like those of Cycads, distinguished from those of ordinar}- dicotyledons by the absence of ducts proper in the woody layers, and by the large areolar discs on the walls of the wood-cells, al- ready noted as being present on the wood of trees of this order (p. 39). The wood of the yew (p. 39) and the Douglas {Abies Douglasit) (orm excep- tions to this structure. It also sometimes hap- pens in firs that the wood is produced in an oblique instead of a perpendicular manner — a peculiarity said to be inherited by seedlings from such malformed trees. Gnetacese. — In this order (which is closely allied to the Coniferas), of which one of the most remarkable plants is Welwitschia mirabilis. Hook. {., discovered in Africa, the woody layers of plants in the section Thoa are separated from each other by the interposition of thin layers of liber. In fig. 77, another anomaly, in a Gnetum, copied from a specimen in the collection of the Faculty of Science in Paris, is given. Brongniart in Ann. des Sc. Nat., ser. i, xvi. 389, t. 20, 21 ; Link, in Ausgew. Abbild. 2. t. i. ; Mohl in Abhandl. Akad. Munich, 1832, and in Verm. Schrift. I9S; Miguel, "Stamm. der Cycas " in Linnea, 1844, (xviii.) 125, or Ann. Sc. Nat., ser. 3, v. ii. 77. — Frag- the stem of' • Fig. . ment of a Gnetum, in which one branch originat- ing at «, takes a spiral turn or two around the stem, to be again incorporated with it at the point b (i-6th nat. size). TI2 Anomalous .stems : sapixdace^. Sapindaceae. — This is a tropical order Iiaving many plants, which twine themselves around other trees {lianas),^ and the stems of Here we see, ist, A primary or central Fig. 79.— Transverse section of a liana of woody mass with the pith in its cen: the family of Sapindaceas (perhaps 5Vr- tre 2d, A circle of secondary woody jania cuspidata ?). Here we see, 1st, A bodies (^' b'), very unequal in size; 3d, central woody body with a central pith 7;/, [Two little tertiary woody bodies b", and an envelope of bark ^r; 2d,Three second- placed in a third still more exterior circle, ary woody bodies 5' b' , without pith, Ijut of which they are the commencement. equally surrounded by a thick layer of bark. which are often angular instead of being round. On transverse section, we see that the stem is in reality m.ade up of several smaller stems united into one solid mass, and surrounding a central stem. This central stem is formed of woody layers, in general not very distinct one from the other, but showing a medullary canal and medullary rays. Each of the smaller stems or woody bundles has in general an excentric medullary canal (figs. 78, 79), in some cases even Avith an imperfect medullary sheath ; but this, it ought to be mentioned, is denied by Naegli, who has made these stems a subject of study. Until recently, it was believed that these secondary or tertiary woody growths on the outside of the main stem were simply branches which had twined themselves around it, and got incorporated therewith. The recent observations, how- ever, of Senhor Netto, a Brazilian botanist, show that neither this explanation nor that of Naegli — that in the Sapindaceae the cam- bium is not formed all around at once, and in consequence leaves outside of it certain portions which become the origin of the exterior woody bodies — will account for all the anomalies of structure we find in the Sapindaceas. There seem in reality to be separate foci of development in some of the stems, and in others — but more rarely — a sort of process of dismemberment which operates on the primitive homogeneous woody mass. 1 Lianas of the Spaniards ; lianes of the French ; and in Brazil, where even palms of the genus Destno7icus furnish examples of these, they are called by the Brazilian Portuguese 5j/><5j. The name " bush-ropes " is generally applied to them in the English colonies. ANOMALOUS STEMS: BIGNONIACE^ : MALPIGHIACE^. II3 Bignoniacese. — This order embraces in it many large trees, as well as climbing and twining plants. In these twiners we find a peculiar organisation. The woody tissue is separated into a num- ber of rays — varying in number — the wanting portion in which is filled up by cellular tissue derived from the bark (fig. 81), owing to the wood, after the liana is some years old, not forming on the four points of the cross passing through the pith and these being afterwards filled up by the increase of the bark at such places. There may be more than four points thus filled up by bark, owing to a similar process going on in the four subdivisions of woody rays, these again being further subdivided, until a stem may show four, eight, sixteen, or even thirty-two such rays separ- ated by infringements of the bark. In Tecoma radicans the woody mass may increase, not by the exterior, as is the universal case among Dicotyledons, but even by the interior, at its limits where it surrounds the pith (Sanio). Malpighiacese. — In this order, which possesses many twiners, the stem is traversed longitudinally by deep furrows, which some- Fig. 80. — Piece of a liana of the order Malpighiacese, which looks like a strongly-twisted cable composed of several strands. We see also in the section that the woody strands are separated for the most part one from another. Fig. 81. — Transverse section of the stem of a liana of the order Bigno- niacecB. tn Pith; (c ec Bark buried in the woody mass ; a Bands of wood, sensibly modified, which e.\tend be- tween the pith or the bark forced in- to its angles. times even penetrate to the heart of the stem, dividing it into a number of pieces, each of which is covered by bark, and in some cases possesses a portion of the medullary canal also. In other cases, only one of the pieces into which the furrows separate it contains the medullary canal. All these pieces are united together by prolongations of cellular tissue, and in a few cases a general external bark surrounds the whole ; so that the divisions would not be suspected from looking at the outside of the stem. H 114 ANOMALOUS STEMS : MENISPERMACEiE, In fig. 80 is shown a rope-like liana of this order, in which the general character of a liana, as well as the particular structure of the stems of this order, are seen. We see here also the curious fact, that as these lianas increase in age, the bark penetrates so deeply into the wood as often to separate the semi-isolated pieces; and when the stem is dry they separate altogether, as in the figure. Menispermacese. — In the twiners of this order (especially in the genera Coccuhes a.nd Cissampelos) the woody layers develop only at one or two points on one side of the stem, while on the other there is no increase whatever. According to Decaisne,^ the stem of the Menispermacese shows : (i.) fibres of the liber elongated, and with thick walls around the internal woody zone ; (2.) between the posterior woody layers a parenchy- ma, resulting from the division of the fibres of the liber with their walls ; (3.) the woody layers, of which a few only are circular, the greater number being unilateral (fig. 82 j. Aristolochiaceae. — In this order, of which the greater portion are twiners. Fig. 82. — Transverse section of a stem of a liana of the order Menis- permacese. Fig 83. — Transverse section of an aged stem of A risiolockia cymbifera, Mart. Decaisne describes the stem as having the followmg organisa- tion : Exteriorly, the suberous layer of the bark is considerably developed (fig. 83, cs), but without forming a continuous coherent ione, but rather disposed in irregular, almost distinct projections. Interiorly, the wood {b) is arranged about the pith (w), not cylin- drically, but divided by the large medullary rays {rvi) into ligneous wedc^es, and more or less divided externally again in a fan-shaped form'' by secondary rays. Opposite the woody bundles or their 1 Archives du Musdum, vol. i., 1839 (Mdm. sur les Lardizabaldes). See also, Radlkofer in Flora, 1858, s. 193. ANOMALOUS STEMS : BAUHINIA. subdivisions are little bundles of liber {lb), each of which appears on transverse section like a small bow. Bauhinia.— In some members of this genus of twiners (order LeguminoscE) the woody fibres are not disposed, in concentric circles. Theyform kinds of vertical and irregular bands, separated by cel- lular tissue, with the medullary canal excen- tric.^ The stem itself, as in fig. 84, is curiously twisted in and out in a " crimped " manner. Duchartre, from whom we copy the figure, thus describes this peculiar- ity : During the first year the woody zones are two — a very small number — circular and concentric ; but some of them are not produced in more than two nar- row portions on opposite sides of the circumfer- ence of the stem. Ac- cordingly, we may de- scribe, each of the crimp- ed stems as presenting to the right or to the left of a regular centre and central pith two large opposite woody wings. In order to complete this irregularity, the ribbon- like stem bulges out greatly at each produc- tion of leaves which are ^'S- ^4- — Portion of the stem of a Bauhinia, the • . base (rt!) of which is almost rounded and caniliculated, attacnecl, alter the alter- whilst the portion higher up becomes crimped, alter- nate arrangement, on "Jtely t° """^^Z'^}^ 'f ' Section of the crimp- , ., 'i ed portion ; yyy Points of the attachments of leaves. the Sides of two surfaces . ' ■ of the stem. The result is a series of bulgings, according to the disposition of the leaf, by which the stem assumes a sort of crimped appearance. The' bark covers all. the exterior of this irregular woody ribbon. There are even more complex arrangements 1 Lindley, Introd. to Botany, f). 78, fig. 35 {vide Richard). Il6 ANOMALOUS STEMS: TERATOLOGY OF THE STEM. among the species of Bauhinia, but the above will suffice to exemplify the more common anomalies. We may, however, touch briefly upon a few others much less common and less known — such as Phytocrene, described by Griffith in Wallich's Plantae Asiaticag rariores, iii. t. 216, in which, according to the figure given by Lindley, the "wood consists of plates containing vessels and woody tissue having no connection with each other, and separated at very considerable intervals by a large mass of prosenchymatous cellular tissue, filled with dotted ducts (bothrenchyma), and representing medullary rays. When the stem is dry, the woody plates separate from the other tissue, in which they finally lie loose." In Statintoiiia latifolia, Euo7iymus imgens, and in diPisonia from Burmah, Lindley has minutely^ described various peculiar anoma- lies in the stem. Dr Hooker has described and figured ^ an interest- ing anomaly in Myzodendron brachystachyum, one of the Zorantha- ceae, while _M. Duchartre has described another anomaly in the stem of Lathrcea claftdestina, a herbaceous plant, the peculiarity being the absence of a medullary sheath and medullary rays. In Melampyrum sylvaticuin, belonging to an order (Scrophulariaceas) nearly allied to that (Orobanchaceas) to which Lathrasa belongs, an identical structure is found.' However, Brongniart described in the Crassulacese — a very different order — a somewhat similar structure (see also p. 84). Endogenous Stems. — There is not a great number of anomal- ous stems belonging to this division. Yucca, however, in one species at least, arranges its woody bundles in concentric circles ; while Smilax, an endogenous stem, but an exogenous root, ap- proaches in structure the stem of Exogens. In grasses the stem is hollow, except at the nodes. TERATOLOGY OF THE STEM.* We have seen that in some cases the plant may be very short- stemmed, or, as it is called, acaulescent ; but a monstrosity occa- sionally occurs, in which a stemmed plant becomes almost entirely stemless, or only presents the stem in the form of short, hard, woody tubercles, thickly clothed with deformed leaves covered with hairs longer and denser than usual. Again, the branches may be arrested in their development. This is of very common 1 Introd. to Botany, i. 213, 218. * Flora Antarctica, i. 298. 3 Ann. Nat. Hist., vol. xv. •» Masters, Vegetable Teratology, p. 53, 455. teratology: terms used in describing the stem. 117 occurrence in the birch, when the branch ceases to grow in length ; at the same time thickening into a bulbous knob at the end, from which are developed numerous small twigs, whose direction is sometimes exactly the reverse of that of the main branch. The branches of the spruce fir, under the attack of a species of insect (an aphis), are apt to be developed into cone-like excrescences. Spines, we have seen, are only abortive branches ; and sometimes under cultivation the spines develop into true branches. Trunks sometimes unite together, as in the case of the plane- trees of Buyukdere, near Constantinople, in which nine trees are wholly or partially united together. A similar deformity is sometimes seen in roots. In Abies pectinata and A. excelsa we will have occasion to notice the natural grafting of roots together • — a very common occurrence. Bulbs cut in two may be united, and throw up a united stem ; and if the two bulbs are of different coloured flowered varieties, the flowers on either side will be of different colours, or sometimes even with the two colours blended together.^ Though, as a rule^ only closely allied plants can be grafted together, yet authenticated cases are on record in which widely different plants adhered naturally — e.g., the union of the " haulms" of wheat and rye, of a species of Sophora to an elder {Sambucus), In like manner it has been found possible to ingraft the carrot and the beet, and the white and red varieties of the beet, together, though in none of these cases are the plants thoroughly joined, the adhesion being little more than the simple contact of living tissues ; while, in the words of Dr Masters, " new matter is formed all round the cut surfaces, so that the latter become gradually embedded in the newly-formed matter." " Knaurs," again, are knots which form on the stemi orn some trees, particularly species of hawthorn, in the formi of woody naasses, from the size of a pea to a cocoa-nut, and which seem shortened branches. They may even be used for the purpose of propagation. The stem may be sometimes, as a monstrosi'ty,, enlarged ; it may be divided ; or, finally, as in the case of bulbs, be sometimes multiplied in number. DIFFERENT FORMS AND TECHNICAL DESCRIPTIVE TERMS APPLIED T©) the stem. The technical terms used to designate the form, cbnsistence, direction, state of the surface, &c., of stems, are numerous; and to have given them in the body of this chapter would be merely to reconvert Botany, as it was in former times, into a mass of names, and a botanical text-book into a vocabulary of the science. I have 1 Darwin, Plants and An. under Domestication, i. 395. •Tl8 TECHNICAL TERMS USED IN DESCRIBING THE STEM. accordingly followed M. Duchartre in this, as in other chapters, in his admirable method of classifying all these in a tabular form, so that at a glance the student may see the term he is in search of. These tables are not to be learned at once, but to be continually referred to during the progress of the student's studies. If he has access to a museum or garden, then he should continually endea- vour to see specimens of each plant, whereon the character given can be studied. Without eventually mastering the technical terms of botany by constant reference to the plants, the science of de- scription will become tedious and unsatisfactory ; while, if the contrary method is adopted, it will be insensibly mastered, with comparatively little trouble, and the knowledge will be per- manent. 1. Direction. — An upright stem (cauHs erectus), raised verti- cally, as it is in most cases. Ex. Yellow loosestrife {Lysimachia vulgaris), Mentha sylvestris. Rectus, straight, and strictus, expressing a more absolute degree of straight- ness, are also terms used by the older systematists ; while laxus or di^usus {loosely spreading) has a contrary meaning, as in Sedum acre (stonecrop), &c. Ascending (ascendens), rising vertically after its lower portion has been lying horizontally ; in other words, ascending obliquely. Ex. Panicum sanguinale (fingered Panicum)i Veronica spicata, Trifolium pratense, &c. Nutant (cernuus, nutans), with the summit bent. Ex. Poly- gonatum imiltiflo7-um (Solomon's seal). Flexuose or zigzag (flexuosus), forming angles alternately from right to left and from left to right. Ex. Statice reticulata (matted sea-lavender), &c. Tufted or cespitose (ceespitosa), " when very short, close, and many together form the same stock " (Bentham). Ex, Carex ccEspitosa. Decumbent (decumbens), bending down and leaning on the earth on account of its feebleness. Ex. Wood loosestrife {Lysimachia ne7norum^ Prostrate or depressed (procumbens, prostratus, depressus, humifusus), trailing on the ground. Ex. Coldenia pro- cumbens, Polygonicm aviculare, Coronopus Rtiellii (Swine's- cress), &c. Creeping (repens, reptans), spread upon the ground, sending out roots at short distances along its length. Ex. Creep- ing crowfoot {Ranunculus repens), and creeping loosestrife {Lysimachia nummularia), Potcniilla reptans, &c. : Climbing (scandens), when it attaches itself to other upright TECHNICAL TERMS USED IN DESCRIBING THE STEM. II9 Stems or. other bodies in order to support itself, either by spiral tendrils, as in the .vine {Vitis), various species of passion-flower (Passijiora), and bryony {Bryonia dioicd), or by adventitious rootlets, as in ivy {Hedera helix), when it is sometimes called radicans. Voluble (yolubilis), twining itself round other bodies by its own spiral form. Ex. Black bryony {Tamils communis), honeysuckles {Lonicerd), French bean {Phaseolus vul- garis), &c. (See p. 78.) 2. Ramification. Simple (simplex), not dividing. Ex. Verbascum tJiapsus (great mullein). Ramose (ramosus), dividing into branches more or less numerous. Ex. Nearly all trees. N.B. — The terms alteriie ramosus (alternately branched), as in Polygonum miiius, Dianthus deltoides (maiden pink), &c. ; deter- minate rainostcs (abruptly branched), " when each branch, after terminating in flowers, produces a number of fresh shoots in a circular form from just below the origin of the flowers " {e.g.. Erica tetralix, and many other heaths, &c.) ; Ramosissiinus (much branched) ; distichus (two ranked), when the branches spread in two horizontal directions, as in silver fir ; brachiatus (bracheate, or four ranked), "when they spread in four directions, crossing each other alternately in pairs," a very common mode of growth in shrubs that have opposite leaves, as the common lilac {Syringa vulgaris), &c., — are refinements of definition still used occasionally and commonly by the older authors, such as Sir J. E. Smith and the immediate followers of Linnaeus. Deliquescent (decompositus, deliquescens), branched from the base, so that it has few divisions. Ex. Most deciduous trees. The opposite of this is excurrent, as in most fir- trees, where the main trunk runs the whole length of the tree, giving off branches in its course. ' When each point Dichotomous (dichotomus). Ex. Val- where it divides erianella olitoria (corn-salad). J forms a bifurcation Trichotomous (trichotomus). Ex.] in the first instance, Nyctago hortensis, &c. a trifurcation in the second, &c. Stoloniferous {?,\.Q\oTi\{zr, reptans), emitting stolons (p. 106). Ex. Chlora perfoliata, Cerastium vulgare, &c. Flagelliferous (flagellifer), emitting towards the base slender leafless branches called flagellce, which (as in the straw- berry) root and form a new plant. Flagella: and stolons are 120 TECHNICAL TERMS USED IN DESCRIBING THE STEM. often confounded under the same name. Ex. Saxifraga flagelliforine of the Arctic Regions. 3. Consistence. Herbaceous (herbaceus), soft and generally green. Woody (lignosus), lignified, and more or less hard in the interior. Fleshy or succulent (carnosus, succulentus), formed for the greater part of cellular tissue, more or less gorged with sap. Ex. Cactaceae. Medullose (MeduUosus), with a large pith or medulla. Ex. Elder or bone tree {Sambucus). Fistulose (fistulosus), with a central cavity (p. 83), which forms a tube in each internode. The contrary expression is solid (solidus). Ex.. Inula crithmoides (golden sam- phire), most of the order Umbelliferae, &c. 4. Form. — Cylindrical or terate (teres), showing, on transverse section, a circular form. Ex. Trollius EuropcBus (globe- flower), Hydrangea hortensis (hydrangea), &c. Half-terate (semiteres) is another term occasionally used. Compressed (compressus), more or less flattened laterally. This compression leads to the stem getting more or less deter- minate forms, expressed by such terms as — Two-edged (anceps), compressed and forming two opposite angles. Ex. Sisyriftchium striatum, and most of the genus Lathyrus. Angular (angulosus, angulare), with angles, the prefix being determined by the number present, e.g. — Triangulare (triangularis). Ex. Cactics triangu- laris, Carex acuta, Scorpis sylvaticus. Quadrangulare (quadran- gulus). Ex. Lamium With three, four, five angles, and so on. Some descriptive botanists reserve these terms , for stems in which the angles / are acute, and talk about tri- gonal, tetragonal, pentagonal stems, and so on, when there are three, four, five, or other obtuse angles. album, and other lab- iatse. Quitiqu angulare (pentago- nal). Ex. Asparagus horridus, &c. Sulcate (sulcatus), furrowed with longitudinal grooves. Ex. Smyrnium Olusatrum (common Alexanders), Coniuni 7naculatjim (hemlock). When the furrows are finer the stem is striated (striatus). Ex. (Enanthe fistulosa (water dropwort). TECHNICAL TERMS USED IN DESCRIBING THE STEM. 121 All comparative > forms of the same term. Nodose (nodosus), having the nodes more visibly swollen out. Articulate (articulatus), when the nodes easily separate. Ex. Samphire, Stellaria, Gemniwn, Indian figs (various spe- cies of Cactaceae), &c. Globular or meloniform (globosus, meloniformis), ball-shaped. Y.^. Echinocactus, fig. $1. 5. Form and Elasticity. Rigid (rigidus, strictus). Ex. Sottchus oleraceus (Sow-thistle"), by opposition flexible (flexibilis). Slender (gracilis), long in comparison with its thickness. Ex. Orchis maculata (spotted orchid), Stellaria holostea (chickweed), &c. Sarmetitose (sarmentosus), woody, long, and slender. Ex. Vine, honeysuckle, clematis. Weak (debilis), slender (gracilis), and the opposite swollen (crassus). Filiform (filiformis). Ex. Zanichellia \ palustris (horned pondweed), Hydro- cotyle vulgaris (marsh pennywort). Setaceotis (setaceus). Capillary (capillaris). Ex. Eleoharis acicularis. Virgate (virgatus), " rod-shaped," woody,' straight, stiff, and somewhat slender. 6. Structure and Covering. Foliose (foliosus), and the opposite, leafless or aphyllous (aphyllus). Winged (alatus), the leafy blades rather prolonged into two wing-like prolongations. Ex. Passiflora alata, Lathyrus latifolius, and other Leguminosse, Carduus acanthoides, &c. Suberose (suberosus), covered by a layer of cork. Ex. Quer- cus suber, Ulmus suberosa. Riniose (rimosus), the bark swollen, cracked, and wrinkled. Ex. Ulmus campestris, Castanea vesca. Spinose (spinosus), armed with spines. Ex. Gleditschia, &c. Warty (verrucosus), with small callous excrescences. Ex. Etionymus verrucosus. Aculeate (aculeatus), armed with prickles. Ex. Rosa spinos- sima, Echinopanax horridum, &c. Unarmed (inermis), without anything of that sort. Smooth (Isvis), with smooth surface. Ex. Etionymus Euro- pCBUS. THE STEM : SUMMARY. . • . Rough (asper, scaber). Ex. Equisetttm hyemale, Jasione mon- tafia (sheep's-bit), &c. - The expressions by which the presence or absence of hairs, asperities, &c., are designated on stems or other organs, being eraployed chiefly for leaves, will be explained at the end of that chapter.^ ... SUMMARY. The stem is not usually present in the lower orders of plants, but, though much abbreviated, is almost invariably in some form a part of the structure of the members of the higher classes of the vegetable kingdom. In size, consistence, &c., it varies much, and gives rise to the various forms of plants popu- larly known, according . to their size, as trees, shrubs, &c. There are three great classes of stems, divided, according to their structure, into Exogenous, Endogenous, and Acrogenous — these three classes corresponding with the three classes of plants known as Dicotyledonous, Monocotyledonous, and Acotyledonous. The first class has a pith, medullary sheath, concentric layers of wood, cambiumj and a bark consisting of Liber or Endophloeum, Mesophloeum, Epiphloeum, and Epidermis; the second has no" con- centric layers of wood, but woody bundles scattered through a cellular mass— the bark being in union with the wood — though each of these woody bundles (as in palms) is composed of elements corresponding to the structure of the Exogenous stem; the third grows by the summit, and shows on transverse section vascular bundles, which grow simultaneously and are connected with the leaves, surrounding a central cellular mass. The development of each of these stems is different. There are also among the Exogenous stems various anomalous forms, which can, however, be referred to the type without much difficulty. There are also subterranean or terrestrial growing stems usually classed as roots, such as the rhizome (iris), sobol (couch-grass), tuber (potato), corm (crocus), stolon (rooting branch), sucker (asparagus), runner (strawberry), bulb (hyacinth), &c. A spine is an abortive branch, and, a tendril is often a thread-like leafless branch, though it some- times belongs to leaves when its character is different. Stems are 1 These are all — and more than all — the technical terms the student will be . lilcely to meet with in descriptions of the stem ; but there are many more, mostly obsolete, — the older descriptive botanists perfectly luxuriating in a barren wealth of terms applied to the stem and leaf ; and their writings bristle with these bits of barbarous Latinity, to define most of which would require a me- dieval metaphysician ! • THE STEM : SUMMARY : BIBLIOGRAPHY. 123 variously shaped, branched, &c., and numerous technical terms are used to express these modifications.^ 1 Bibl., Mohl (on the liber) in Bot. Zeit. xiii. (1855), 873, or in Ann. des Sc. Nat., 46 s6t., v. 141 (1856) ; Mirbel, Mdmoir sur le Liber, and papers in Ann. des Sc. Nat., 2^ ser., xx. ; Naudin in ibid., 3^ s6r., i. ; Trecul in ibid., 36 s6t., xvii. ; Henfrey in Ann. of Nat. Hist., 2e s^r., i. ; Schacht, Lehrbuch der Anat. und Phys. Gewaechse, and Der Baum, 216, 301-334 ; CIos, Cladodes et axes ail^s in Mdm. de I'Acad. des^ Sciences de Tpulous^, 1861 ; Chatin in Comptes rendus, Ix. 611 (27th March 1865); Hanstein Untersuch. iiber der Bau u. d. Entwick. d. Baumrinde (1853) ; Radlkofer in Flora, 1858 (§§ 193-206), and Ann. des Sc. Nat., x. (1858); Naegli, B6itragezurWiss. Botanik (1858), Heft I. ; das Dickenwachsthum des Stengels . . . bei den Sapindaceen (1864) ; Gaudi- chaud, Recherches sux I'organographi^, &c. ^1841) ;., Rauwenhoff, Archives Neerlandaises, y. 1870 ; and various papers by Van Tieghen, Tulasne, Cas- pary, &c., in addition to the authorities quoted in the text. CHAPTER II. THE ROOT. The Root (radix) or descending axis of the plant is that portion of the vegetable organism which fixes it in the soil, extracts the nourishment from the medium in which the plant grows, and performs other minor functions necessary to vegetable life. In early life the stem and the root are in reality one ; but in the more mature state of the plant, though continuous one with the other, and in some respects insensibly graduating into one another, yet a tolerably certain line can be drawn between them. The root has no perfect bark, and only a thin epidermis, and few or no stomata ; it has no true pith, and no medullary sheath ; it has no true leaves, but only cellular papillse and absorbing hairs. It has in general, however, no true leaf-buds either, though an excep- tion is found in Mountain peony, Pyrus Jap07iica, Anemone Ja- ponica, &c. Finally, the root, unlike the stem, grows not through- out its entire length, but chiefly at the end. The roots of some plants, like the plum, apple, poplar, and hawthorn, may produce buds when cut off from the parent plant during the growing season, and are therefore capable of being propagated by root-cuttings. In the vast majority of cases the root is fixed in the earth, from which it absorbs the nourishment necessary for the growth of the plant; but in the case of the parasitic plants known as epiphytes, such as the mistletoe {Viscuin), broomrape {Orobanche), &c., the plant derives its nourishment from some other plant on which it fixes itself. In the case of water - plants, like the duck-weed {Lemna), the water is the medium in which the root exercises its functions; and in the orders Orchidacece, B^'oineliacece, Aroidta:, &c., many species derive their nourishment from the moisture contained in the air alone, the plants twining themselves on trees, with the roots suspended in mid-air. Accordingly, roots may be divided, according to their function, and the medium in which they exercise this function, into — i. Terrestrial; 2. Aerial j and 3. Aquatic. In most of the lower cryptogamic plants, such as lichens and Algae, there is no true root, the roots so called being merely fulcra THE root: fulcra of the ivy, ampelopsis, etc. 125 to attach the plant to the rock or other substance on which it grows, and in no way performing the absorbing function of a true root, these plants being cellular throughout, and absorbing their nu- triment over their entire superficies. In the case also of the ivy {Hedera helix), similar fulcra or crampons arise from the stem and fix it to the wall or tree on which it grows, though it has been doubted whether these crampons of the ivy do not in reality absorb nourishment, the ivy often growing after its connection with the soil has been severed (fig. 85). In Ampelopsis similar thread-like tendrils, terminated by a disc - like sucker, come out from the stem and fasten the plant to the wall or other support on which it climbs. These rig. 85.— Fragment of the stem of tendrils, like those of the vine, are only ll^l modified branches. In A. VettcJm they originate from the development of a large branching hair from every cell of the epidermis of the part of the club-shaped end of the tendril, which is next to the body to be adhered to. They have little tendency to coil round any fixed object ; and, like the branches of the plant on which they are found, turn away from the light, thus affording a good example of what has been called "negative heliotropism." In the cells of the tendril, crystals of oxalate of lime are found.^ In A. hederacea, Dai-win found that one tendril with five discs supported a weight of 10 lb. In the dodder {Cusaitd) the roots take the form of suckers {haicstorid), arranged along the stem, which attach the plant as a parasite to some other (fig. 86). These are, however, of the nature of true roots, absorbing sap from the plant the dodder is parasitic on, eventually destroying it ; while in the case of the ivy, the death of the plant round which it winds itself is effected by a species of strangling or compression of the sap-vessels. In the dodder there is at first a true root absorbing nourishment from the soil ; but it dies away as soon as the suckers are properly developed, leaving the plant dependent for nourishment on them alone : while in the case of the ivy the fulcra remain throughout life. The root is the first part of the plant which comes out of the seed, and varies in the rapidity of its growth in Comparison with the stem in different species. In some it grows rapidly, and the stem slowly; in others quite the reverse. Again, some plants — 1 W. R. M'Nab, Trans. Bot. Soc. Edin., 293. 126 THE ROOT : EFFECTS OF SOIL ON LENGTH AND SHAPE. as many Coniferae— are remarkable for the great development of the stem compared with the comparatively feeble development of root; while in others— such as the common Medicago lupii- Una or "nonsuch" — the length of the root is out of all pro- portion to the length of the stem. In Megarhiza, a genus of North-West American Cu, curbitacese (gourd order), the plants of which are comparar tively small in size, the root is as large as a flour-cask. The looseness or compactness of the soil has an effect on the shortness or length of the roots ; and in sandy downs the root penetrates deeper and deeper in order to find the moisture it requires. In a rich and tenacious soil the roots of the maize will reach but 2 or 3 feet ; while in a sandy soil they have been traced 15 feet. Lucerne roots occasionally ac- quire a length of 30 feet. The roots of the Capparis spi?iosa will often be 40 feet in length, and those of the ash as much as 95 feet. Moisture also has the effect of increasing the length and the ramification of roots, as can be well seen when these enter drains and often choke them up entirely. - It was found by Sachs ^ that the roots of a plant accustomed to grow in earth were not unable to exercise their functions in water, and the roots of water-plants in earth, but that new roots were in either case developed to suit the new medium in which the plant found itself — these new roots, however, being anatomically the same as their predecessors. When parsnips, carrots, and liquorice- roots are grown in sand, they become covered with delicate bristle- like filaments. The Phleicnt nodosjim of some authors is only a variety of P. pratensc (timothy grass) grown in a dry soil ; in damp soil it is fibrous and luxuriant. Alopecurus geniculatus (marsh fox- tail grass), which has naturally a fibrous, creeping root, has been known to develop an ovate juicy bulb when grown on the top of a dry wall. Though the action of light is unfavourable to the growth of roots, yet it is not absolutely fatal ; for a root will develop . itself to its full dimensions without ever touching the soil, Botanisobe-Zeitung, i860, p. 113. • ■Fig. 86. — Dodder (Ciiscaia jnajoi) in flower, attached to a fragment of a living stem. At a we see five suckers ranged in a row, by which the plant e-vtracts its nourish- jnent from the plant to which it clings. THE ROOT : GROWTH IN WATER, ETC. 1 2 7 as when plants are germinated on a wet sponge, and then trans- ferred to water, as in the numerous experiments of Sachs and Fig. 87. — Cephcelis Ipecacuanha, showing the long annulated root used in medicine. others. In these experiments, maize and other plants germinated, grew, leafed, flowered, and fruited, without ever touching a particle of soil. However, if a plant thus germinated on a wet sponge, or similar medium, be transferred to the soil, it will die if not frequently watered ; but if a plant grown in water, but started in the soil, is similarly treated, it will be quite unaffected, and grow without any more water than what may be' contained in an ordinary soil. Plants of dry countries — ^like the Pampas of America— are very irttoreralit of-rnoistu're ; and if care is not taken' to keep tlieir roots from moisture, except in very slight amount, they will droop. 128 DEVELOPMENT OF THE ROOTS OF DICOTYLEDONS. DEVELOPMENT. When the seed of a dicotyledonous plant is subjected to germinat- ing influences (moisture, heat, and the oxygen of the air), a swelling begins to appear, which results in the embryo bursting its enveloping coats, and the radicle appearing. This radicle — the commencement of the future root — immediately, if the position of the seed permits it, or if not, as soon as possible by a circuitous route, if necessary — directs itself downward into the earth. It is always the inferior or radicular extremity of the embryo which develops itself into the radicle, continuous with the stem, which is to continue it upwards — a circumstance Richard considered characteristic of the Dicoty- ledons, and which he styled by the name Exorhizal {e^o>, out of; ptfa, root). This radicle, as soon as it has fairly got fixed in the soil, begins to throw out on every side more minute threads — Fig. 88.— Simple t.-ip-root of Attacoyclus Pyrethrutn. radiculcC or rootlets— which fibres in their turn rapidly branch, until the original axis (or caudex) is soon surrounded by them, the petiole forming a subterranean tree-like mass, which, as a DEVELOPMENT OF THE ROOTS OF MONOCOTYLEDONS. 1 29 whole, we call the root. In some cases these radiculee are never sufficient in number to surpass the original root in importance, that part always maintaining its original pre-eminence ; but in other cases, the radicles increase so in number and size that the original structure is entirely concealed by the fibres which it had given birth to. In the first case, the root is called a tap-7'oot (fig. 88) ;^ in \}[\t second, a fibrous root (fig. 89). The amount of roots on a plant is very much more than is usually supposed, it being dif- ficult to extricate them entire from the earth. Schubart found the roots of winter wheat penetrated as deep as seven feet in a light subsoil forty-seven days after sowing, and that the quantity of roots in proportion to the entire plant decreases from forty per cent on the last day of April to twenty-four per cent in May. Hell- riegel estimated the length of the roots of a barley plant in a vigor- ous condition at 132 feet, and that of an oat plant at 154 feet ; and that only ^th of a cubic foot of soil would suffice for a barley plant, and Tfd of a cubic foot for an oat plant to develop in it. Tap-rooted plants seek their nourishment g^erally at a greater depth than fibrous-rooted ones, which spread through the sub- soil, and are accordingly more affected by wet and drought than the former. Development of the Roots of Monocotyledons.— The de- velopment of the root in this class of plants (grasses, &c.) is dif- ferent from that of dicotyledons. In the great majority of cases, the radicle, as it pierces the lower part of the embryo, is covered with a cellular sheath, and gives rise to numerous fibrill^, which are similarly covered. This covering Mirbel terms the Coleo- rhiza;^ and Richard, to distinguish their mode of development from that of dicotyledons, called them Endorhizal.^ In after-life they generally retain this compound character, though, if the plant is perennial, the first-formed roots die, to give place to others formed farther from the central axis of the plant* Schleid en and other authors are inclined to think that there is no true root in monocotyledons, but that what goes under that name is merely an adventitious root, such as is developed when a cutting of a plant is placed in the soil. A great number of mono- cotyledons have, however, no coleorhiza on their roots. The true radicle remains a rudimentary axis, as Planchon shows in Aponogeton distachyton, for a short time, or, as in the palms, for a much longer period ; but more ordinarily it is of shorter duration, ^ Racine pivotante of the French botanists. » KoAeds, sheath ; pifa, a root. » 'Ev5oi', within. * We must, however, remember that this Endorhizal and Exorhizal char- acter of the roots in Mono- and Di- cotyledons, is not universal, and that there are various exceptions to the rule. Palms, e. g. , have exorhizal roots, while the Indian Cress (Tropceolum, a Dicotyledon) has endorhizal ones. I 130 ELONGATION OF THE ROOT : RHIZOTAXIS. and is replaced by the adventitious roots, which are transitorily developed round the base, or are entirely confined to the inferior portion of the stem, or they may appear gradually higher and higher up. But in certain species the stem, getting gradually little by little lost, is finally supported, as in the case of the Iriartea exorhiza, an American palm, by these adventitious roots, at a height of three or four feet above the earth. In a word, although in monocotyledons the true radicle is developed at germination, yet it scarcely shows itself, and disappears more or less completely. In every case it is of secondary importance; and the nutrition of the plant depends upon the secondary or adventitious roots, which are produced either at first, or soon after the plant has commenced an independent life. Elongation of the Boot. — Duhamel, and more recently and exactly E. Ohlerts,^ have shown that the root increases in length by its inferior extremity, and that the growth is limited to a space about one-sixth of an inch from the tip. Wiegand, who has made similar experiments, showed that the lengthening was chiefly manifested towards the outer extremity of the roots. Dividing the young radicle of a sprouted pea into four equal parts, by ink- marks, he found that after three days the first two divisions next the seed had scarcely lengthened at all, while the third was double, and the fourth eight times, its previous length. This arrangement per- mits the thin thread-like radicles of plants, which are the chief parts concerned in nutrition, to penetrate into every crevice among rocks, and to seek nourishment in the most impervious soils. If the main roots of a tree meet with an insurmountable obstacle to their elongation, they will concentrate all their energy on the radicles, which increase in great numbers. Hence gardeners, when they wish to transplant a bush or small tree without danger, cut off its tap-root, the result of which is that radicles are developed, when it can be more safely removed. The autumn, when the year's growth is completed, and the leaves become inactive, and the rootlets also cease their functions and get covered with a thickish epidermis, is the best time for transplanting. Rhizotaxis. — We shall by-and-by see that the leaves are ar- ranged on the branches according to certain fixed mathematical laws, and that even the branches themselves are not placed on the trunk without order. At first sight it might be supposed that the radicles were produced ai-ound the caudex without any approach to order, though, knowing that the root bears an analogous char- acter to the rest of the tree above ground, we might expect to find somewhat similar laws regulating its structure. In the middle of the last century, Bonnet first announced that the radicles in the haricot, pea, bean, buckwheat {Fagopnan esailciiteiun, Moench.), 1 Einige Bemerkungen tiber die Wurzelrasern, — Linnea, 1837, p. 609-631. RHIZOTAXIS : STRUCTURE OF THE ROOT. 13I were arranged around the caudex in four exact parallel lines, at equal distances the one from the other; and subsequently a num- ber of other botanists have announced various observations on the same subject regarding other plants. The most complete of these are, however, those of Clos,^ who has made what he calls Rhizo- taxis the subject of two elaborate memoirs. The regular arrange- ment of the radicles on the main axis is chiefly observed in the young plant, and gets less and less apparent as the plant increases in age. All the radicles on every root are produced one above another, so that they appear on the root in the form of longi- tudinal lines. However, in a certain number of cases the lines follow an oblique and not a rigorously vertical course. This Clos calls "the law of superposition." The number of these longi- tudinal rows is fixed and determined either for the plants of the same order, or for those of the same genus, or at least for the individuals of the same species. The rows are separated from each other by equal spaces ; and in number, according to the vigour of the plant, are from two to five, the latter number being rare. The radicles are arranged in two lines in the orders Papa- veracecE, CrucifercE, Resedacecc, and GeraniacecB j in four lines in Malvacece, Euphorbiacecz, Umbellifera:, Labiatce, Verbenacecs, &c. The number three is much rarer than the preceding, and is ob- served in some Leguminosce — e.g., in the genera Vicia, Trifolium, Lathyrus, Coronilla, &c. The number five is even less frequent, and is seen in the Coinpositce, where, however, the number two is not rare ; and again in the Solanacece. This remarkable arrange- ment is, according to M. Clos, connected with the disposition and number of fibro-vascular bundles in the root of the plant.^ STRUCTURE OF THE ROOT. Pileorliiza. — This structure, so named by TrecuF (ttIXos, cap ; root), consists of a thin layer of loose cells surrounding the growing point of the root like a sheath. In Lemna it is well de- veloped, and sometimes called in that plant the ampulla. It effec- tually protects the tender floating root from the shock of foreign bodies, and against the attack of minute animals. Coniferae have the pileorhiza well developed, though in chestnuts, birches, and other trees it is thinner. On the adventitious roots of one of the screw- pines {Pandanus odoratissimtis) it is remarkably well developed. When the root of this tree dries and contracts, the pileorhiza is 1 Ebauche de la Rhizotaxie, 1848 ; and Ann. des Sc. Nat., 1852, t. xviii. * Duchartre, 1. c. 208. ^ Duchartre thinks that, according to strict etymology, it should be pilorhixa. The German wurzelhaube and wurzelmiltze mean the same thing. 132 STRUCTURE OF THE ROOT: PILEORHIZA : SPONGIOLES, Fig. 90. — Extremity of the root cut longitudinally, much magnified. It shows the radicle hairs (rh), the pileorhiza PA, and the growing and absorbing point S. The so- called " spongioles" are shown as loose cells near the extremity. some longitudinal rows of cells, which sometimes contain starch and surmount the growing point of the root. The rest of this cap consists of layers of cells parallel to the external surface. It is produced at the growing extremity of the root by the disintegra- tion or casting off of the cells which form that portion, and which, after disengaging themselves from the cell-tissues proper, soon die, merely forming an elastic cap to protect the tender point of the root. In 1849, Goldman^ showed that after the germination of the plant the radicle detached a yellowish mucilage in which are very delicate cells, feebly united together, constituting probably the commencement of the pileorhiza and the early cell-exfoliation which in after-life keeps it up. The cells of the pileorhiza are filled with air instead of sap. Spongioles. — The growing point of the root is covered by the pileorhiza, and is attached to the middle of that cap. It is com- posed, like every growing point, of very delicate minute cells in the midst of growing parenchyma, and only differs from the cellular mass, which forms the growing point of the stem, in that the latter gives birth to leaves and the rest of the axis, and the 1 Flora, 1853, No. 17. ^ Bot. Zeitung, 1849, p. 884. GENERAL STRUCTURE OF THE ROOT OF DICOTYLEDONS. J33 former gives rise only to the continuation of the root. This point is called the spongiole or spongiolet, from a mistaken idea of its absorbent function. It was at one time commonly taught that this was the growing and absorbing point of the root. This is not so. The growing point of the root is just behind the apex, and there the root increases by multiplication of cells, casting off the old ones, which constitute these so-called spongiolets which terminate every final subdivision of the root. Ohlerts^ and Link^ showed that not only are they not the absorbents of the root, but in reality that they are denser than the rest of the tissue, and in all likelihood perform that function, if at all, only to the most limited extent (fig. 90). General Structure of the Root. Dicotyledons. — The general structure of the root is very similar to that of the stem, but with various differences. Thepit/i is not always found in the root (e.g., Cicuta virosa), and when found is in general reduced to a mere thread,^ and with no medullary sheath. In the radicles it is difficult to recognise it. The wood of the root is produced in annual zones, as in the stem, but the analogous elements com- posing it are in the root much larger than in the stem — the fibres, cells, and vessels of the woody parenchyma being in the for- mer to the extent of twice, or even four times, the same elements in the stem. For instance, in the wood-cells of the roots of Coni- ferje there are, instead of a single file of areolar discs, two to four longitudinal rows of these. On the other hand, the medullary rays in the root are much less numerous and distinctly marked than in the stem ; and the fibres in the root are irregularly inter- laced, so that on that account the roots are rarely of use in carpen- try. The dark in the root has all the anatomical elements arrayed in the same order as in the stem. It differs, however, in the larger size of the fibres of the liber, in the greater development which the cellular envelope often attains in the root, particularly of herbaceous plants, and in the stem possessing a much greater development of the suberous layers of the bark. There is no chlorophyll, except in aerial roots. The cambium is rich in nitro- genous substances, and the cells of the root often contain crystals. The slight development of cork is in consequence of the root- tissues being so short a time in a growing condition, so that, before the suberous layer has time to form, the vitality has de- parted from these tissues. The Epidermis^ is very thin, and not always present in a perfect form. Its cuticle has rarely stomata, but it is often covered in its young state with hairs, which are generally simple, but in some plants, such as Saxifraga sarmcntosa, ^ Linnea, 1837, s. 609. 2 Ann. des Sc. Nat., ser, 3, xiv. 10. 'Schacht, Lehrbuch der Botanik, &c., ii. s. 173. * Sometimes called the EpibUma, a most unnecessary multiplication of terms. 134 GENERAL STRUCTURE OF ROOT OF MONOCOTYLEDONS. Anemo7ie apenninn, Opimtia fictis indica, Caletidulamicrmitha, and Brassica Rapa, are branched. These radicle hairs serve the pur- pose of absorbents. They have been studied with great care by Gasparrini.- They are very minute, and consist of tubular elon- gations of the external layer of root-cells ; and through them the actual root-surface exposed to the soil becomes something incal- culable. The older roots lose their hairs, and suffer a thickening of the outermost layer of cells ; these dense-walled and nearly impervious cells cohere together and form a rind which is not found in the young and active roots (Johnson). These hairs are most abundant in plants growing in poor soils, and on roots with dense surfaces, such as the CactacecB, EuphorbiacecB, pines, the Hydrocharis, &c. The silver fir {Abies picea), and other species of that genus, have no root-hairs ; but this want is compensated by the delicate absorbing cuticle and the great number of rootlets, which, perishing before they become superficially indurated, are continually replaced by new ones during the growing season.^ They are also wanting in Monotropa hypopitys (yellow bird's- nest), and Cicuta virosa (water-hemlock). The root-hairs adhere very closely to the soil, and are very active in their function of absorption over the newly-formed part of the roots, where alone they are found. Monocotyledons. — In monocotyledons there is a considerable difference between the structure of the root and the stem, (i.) In palms there is a large cortical zone, swollen, loose, and spongy, and a great central woody mass not divided into distinct scattered bundles as in the stem, and surrounding a mass of parenchyma, remarkable for its series of vessels decreasing in size from within outwards, and the presence of unrollable tracheae. (2.) In other mofiocotyledofis the root is very similar to that of the palms in pos- sessing the continuous fibro-vascular zone ; but, on the other hand, is remarkable in possessing one or more layers of thick-walled hard cells, which Schleiden has compared to a kind of sheath {Kern- scheide). It is well seen in plants of the genus Smilax. (3.) Cer- tain epiphytal Orchids and Arads have, as we have already noticed, aerial roots, which have been the subject of considerable research among botanists, who are by no means agreed as to their nature. They are in colour grey or white, often bright-coloured, and their extremities more or less green. Schleiden's description of the struc- ture of these aerial roots in Pothos crassineruis may be taken as the type of all. The roots in this plant are provided with a pecu- liar epidermis possessing stomata, which corresponds to the pileorhiza in subterranean roots. The semi-lunar cells of the stomata are filled with a brown granular matter, and are elevated above the surface of the epidermis, and form a special tissue 1 Schacht, Der Baum, p. 165. STRUCTURE OF THE ROOT OF ACOTYLEDONS. I35 whose walls exhibit the most delicate spiral fibres.^ These spiral cells are full of air, a fact which explains the white colour of the roots containing them. The cells at the extremity of the root are full of liquid, which allows the green parenchyma lying under them to be seen. This layer of fibrous cells Schleiden called the Valamen radicum or root-veil (Wurzelhiille), Chatin the epider- inoidal membrane, and Oudeman the Endoderm — each of these botanists differing in opinion regarding its character, which is as yet imperfectly known. A cotyledons. — In vascular cryptogams the structure of the root shows a simple central vascular bundle, immediately surrounded by a cellular bark, which in its turn is covered by an epidermis composed of two layers of cells, and which bears a number of hairs, these hairs differing from the radicle hairs already described in the higher classes of plants by their brown colour and large size. The centre of the vascular bundle presents no sign of pith. In ferns and Equisetaceae the root and stem are strikingly different. In Lycopodiaceas, however, the stem is simply the central vascular bundles ; but in this order of plants the root is again distinguished from the stem, in so far that in the former the cellular zone which surrounded the vascular bundles is formed of cells much smaller and closer than those in the stem. In these plants the root springs from any part of the spore, and hence to the roots of this great division has been given the name of Heterorhizal? ADVENTITIOUS ROOTS. These occur normally in many plants, and may be produced from cuttings, even from leaves when placed in favourable situations ; but they usually spring from plants in moist, warm, shady places, as in the depth of the tropical forests. Palms and other such trees are particularly distinguished by the posses- sion of them. In Madeira and Teneriffe, Laurus Canariensis, a large tree, sends out during the autumn a great number of adven- titious or air roots, which surround the stem and grow to the thickness of the finger ; in the following autumn they dry and fall to the ground, giving place to new ones. Indian corn, oat, buck- wheat, valerian (fig. 91), grape vine, and other plants of temperate regions, if subjected to the combined influence of heat, moisture, and shade, will often produce these air-roots. Contrary to the opinion of linger and Chatin, Duchartre,^ as already mentioned, 1 Principles, p. 79. Link (Elem. Phil. Bot., p. 393) first discovered this Inyer. * 'Erepoc, diverse. ' Experiences sur la v^g^tation des plantes Epiphytes, Journ. de la Soc. imp^r. et centr. d'Hort., ii. 67, 79. 136 ADVENTITIOUS ROOTS. the under- produce no In Epiphy- Fig. 91. — Fasciculated adventitious roots of VaieriaTta officinale. thinks that these air-roots do not absorb moisture from the air, but dew and rain ; the first-named view is probably more correct. In these aerial roots there are scale- like leaves, and the epidermis is green, but, unlike ground root, they fibrillee or rootlets, tes, De Luca detected all the inorganic constituents of plants. Their absorbing power is pro- bably also assisted by the spongy envelope of their roots collecting water to yield it up to their other root-tissues.^ In the case of the screw-pine, Pandaims, and other palms, &c., these adventitious roots attain great dimensions, coming out from the stem at a height of several feet from the base of the trunk. In the gigantic banyan tree {Ficus Indicd), which flourishes on the banks of the river Nerbuddah in India (and which tradition reports to have sheltered Alexander the Great), the adventitious roots are so large as to appear like trunks springing (as they also do in the mangrove) from both trunk and branches; so that this tree is composed of 350 large trunks and more than 3000 smaller ones. At one time, before part of it was carried away by floods, it was capable, it is said, of sheltering 10,000 men; but even yet, 7000 people could repose under its shade. These adventitious roots often proceed from places where the epidermis has been injured (as frequently is the case in the olive), or where the sap has met with some obstacle to its free circulation, and, in particular, at those knots or nodosities which occur acci- dentally on the stem and branches. In the screw-pine they fol- low a spiral order of development. Often (as in the mangrove) the main root will decay, and the plant be entirely dependent on these aerial roots. In this last-named tree — so characteristic of the low, swampy, sickly shores of various countries — the tend- ency to sprout in the air is shown even in the embryo, which begins to germinate while the fruit is yet attached to the parent branch, often elongating its radicle to the length of a foot or more before the fruit falls to the ground. The Lianas, or woody climbers, which obstruct the tropical forests of the Isthmus of Panama and Nicaragua, send out these aerial roots freely ; many of which reach the ground, when they enlarge in diameter and form new trunk-like supports. When cut 1 Chatin, Comptes rendus, 1856. DECIDUOUS ROOTS : FUNCTIONS OF ROOTS. in two, the lower end of the severed stem sends down a root to re- establish its connection with the ground. L^vy, a French traveller in Nicaragua, finding one belonging to a species o{ Bigno7iia in this condition, from which hung roots a foot long, cut them off; two days afterwards it had produced new roots of the same length. Cutting it again, it promptly gave out new roots, but more slender ones. He repeated the process up to the eighth time, but the new roots were now so slender and feeble that he desisted.^ In some plants (the vine, for instance) adventitious roots are produced as the result of circumstances impairing the proper action of the ordinary subterranean roots ; and in old willows, in which the stem is more or less decayed below, adventitious roots will be produced on the upper part of the tree, as seemingly an attempt to obtain fresh supplies through a more vigorous and healthy channel.- Deciduous roots. — According to Munter, the roots of the yellow water-lily {Nuphar luted) are deciduous, leaving on the rhizome holes about the size of peas, and very like in appearance to the human acetabulum, and at the bottom of the pit a bundle of broken-off woody fibre, not unlike the ligamenttim teres, marking the places where the roots separated spontaneously. Even while the root is attached to the rhizome, the bark of the latter is raised to give origin to the protuberance (or " limbus " as he calls it) which surrounds the edge of each little hole.^ FUNCTIONS OF ROOTS. A knowledge of the physiology of the root is of the highest importance in understanding the growth of the plant, for on it depends the nutrition of the vegetable organism. Its chief func- tions may be considered under the heads of fixation, absorption, and respiration, as a magazine of nutriment, and as a dubious organ of excretion. (i.) As an Organ of Fixation.— Without being fixed in the soil, the plant would be unable to extract the nutriment by which its tissues are formed. This is a necessity of plant-life so manifest that it is unnecessary to do further than mention a proposition so self-evident. It has, however, been supposed that the cruciferous plant popularly known as the "rose" of Jericho {Anastatica hiero- chuntica, L.) was an exception to the rule that all plants must be fixed; but in reality it is not, for it only gets unrooted when it dies 1 Bull. Bot. Soc. Fr., Nov. 1869. ' Masters, Teratology, 156 ; see also Trecul, Ann. Sc. Nat. , v. 340, and vi. 303. * Annals of Nat. Hist., xvi. 236. 138 FUNCTIONS OF ROOTS : FIXATION — ABSORPTION. away: and the other example of the "manna" which often falls in the desert is equally fatal to the idea mentioned, for the plant is a lichen {Sphoerothallia esculentea, Nees.), which, though often carried up in great quantities by the wind, is naturally attached to tiny fragments of rock. The Lemna, which seems to float in the water, is equally a proof that a plant must be rooted ; for the medium from which the plant extracts its nourishment must be looked upon in the light of its soil. The position of the root, buried in the soil, enables it to escape the trying vicissitudes of climate to which the rest of the plant above the soil is subjected — the heat of summer and the winter's cold — and so assists in preserving the life of the plant. Equally it has an effect in modifying the coldness of the sap when the ground is of a low temperature, and in cooling it when the soil is arid and burning, though in reality this effect has been much exaggerated by theorists, — the sap in summer never having a noxious degree of warmth ; and in winter, when the sap is very cold, there is little or no circulation of juices. (2.) Absorption. — All nutriment must pass into the plant in either a liquid or gaseous state. Solid particles, no matter how minute or how delicately suspended in liquid, cannot enter the circulatory system of the plant. Every part of the root — with perhaps the exception of the " spongioles " — which is young and delicate, is constantly performing this office, and only ceases to do so when the parts get impervious by the formation of the suberous layer in the bark, or by the thickening of the epidermal cells. When the radicle hairs are present, they perform an important part in the function of absorption. Hence Gasparrini called them Suckers. As soon as the parts of the epidermis on which they are situated cease to absorb, these radicle hairs die away, but are renewed on the newer and pervious surfaces of the rootlets. It has also been found by the experiments of De Saussure that each plant can take up from the soil a different amount of each substance contained in it, even though these substances should be all in the same propor- tion in the soil originally ; in other words, roots have a selective power, and only take up what is necessary for their life, and in the proper proportions too. Saussure considered that this prefer- ence of a plant for one substance before another in the same liquid was due to the different degrees of fluidity or viscosity of the different substances ; so that the rootlets of the plant are filters of the most perfect and delicate description possible. This simple mechanical explanation is not, however, held by all botanists — some maintaining that the faculty of selection by roots is allied to an instinct. But this doctrine is difficult to hold in the teeth of the well-known fact that they will absorb the most energetic poisons, which will produce on their organism fatal effects ; but probably FUNCTIONS OF ROOTS : RESPIRATION. the poisons so deaden and destroy the delicate tissues as to render their power of selection inert. On this theory — that roots are capa- ble of selecting- the materials useful for the plant to which they belong, and of rejecting materials unnecessary or innocuous — is founded the whole doctrine of the "rotation of crops," so uni- versally adopted by modern agriculturists. The force with which active roots absorb moisture is very great. Hales found that in the spring time the pressure exerted on a gauge attached to the stump of a grape vine supported a column of mercury 32I inches high, or equal to a column of water 36^ feet high. Subsequently, Hofmeister found that in a potted kidney-bean {Phaseolus multi- flonis) the force of the ascending sap could support 6 inches of mercury, in the nettle 14, and in the vine 29 inches. Heat in- creases, and cold decreases or altogether stops, the absorbing power of the roots. Roots can perform their functions under extraordi- nary circumstances. Sonnerat discovered in the island of Lucon a rivulet the water of which was so hot that a thermometer im- mersed in it rose to 174° Fahr. Swallows, when flying over it, dropped down motionless. Notwithstanding this heat, he ob- served on the banks two species of Aspalathus and a species of vine {Viiex Ag)ms-Cash(s), which with their roots swept the water. In the island of Tanno, the Fosters, who accompanied Captain Cook round the world, found the ground near a volcano as hot as 210° Fahr., and at the same time covered with flowers.^ (3.) Eespiration. — Roots, though buried in the earth, require air just as much as do the leaves, and equally die if they cannot come under its influence. To this is probably partly due the fact of roots seeking and often filling up drains. The experiments of De Saussure showed that if roots are plunged into hydrogen, nitrogen, and, above all, carbonic acid gas, the plant will die in the course of a few days. This fact explains why often in cities trees die when their roots are subjected to the influence of soil impregnated with ordinary coal-gas escaping from the neighbour- ing pipes, or from entering sewers where various noxious gases are emanating. It also shows the advantage of frequently loosen- ing the soil around plants so that air as well as moisture may the more easily reach their roots. For the same reason trees should not be surrounded by pavement if they are to be kept in good health. Hence stones in soil are really beneficial — in so far that by preventing the finely powdered earth being caked by rain, they allow of a freer access of air to the roots. One of the earliest observers who called attention to the practical application of the above fact was our friend Mr Anderson— Henry, who observed that some cuttings placed in water which was not aerated, and over which a film sufficient to exclude the air had gathered, threw 1 Willdenow's Principles of Bot. (English Trans., 1811), p. 262. 140 FUNCTIONS OF ROOTS : A MAGAZINE OF NUTRIMENT. out roots from the stems above, but not from those parts which were beneath the water. (4.) The Root as a Magazine of Nutriment.— In fleshy roots like the turnip and carrot the absorption is chiefly through the small radicles or rootlets which go off from the main root or cau- dex — this portion serving the purpose of a storehouse for sugar, pectose, and other nutritive matters, which in these biennial plants are required to support the plant during the exhaustive flowering season in the second year. After the carrot or other such plant has flowered, it is found that the caudex is quite exhausted of its nutri- ent matter. The farmer, by increasing by means of cultivation the size of his root crops, increases the store of nourishing matter, and then, by removing them from the soil in the autumn, he pre- serves for the use of his stock the nutrient substances which would otherwise have gone in the ensuing summer to support the growth of flowers and seed.^ In terrestrial orchids (fig. 89) there is a store of starch and gum con- tained in the tubercular swellings of the roots which is applied to the nutrition of the plant. In other roots, such as those of Spondias tuber- osa (hog-plum), the tu- bercles contain a large quantity of clear fluid — in the example mention- ed, upwards of a pint ; and in certain plants found in the Desert ot Sahara this store of wa- ter, according to Living- stone, serves an import- ant use among the in- habitants of that arid waste. (5.) As a Floating Or- gan.— A fifth use of roots may be noted. Charles Martins ^ has shown that in certain aqua- tic species of the genus yussiaa, some of the roots are transformed into ovoid or cylindrical swimming bladders, composed of a lacu- nary tissue filled with air (p. 32), in order to sustain the plant in the water. In most aquatic plants this r6le is performed by Fig. 92. — Tubercles of Orchis maculata. These tubercles give the character to the " scrotiform " or " palmate " root of the older authors. By some French writers they are called " Ophrydo-bulbs." 1 Johnson, How Crops Grow, p. 241. 2 M6m. de TAcaddmie de Montpellier, vi. de France, xiii. 169. 352; and Bull. Soc. Botanique FUNCTIONS OF ROOT: FLOATING ORGAN: EXCRETION. 14I transformed leaves, as in Utricularia vulgaris, Trapa iiatans, Aldrovandra vesiculosa, &c. (6.) Excretion of Roots; Antipathies and Sympatties of Plants— Some agriculturists believe that they have obsen^ed facts sufficiently numerous to show that certain plants are noxious to those which grow alongside of them. Thus, they say that darnel-grass {Lolium temulenium), flea-bane {Erigerojt acris), are hurtful to wheat ; the creeping thistle {Cirsium arvense) to oats; purple spurge {Euphorbia Peplus) and field scabious {Knautia arvensis) to flax ; corn-spurry (Spergula arvensis) to buckwheat {Fagopyntjn esculenteuiii), — and so on, with a long list of other plants in cultivation. In a word, they consider that certain plants show antipathies to others ; and this is due to the fact that the roots of these plants excrete matters which are injurious or even fatal to the life of the plants which are supposed to be anti- pathetic to them. On the other hand, it is believed that some plants are sympathetic towards others. Thus, wheat is popularly supposed to be an excellent crop to precede any leguminous plant, and that this is due to the fact that the wheat has excreted some substance or substances from its roots which is beneficial to the life of the peas or beans. This is a very old doctrine, espoused as early as the days of Duhamel, and since then discussed by Brug- mans, Plenck, Humboldt, Macaire-Prinseps, De Candolle, Bou- chardat, Chatin, Bracconet, Cauvet, Unger, Meyen, Walser,Trinchi- netti, Garreau, Brawers, Sachs, and other distinguished observers, and rests solely on the idea that roots have the power of excretion. Have they, then, this power? It appears, from numerous obser- vations by the most accurate observers, that there is really no such function in roots, and that any facts which might be sup- posed to fortify a contrary view rest on insufficient grounds, and are referable to other causes. Accordingly, the idea of antipa- thetic' and sympathetic plants is not proved. Indeed, even sup- posing that these excretions could remain in the soil long without undergoing chemical change, it is difficult to see how many plants could grow on the same field if this were true ; or how, if a plant sends out noxious substances into the soil, great tracts of country could be covered with the . same species ; how forests could be composed of different species ; or, indeed, how an isolated tree could flourish for hundreds of years in a soil impregnated with its own excretions. Each plant has, however, the power of mak- ing the soil less suited for others of the same species, or of other species of the same family which succeed it, though improving it for species of another family. Oaks, for example, render the soil more suitable for firs, and vice versa. — See " Nutrition," chap. v. 142 TECHNICAL TERMS USED IN DESCRIBING ROOTS. DIFFERENT FORMS OF ROOTS. There are numerous modifications of roots, owing to the varied situations in which it is necessary for them to pursue their func- tions. These different forms may, however, be referred to their duration, their situation, their divisioti, their consistence, their form, and the character of their surface — an arrangement M. Duchartre has adopted, with the result of considerably simplify- ing the subject, and in which, with some alterations and additions, I have followed him in this and other chapters.^ It is not, how- ever, always possible to accurately define the different forms — one running into the other by various intermediate gradations. 1. Duration. Annual (radix annua), duration limited to one year — i.e., such plants die after one flowering season. Biennial (biennis), living two years ; in other words, they flower in the year succeeding that in which they are sown. Annuals and biennials are sometimes included under the term Monocarpic^ which De Candolle applied to them. Perennial (perennis), living more than two years.^ To these the term Caulocarpic is in like manner sometimes applied, in contradistinction to rhizocarpic, used in reference to herbaceous plants. In a herbaceous perennial the only part which remains after flowering is a small perennial por- tion in or close to the earth, called the stock. The other kinds of perennials are shrubs, trees, &c. 2. Situation. Subterranean (subterranea), the ordinary case. Aquatic (aquatica), floating in water. Ex. Lemna, Utrictt- laria, Trapa natans, &c. Aerial (aeria), the major part out of the earth — orchids, &c. In older books the term was often applied to roots grow- ing on some part exposed to the air — e.g., such parasitic plants as mistletoe. ^ Similar tables will be found in that remarkable book, Gray's Natural Arrangement of British Plants, vol. i. (1828). 2 MoTOs, alone, and icapTros, fruit ; while Perennials were callefl Polycarpic — TToAiis, many, and Ka.fm>v\Xov, leaf ; also sometimes styled the Diploe (SiirXois, a NORMAL HISTOLOGY OF THE LEAF. pears, is therefore made up of the ramifications of the veins, and the cellular parenchyma or tissue. This parenchyma is of great el Fig. 96. — Transverse section of a leaf of Zostera mariita, L., showing the aerifer- ous canals, 1 1 1 1, separated by partitions cl, formed by a single row of cells ; « Nerves ; ep ep Epidermis \ flfl fl Little bundles of very long straight cell.s, with very thick walls, believed by some to be liber-cells. importance, for in it is contained the chlorophyll, which gives the familiar green colour to the leaves, and in the cells composing it the elaboration of the sap goes on until it is fitted to be distri- buted throughout the tissues for the nutrition of the plant. Let us now consider this structure somewhat more minutely. Normal Histology of a Leaf. Fig. 97. —Transverse section of a leaf of Posidonia. Caulini. ep ep Epidermis on both surfaces, with up- right cells filled with chlorophyll ; pr Parenchyma composed of large cells. Fig. 98 — Transverse section of a leaf of Pelargonium inqiciti- ans. Ait , showing branched par- enchyma, with lacunae, pr' pr', of which it is chiefly composed ; pr " Palisaded" or upper layer of oblong or ovoid cells ; ep, ep, Epidermis. The cells are filled with chlorophyll. —Cut a thin transverse section (at right angles to the surface) of any of the more common leaves, such as that of the apple, pop- covering). It has not, however, the most remote connection Vi^ith the similarly named structure in the skull. 154 NORMAL HISTOLOGY OF THE LEAF. lar, beech, or cultivated "geranium" (fig. 98), and put it under the microscope. Then the following structure ought to be seen, com- mencing from the upper towards the under surface : First, there is a single layer of firm flattened epidermal cells ; under these lie an upright row of more or less large rounded or elongated cells ; * under these, again, is a loose parenchyma of smaller irregularly-shaped cells, loosely united together so as to leave numerous spaces be- tween them ; and finally, bounding the inferior surface, and form- ing its epidermis, is a similar flattened layer of epidermal cells, but without the vertical layer of elongated cells found immediately under the epidermis of the upper surface. The loose spaces be- tween the cells of the middle parenchyma contain air, and com- municate with each other ; while here and there, in the midst of the cellular tissue, will be seen the cut ends of woody bundles — the ribs which ramify through it (fig. 96,7?). These nerves, as we have already seen, are a continuation of the petiole, and get smaller and smaller as they subdivide, until at last the most minute subdivisions consist simply of a spiral vessel with a few elongated cells. The s^oTi^'^ parenchyma'^ is of a pale-green colour, and contains less chlorophyll than the upper row of vertical cells ; and for this reason the under surface of the leaf is in general paler than the upper. The irregular network of cells, with open spaces, generally corresponding to the stomata, has also some effect on the paler character of the under surface of the leaf. The leaf chlorophyll also contains less iron than that of other portions of the plant. The under surface of leaves not being so exposed to the direct rays of the sun as the upper one may have also an effect in causing less development of chlorophyll on the under surface. Under the absence of light, it may be remarked, chlorophyll gets yellow, and loses its iron, and the juices, from being acrid and bitter, get mild and sweet ; though, if the surface is exposed to light, the normal acridity and bitterness again return ; the green colour and the iron likewise return at the same time. It is on this principle that celery is earthed up, in order that, by blanching, it may lose its natural acrid qualities. The epidermis is composed of a flattened row of cells, the shape of which varies in different plants. They are, however, most regu- lar in shape in monocotyledons, when they are arranged in lines, and of a parallelogramic shape (fig. 34). In many plants, especi- ally in Dicotyledons, they are of a wavy irregular outline. The two forms may possibly be in some way connected with the differ- ent venation found in the leaves of these two great divisions of 1 Sometimes called the Palisaded layer, from their resemblance to the pali- sades or pickets of a fence. 2 Sometimes called Diachyma (Sio, in midst ; x^f"*. tissue). NORMAL HISTOLOGY OF THE LEAF. plants (p. 73). In the stone-crop, house-leek, and suchlike plants, the epidermis is easily torn off ; but in other cases the cells are so firmly coherent as to form a fine membrane. Like the same structure throughout the plant, the epidermis contains no chlorophyll, but is colourless, the green colour of leaves being owing to the chlorophyll contained in the parenchyma between, and which is seen through the transparent epidermal cells. While the parenchyma of leaves contains starch, chlorophyll, and even crystals of little soluble substances, the epidermal cells contain none of these. They are, however, richer in nitrogenous mate- rial. Essential oils and resins are secreted by special groups of cells, and contained in particular reservoirs, as is seen in the leaves of Hypericum (St John's wort), citron, orange, &c. These are spherical in the orange, cylindrical in conifers, &c. ; but they are always surrounded by the cells which secrete the oil or resin. In UrticacecB, AcaiithacecB, &c., are seen pediculated bodies (cysto- lithes) formed of cells, the walls of which are impregnated with carbonate of lime (p. 30). The leaves of many grasses, and the leaves of Moquilea and PetrcBa, are so impregnated with silex, that, if burnt, there will remain behind a perfect skeleton of the leaf, with the outline of the stomata and hairs.^ The object of this firm epidermis over the whole surface of the leaves, and especially on the upper surface, where it is assisted by the layer of vertical cells, is to prevent too rapid evaporation from the surface of the leaves. Accordingly, we find that in some plants which admit of copious evaporation there is more than one layer of epidermal and vertical cells. In the oleander, which we have already (p. 55) noted as remarkable for the sto- mata at the bottom of pits on the under surface of its leaves, the epidermis on the upper surface of the leaves is composed of thr6e layers of thick-walled cells, and two layers of vertical cells. In most plants which thrive in a dry atmosphere the epidermis is thick ; and it is owing to this very fact that they thrive. In plants such as the aloe, which bear great droughts, there is generally a thick epidermis. Furthermore, this layer of epidermal cells is waterproof from the deposition of wax, which either forms a coat- ing inside the cells, and gives the glistening appearance to many glaiicous -\ea.ved plants, or appears in the form of a powdery "bloom," which easily rubs off, as familiarly seen in the cab- bage, &c. In many plants which yield wax, it exists in a thick coat, as on some fruits. In the CactacecB, the cells of the parenchyma beneath the epider- mis are also much thickened by deposits, so as almost to obstruct exhalation through the epidermis ; and it is probable, as Dr Gray remarks, that this may be found to be more common in leaves ^ Schacht, Lehrbuch der Anat. u, Phys. d. Gewccchse, ii. s. 121. 156 DEVIATION FROM THE NORMAL STRUCTURE. " which remain on the plant for more than one season, than we have hitherto supposed. Exhalation is, however, absolutely necessary, in order that the plant may be enabled to concentrate the crude sap ; and accord- ingly, a provision is made lor this moderate and regulated evap- oration in the stomata, the structure and character of which we have already discussed in our earlier studies of the microscopic structure of the plant (p. 54). With a very few exceptions {Passe- rina kirsiita, L., &c.), the under has always more hairs on its epi- dermis than the upper surface, though both, in most cases, support more or less of these cellular appendages, as well as glands of various kinds (p. 61). Deviations from the Normal Structure. — Though the general structure of the vast number of leaves is as we have described it in the foregoing paragraphs, yet there are a few exceptional structures found. In an elementary treatise, space cannot be spared to note all of them, even were it advisable. A few, however, of the more remarkable may be called attention to. In many mono- cotyledons, and in some dicotyledons, there is no distinction be- tween the loose lacunary parenchyma and the infra-epidermal vertical layer (the " palisaded cells ") ; and the whole parenchyma between the two layers of epidermis is composed of loose rounded cells, full of lacunse [e.g., in the hyacinth). Again, in most leaves the chlorophyll is homogeneously scattered ; but in a few plants with variegated leaves, like Begonia sanguinea, Peperomia blanda, &c., it is isolated in particular spots. The leaves of - orchids show three types of structure : i. Like ordinary leaves ; 2. With collections of spiral cells in the parenchyma, which is green throughout its thickness ; 3. With a middle layer of green J cells, separated from either layer of epidermis by a layer of colourless cells, — but more often there is only a single layer of colourless cells inferiorly with spiral cells, while the parenchyma under the upper epidermis is composed of seven or eight layers of cells, of which some only are spiral. There are several other less important modifications of structure in other plants, and for a de- scription of these the student is referred to the exhaustive memoirs ^ of Brongniart ^ and Trecul.^ Succulent Plants.— \n fleshy plants like the Cactaccce, stone-crops, ! aloes, &c., there is a great amount of water contained in the par- i enchyma of the leaves. This is not, however, owing to absence of I stomata, but to the thicker epidermis, or to the deposit which | forms in the infra-epidermal cells. The stomata are usually abundantly scattered over the epidermis of these plants, but except in young and growing parts, seem to open less than in ordinary 1 Ann. des Sc. Nat., S(?r. t. xxi. (1830). f 2 Bull. Bot. Soc. Fr., ii. 448 {1855). I LEAVES OF SUCCULENT AND WATER PLANTS. 157 plants. The result is, that the tissue is gorged with sap during the hot season when it is required by the plant, which retains it with great tenacity. Hence such plants are well suited for resist- ing great droughts, as seems evinced by the fact that they inhabit arid places, where the sun's rays beat down with a rigour unabated by any modifying circumstances of shade. Thus we find Cactaceas in the torrid Colorado desert, and the Tierra caliente of Mexico ; Stapelias, Aloes, and Euphorbias in the sandy African wastes ; or still more familiarly, the ordinary stone-crops {Sedum) and house- leek (Sempervivwn tectorutn) prospering in places where they can receive but little moisture. Yet, by economising what they receive, they live and prosper where others perish. The drier the atmo- sphere, the more unwilling are succulent plants to part with their moisture ; hence they can live in our rooms, where the air is much drier than outside : and for this reason ferns and other plants which part easily with moisture do not grow readily, unless con- tinually watered, unprotected in rooms where there are fires, or the atmosphere of which is very dry. {See Transpiration, chap, v.) Structure of the Leaves of Water-Plants. — I n the leaves of plants which either float on or are submerged in water, we find an inter- esting modification of structure to suit their peculiar mode of life. As already remarked, with a very few exceptions there are no stomata on the under surface of floating leaves, or on either sur- face of submerged leaves. The thin epidermis, however, serves the purpose of transpiration and respiration. In some submerged leaves, though the nerves are present, they lose their vessels, such being no longer needed for the purposes of nutrition of plants sub- merged in their medium from which they draw their food ; while it often happens (as in Trapa natans, water-caltrops, Ranuncubis aquatilis, water-crowfoot, &c.) that the nerves of the submerged leaves are left free without any intervening parenchyma, and look like roots floating in the water. In the leaves of nearly all water-plants (fig. 97), and remarkably so in the huge ones of Victoria regia, there are large air-cavities, with, however, no direct communication with the exterior.^ In Zostera marina (fig. 96), and o\h&x Naiadacece, there are nei-ves with- out vessels, these nerves being arranged in equal parallel lines con- nected by transverse branches, with a row of cells superiorly not unlike the "palisaded cells," but without epidermis; and contrary to what we find usual in land-plants, this infra-epidermal layer is gorged with chlorophyll. In Potamogeton (ordinary pond-weed), Zan7iichellia (horned pond-weed), &c., there is no derma, only a cuticle (p. 52) of excessive thinness, and no woody bundles ; but 1 Such lacunae are also seen in the stem of some marsh-plants— as, for ex- ample, the beautiful structure seen in the aerial stem of Hippuris vulgaris, the common "marestail." 1 158 LEAVES OF WATER-PLANTS — ASCIDIA. these are replaced by a series of elongated cells which take their p place. I : In Utriciilaria (order Lentibulariaceas) we have another arrange- ment for floating the plant. Small ascidia or sacs ^ (figs. 99, 100) Fig. 99. — Fragment of the stem of UtricH- laria vulgaris, L. f t' Subdivided branches, each bearing several leaves, and the ascidia tu. Fig. 100. — An ascidi- um of U. vulgaris, com- plete on its pedicel, b Its wall, externally much swollen ; a filaments which surround its open- ing (magnified). are connected with the leaves, which, about the time of flower- ing, are filled with air, and buoy the plant to the surface. The structure is shown in our figures. These ascidia are probably, from their axillary situation, to be looked on as modified branches (Schacht) ; or, according to some (Schleiden, Goppert, Benjamin), as a part of the leaf itself. The opening of each sac is surrounded by forked hairs composed of four cells, and is closed by a trans- verse cellular membrane, like the valve of a pump, capable of opening from without inwards, and which resists when it is pressed from within outwards (Benjamin). The walls are com- posed of from 2-4 layers of cells, bag-cavities between which establish a communication with the interior of the sac and the outside air, the mouths of such openings being guarded by cells analogous to the stomata. Goppert has found in the interior layer ot cells a blue matter somewhat analogous to that found in flowers. The physiological function of these ascidia is full of interest. At first they are filled with a somewhat gelatinous liquid, which by its weight assists in retaining the plant at* the bottom of the water. Very soon the branching hairs already described, which project into the interior, secrete a gas which accumulates as the gelatin- ous substance diminishes. By-and-by, when the vessels are full, the plant gets light and buoyant, and disengaging its roots from the soil, rises to the surface of the water and flowers. The flower- ing over, and the fruit mature, the air disappears from the ascidia, the valve allows the water to enter, and again the plant sinks to 1 'Ao-Kos, sac ; also called ampullcs (Bischoff ). LEAVES OF WATER-PLANTS : DEVELOPMENT OF LEAVES. 1 59 the bottom, to remain there until spring stimulates its ascidia again into activity. Altogether, the physiological history of the Utricu- laria (or " bladderwort," of which we have three species in Bri- tain) is one of the most beautiful we can meet with in vegetable biology.^ In some other plants, such as Pontaderia crassipes. Mart., of Brazil, P. azurea, of South America, and Trapa natans, the petioles of some of the submerged leaves are dilated into air-cavities which act as floats. The submerged leaves of the latter plant consist simply of ribs floating free without parenchyma (as in other plants, p. 173), while the leaves in contact with the air are of the ordinary structure. A somewhat analogous structure to the inflated petiole of Trapa natans is found in the fistulose leaves of Allium, Lobelia, Dortnianna (divided into four cavities), &c. In the lace-plant of Madagascar {Ouvirandra fenesiralis), there is an open netwoi-k all over the floating leaf, formed by the absence (or rupture ?) of parenchyma within the meshes of the network of veins ; while in Monstera Adansonii, Schott,^ there are in the leaf distinct holes, oval or oblong, directed more or less obliquely to the side, and from 2 to 4 centimetres in size. The parenchyma is, however, continuous in the young state of the leaf. The changes have been very lucidly described by Trecul. Lacunee appear in the centre of the mesophyll, the cells round which lacunae become colourless, and multiply so as to form walls to them. After a short time gas accumulates in the lacunae, which puffs out the superior, and by-and-by ruptures the inferior epidermis ; the superior epi- dermis soon goes also, and the apertures are complete. Such leaves are styled fenestrate? If a plant oi Marsilia qtiadrifolia is sunk beneath the water, Hildebrand has shown that the growing leaves will elongate their petioles even to the extent of three feet, to allow the leaves to reach the surface. DEVELOPMENT OF LEAVES. (i.) The first appearance of the leaf is in a minute more or less elongated parenchymatous and exceedingly delicate point, pro- duced at the extremity of a stem or branch while in full vital activity in spring. This constitutes the growing point. (2.) After some time there appear little projections or papillae of cellular tissue on its sides. These are the future leaves. Then ^ Vide. Duchartre, lib. cit. p. 300. I give the above facts on his authority, not having seen Goppert's or Benjamin's papers, nor having been able to re- peat their observations at the date of writing. * Dracontium pertusum, L. ; Scindapsus pertusus, Sch. ; Pothos repens. H. P. ' Fenestra, a window. i6o DEVELOPMENT OF LEAVES. the central cells in the middle of the papillae begin to elongate, and so form the veins, which at first consist of tracheae and annu- lar vessels. At the same time the papillae rise little by little out- wards, and in due course take a definite form, until each has assumed the form characteristic of the leaf of the particular plant it is found on, or the particular part to which such a leaf is proper. This development of the leaf, briefly sketched in a few words in the preceding paragraph, takes place after two main types— viz., the basipetal^ and the basifugaP methods. Let us explain these somewhat more in detail. In the " basipetal " method of develop- ment, the portion of the papillae which first appears is what after- wards constitutes the summit of the leaf : this does not afterwards increase much, the additions to it being made by the base, while the leaf is gradually pushed further and further out of the axis on which it grows. On the contrary, in the " basifugal " develop- ment, the active forces by which the leaf is formed reside in the superior part of it. Accordingly, the new tissues are there formed, and the portions at the base are oldest, while those at the sum- mit are the newest. This is a much rarer type of development than the former. Appearaiice of the Leaflets and Lobes. — Take cfny compound leaf — that of the rose, for example — and we see arising from the axis an elongated cellular body which is the common petiole. Smaller papillae appear on either side ; these are the leaflets. If the leaf is of the basipetal type, the odd lobe is an imparipinnate leaf, and the upper ones generally are first formed, and are always further advanced than those lower down. This is also the case in some digitate leaves. However, in the walnut and other large compound leaves of that nature, the formation proceeds from below upwards, and new leaflets are formed at the apex after the lower ones are fully blown. The pinnate leaves of most leguminous plants {Galega, false acacia {Robinia Pseudacacid), Mahonia, &c.) are also of the basifugal type. All leaves are at first entire ; the lobulation and other divisions of the margin appear subsequently, and follow a similar law of development to that of the leaf itself. It thus appears that in some simple leaves the upper portion, and in some compound leaves the upper leaflets, appear first; and that in others this order of development is reversed, — these two t)rpes constituting respectively the basipetal and basifugal mtihods of leaf-development. Appearance of Stipules, Sheaths, and Petioles. — It has been asserted by Mercklin and others, that the limb of the leaf and the summit of the petiole are developed before the stipules and the inferior part of the petiole. Trecul and Schacht have, however, shown that this is incorrect, and that the stipule, when present, 1 Basim patens. " Basim fugens. DEVELOPMENT OF LEAVES : LEAF-BUDS. l6l is early developed, even before the papillae vi^hich form the future leaflets, or the lobes, have made their appearance. It often, how- ever, falls off or gets arrested in development in an early stage, especially among plants of the order Cruciferae (p. 150). When there is a sheath it always shows itself first; and, lastly, the petiole appears — in simple leaves, after the limb has attained some size, but, in compound leaves, before any of the leaflets have appeared ; since, as we have already seen, it is the common petiole from which these leaflets spring on either side. Once formed, however, the petiole elongates rapidly, especially in the upper portion. However, in some cases it is almost sta- tionary at the base, while the upper portion develops rapidly. The same law holds true in regard to the formation of the ribs and veins, and their ramification through the parenchyma. The sheath in most monocotyledons, and the stipules, are at first continuous with the blade, only separated by a constriction, but they are afterwards separated from it. The stipules remain- ing near the axis develop rapidly, and are often larger than the leaves, and, as in the case of the maple, form the covering for the young leaf. These two types (the basipetal and the basifugal) of develop- ment may be mixed — e.g., when the lobes commence from above downwards (basipetal), and the veins ramify from base to summit (basifugal) ; but as these are only modifications of the two main types, it is unnecessary to enter into a further consideration of them. Lastly, the stomata make their appearance in the manner already described (p. 55).! LEAF-BUDS. Leaf-Buds are like ordinary buds (p. 74) ovoid or elongated, generally pointed at the summit, and are produced either at the extremity of the stem or branch, or more commonly in the axil of ^ A much more elaborate and somewhat different account of the de- velopment of the leaf has been given by Eichler and others. At the same time it is very complicated, and therefore as much calculated to confuse as to instruct the student, however valuable it may be to the more learned botanist. After paying some attention to the subject, however, I am not cer- tain that it is any improvement on the older account, unless an infinitude of new technical names be taken as such. See Eichler's Zur Entwickelungs- geschicte der Blattes, 1861 ; and a summary, with additional notes, by W. K. M'Nab, in Trans. Bot. Soc. Edin., 1865-66; Steinhul in Ann. des Sc. Nat., 1837, viii. 257-304 ; Mercklin Zur Entwickelungsgeschichte der Blattgestalten, 1846 (and Abstract in Ann. des Sc. Nat., 1846, vi. 215-246) ; Trecul in Ann. des Sc. Nat., 1853, 183-190 ; Schacht, Lehrbuch, t. ii. (1859), sec. 104 et seq ; Wretschko, Sitzungsberichte, &c., 1864, s. 257-280, &c. L 1 62 DEVELOPMENT OF LEAVES : PRyEFOLIATION. the leaf, in the manner described, and become prominently marked when the leaf falls, the bud being then ready, when the spring comes, to take its place. The bud has sometimes been compared to an embryo, but it differs essentially from an embryo in so far that it cannot produce a new branch or leaf unless attached to a living stem. Most frequently in temperate countries the bud is covered with scales,^ — these scales in their turn being often covered with a resinous substance, — the whole serving to render it impervious to moisture, and to protect it against cold. In tropi- cal countries naked buds are not uncommon : the black-thorn {Rhammis Frangiila) affords a rare example of such in this country. These protecting covering scales are, in most instances, various organs arrested in their development ; in some cases they are leaves, stipules, or even the persistent bases of preceding leaves. When the bud, as in the case we have more particularly to deal with just now, contains the young leaves, it is called a leaf-bud ; if it contains the young flower, it is a flower-bud. The bud, as the growing point of the stem, we have already adverted to in our account of that portion of the plant ; while the turio, bulb, and bulbule we have already classed, for the sake of convenience, among the forms of underground stems, though in reality they are modified buds. PRiEFOLIATION. PrcBfoliation, or as it is sometimes — though somewhat unmean- ingly— called, by Linnaeus's term, Vernation, is concerned with the different ways the young leaf is arranged inside the bud. We may view this in two lights, — viz., ist, the way in which the individual leaf is folded on itself; and 2d, the way all the leaves inside the bud are arranged in reference to each other. This is not the same in every species of plant. Therefore, in reference to the first rela- tion, we may class the different ways leaves are folded under seven diff"erent heads,, as follows : — A. Folded Leaves. 1. Conduplicate (fig. loi) — folded from the midrib, so that one half is applied by its upper surface to the other half. Ex. Oaks, Magnolia, Almond, Syringa {Philadelphus coronarius). 2. Reclinate or inflexed — when the apex is bent to the base. Ex. Tulip-tree {Liriodejidron ttdipiferd). Aconite {Aconittcm Na- pellus). 3. Plicate or plaited (fig. 112) — when folded like a fan. Ex. Vine, Maple, Gooseberries. 1 Tegmenta or ferules. Buds are the hybernacula, or winter-quarters, in the somewhat romantic nomenclature of Linnaeus (p. 74). PRiEFOLIATION. 163 B. Rolled Leaves. 4. Convolute (fig. 104)— when rolled from one edge in a single roll. Ex. Apricot, Plum, Barberry, Arum. Figures showing the different forms of praefoliation. Fig. loi, conduplicate. Fig. 102, involute. Fig. 103, revolute. Fig. 104, convolute. Fig. 105, demi-equitant. Fig. 106, twisted. Fig. 107, imbricate. Fig. 108, equitant. Fig. 109, induplicate. Fig. no, valvate. Fig. in, qircinate. Fig. 112, plicate. 5. Revolute (fig. 103) — when each edge is rolled outwards from the midrib. Ex. Rosemary, Azalea, Sorrel. 6. Involute (fig. 102) — when each edge is rolled inwards towards the midrib. Ex. Water-lily, Violet, Poplar, Bean, Honeysuckle. 7. Circinate (fig. in) — rolled at the top in the manner of a crosier. Ex. Ferns, Sundews (Drosera), Pilularia. In addition to the two great classes given, M. Clos has estab- lished three others, — viz., those with plain vernation, those with cylindrical vernation, and those with crumpled vernation ; all of these classes, however, merge by various transitions one into the other. As regards the way leaves are arranged in the bud in relation to each other, five classes may be noted : — A. Straight Leaves. 1. Valvate (fig. no) — when they touch each other simply by their contiguous borders. 2. Induplicate (fig. 109) — when the outer successively overlap the inner ones, by their edges at least. In this case the phyllotaxis is exhibited in the order of overlapping. 3. Imbricate (fig. 107) — when the outer leaves overlap the inte- rior ones more or less by their sides. Ex. Lilac, Laurel, Ash. Twisted or spiral (fig. 106) is only a modification of this. In the above three forms of prasfoliation the leaves were tolerably straight or convex, and not doubled on themselves. In the next two forms, however, we find the opposite arrangement. B. Leaves Folded in Two. (Conduplicate.) 4. Equitant (fig. 108) — when they successively embrace each other. Ex. Iris, Privet. 5. Demi-Equitaitt, or Obvolute (fig. 105)— when only one-half of 164 PRiEFOLIATION : VENATION. a leaf embraces one-half of another, Ex. Sage {Salvia officinalis), Scabiosa, Pink. The same names are applied to the full-grown leaves when they are so situated as to necessitate such names being applied, as when they embrace or overlie each other. Under the name of aestivation or prasfloration, these names are also applied to the parts in the flower-bud. Some plants, like the Magnolia, Duvaua, Isatis, Rheum, Cupuli- fercE, &c., have a double prasfoliation. Etiologically, the praefoliation is often determined by a contraction or constraint caused during the period of the development of the limb. Some orders, related to each other by natural affinities, show a uniformity in their prae- foliation, and all the members of many orders have equally a uni- form prasfoliation — e.g., Iridacece, Hamodoracece, HypoxidacecB (Amarillydaceas) — with conduplicate prefoliation ; Scitavtejiacece, with convolute prasfoliation; Malvacea, conduplicate; Hippocasta- nacece, conduplicate ; Verbenacece and Globulariacea, conduplicate ; LetiiceracecE (Caprifoliaceas), involute ; CornacecB and Carryacece, also involute, &c. Again, while a number of orders and families have a single kind of prasfoliation, there are others which show two, three, four, and even, as in the case of the Labiatce, five types. Certain ano- malous types in certain families are also distinguised by peculiar prasfoliation — e.g., the genus Podophyllum among the Berbej-idacece, Ginkgo among the ConifercB, Futikia among the Hemerocallidece (Liliaceas), Fabiana among the Solanacece, &c. Acorus has three modes of praefoliation in the species composing the genus ; Allium four, — and so on. Prasfoliation is, however, often useful to co- ordinate doubtful genera and species.^ VENATION. The forms of leaves are almost infinitely various, but in most cases the leaves of each species keep certain determinate forms, which, in common with other characteristics, are useful in the characterisation of the species. The names applied to leaves are for the most part arbitrary, and derived from a supposed or real likeness to some natural, artificial, or other object. Until recently there was no philosophical account of the laws of structure regulating the formation of these variedly outlined organs, and, accordingly, to remember the numerous names applied to the different kinds of leaves was a tedious task on the student's 1 Clos., Monographic de la prdfoliation (Mem. de I' Acad. Imp. des Sc. de Toulouse, 70 ser. t. ii. 91-134, 1870), and Bull. Soc. Bot. Fr., 1870, p. 122, 123. PRiEFOLIATION : VENATION. 165 memory. De Candolle has, however, considered that these forms may be reduced to a few types, dependent on the different forms and reticulations of the midrib and veins. The student will, however, have already seen that, though this theory is useful as an aid to memory, it will not explain the fortn of the leaves, for the parenchyma is developed in the vast number of cases before the midrib is formed. De Candolle's theory will only " account for the mutual adaptation and correspondences of outlines and framework." Viewing it in this light, we shall now explain the main points of it, commencing first with the venation, ox nervation, as it is sometimes called. The veins are the subdivisions of the petiole, forming the frame- work of the leaf, (i.) In a typical dicotyledonous leaf like that of the elm, for example, the petiole is continued straight up into the laminse, attenuating near the type, and dividing the leaf in two equal parts. This middle branch is called the midrib. (2.) On its passage upwards the midrib gives off ribs or nerves properly so-called. (3.) These ribs in their turn give off other smaller ones, called veins ; and (4.) finally, these give off others which constitute the final subdivision of the petiole, and which by their anastomosis form the fib/ous network of the leaf — viz., the veinlets or little veins. Though these terms are applied, the student must remember that in reality the subdivisions of the mid- rib have no connection of the most distant character with nerves, and hardly more with veins. The Vetiation presents various primary modifications — (i.) Either the vessels composing the petiole divide at once when they enter the blade into several veins which run parallel to each other to the apex connected by simple, feeble, transverse veinlets ; or, (2.) The petiole is continued into the blade, in the form of one or more principal or curved veins, which send off branches on either side— the smaller ones anastomosing with one another in a kind of network. The first is the great division of parallel or curved veins char- acteristic of the great division of plants called Monocotyledotis or Endogensj the second isthe reticulated or netted (or angular-veined) veined leaves equally characteristic of the Dicotyledons or Exogetis. In Ferns, again, there is an intermediate variety of venation — viz., furcate or forked. There are, however, a few exceptions, as we shall by-and-by see, though for all practical purposes the rule as given may be taken as general. The minor modifications of venation depend upon the more or less marked character of the veins, on the greater or less thickness of the interposed parenchyma, or the number of vessels composing the veins, and on the method in which the secondary veins or ribs are given off from the primary one or midrib, which is simply a i66 VENATION OF LEAVES. continuation of the petiole. Wt; can detect four types in which the ribs are given off from the midrib : — (i.) Pinnitierved Itaivts, in which the ribs are g^ven off on either side of the midrib at an acute angle, like the pinnas on a com- pound leaf. (2.) Palminerved leaves, in which the midrib divides at the base into 3, 5, 7, or a greater number of strongly marked divisions, nearly as thick as the midrib itself, the whole bearing a rude resemblance to the palm of the hand with the fingers extended. A good example is seen in the leaves of ivy, maple, gooseberry, and mallow. (3.) Peltinerved leaves, in which the petiole enters the leaf at or near its centre, and gives off veins in a radiating manner. (4.) Pedinerved leaves. This is seen in most composite leaves, such as those of Dracimailus vulgaris. Here the petiole divides at entering the leaves into three main divisions. The middle one, or the continuation of the petiole, is in general feeble, and supplies a single segment ; the other two come off at right angles at the base of the first, and are much more strongly marked. Each of these splits into two divisions, the upper division of each supplying a leaflet, while the under division sp^ts into three or more to supply as many secondary divisions of the compound leaf. Very frequently the midrib is not present. Sometimes the veins go straight to the margin, as in the beech and chestnut; while in others, they are divided into veinlets long before coming to the margin. When the midrib gives off a very strong primary vein on each side just above the base, as in the sunflower, it is said to be triple- nerved j if two are given off on each side, quintuple-nerved, or ribbed. Occasionally they converge to the apex, looking like parallel veins ; but they are not so, as the intermediate small netted veins show. " Nerved," it may be remarked, is often applied to ribs when not prominent or strong, though they may branch before reaching the apex. Normally, the veins never appear at the surface unless it maybe in the form of the spines on the edge of the leaves of various plants, such as the holly. However, in an abnormal condition of this latter shrub, they appear in the form of prickles on the upper surface of the leaf, constituting the cultivated variety known as Ilex Aquifolium ferox. Correspondence between Venation and Ramification. — Principal M'Cosh and Professor Dickie consider that they have traced some connection between venation and ramification ; and certainly there seems something more than mere coincidence in the numerous examples they quote in support of their ingenious and interesting CORRESPONDENCE BETWEEN VENATION AND RAMIFICATION. 167 speculations. The following are some of the chief laws which they consider they are justified in asserting as having been made out : — (i.) In plants with woody structure there seems to be a corre- spondence between the tree and the leaf in this respect, — that a leaf without a petiole implies a trunk naturally branched from the ground ; and a leaf with a petiole implies that the species of tree on which it grows has naturally a bark trunk. Ex. Beech. (2.) There is a correspondence between the disposition and dis- tribution of the branches and the disposition and distribution of the leaf-veins. Ex. Beech, Poplar, &c. (3.) There is a correspondence between the angle at which the branches go off, and that at which the lateral veins go off. In most plants with a woody structure, the angle of both vein and branch is between 45° and 60°. In the greater number of her- baceous plants, it varies between 25° and 45° ; but both in trees and herbaceous plants there are angles as acute as from 10° to 15", and so obtuse as 70° or 75°. (4.) There is a correspondence between the curve of the veins and the curve of the corresponding branches.^ Of late years much attention has been paid to the venation of leaves, with a view to finding characters to distinguish various species of fossil plants. More especially have fossil ferns been studied from this point of view by Brongniart, Presl, Gaudichaud, &c. ; 2 and the same attention has been paid to this, and with marked success, by Ettingshausen, Pokorny, Von Buch, and more especially by Oswald Heer, in the determination of the species of tertiary plants. The late Professor Oersted, of Copenhagen, has also applied the venation to the classification of Cupuliferce.^ It has been positively affirmed that though a large number of the Umbelliferas have a venation like the rest of Dicotyledons, yet that about one-half of them there is a peculiarity in the existence of a vein at the very edge of the leaf itself, and which more or less entirely fringes its whole margin. The venation of the umbelli- ferae — a puzzling order to determine the species of — is very vari- able in different species, " but constant and highly characteristic in each species." * As a rule, however, the leaf is too variable to use as a character for species. 1 Typical Forms and Special Ends in Creation, p. 111-123, and the Rev. Dr Macmillan's Foot-Notes from the Page of Nature, for a discussion on some similar points in vegetable morphology. * Dr Hooker has, however, shown that it is impossible to distinguish fossil ferns by their venation only (Mem. Geol. Survey of Great Britain, vol. ii. part 2. P- 387)- » Bidrag til Egeslasgten Systematik. (Nat. Foreriing Vidensk. Meddelser, 1866, p. 1-96), &c. * Gorham, Quart. Journ. Mic. Sc., 1868 (No. xxix. n. 3), p. 25. i68 FORMS OF LEAVES — MARGIN. FORMS OF LEAVES. According to De CandoUe's theory, the shape of the leaf may be viewed as dependent on the distribution of the veins, and the quantity of parenchyma scattered through their interstices — the general outline being determined by the divisions and direction of the veins, by the greater or less abundance of parenchyma, through the midst of which the veins are distributed. This proceeds on the assumption that the blade is an expansion of parenchyma, in which the former veins are ramified. For example, if the principal veins of a pinninerved or feather- veined leaf are not greatly prolonged, and are about equal in length, the leaf will be more or less elongated ; and if, in addition, the ribs given off from the midrib are very short in proportion to the midrib, the leaf is linear j if they are longer in proportion, the leaf will be oblong, which a slight rounding of the edges converts into an oval or elliptical outline. If the veins near the base are the longest, and especially if they curve towards their extremities, the edge is lanceolate or ovate, or some intermediate form. But if they are developed beyond the middle of the blade, the leaf be- comes obovate or cimeiform, — and so on. Again, many leaves have a sinus or rounded incision at the base, which, according to this theory, is produced by the ribs or their ramifications being directed backwards — producing the retii- form leaf. When the two sides of such a leaf come together, the result is an orbicular or peltate leaf. When the veins run parallel (as in grass), the leaf is necessarily linear ; but if they diverge, the result is an oval form, or some modification of that form. [For a tabular synopsis of the different forms of leaves, see p. 202.] Margin. — The margin is entire when there are no breaks in it whatever. According to De Candolle's hypothesis, notches, serra- tions, &c., are owing to an insufficiency of parenchyma to fill up the outline. Hence the sub-aquatic leaves of Ranunc2ilus aqua- tilis {e.g.), which are said usually to be " foliformly cut," are in reality only the skeleton of the leaf without any intermediate par- enchyma to fill up the interstices ; while in the other leaves — aerial leaves of the same species — there is a sufficiency of parenchyma, the result of which is that these are only lobed. However, as we have already seen, though this hypothesis of De Candolle is useful as an aid to some more philosophical classification of leaf-forms, yet the parenchyma, and therefore the outline of the leaf, being formed before the vein, it is in reality untenable in a strictly scien- tific aspect. According to his hypothesis, monocotyledons being parallel- FORMS OF LEAVES — COMPOUND LEAVES. 1 69 veined, would necessarily have entire leaves, while dicotyledons would in most cases have the margins of their leaves divided. In reality this is what we find in most cases in these two great divi- sions of plants. The extent of the division of the margin is expressed by the adjectives, dentated, serrate, crenate, &c. [vide table on p. 206]. If the indentations are deep, the leaf is fissured j if shallow, lobed ; if the division is deep, rounded, and generally acting as the divi- sion between the two sides of the leaf, it is called a simis. Leaves divided by fissures are in general described by the affix fid. Hence {e.g^ a leaf which presents a number of deep, almost symmetrical fissures on both sides of the midrib in a feathery manner, is called pinnatifid — that is to say, the lobes resemble the leaflets of a pin- nate leaf. If the divisions are still deeper, the lobes are then called partitiom (De CandoUe), and the leaf is partite. This designation entering in the formation of composite words, is used to designate the particular form of leaf. Thus, if a leaf is divided on the edges like a pinnatifid leaf, but more deeply, it is called pinnati-partite. Fi- nally, when the margin of the leaf is cut up in an irregular manner, and so deeply that it is with difficulty that the original form of the leaf can be traced, it is called dissected — this word also entering into compound adjectives like the other. Thus we qualify a leaf as pinnati-sected when it is divided on the plan of pinnatifid and pinnati-partite leaves, but much more deeply. All these terms, as well as those applied to the apex or base of the leaf [table, p. 203], are equally applicable to petals, sepals, &c., and many of them are also applicable to the stem and stalk. COMPOUND LEAVES. Hitherto all that we have said has related to simple leaves ; or, in other words, leaves in which the vascular bundles composing the petiole expand out into one blade alone, and in which, if there are divisions, these divisions are not articulated to the midrib or to the petiole by their own petiole, but are all one piece (fig. in). On the contrary, in compound leaves (fig. 113), the vascular bundles expand in several blades, distinct one from the other, which form leaflets, united by their own petioles to the common petiole. There are, however, transitions from the one type to the other. Compound leaves may again be divided into two great divisions— (i.) Pinnate, and (2.) Palmate or Digitate leaves. 1. Pinnate Leaves. — In these leaves (fig. 113) the leaflets or pinns are arranged along the two sides of a common petiole, by secondary petioles (or petiolules). After a number of pairs of leaflets have been borne along the sides of this common petiole, the common FORMS OF LEAVES— PINNATE LEAVES. leaf may end in an odd one— the leaf is then said to be impari- pinnate, as in the vetch tribe ; or the leaf may end abruptly, ter- Fig. 113. — I mparipin- nate leaf of the false Aca- cia (Robinia Pseuda- cacia, L.) Fig. 114. — Compound unifoliate leaf of the Orange {Citrus Au- rantiujn, L.) f La- mina ',/' Petiole, wing- ed on either side ; a Point of union of the two, marked by an arti- culation. minating in two leaflets, as in the common garden-bean [Faba vulgaris), when the compound leaf is said to be abruptly or pari- pinnate. An imparipinnate leaf is said to be trifoliate or ternate when it is composed of a single pair of opposite leaflets, and ter- minated by an odd leaflet (as in the haricot bean). The degree of subdivision does not end here. Not only does the common petiole bear leaflets, but secondary pinnate petioles, which in their turn give attachment to leaflets arranged on them. Such leaves are called bipinnate, as in the common sensitive plant {Mimosa pudica). A number of plants are even more compound than that, since their primary petiole divides into secondary petioles, which in their turn bear tertiary lateral petioles ; and it is only on these, however, that the pinnate leaves are borne. Such leaves are thrice pinnate or tripinttate, or decompound. They may be even supra-decompound, or still further subdivided. Pinnate leaves may be composed of a greater or less number of leaflets. The leaflets, again, may be opposite — i. e., in two's opposite to each other {opposite-pinnate), or alternate {alternati-pinnatc). In oppo- site-pinnate leaves (which are also often called conjugate leaves), FORMS OF LEAVES — PALMATE LEAVES. 17 1 the number of leaflets arranged along the common petiole may be variable ; while the words tmijugate^ bijugate, trijtigate, qnadri- jugate, and tnitltijugate, express whether there is one, or two, three, four, or a greater number of pairs of leaflets. Fig. 115. — Plant which chiefly yields the gum-arabic (7I/zV«w« Arabicd) ; flowering branch [a) and fruit (V). The leaves are bipinnate. 2. Palmate, or Digitate Leaves.— In this form of leaf the leaflets radiate from the summit of a common petiole, and from its resem- blance to the hand,^ or outspread fingers,^ it derives the two names it is equally known by. The leaf of the horse-chestnut (fig. 116) is a good example. In a palmate leaf there may be a variable number of leaflets. Thus, in the trefoil or clover {Trifolhnn pratense), and Hedysartim gyrans, there are three {digitately-tri- foliate, alternate^) ; in Pavia five {digiiately-quinquefoliate) ; seven * Unum, one ; jugum, a yoke. ' Palma, the palm of the hand. 8 Digitus, a finger. * It is sometimes not very easy to say whether a leaf is trifoliate or only imparipinnate, when, as in the latter case, there happen only to be two side leaflets, and the odd one terminating the common petiole. However, if on examining the attachment of the odd leaflet it is found (as in the clover) to be 1 1 172 FORMS OF LEAVES — PALMATE LEAVES. I Fig. 116. — Compound digitate leaf of Horse-chestnut {^scjilus Hippocastatium) . {digitately-septemfoliateYm the horse-chestnut (./fi'jf^/^j Hippocas- tajtuni) ; or, as in some species of lupin, a great number {digi- tately-imcltifoliate). Digitately-peltate Leaves. — De CandoUe has applied the name of compound peltate leaves to the leaves of Sterculia fcetida, and a few other suchlike. Ex- amine the figure of the peltate leaf at p. 202 (fig. 128), and sup- pose that each of the radiating nerves was replaced by distinct separate leaflets, then we would have such a leaf as that which we have indicated. Digitately-pinnate Leaves are those in. which the secondary- petioles, as in some Mimosas, bear secondary leaflets, thus simulating pinnate leaves. In Bigeminate leaves each of the secondary petioles bears a solitary pair of leaflets. {Ex. Mimosa ungius-cati). In Bipinnate leaves of the palmate type, each of the secondary petioles bears pinnas along its sides, just like ordinary pinnate leaves. Ex. Mimosa julibrizin. Finally, cases occur in which the secondary petioles divide into tertiary petioles bearing leaflets. Or a case may be in which the common petiole divides into three secondary petioles, each divided into three tertiary petioles, bearing each their leaflets, as in Actaa spicata, Epimedium alpinwn, &c. The leaf of the citrons and oranges (fig. 114) — an order of which all the other members have compound leaves — might seem at first sight simple ; but on exam- ining it closely, there is seen an articulation at a, by which the single blade /attaches itself to the petiole which is marked by two winged foliaceous expansions on either side. This may be said, therefore, to be a pinnate leaf, the lateral leaflets of which have become abortive, since only the odd terminal leaflet remains, but which, by way of compensation, has taken a considerable de- velopment. There is something analogous also seen in some leguminosas. Such a leaf may be called a unifoliate compound leaf. from about the same level as the two side leaflets, it may be safely pronounced to be a trifoliate leaf ; if, on the contrary, the odd leaflet (as in fig. in) is much above the point of attachment of the side ones, then little doubt need remain regarding the pinnate character of such a leaf. SUCCESSION AND VARIABILITY OF LEAVES. Succession of Compound and Simple Leaves. — Some plants produce at first compound, and then at a subsequent stage simple leaves, or reciprocally. For instance, Dr Geo. Lawson showed that the common gorse or whin {Ulex) at an early stage gives birth to a dozen or twenty leaves, provided each with three leaflets, but by-and-by it commences to produce spines, while simultaneously the leaves are reduced to simple little scales. On the other hand, in certain Australian Legummosa, the stem bears at first simple leaves, which give place by-and-by to compound ones, after the stem has grown considerably. Variability of Leaves. — Finally, it ought to be added, that the leaves on some plants are very variable, according to their position on the stem or branches, as may be seen by examining a plant of ivy or a bush of holly. In the ivy, for instance, the leaves in the vicinity of the flowers are differently shaped from the ordinary ones, in so far that they have no lobation at the margin or cleft at the base, and become nearly twice as long as broad. In the "snow- berry" {Syvtplocarpus raceinosus) of North-west America, the first leaves produced on the branch are undivided. However, as the vegetative energy increases, the next leaves produced become more or less cut on the edge, the next less, until, finally, when the year's growth is completed, the uppermost of all are entire. (See also fig. 115.) In Broussonetia papyri/era, out of the pith of which paper is made, and out of the liber of which the Polynesians weave their I cloth, Duchartre notices the extreme diversity of the leaves, from being perfectly entire to deep lobation. Again, in the water-crow- foot {Ranunculus aquatilis), we see the upper leaves entire, and the lower ones, which are immersed in the water, so divided as to be reduced to nerves without parenchyma. The same appearance is seen in Cabomba oblongifolia, another water-plant, &c. (p. 1 59, 168). In Za/m^j^S'aj'ja/raj some leaves are entire, others two-lobed, and others three-lobed, even on the same branch, according to the height they are placed on the stem or branches. In Gleditschia triacanthus, the pinnately compound leaves, instead of having, as is usual, only a single leaflet borne on each petiolule, have occasionally on each petiolule several little leaflets ; in other words, the leaflets become themselves compound.^ The proportion between the differ- ent parts of the leaf also sometimes varies according to the position of the leaf on the stem. Thus, in general, the sheath — when this IS present— is more developed than the blade in leaves placed at the base or at the summit. Leaves will also often be entire, re- pand, crenate, or serrate, on the same plant, as seen in the common holly ; and in some North-west American oaks {Q. agrifolia, Sec), one side of the leaf may be dentate, and the other entire.^ 1 Payer, Elements, &c., p. 36. s See my Horae Sylvanse, p. 72. 174 PHYLLOMORPHISM. Phyllomorphosis. — The study of the succession and variation of leaves during different seasons has received some attention of Fig. 117. — Plant of Campanula rotundifolia, L., showing the difference between the configuration of the radicle leaves ff, and the othersy^. late years — chiefly by Schleiden, Braun, and Rossmann — and has received the name of Phyllomorphosis. They consider that all the variations of leaves may be traced to — (i.) alterations in the form of the limb ; (2.) alterations in the form of the petiole ; or (3.) de- pendent on the two parts developing equally. The basilar ItsS, or that w^hich in most monocotyledons, and in a fev^r dicotoyledons (strawberries), first appears on the branch, and is distinguished ANOMALOUS FORMS OF LEAVES. from those which follow by being small, thin, membranous, pale, and most often placed on the inner side of the branch, the Ger- mans have called vorblatt, and the French (Gay) pr^feuille. It may be translated into Latin as prof 0 Hum, and seems destined to act as a shelter to the younger parts found below it.^ ANOMALOUS FORMS OF LEAVES. TTnsynmietrical Leaves. — In most leaves the two sides are about equally disposed on either side of the petiole, or of the midrib ; but in Begonia {e.g), one side is frequently much larger than the other, and the leaf is therefore oblique. Vertical and Equitant Leaves. — In most leaves one surface is presented to the sky, the other to the earth, and if this arrange- ment is disturbed, the leaf will twist back again to its normal position when the restraining influence is removed. In Iris, however, two surfaces are apparently equally exposed, but this is not so. In that genus of plants we see through life an arrange- ment only seen in some other plants while in the bud — viz., they are equitant near the base, the whole leaf being also conduplicate. The upper portions of the leaves are in reality folded on themselves, so that what would naturally be the upper portion of the leaf is consolidated more or less in early life to the opposite half, the green portion exposed to the air being really the under surface of the leaf. True vertical leaves are seen in Callistemnon and other Aus- tralian myrtles, and are caused by a twisting of the petiole. They, in common with the Acacias, with Phyllodia(p. 151), assist in giving a peculiar character to portions of the Australian landscape. In Alstrcetneria, the leaf is twisted, so that at one time what is really the upper surface seems as if the inferior, and vice versa. Leaves with no distinction of petiole and lamina are seen in the Iris, Daffodil (Narcissus) onion, leek, (Alliitm porrum"^) and pines, and also in cedars, Arborvitas {Thuja and Libocedrus), &c., where they are scale-shaped. Succulent Leaves -we. have already seen in the stone-crop, house- leek, &c. ; while leaves as scales are seen in the toothwort {Lathraia), which is parasitic on the roots of other trees, and on the vernal stem of perennial herbs " near or beneath the surface of the ground," on asparagus-shoots, &c. The actual foliage of pines, according to Gray, originates from ^ For a full account of Phyllomorphosis, see J. Rossmann's brochure, entitled Beitrage zur Kenntniss der Phyllomorphose, 1857. * Generally believed to be a cultivated variety of A. A^npcloprasum, L., the largest of our British species of the genus. 176 ANOMALOUS FORMS OF LEAVES — TENDRILS. a branch in the axil of their dry bud-scales, which are the primary leaves. Leaves as tendrils (cirrhi), are seen in the pea tribe, Fumaria capreolata, Methonica gloriosa, various species of Clematis and Solanum, &c. This is, however, best seen in pinnate compound leaves. In fig. 1 18 is seen a leaf of the common Lathyriis latifoHus, Fig. 118. — Entire Lathy rtts latifolius, L. st Stipules; y"The two leaflets remaining in a normal state ; v Branching tendril (one-fourth nat. size). st being the stipules, / the two leaflets remaining in the normal condition, v the branching tendril. Here it is the petiole which is prolonged upwards, with the leaflets which would have otherwise been attached to it, atrophied, and taking the form of a branching tendril. Another kind of tendril, not so easily explained, is seen in the genus Smilax. Here just beneath the sheathing base of the true leaf are two simple opposite tendrils. These may be explained as being (i.) either two petiolary glands which have become much enlarged and exaggerated ; or (2.) the degenerated forms of two leaflets ; or (3) two basilar segments of the leaf (De Can- dolle) ; or (4.) finally, as two transformed stipules. The second of these explanations, by A. St Hilaire, is the one most generally held ; while the last, which we owe to the late Hugo Von Mohl, is scarcely tenable in the face of the fact that the whole of the monocotyledons (to which the Smilacece, in which is included the genus Sjnilax, belong) habitually want lateral stipules. The last kind of leaf-tendrils we shall notice are those produced by the prolongation and union of the nerves on one side of the blade. These are seen in Gloriosa {Liliacece), and more parti- cularly in Flagellaria Indica. We have already noticed another kind of tendrils produced by the degeneration of the branches or some other portion of the axis (p. no). Finally, we may advert to some kinds of tendrils seen in melons {Cucuniis Melo), Cucurbita, and various other plants of the order Cucurbitaceas, the morphology of which is obscure. Here they frequently spring from under the LEAVES AS SPINES : PITCHER-PLANTS. 177 attachment of a leaf, and have been the subject of numerous rival theories by Fabre, Clos, Naudon, Guillard, Tassi, Lestiboudois, Cauvet, Payer, Aug. St Hilaire, Stocks, and others. They maybe possibly degenerated leaves, which existed at each node, stipular organs, the product of the deviation of one of the woody bundles destined for the leaf (Payer) ; a leaf deprived of its parenchy- ma, and reduced simply to its nerves (Cauvet), or an atrophied branch. Either theory has its supporters, and even the choice does not end here — for there are numerous others with^ which the student need not, however, trouble himself. The position of a tendril is important to note, because it points out the nature of the organ. Hence in the vine the tendril is looked upon as an abortive raceme of flowers. It may be either simple, as in the Bryony {Bryonia alba), or branched, as in Cobcea scandens (a Mexican climbing plant cultivated in gardens.) Leaves as Spines. — We have already considered spines as degenerations of the axis, or of some part of it (p. no). In some other plants the nerves of some leaves alone remain, and become very indurated, the result of which is, that, as in the barberry {Berberis vulgaris), spines are found in the places where, under other circumstances, leaves would be situated. Again, in the species of Astragalus which form the section Tragacantha, the common petiole of the pinnate leaf terminates in a point, and little by little, especially after the fall of the leaflets, becomes indurated, and remains attached in the form of a long spine. Lastly, in some monocotyledons we see the ribs prolonged on the surface of the leaf into a sharp spine, and not unfrequently the teeth terminate also in sharp points. Both of these modifica- tions we see in the leaves of Agave Americana, which on that account is used in Algiers and elsewhere to form hedges of an almost impenetrable nature. In the false acacia, and Paliurtcs, we find spines to the right and left of the base of the leaflets, showing that they are trans- formed stipules. Pitcher-Plants. — Certain plants are popularly known by this designation on account of the leaves being either altogether or in part in the form of ascidia or hollow open sacs more or less pitcher- shaped. Something similar we have already seen in the utricles of Utricularia. These pitchers, which we now propose considering, are in many points, however, widely different. In Sarracenia ("Trumpet-flower," " Indian cups," or "Side-saddle flower,") and Darlingtonia, plants of the swampy regions of the north-eastern and southern portions of the Eastern United States and of Cali- fornia respectively, all the leaves are infundibuliform open pitchers, with a longitudinal wing on their anterior aspect. In Darling- ^ Bull. Soc. Bot. de Fr., vols. ii. iii. iv. and xi., &c. M 178 PITCHER-FORMED LEAVES. totlia arid S. psittacina the "pitcher" is arched like a hood, and in the first-named genus is terminated by " a two-lobed foliaceous appendage," like the forked tail of a fish. In Cephalotus follicu- laris, a little plant of South-western Australia (fig. 119), there are two different forms of leaves. In our figure ( 1 19) is represented an entire tuft somewhat smaller than nature, and in fig. 120 is shown an example of each kind of leaves of the natural size. Round the edge of the pitcher is a sort of pad {b) which assists, in company with the Fig. iig. — Entire tuft of Cephalotus follicularis, La- bill. ; _/y" Normal flattened leaves; u Ascidia, with their opercula op (smaller than nature). operculum (/"'), in closing the mouth.^ In Nepeiithes, a genus comprising several species found in Mada- gascar and the Malay Islands, there is an advance on the organi- Fig. 120. — An ascidium of Cephalotus follicularis, isolated, and represented of the natural size, with two normal or flattened leaves, of which one,y', is full grown ; /" Body of the ascidium ; b Ring which guards the orifice ; /' Its operculum. sation, as seen in the foregoing plants. Here it is somewhat diffi- cult to trace the homologues of each part of a simple leaf in the complicated structure before us. In fig. 121, one of these plants 1 Hence this is the Calyptrimorphous {KoXvutpa., a covering or cap, and fiop<|>i), a form) mode of growth, according to the very unnecessary nomencla- ture of some name-manufacturer. PITCHER-FORMED LEAVES. 179 {Nepenthes ampullaria) is shown as bearing two leaves in different stages of development; («) is the basilar portion, slender and Fig. 121. — 'fragment of Ne^entftes ampullaria, Jack. short; {b) a portion more expanded, thin and foliaceous, with a strong median vein ; {c) a prolongation of that vein in the form of a slender cord ; {d e) is the pitcher, and (/) the operculum. This operculum is closely applied over the orifice of the pitcher in the young state of the plant, but when it is raised the organ has then completed its development. There is no particular dilatation at the point where the cord {c) joins the pitcher ; but on either side are two remarkable glands fringed with long hairs {d). In i8o PITCHER-FORMED LEAVES. the interior of this curious organ is a glandular cellular tissue which secretes a watery liquid. In Heliomorpha of British Guiana the operculum is represented by a small concave terminal appendage — the pitcher being not always completed to the summit. Opinions are divided as to what the different portions of the organism are analogues of. Some consider that the expansion {b) is the true petiole, which in some leaves we have seen is developed upwards in the form of a tendril ; only in this case, instead of a tendril we have a pitcher, while the lid {f) is looked upon as the true blade.^ Others, on the contrary,^ view the pitcher as the ana- logue of the blade, and conclude that all the inferior portions must be considered petiole and sheath. The first of these opinions has been adopted by Dr Hooker, with the modification that the tendril formed by the prolongation of the midrib carries a termi- nal gland, of which the pitcher is nothing more than a particular development.^ Finally, M. Baillon, from the study of the development of Sar- racenia purpurea — perhaps the most common species, and the one generally cultivated in this country — considers that the origin of the lid, and of the more or less distinct lateral projections which often accompany it, is the result of an inequality in the develop- ment of the apex of the leaf, the upper margin of which increases most rapidly, and afterwards becomes slightly contracted at its base. Consequently the lid and the projections which accompany it are not a lid, but the unequal lobes of a limb that existed before them. The keel of the leaves of the Sarracenice. appears to be nothing but an exaggeration of the nervure or projecting crest, which often stretches along the lower surface of the limb of pel- tate leaves from the insertion of the petiole to the bottom of the sinus presented by the base of the limb. Its vertical direction in Sarracenia is merely the consequence of the extreme depth ac- quired by the immediately peltate limb of the leaf.^ The pitchers which grow on the upper branches of one of the plants (at least) are said to have often adventitious rootlets de- veloped in them,^ which in a hot climate may be useful in supply- ' Aug. St Hilaire (Morphol. vdg^tale, p. 142). On this view the winged margins of the petioles of Citrus hystrix or of Dionrea, if approximated and amalgamated, would be equivalent to the pitchers of Nepenthes, Sarracenia, &c. 2 Duchartre, Eldm de Bot., p. 310. 3 Trans. Linn. Soc, vol. xxii., p. 415-424, pi. 69-74. •* Comptes rendus, Nov. 7, 1870, p. 630 ; and abstract in Ann. Nat Hist., vol. vii., 4th sen, 1871, p. 448. B Viz., in Dischidia Kafflesiaiiia (order Asclepiadacese), which climbs to the top of the loftiest trees— the pitchers are generally confined to its upper part. ■ In the case of this plant they are true leaves modified, and accompanying the BRYOPHYLLUM : PHYLLOTAXIS. l8l ing moisture to the parched upper leaves, where there is much more evaporation than down below. Insects are often drowned in thefluid secreted in these cups, either accidentally, or are deposited there by other insects.^ A particular species, however, has its habitat there. Some wild animals— such as monkeys— take advantage of it to quench their thirst. In most cases this water is derived from the plant itself, for the lid is so constructed that rain cannot enter. What good plants rooted in wet bogs — for such are the exact loca- lities for Sarracenia and Darlingtonia, as the writer has observed in California — can gain from secreting or gathering water in their pitchers, it is impossible to say. Equally difficult is it to account for the presence of the dead flies, unless they act as a kind of manure. Yet Sarracenia, Darlingtonia, Sec, are almost invariably crammed with insects, and the hairs which line the interior of the pitchers are so placed as to allow of the insects entering with ease, but not of escaping. In the onions {Allum cepa, &c.), some Convallariae, &c., the leaves are hollow. Bryophyllum, &c. — This genus of plants derives its name from habitually producing buds on the edges of its leaves. They are also produced as a habitual character on the edge of Malaxis paludosa, and on the surface of Ornithogalum thyrsoideunt, and occasionally- on the edge of Cardamine pratensis. Nasturtium officinale, and Drosera. In the Radick Islands of the Pacific Ocean the natives rear the Arum esculentum by planting the leaves. The leaves of Gesnera, Gloxinia, Achimenes, &c., will also produce young plants if a notch is cut in the thick veins. PHYLLOTAXIS.^ That leaves are not attached to the stem and branches with- out regard to some fixed arrangement, is apparent on the most superficial observation. It is only, however, when we come to other leaves still in their normal condition. Accordingly soine have hesitated to consider these as coming under the same category as those of Nepenthes, Cephalotus, &c. Equally problematical as to their analogy are the Ascidia of the order Marcgraviacece, which open below. They are generally believed to be modified leaves of the nature of bracts. For general account of the pitcher- plants in addition to the papers quoted, see J. D. Hooker in De Candolle's Prodomus, vol. xvii. ; Nature, 1871, p. 147; and notices in the same volume (P- 54. t67, and 159), by Buckton, Worthington Smith, and W. Robinson. ^ See a most peculiar case related by Sir J. E. Smith, Introd. to Botany, chap, xvi., of a Sphex or Ichneumon dragging large flies to Sarracenia adiinca (variolaris, W.), and forcing them under the lid. The leaves were all crammed with dead flies, and 5. purpurea is in like manner used as a similar storehouse. His idea, that the ' ' air evolved by these dead flies may be beneficial to vege- tation," is, however, open to question. 2 "WXAoi/, leaf; rafts, arrangement. It is also sometimes called Botaiiometry, from ^oranj, herb, and fierpoi/, measure. l82 PHYLLOTAXIS : ALTERNATE LEAVES. examine this order more closely that we see that this arrangement is of a most complex and interesting character, involving certain mathematical principles. We have not as yet seen this in any other department of Botany. The study of this constitutes Phyl- lotaxis, or leaf-arrangement. There are three principal ways in which leaves are arranged on the plant — viz. : 1. Alternate or scattered, when no two leaves are exactly oppo- site to each other, but alternate, to a greater or less extent, with the others on the same stem and branches. 2. Opposite, when two leaves are placed exactly on opposite sides of the same stem or branches. 3. Verticillate, when three or more leaves are attached around the stem at the same level. This arrangement generally occurs at nodes. Let us consider each of these modes of arrangement some- what more in detail. 1. Alternate Leaves. — This is the most common method of arrangement, and is normal in nearly all monocotyledons, and in many dicotyledons after the first and second nodes. It has, how- ever, several variations, which may be briefly noticed. First, how- ever, let us premise that all alternate or scattered leaves are dis- posed on the axis in a continuous spiral. Take, for instance, a branch of the poplar, pear, prune, or peach : we see alternate leaves. But, on examining carefully, we do not find each leaf exactly above the one below ; but still, following in the direction of a line drawn round the stem and touching each leaf in succession, we will find, by-and-by, one exactly over the one we commenced with. In this case it happens to be the fifth ; and so, if we go winding around the stem, we will always find the same number of leaves intervening between the one with which the spiral commences and the one which is directly over it, and which, for the sake of convenience, we may call Zero. Hence, commencing with it and winding round the stem, in the leaves of the trees mentioned, we will not find one directly over it until we come to the fifth. This distance described round the stem is called the cycle} Then commences another spiral, which ends at the tenth ; over the tenth is the fifteenth, and so on. We find, further, that we had to wind twice round the stem before arriving at leaf 5 directly over zero, and that it has taken five leaves to complete the cycle. Let us, however, commence our description of the chief forms of Phyllotaxis in alternate leaves, by describing the simplest and then the more complicated. Distichous,^ or two-ranked arrangement. — In this variety the leaves are placed in two upright rows, each alternate leaf being 1 KukAos, a circle. ^ Aianxos, in two rows. ALTERNATE LEAVES : TRISTICHOUS ARRANGEMENT. 1 83 exactly on opposite sides of the stem from the one which preceded it. Thus, the second is on the side furthest from the first; the third equally distant from the second ; the fourth bears the same relation to the third, and so on throughout, — the leaves thus form- ing two vertical rows. Leaves arranged in this manner are known as the disiichoiis or two-ranked arrangement of Phyllotaxis- Hence on one side we have the ist, 3d, sth, 7th, and so on; and on the other, 2d, 4th, 6th, Sth, &c., counting by a spiral line wound around the stem, and touching each leaf in succession. We find this, the simplest mode of Phyllotaxis, in all grasses and many other Mono- cotyledons, such 2.5 Amaryllis, several tropical orchids. Aloe pli- catilis, &c., and among Dicotyledons in the linden {Tilia), Pali- urtis, elm {Ulmus cafiipestris), camellia, &c. Tristichous or three-ranked arrangement. — This we find com- monly in sedges and other monocotyledonous Jplants, and in the elder {A. glaucd) among other Dicotyledons. For instance, take any leaf at pleasure, and numbering it i, pass a line round one-third of the stem as we ascend to No. 2 ; another third to No. 3 ; another brings us round to the point over No. i, and here leaf No. 4 is placed ; No. 5 is, in like manner, over No. 2, and so on. We therefore see that in this tristichous arrangement there are three vertical rows of leaves on the stems — one containing Nos. I, 4, 7, 10, &c. ; the second, 2, 5,- 8, 11, &c. ; and a third contain- ing 3, 6, 9, 12, — and so on. If a line is drawn from the insertion of one leaf to that of the next, and so on to the 3d, 4th, and the rest in succession, it will be seen that the line winds through the stem in a spiral manner as it ascends. In the first, or distichous, mode of Phyllotaxis, the second leaf is separated from the first by one-half the circumfer- ence of the stem, and having completed one turn round the stem, the third leaf begins the second turn. Again, in the tristichous arrangement each leaf is separated by athirdof the circumference or cycle, and a fourth leaf commences a second cycle, which goes on in the same way. In other words, the a7igular divergence or arc interposed between the insertion of the two successive leaves in the first (distichous) is \, in the second 3 of a circle — these fractions representing not only the angles of divergence, but the whole plan of these two modes.^ Thus the numerator denotes the number of times the spiral line winds around the stem before it touches a leaf directly over the one it be- 1 A circle being 360°, when we state the fraction of some form of Phyllotaxis to be, say |, we mean to intimate that the angular divergence of each of the leaves which compose the cycle, viewed in relation to that which preceded it or followed it, is two-fifths of a circle, or 144° ; when the Phyllotaxis is distichous, or \, the angular divergence is one-half of a circle, or 180° ; when it is tristichous (i), it is one-third of a circle, or 120,— and so on. 184 ALTERNATE LEAVES : PENTASTICHOUS ARRANGEMENT. Fis^. 122. gins with, while the denotninator expresses the number of leaves that are laid clown in the course which forms the cycle. Pentastichous, qidticuncial, or five-ranked arrangement {^gs, 122, 123). — This is seen in the apple, peach, cherry, poplar, &c. Here we have five leaves in each cycle, the sixth commenc- ing a second. Here we must describe two revolutions around the stem before the first leaf is exactly over the sixth, five leaves intervening, each being placed at an interval of |ths of the circumference. Hence | is the fraction by which the arrangement is expressed — i.e., 2 (the numerator) expresses the number of turns described round the stem, and 5 (the denominator) the number of leaves in the cycle, or the number of vertical ranks in such a stem. The above ex- amples will sufficiently explain the nature of these arrangements. They do not, however, stop here, as will be seen by the following synopsis of some other forms of Phyllotaxis — each, however, proceeding on the plan as indicated above : — In the holly, Aconite, the tuft of leaves at the base of Plantago, &c., the I arrangement is seen. II wormwood, ts- II Pinus (Pinea), cones, &c., ttt. II Plantago media, &c., si- II cones of some other pines, \\. With a few exceptions, this consecutive series comprises within it all the varia- tions of the kind of Phyllotaxis that are known to occur. The higher fractions chiefly occur where, as in the house-leek (fig. 127), and scales of pines, cones (fig. 126), which are modifications of leaves, the leaves are crowded on the stem, or as in the leaves of firs, &c., which are numerous and small in proportion to the circumference. Where the internodes are long and the base of the leaves broad, it is often difficult to say which leaf stands over another, or where the internodes are short, to follow the succession of the intermediate leaves, though it may be easy to follow the Fig. 123. Fig. 122. — Diagram of the five- ranked arrangement of leaves. A'spiral line is drawn ascending the stem, and passing through the successive scars which mark the position of the leaves from i to 6. It is made a dotted line where it passes on the opposite side of the stem, and the scars 2 and 5, which fall on that side, are made fainter. Fig. 123. — A plane horizon- tal projection of the same ; the dotted line passing from the edge of the first leaf to the second, and so on to the fifth leaf, which completes the cycle, as the sixth would come directly before, or within, the first (after Gray). ANGLE OF divergence: SECONDARY SPIRALS. 1 85 superposition of the leaves. However, if we can count the num- ber of vertical rows, that gives the denominator of the sought-for fraction (e'.^., if 8, it is referred to the § arrangement; if 13, to the and so on). We often find the same arrangement pre- vailing in the parts of flowers, and a similar law regulated the Phyllotaxis of extinct plants like the Lepidode7idro7is, Sigillarias, &c. We further find, on examining the series just given, that (i) ike numerator of each fraction is the sum of the numerator of the two preceding fractions, and that the denonii7iator of each fraction is the sum of the denominator of the two preceding ones; (2) we also find that the nutnerator of each fractioft is the de7tominator of the next but one precedi7ig it. Take, for example, the more common frac- tions— 112 3 5 8 13 TTi 3i r> 8' r3> ^T' With the exception of \, \ (the distichous and tristichous arrange- ments), which are, in a manner, a kind of point of departure for the others, we see these curious facts exemplified. For instance, f {qui7icu7icial arrangement), a common fraction among leaves, is composed of the sums of the preceding numerators (i) of | and i, and of the two preceding denominators (2 and 3) of the same frac- tions ; in the sum | which follows, it is formed by the two nume- rators and two denominators of the two fractions \ and f which precede, — and so on in exactly a similar manner with the others. Again, taking |, we find the second rule demonstrated, — here the numerator is 3 ; and 3 is also the denominator of the fraction |, the next but one preceding it : so with ; here 5 is the numerator, the denominator of |, the fraction the next but o/te precedi7ig it. l7nporta7ice of the A7tgle of Diverge7ice. — N. J. C. Miiller and others have shown that the angle of divergence has considerable influence on the mode in which the cell terminating the axis is divided. For instance, in the \ arrangement, the terminal surface of the axis is lenticular, and the cell which composes it is divided by two partitions ; if the 3 arrangement prevails, the terminal cell shows four triangular surfaces, one of which is horizontal and terminates the axis ; moreover, it always remains in the same form, notwithstanding the partitions which it successively produces. Similar correlations exist among the other forms of Phyllotaxis.^ Secondary Spirals. — In the examples given we have seen the leaves forming but one spiral around the stem. However, in some ^ Untersuchungen iiberdas Wachsthum der einzelligen Vegationspunkte und die Bedeutung der Schimper- Braun'schen Divergenzwinkel (Verhand, der naturhistorisch-med. Vereins zu Heidelberg, vol. v. N^ iii., ss. 75-77); and Bot. Zeit., 1869, 24, 25, tab. ix. ; Geo. Henslow on Variations of the Angle of Divergence in Hellcborus tnberosus, Trans. Linn. Soc., .\xvi. 647. i86 SECONDARY SPIRALS. Stems, where the leaves are very numerous and closely crowded on one another, and especially when they lose their character of leaves, and are reduced to the state of scales and bracts (as in the cones of firs and the involucre of Composites), we sometimes see several parallel and oblique spirals, some towards the right, others towards the left. Take, for instance, a house-leek (fig. 127) or the cone of a fir (figs. 124, 125, 126) : there is, in addition to the primitive spiral, which it is sometimes difficult to detect at first sight, other spirals which are called secondary, and which are generally much more marked than the primitive one. Again, while this primary or generating spiral embraces a complete series of the leaves of the stem — /. e., the spiral passes through every leaf of the cluster, — the secondary spirals are invariably partial — i. e., they never pass through more than a certain number of the leaves of the series. Thus, for example, supposing each leaf numbered, the generat- ing spiral passes through the leaves o, i, 2, 3, 4, 5, &c., while the secondary spirals pass through the numbers i, 3, 5, 7, &c., or 2, 4, 6, 8, &c. It may be well, however, to remark here, that the differences between each of the numbers of the series of a second- ary spiral express the number of the secondary spirals and par- allels which show themselves on each side of the axis of a branch. Thus, in Euphorbia Characias, Richard shows that there are two secondary spirals, the one composed of the figures i, 3, 5, 7, 9, the other of the figures 2, 4, 6, 8, 10. But the figures represented by these two spirals in union comprehend the whole series. If there are a number of secondary spirals, the figures representing each of the leaves of which each is composed present always between them a difference equal to the number of spirals. Take, for instance, the cone of the Scotch fir {Pinus sylvestris). Here we see eight secondary and parallel spirals going from left to right, and comprising, when all united, the whole scales of the cone. In like manner, there are thirteen others going in an op- posite direction — viz., from right to left — and, like the former, comprising all the scales in the cone. In following up one of the spirals going from left to right (or si7iistro7'sal), we see that, in commencing at scale No. i, the spiral passes successively through Nos. 9, 17, 25, 33, but that which commences at No. 2 passes through Nos. 11, 18, 26, &c. — the difference between the numbers which form one of the secondar}^ spirals being 8. Now this num- ber exactly represents the number of secondary spirals — parallel and sinistrorsal. On the other hand, look at one of the secondary spirals which is directed from right to left {dextrorsal). Com- mencing at scale No. i, that spiral passes by i, 14, 27, 40, 33 ; or, commencing at No. 9, it passes through 22, 35, 48, 61, &c. In other words, the difference between each of the numbers in these SECONDARY SPIRALS. 1 87 dextrorsal secondary spirals is 13—13 being also the number of those in the cone. And so on. Again, in fig. 124, is shown the strobilus or cone of a pine — the sg sg', which cover the "naked" Fig. 125. — Pinus mariiima, with staminate seeds g; em " Embryo " (or young flower, strobilus (cone), and various details of plant) shown in longitudinal section flowers, ovule, and seed. The leaves are in fas- in the seed. cicles. inferior portion, which is entire, showing distinctly the scales sg, with their convex quadrilateral extremities sg', arranged so as to show several secondary spirals, some directly from right to left, others from left to right. How to determine the generating spiral by the aid of the second- ary spirals will have been somewhat apparent to the student from the study of the foregoing figures. However, again referring to the figures, let us explain this somewhat more in detail by i88 SECONDARY SPIRALS. their aid. The best way to do so is to write on each scale or on each leaf the number to which it is entitled, in the order of the unknown spiral — a number which the secondary spiral furnishes the means of determining. For example, if in fig. 124 there exist eight secondary spirals, apparently well marked, winding from left to right, and five going from right to left, that knowledge alone would show us how to number all the scales. It would fol- low that the eight parallel spirals which go from left to right, and embrace among them all the scales, would none of them have in the course of its spiral more than | of the sum total. Con- sequently, on the spiral a a' (for example), if the inferior scale is numbered i, that which. would follow suit would be number 9, and the following ones successively 17, 25, 33, &c., always 8 intervening between each member. In this manner we would number all the scales of that spiral. On the other hand, the five spirals running parallel in the opposite direction — viz., from right to left — would embrace among them all the scales, and none would embrace in its spiral more than -J-th of the sum total. Ac- cordingly, these scales would be numbered with intervals of 5 between them. Consequently, the scale which is the point of departure will be numbered i, and those which follow suit 6, 11, 16, 21, &c. For the second of these spirals, the point of departure will be the number 9 already written, and the scales which fol- low it in the line of the spiral will be marked 14, 19, 24, 29, &c., since we write 9, less 5 — i. e., 4 — beneath. For the third of these spirals, the point of departure will be the figure 17 already written, and the scales which form it will be numbered 22, 27, 32, 37, &c., above— 12, 7, and 2 below. In numbering, according to the same principle, the scales which are comprised in the two last spirals directed from right to left, we will also require to inscribe a number on each. We will not, however, require in this case to do more than write the numbers in their natural sequence, i, 2, 3, 4, 5, &c., to ascertain the course of the generating spiral, which we now see pertains to the ^3 fraction. In fact, whenever we see, as we do now, that scale 14 is directly over scale i, the cycle is seen to be composed of 13 scales, to which belongs the number of spirals 5 ; hence xa is the fraction expressing the Phyllotaxis of the generating spiral.^ This will perhaps be more apparent if, following Gray, we lay down on a plane surface a vertical projection, representing the generating and secondary spirals of the white or Weymouth pine {Pinus strobns), alongside of the cone itself, with the scales num- bered (fig. 126). The arrangement is the ^g. It might also be represented in the rosettes of leaves in the house-leek (fig. 127). Here we see a set of secondary spirals, " eight in number, with the 1 Duchartre, lib. cit., p. 377. SECONDARY SPIRALS. 189 common difference eight— viz.. that of which the series i, 9, 17, 25, is a representative. The set that answers to this on the opposite direction— viz., i, 6, 11, 16, 21, 26, with the common difference 5— o-ives the numerator, and 5 + 8 the denominator, of the fraction In the figure of the cone, part of the numbers are of course out of sight on the other side of it. 27 23 25 24 23 22 21 20 18 19 17 16 IS 14 13 12 II 10 Vertical projection of the arrangement. Fig. 126. — A cone of the White Pine [Pinus stro- bus) on which the numbers are laid down, and the leading higher secondary spirals are indicated ; those with the common difference 8 are marked by dotted lines ascending to the right ; two of the five that wind in the opposite direction are also marked with dotted lines ; the set with the common difference 3 in one direction, and that with the common differ- ence 2 in the other, are very manifest in the cone (after- Gray). Secondary spirals owe their existence to the excessive shortening of the axis bearing scales or leaves. When this axis is sufficiently 1 90 RECTISERIAL AND CURVISERIAL LEAVES. long, the secondary spirals disappear, and the generating or pri- mary one becomes apparent. In some stems of Limim and Scdian in a young state, the cylindrical leaves are much crowded, and secondary spirals are more apparent than the primary one ; but as the axis lengthens, these secondary spirals disappear, and the generating one becomes apparent. So that a plant may have at its base a | arrangement, and also a | at its summit, as can be seen by watching the development of Echinocactus spiralis, one of the Cactaceas, from the young to the adult the'hou7e-kdc" with 'the State, &c. All dicotyledonous plants, it may rosette of leaves unexpand- also be noted, have their first leaves oppo- ed, exhibiting the A arrange- .. umii - it r^i i- i ment, the fourteenth leaf be- Site, while later m life many of them display ing directly over the first leaf the alternate arrangement. (after Oray). ... . , , The generating spiral may either go to the right or to the left, and may be the same in the stem and in the branches, as in the bird-cherry {Prunus Padus). In this case it is said to be homodromous?- If the spirals in the stem and branches turn in opposite directions (as in Liquida7nbar Styraciflud), it is, on the contrary, said to be heterodromous? In a homodromous spiral the leaf from the axis of which the branch springs begins the spiral in that branch. The Phyllotaxis is generally uniform in the same species, but it occasionally varies in different parts of the same plant by the multiplication by division of the ridges on which the leaves are placed, and therefore of the verticals, "as in the example oi Echino- cactus just mentioned. The Phyllotaxis, however, often varies in closely allied forms. For instance, in the European larch {Larix EuropcBo) it is ; while in the common American larch (Z. pen- dula) it is I ; the white pine {Pinus strobics) is x^s ; but other species of the same genus are -fx, ii. It, &c. Rectiserial and Curviserial Leaves. — In the cases of Phyllo- taxis represented by the higher fractions, it is not always easy, or even possible, to say whether a particular leaf is exactly over another one — say, that the 9th, 14th, 22d, 35th, or 56th is exactly above the first, or a little to the side of it in the vertical line. In these cases the difference of the angle of divergence between a higher and a lower fraction must be very slight indeed. For instance, in the arrangement, it is 138° 24', and in all the higher fractions it is 137°, with the addition of a variable num- ber of minutes, which approaches nearer and nearer to 30'. MM. Bravais consider all these "mere alterations of one typical arrange- ment—namely, with the angle of divergence 137° 30' 28"— which is 1 "Ojiids, like, and Spo(ao9, course. * 'Erepos, other. OPPOSITE LEAVES : VERTICILLATE LEAVES. 191 irrational to the circumference — that is, not capable of dividing it an exact number of times, and consequently never bringing any leaf precisely in a right line over any preceding leaf, but placing the leaves of what we take for vertical ranks alternately on both sides of this line, and very near to it, approaching it more and more, without ever exactly reaching it." Such forms MM. Bravais dis- tinguish as curviserial, on the idea that the leaves are disposed on an infinite curve, and are " never brought into exactly straight ranks." The rectiserial ones are those which arrange themselves into exactly vertical ranks, owing to the leaves being arranged on an integral part of the circumference. Other series of Cycles. — Though the forms of Phyllotaxis which we have given are those most commonly seen, yet the student ought to be aware that others — though so rarely that he need not trouble himself with more than the acquisition of a passing ac- quaintance with them — are met with in some plants. There are indeed two series, the terms of which are connected in this man- ner, that the two first terms once known, we can deduce by simple addition those which follow in the cycle of which they are com- ponent members. These two series are as follows : — 3. T. 7. A, A, IS, &c. %> Zi at Tl, its, ^y, CS£C. Again, in palms, Martius has shown that the spirals i, f, f, |, ^, occur; while species of the genus Fmi/s show t, ts, sV. ttt'U, arrangements. These are, however, exceptional cases. 2. Opposite Leaves. — This is the next most common arrange- ment ; and in some orders, like Labiatae, it is the normal Phyllo- taxis of all the species belonging to them. In most cases the pairs of opposite leaves alternate with one another in a decussate man- ner—that is, the second pair crosses the first at right angles, and so on : so that the third pair is directly over the first; the fourth over the second ; the fifth over the third,— and so on. In these cases it will be at once evident that such leaves will describe • cer- tain vertical lines along the stem, such verticals being four, while the number of leaves is only two. Occasionally the leaves are not exactly decussate, but are arranged so that they somewhat deviate from this line, and several pairs of leaves have to be passed before we find a pair placed exactly over the pair we started with. In this case there is a spiral arrangement, coming under the head of one or other of the modes of Phyllotaxis already described. In this case, however, instead of alternate leaves we have a pair at each node. 3. Verticillate Leaves.— In this case, sometimes, the whorls are also decussate, so that the leaves of each whorl correspond to the interspaces of the leaves of the whorl beneath it. In other T92 CONSTANCY OF PHVLLOTAXIS : FASCICLED LEAVES, cases they wind spirally, so that a number of parallel spirals ana- logous to the secondary spirals of opposite leaves wind around the stem. In this case the angle of divergence is represented by the number of leaves which compose the vertical, and the number of spirals which are described around the stem. In this as in the case of opposite leaves, it will also be apparent that the leaves ought to form a series of marked vertical lines, of which the number is always double that of the leaves of each vertical. For instance, when there are three leaves in a whorl, there will be six vertical lines on the stem ; when four, eight ; and so on, just as in the case of opposite leaves there were four when the leaves were only two at each node. ,:, Verticillate leaves are said to be ternate, qttaternate, quinate. Sec, according as there may happen to be three, four, five, or a greater number of leaves. Coftstancy or irregularity of Phyllotaxis in Genera, Species, &c. — With a few exceptions, when the opposite or alternate mode of leaf-arrangement is found in a species, it is generally always con- stant in every individual of that species, and often also in all the species of the family. Yet, as seen in the snapdragon {Ajttirr- hintttn) and myrtle, both modes may occur in the same plant. In Dicotyledons, necessarily the first leaves must be opposite, though it does not always follow that they will retain this Phyllo- taxis throughout life, but may change to alternation, either in the early leaves or in those which come from the stem at a later period of life. Again, in Monocotyledons, the first leaves are necessarily alternate ; but, unlike Dicotyledons, they generally retain this arrangement through life. Though we are unable to find character in Phyllotaxis constant enough to aid us in classifi- cation, yet some orders are characterised by one kind, or by the prevalence of one kind, of Phyllotaxis — e.g., Labiatce by decus- sate ; Boraginacecs by alternate ; TiliacecE chiefly by distichous ; CinchoftacecB by opposite ; GaliacecE by verticillate, &c. Fascicled Leaves. — The pine, larch, &c., commence with a whorl of leaves, but subsequently bear alternate ones in the form of tufts or fascicles (fig. 125), which are "really the leaves of an axillary bud." In this case the axis has not lengthened, other- wise the leaves would be markedly alternate, as can indeed some- times be seen in the leaves of the larch, &c., which elongate into ordinary shoots, bearing alternate leaves. In these fascicles there may be two or more leaves, the number in a fascicle being char- acteristic of different species of Pinus. Lestiboudois, Brongniart, and other botanists, believe that the position of leaves, whether alternate or opposite, is closely connected with the arrangement of vascular bundles on the stem. When these bundles are arranged in two regular and equal groups, if the exterior bundles of each group unite, they form the midrib of the leaf, which in that case PHYLLOTAXIS; ABNORMAL ARRANGEMENTS. 1 93 corresponds to the interval of two groups, and the leaves are oppo- site. On the other hand, they are alternate vv^hen the vascular circle of the stem has undergone a modification in its elements. Abnormal Arrangements.— Occasionally we find some plants in which, owing either to the twisting of the stem or some abnormal- ity in the disposition of the leaves, the foliage does not come under any of the forms of Phyllotaxis we have already described. In Sola7ium Guineense, Lamk., the leaves are arranged in twos, in a twin-like manner, side by side on the same level on one side of the stem. Numerous different explanations have been tendered regarding this by Naudin, Wydler, Clos, Cauvet, and other bot- anists, with a resume of which we cannot, however, charge our space.^ Having now briefly given a sketch of the chief facts made out regarding Phyllotaxis, let us recapitulate in a few aphorisms the most salient points which we have already discussed somewhat more diffusely ; — 1. Alternate leaves are disposed in a continuous spiral line. 2. In taking any leaf as the starting-point, we always find sooner or later in the line of the spiral some leaf which is exactly superimposed on it. 3. The space of the spiral line stretched between two such corresponding leaves is the cycle. 4. The number of leaves necessary to form a cycle is generally the same for the individuals of the same species, but often varies in the different species of the genus. 5. This spiral Une may wind around the stem once, twice, or several times, before it lands at a leaf placed directly over the one it started with. 6. We express the disposition of leaves on the stem by employing a fraction, the denominator of which is formed by the number of leaves in the cycle, and the numerator by the number of turns of the spiral. 7. The more common arrangements may be represented by the following fractions : — 1113 S 8 13 Stro T> 31 g> T3> UTi 5T> O'C. 8. The fractions representing the composition of the various circles form a series in which each of these numbers is the sum of the numerator and deno- minator of the preceding fraction. 9. The angular divergence of leaves is the angle formed by each leaf with that which either follows or precedes it. This angle, it necessarily follows, comprises a fraction of the circumference of the stem. 10. The connection of the angle of divergence with the circumference of the circle is always expressed by the fraction which represents the circle. ^ For a description of some abnormalities in the cones of Pinus pinaster, see Professor A. Dickson in Trans. Roy. Soc. Edin., vol. xxvi. The cones de- scribed showed transition from one spiral system to another by what has been called "convergenceof secondary spirals." These transitions are due to the •ion of two consecutive scales in some one of the secondary spirals. The ndisturbed set of secondary spirals, as running continuous through the two stems, Dickson terms "constants." N 194 USES OF THK LEAF. 11. The spiral line, which touches all the leaves in its line, is the primary or generating spiral. 12. Independently of the generating spiral, there exist several others either to the right or to the left of the axis, which are very marked when the leaves are numerous and much crowded together ; these are the secondary spirals. 13. Secondary spirals never touch a consecutive series of leaves in describing their circles around the stem. 14. Numbering each leaf, we find that the blanks in the consecutive numbers which occur in the course of a secondary .spiral express the number of the secondary parallel spirals. 15. In order to ascertain the number of secondary spirals which exist in an assemblage of leaves or scales, proceed as follows : i. Number exactly each of the scales or leaves, and ascertain thence the generating spiral, which may not be at first apparent. 2. Determine the number of leaves or scales which constitute the cycle, that number being equal to the sum of the secondary spirals which wind to the right or left of the axis. 3. Ascertain the number of turns of the spiral comprised between the two extreme points of the cycle, that num- ber being always equal to less than the two numbers expressing the secondary spirals to the left and right. In this manner we arrive at a fraction express- ing the disposition of the leaves or scales. 16. Opposite or verticillate leaves alternate generally exactly in two succes- sive verticils. In this case they are decussate. 17. In some cases they are not exactly decussate, in which case the leaves describe a spiral. 18. Monocotyledons must necessarily be in their first stage alternate-leaved, and so in most cases remain through life. Dicotyledons must, on the contrary, be first opposite-leaved, but they do not always remain so in after-life.i USES OF THE LEAF. The main use of the foliage is to expose the crude juices to the action of the sun and light, and then to elaborate them for the use ^ Richard, 1. c, p. 127. Originally called attention to by Bonnet in 1799, and even possibly still earlier by Sir Thomas Browne, it is only within the last forty years, thanks to the researches of C. F. Schimper (Geiger's Magazin, vol. x.xviii., and as a separate publication), Alexander Braun (Acta. Acad. Caesar. Leop. Carol. Nat. Cur., vol. xv., 1831, and separate publication), the Brothers Bravais (Ann. des Sc. Nat., 1837 and 1839), and Alph. de Candolle, that we have attained to anything like determinate ideas on the subject. Of late years the subject has been tinkered by various inferior hands, but their observations are not of importance sufficient to occupy space by a reference to their publica- tion, or for the author to risk the responsibility of asking the student to waste liis time in perusing them in the hope of disinterring a useful fact from the insuffer- able quantity of pretentious verbiage in which it may be buried. An exception to this rule is, in addition to the paper of Alexander Dickson quoted, that by the same botanist on the Phyllotaxis of Lepidodendron and Knowia (Joum. Bot., 1870, p. 233), Airy's Memoir (Proc. Roy. Soc, vol. xxi.), and an Attempt to explain Phyllotaxis on the Principle of Natural Selection and the Survival of the Fittest, by Mr Chauncey Wright, originally read to the American Scientific Association, but which I only know from an abstract by Mr Bennett in ' Nature, ' 1872, p. 4. DURATION OF THE LEAF. of the growing plant. To do this it absorbs air through its stomata, or in the case of water-plants through its delicate epi- dermis, and also discharges by evaporation, in order to thicken the crude sap which it has drawn up from the stem, a large amount of moisture. The leaf is thus at once the stomach and the lungs of the plant. Its twofold functions may therefore be better considered when we come to discuss nutrition as a whole in the course of the next two chapters. DURATION, FALL, AND DEATH OF THE LEAF. Duration.— This is variable in different species and orders of plants. In some the leaves fall soon after their development, and are called fiigaceotisj while others are called evergreen, from the plant on which they are found seeming as if covered with the leaves all the year round. This is, however, not so in reality, for the leaves of the last season only remain attached to the stem until the development of those of the next spring, when they fall — the result, however, being that the plant is covered with a con- tinual mass of green leaves, which in popular belief are the same as it was clothed with in the former season. A common idea pre- vails that pine, and other trees of that order, do not shed their leaves. Any one who has, however, passed through a fir-wood and seen the thick carpet of the fallen acicular leaves, will be convinced that this popular notion is erroneous. The truth is, that in these trees the leaves are persistent often for several years — e.g., in the " Scotch fir " {Pinus sylvestris) for four, while in the firs, according to the observations of Schacht, and also of Cleghorn and Brandis,^ the leaves will often remain attached to the branches for ten or twelve years, and then fall.^ In tropical countries plants lose their leaves during the dry season, and develop their new ones during the rainy one, as in the "Catingas" of Brazil. A similar phenomenon is seen in some plants of more temperate countries. For instance, Anagyris fatida, a leguminous plant indigenous to Algeria and France, leafs in November, flowers in December, keeps its leaves during the winter and spring, finally ^ Journ. of the Agri.-Hort. Soc. of India, xiv. 272 (1867). * For instance, among the Himalayan Coniferse, the leaves of Piiius Webbi- ana and Abies Smithiana will remain attached for 8-10 years, those of Ccdrus Deodara 5 years, while those of Pmus longifolia and P. Gerardiana will only remain for from 2-3 years. Mr Meehan, following up the observations of Dr Alex. Dickson on the Phylloid shoots (or branches) of Sciadopitys vcrticillata (Proc. Bot. Congress, 1866, p. 124), considers that the true leaves of Coniferas are adnate with the branches ; that adnation is in proportion to vigour in the genus, species, or individual ; and that many so-called species of Coniferas are the same, but in various states of adnation. Since then similar views have been brought forward by Carri^re. 196 FALL OF THE LEAF. shedding them in summer after its seeds are ripe. In Ferula glauca, Canarina Cainpanula, and Cerinthe major, we see much the same thing; they produce their leaves at the approach of winter, after being bare all summer. Climate has a great effect on the fall of the leaf. According to some recent observations by M. Sagot, it appears that vines and various European fruit-trees transplanted to the Canary Islands, do not there lose their leaves at the approach of winter, as in temperate countries, but they fall slowly one by one — so that the trees are rarely entirely denuded, the next year's leaves having appeared before the last season's have fallen. In most plants, however, of temperate countries, the leaves are produced in spring, last through the summer, get discoloured in autumn, and finally get stiff and lifeless, and fall at the approach of winter.! Such leaves are, in contradistinction to the fugacious and evergreen ones, said to be deciduous or caducotis. It is a com- mon impression that it is the action of the frost which causes the fall of the leaf. This is not so. When leaves are nipped by the frost they become black, but often remain long attached to the branches in that condition. " Death, indeed, is often more a con- sequence of, than a cause of, the fall of the leaf;" but leaves fall often long before the vitality has departed from the tissues of which they are composed. Again, in palms and most endogenous plants — familiarly in grasses — the leaves die, get brown and dry, but still remain attached to the stem : and in some exogenous trees even — as the beech and oak — the leaves will remain through the winter attached to the stem, though their vitality is to a great extent gone, and only fall when the new buds expand with the spring ; such leaves are said to be marcescent. We must therefore distinguish between the fall and the death of the leaf. Fall. — The apparently simple act of a leaf falling to the ground is an important physical act ; but its prior detachment from the branch is not less a complicated physiological phenomenon, and has given rise to numerous rival explanations of the mechanisms involved in the process. Schacht, Mittenius, Mohl, Inman, and others, have in late years paid attention to the subject; but Mustel, Murray, Vrolik, Link, and De Candolle, have equally put forward rival theories of the mechanism of the fall of the leaf. Perhaps the explanation given by Inman is that most consonant with facts, and this we shall adopt. First, however, let us premise that the separation is caused by an articulatiott or joint, which forms between the basal end of the petiole and the stem to which it is attached. " The formation of the articulation is a vital process, a kind of disintegration of a transverse layer of cells, which cuts off 1 It is rarely, however, that all the leaves on a plant last the whole summer— the lower or earlier foliage usually perishing while fresh leaves are being pro- duced above. DEATH OF THE LEAF. 197 the petiole by a regular line, in a perfectly uniform manner in each species, leaving a clean scar at the insertion. The solution of continuity begins in the epidermis, where a faint line marks the position of the future joint while the leaf is still young and vigor- ous ; later the line of demarcation becomes well marked, internally as well as externally ; the disintegrating process advances from without inwards, until it reaches the woody bundles : and the side next the stem, which is to form the surface of the scar, has a layer of cells condensed into what appears like a prolongation of the epidermis ; so that, when the leaf separates, the tree does not suffer from the effects of an open wound. The provision for the separ- ation being once complete, it requires little to effect it, — a desicca- tion of one side of the leaf-stalk, by causing an effort of torsion, will readily break through the small remains of the fibro-vascular bundles ; or the increased size of the coming leaf-bud will snap them : or if these causes are not in operation, a gust of wind, a heavy shower, or even the simple weight of the lamina, will be enough to disrupt the small connection, and send the suicidal member to its grave. . . . The fall of the leaf is not an accidental occurrence, arising simply from the vicissitudes of temperature and the like, but a regular and vital process, which commences with the first formation of the organ and is completed only when it is no longer useful ; and we cannot help admiring the wonderful provision that heals the wound even before it is absolutely made, and affords a covering from atmospheric changes before the part can be subjected to them." ^ It follows, then, that in exogenous plants in which the leaf is united to the stem or branch by a moderate -sized articulation, it will fall either at the commencement of the winter, or, if it survives through that season, the enlargement of the circumfer- ence in woody plants in the spring will assuredly detach it. The same is true of leaves which fall at other seasons. In endogen- ous plants, however, in which there is no distinct articulation, and the base of the leaf is expanded into a sort of ochrea, as in grasses, the leaf dies, but remains attached in a dry and lifeless state. Death. — The reason why leaves are only temporary, and of one season's duration, is as follows : The water absorbed by the root and carried up into the leaves is impregnated with a greater or less amount of mineral matter, according to the character of the soil in which the plant grows ; the moisture exhaled is pure water, and accordingly the lime or other earthy matter remains behind, incrusting the walls of the vessels and cells, until, in the course of time, they are entirely choked up, and the leaf must die for want ^ Inman in Henfrey's Botanical Gazette, i. 61, teste Gray, 1. c., p. 173 ; and in Proc. Lit. and Piiil. Soc. of Liverpool, iv. 89. See also Ledeganek in Bull. Sec. Bot. Be'g., t. X. (1872). 198 AUTUMNAL COLOUR OF LEAVES. of the necessary nourishment. Accordingly, we find that leaves in the autumn contain much more mineral matter than in the spring, and their vitality is more or less active in proportion. Thus when the leaf falls it returns to the soil a certain amount of the inor- ganic ingredients which the root has extracted from it in the course of the growing season. Autumnal Colour of Leaves.— As the vessels of the petiole, &c., get closed by the inorganic deposits described, the leaf generally changes from the usual green to the various colours characteristic of the autumnal foliage of the different species. In some species — such as birches and willows— they assume a yellowish colour. In Czssus quinquifolia the colour is bright red. In the broad- leaved American maple {Acer macrophylhwi) it is yellow. In the vine the colour of the autumnal leaf is also red, and the degree is in proportion to the darkness of the fruit, the black-fruited grapes having the leaves dark, while the red ones are lighter coloured ; finally, in the white-fruited varieties the leaf is either yellow or feebly reddish. It is this variety of the coloration of leaves before their fall which gives a peculiar beauty to woods in the autumn — a charm even greater than they possess earlier in the year. It is probable that these changes in colour are due to changes in the chlorophyll by oxidation, though some chemists have traced them to the production of special products of a waxy nature — viz., erythrophyll, which is red, and xanthophyll, which is yellow. Lastly, it must be mentioned that Mr H. C. Sorby has announced that he has detected in the leaves of different plants several dozen colouring matters — and far more in the petals and fruits — which number, he believes, will even be much increased by further research. Many of these colouring matters, which give the various tints to foliage, are mixed up together, so that analysis is by no means easy. He has, however, divided them into five great groups, the members of each group being related to each other not only chemically and optically, but having also a similar connection with the growth of plants. These groups are : i. The Chlorophyll group, distinguished by being insoluble in water, but soluble in alcohol and bisulphide of carbon. 2. The Xantho- phyll group, insoluble in water, but soluble in alcohol and in bisul- phide of carbon, comprising two substances common in leaves — one being more and the other less yellow. 3. The Erythrophyll group, soluble in water, in alcohol, and in ether, and insoluble in bisulphide of carbon. Those met with in leaves are more or less purple, made bluer by alkalies, and redder by acids. 4. The Chrysotannin group, soluble in water, in alcohol, and in ether, but insoluble in bisulphide of carbon. This group contains a great number of yellow colours, some so pale as to be nearly TERATOLOGY OF THE LEAF. 199 colourless, and others of a fine dark golden-yellow. 5. The Phaiophyll group, insoluble in bisulphide of carbon, but of very variable solubility in water and alcohol. It comprises a number of more or less brown colours. The various tints of foliage depend, according to Mr Sorby, almost entirely on the relative and absolute amount of these various colours ; but still much requires to be done before we are well acquainted with all these relationships. In the mean time, however, the classification of De Candolle (Section V.) may be received as meeting the present state of inquiry on the subject.^ Irregulaiity in Appearance of the Leaves. — In most plants the leaf appears in spring before the flowers ; but to this rule we must make exception in favour of the ash, hazel, Daphne Mezereum, some species of Calycanthus, and frequently the various species of willows. In Colchictini and saffron the flowers develop in autumn and the leaves the spring following. On most trees the first leaves show themselves on the upper branches, but in Stercularia platani- folia there is an exception. In the " nettle-tree " of the south of Europe {Celtis australis) there is another abnormal foliation. In spring certain branches distributed irregularly on the top of the tree are covered with perfectly developed leaves and flowers, whilst upon others the buds are not even swollen by the spring sap.^ TERATOLOGY OF THE LEAF. Among rnonstrosities to which leaves are subject may be men- tioned fission or division into two or more parts, though some leaves constantly exhibit this process of fission {Salisbiiria adianti- foHa, &c.) We often see this in the fronds of ferns, the tips of which bifurcate or even trifurcate. Dr Masters gives a list of about eighty species of flowering plants which have been noticed as subject to this malformation. Phyllomania is when there is an unwonted developm'ent of leafy tissue ; pleiophylly is when there is an absolute increase in the number of leaves starting from one particular point, as "well as those in which the number of leaflets in a compound leaf is preternaturally increased." The leaves of Heteracentron macrodon have been known to produce leaflets from their upper surface, and to this monstrosity Morren has applied the term autophyllogeny. The four-leaved shamrock {Trifolhim repens) is an instance of a compound leaf producing an extra number of leaflets ; but five and six adventitious leaflets are almost as com- 1 See Sorby, Proc. Roy. Soc, .\v. 433, xxi. No. 146 ; Phil. Mag., xxxiv. (1867) 144 ; Quart. Journ. Mic. Sc., 1869, p. 43, 358 ; Month. Journ. Mic. •Sc., iii. (1870) 229 ; Quart. Journ. Sc., n.s., ii. {1870) 64; Nature, 1871, p. 341. " Charles Martins in Revue horticole, 1857. 2 00 TERATOLOGY OF THE LEAF. mon as four, and a case is recorded in which seven leaflets were borne by the clover. Frondiferous leaves have much the appearance of branches provided with leaves, and this condition merges into that of Gesnera, Cardamijie, &c., in which an adventitious bud is placed on the surface or edges of the leaves. Some Begonias form con- necting links between the two conditions. In them the branchlets (ramenta) become leaf-like and bear small bulbils in the axil. Equally with the leaf the stipules are subject to a teratological in- crease in number. Polyphylly is the term applied when the mem- bers of any particular whorl are increased in number, the whorls themselves not being necessarily augmented. Leaves sometimes unite to each other by their surfaces, or even unite to the axils from which they spring. In the lime, the leaf and bract naturally unite to the peduncle. Adventitious leaves may form in various ways and in unusual situations. They have been seen to be produced from the hip of the rose, the ovary of the Nymphcea, &c. ; or leaves may be produced on a usually leafless inflores- cence. They may be produced in place of flower-buds, and the case of viviparous plants is one in which we see either the peti- ole or a part of the inflorescence so altered. Cornute leaves are those in which the midrib, after running for a certain distance, suddenly projects, often in a plane different from that of the leaf; then, if another part of the blade is attached to it, an interrupted leaf, as seen in some varieties of the hart's-tongue fern (Scolopen- drium vtilgare) and Codiceicm variegatiim, is produced. A co- hesion of parts will sometimes produce an apparent displacement or disarrangement of the phyllotaxis. The elongation of water- leaves, to keep pace with the corresponding growth of the stem, is well seen in Ranunculus fiuitaiis, &c. These and other terato- logical variations of the leaf lead Dr Masters to the following conclusions : " In many cases of so-called metamorphosis it is the sheath of the leaf that is represented, and not the blade. In nor- mal anatomy the sepals, petals, carpels, and even the stamens, as a general rule, correspond to the sheath rather than to the blade of the leaf, as may be seen by the arrangement of the veins. The blade of the leaf seems to be set apart for special respirator}' and absorbent offices, while the sheath is in structure, if not in office, more akin to the stem. It would not be easy, apart from their position, to distinguish between a tubular sheathing leaf and a hollow stem. The development of adventitious growths ... is closely connected with the fibro-vascular system of the leaf, so that no sooner does a new growing part originate, than vessels are formed to connect the new growth with the general fibrous cord."' From this M. Casimir de Candolle is led to consider the leaf a composite structure. The morphological unit is, according to 1 Teratology, p. 477. MODIFICATIONS OF THE LEAF, 20I him, the growing point and its corresponding fibro -vascular bundle.^ MODIFICATIONS OF THE LEAF. These may be arranged in systematic form, chiefly as regards (i) their situation ; (2) their attachment ; (3) their configuration ; (4) their direction ; (5) the state of their surface ; (6) their colora- tion ; (7) their nervation ; (8) their duration ; (9) their divisions ; (10) their composition ; and (11) their substance. I. Situation. Seminal (folium seminale), when in the embryo, and then called cotyledons. Primordial, the first leaves produced above the soil. Usually both coty- ledonary and primordial leaves are only temporary, and accordingly perish soon after the ordinary leaves are developed. Radical (radicale), leaves developed from the root. E.x. Primrose, Plan- tago. Anemone Pulsatilla, &c. ; they frequently differ in shape and size from the others (fig. 117). Cauline, raineal (caulinum, ramium), borne at some height on the stem or branches. Ex. Polemonium cceruleum (Jacob's ladder), Paris quadri- folium (herb Paris), &c. Floral (florale), applied to the leaves out of the axes of which the flowers arise, and which in colour and texture do not differ from ordinary leaves. If they are different from ordinary leaves in these two respects they are called bracts. II. Attachment. Sessile (sessile), without a petiole. Ex. Green Alkanet [Anchusa semper- vivens), common butterwort {Pinguicula vulgaris), mint {Mentha syl- vestris), see p. 147. Amplexicaule, or embracing (amplexicaule). Ex. Homed or sea-poppy (Glaucium luteum), the common poppy {Papaver somniferum), field gentian {Gentiana campestris), &c. Semi-amplexicaul is applied when the petiole only surrounds a portion of the stem. Perfoliate (perfoliatum), when the limb appears as if perforated (Lonicera) by the stem. Ex. Hare's-ear or thorow-wax [Buplevrum rotundi- folium), honeysuckle, &c. Connate (f. connata, f. coadnata), opposite leaves, united one to another by the base. Ex. Yellow- wort {Chlora perfoliata), fuller's teasel {Dip- sacus fullonuin), soapwort (Sapotiaria officinalis). Decurrent (decurrens), when the substance of the limb prolongs itself in the form of a wing down the stem, below the point of attachment. Ex. Bog asphodel {Narthecium ossifragum), comfrey {Symphytum officinale), spea.r thistle {Carduus lanceolatus), &c. Petiolate (petiolatum), furnished with a petiole. Ex. The majority of leaves, oaks, hawthorn, chestnut, &c. Vagittate (vaginaris), having a sheath which surrounds the stem. Ex. Most grasses— Phleum alpinum (Alpine Timothy-grass;, Sea- Maram {Psamma arenaria). ^ Th^orie de la Feuille, p. 26 {teste Masters, 1. c.) 202 MODIFICATIONS OF THE LEAF. III. Configuration.! '' Orbicular e (orbiculare), or peltate (shield-shaped), forming a circle, with the petiole inserted near the middle. Ex. Victoria regia, and Brasenia peltata (water-shield, N. O., Cabombacea). It is simply a cordate leaf with the auricles united. However, precise examples are rare (fig. 128). Subrotund (subrotundum), approaching to the circular form. Ex. Winter green {Pyrola rotundifolia), loosestrife (Lys- itnachia repetis), round-leaved mint (Me7itha rotundifolia), &c. Ovate (ovatum), in the form of a flattened egg, the broadest end at the base. Ex. Large periwinkle ( ViJtca majcr). It is one of the most common forms of leaves. Obovate (obovatum), the reverse of the above. Ex. Primrose, and daisv , Fig- --Simple peltate [Bellis perermis). leaf of Indian cress t^,?-.,- ■ / .,. \Tropceoluvimajus, L.] Elltpttcal (ellipticum), m the form of an ellipse, or without either extremity larger than the other. Ex. Lily of the Valley, and other Con- vallaricB, Hieraciuin repens, van Oblong (oblongum), three or four times as long as broad, and with a rounded extremity. The term is used with great latitude, \ and is often vaguely applied to contrast a not very decided form with one which is round, ovate, linear, or other precise form, /"r/f^w^^/ar (triangulare), three prominent "angles, without refer- ence to their measurements or direction." Ex. Goosefoot [Chettopoditim), scurvy-grass (Cochlearia Danica), and birch (Betula alba). Quadrangular (quadrangulare), with four angles. Ex. Tulip-tree (Liriode7idro7i tulipifera). Z)«//<7z^^ (deltoida), trowel-shaped, "having three angles, of which the terminal one is much further from the base than the lateral ones." Ex. Good King Henry {Clunopodium Bonus Henricus). Rhomboid (rhombeum), rhomboid or diamond-shaped, approach- ing a square. Ex. Trapa uatans (floating leaves), stinking goose-foot {Chenopodium Vulvaria), &c. The four forms above named are not very constant, and are by some authors merged as varieties of some of the others named. Long use has, however, made it convenient to retain them. Paiiduriforvi (panduriforme), fiddle-shaped, broad at the two ex- tremities, and contracted in the middle, like a fiddle (irai^oCpa). Ex. Fiddle-dock [Ruviex pulcher). Laiiceolate (lanceolatum), narrow oblong, and tapering towards a point like a lance. Ex. Ribwort plantain {Plantago lanceo- lata), wild tulip (Tttlipa sylvestris), Sic. Spathulate (spathulatum), in the form of a spatula — i. c., enlarged towards the summit. Ex. Water - chickweed (Montia /on- tana), Silene otites (Spanish campion). Gene- ral Con- tour. I As regards simple leaves. MODIFICATIONS OF THE LEAF. 203 Gene- ral Con- tour. (Linear (lineare), ribbon-shaped— z. c. , long, narrow, with parallel ' sides, and about an equal breadth throughout. Ex. Most grasses. Acerose is a closely allied form. Such leaves are needle-shaped, j linear, and evergreen, generally acute and rigid (firs). {subulate (subulatum), shaped like an awl (subula) — i. e., very straight and pointed, generally stiff. It is also only a variety of the above. Ex. Yews, junipers. It is sometimes applied to leaves tapering from a thickish base to a point (e.g., Salsola Kali). 130. 132. 133- 138. Fig^ures showing the different forms of the apices of leaves. Fig. i29,retuse. Fig. 130, apiculate. Fig. 131, bifid. Fig. 132. emarginate. Fig. 133, mucronate. Fig. 134, cuspi- date. Fig. 135, tridentate. Fig. 136, cirrhose. Fig. 137, acute. Fig. 138, acuminate. Summit. ( f Acute (acutum), narrowing insensibly to a point. Ex. Pale flax {Limcm angustifolitim), lady's slipper [Cypripedium), &c. (fig. 137). It is a very common form. Acuminate (acuminatum), narrowing more or less abruptly just below the summit into a kind of sharp point. Ex. Common reed (Arundo phragmites), sea -sedge (Scorpus maritimus), &c. (fig. 138). Mucronate (mucronatum), surmounted by a little point (mucro). Ex. Thistles, butcher's - broom (Ruscus aculeatus), &c. (fig. I33-) Cuspidate (cuspidatum), surmounted by a stiff sharp spine, more distinct from the rest of the leaf than in an acuminate leaf. Ex. Sea-lavender (Statice Limonum), (fig. 134). It is, however, often used in the same sense as acuminate. Aristate is used when the point is of a hair-like fineness. Obtuse (obtusum), blunt, and more or less rounded at the summit. Ex. Primrose, snowdrop, Hypericum quadrangulum. Truncated (truncatum), cut across transversely at the extremity. Ex. Liriodendron tulipifera. Retuse (retusum), marked at the summit with a broad, more or less shallow sinus. Ex. Rumex digynus (fig. 129). Emarginate (emarginatum), with a more or less angular notch at the summit, which is generally more acute than in the preced- V, ing cases. Ex. Bladder senna (Colutea arbor esce7is), (fig. 132). ( Cuneate (cuneiforme, cuneatum), when broadest above the middle. Base, -s with an acute tapering base, something like a wedge (cunem). V Ex. Saxifraga tridactylites. MODIFICATIONS OF THE LEAF. ■ Flabdliform (flabelliforme), fan-shaped or broadly cuneate, and rounded at the top. Ex. The leaves of most Palms, Salisburia asplenifolia, &c. Truncated, ^with the base or apex truncated, rounded, &c. Rounded, &c., j Vide tit antea (figs. 130, 131, 135, 136). Cordate (cordiforme, cordatum), ' ' heart-shaped, " with the two sides of the laminae, on either side of the petiole, rounded (forming auricles, or "little ears"), and with a sinus between the two, giving it somewhat the form of a heart (cor), as seen in playing- cards. Ex. Black bryony ( Tamtis communis). Reniforin (reniforme), " kidney-shaped," with a sinus in the middle, and forming two large lobes on either side of the petiole, the leaf broader than long. Ex. Asariim EuropcBum, Sibthorpia Etcropma, Oxyria reni/ormis, &c. Sagittate (sagittatum), shaped like an arrow (sagitta)— z. e., pro- longed at the base, with two equal, angular, acute lobes, the points of which are parallel, and with a deep triangular notch between them, in the middle of which the petiole mns. Ex. Water-soldier {Sagittaria sagittifolia), sorrel-dock (Rumex . acetosa). Hastate (hastatum), " halbert-shaped " — i. e., prolonged at the base into two acute diverging lobes. Ex. Cuckoo-pint (Arum maculatuvi), Rumex Acetosella, &c. Lumilate or falcate (lunulatum, falcatum), crescent-shaped, like a half-moon or a scythe, when the curved auriculse are directed towards the stalk or from it. Ex. Passiflora lunata. IV. Direction. Erect (erectum), so placed as to approach towards the stem. Ex. Ju>tcus articulatus (bulrush), Typha latifoHa, Sagittaria, &c. — Or even it may be nearer, and in contact with it, when the leaf is said to be adpressed (adpressum). Ex. Zeranthemum sesamoides. Paiulate (patens, patulum), or very patulate (patentissimum), or hori- zontal, making an angle with the stem of about 45° in the first case, and at right angles in the second. Ex. Sea-purslane {A triplex por- tulacoides), snap-dragon {Antirrliinum vulgare), of the first ; while Gentiaiia campestris and Nepeta Glechoma (ground ivy) are good ex- amples of the second form. In-flexed, incurved (inflexum, incurvum), curved with point towards the stem. Ex. Erica impetrifolia. Reflexed or recti7iate(x&^e.yiuxr\), with the summit curved towards the base. Ex. Erica retorta. — And if this is carried further, then it is/(?«Toi', a plant. 2 Forchammer in Journal flir Prakt. Chem., s. 36 ; Anderson, Trans. High- land and Agric. Soc, 1855-57, p. 349. ' Risse in Sachs' Experimentale Physiologic (French trans.), p. 143. 230 USES OF MINERAL INGREDIENTS OF PLANTS. C/ilon'ne (CI)— The probabilities are that it is present in all plants, and is essential to their growth. In nature it is usually as- sociated with sodium in the form of common salt: and in this form they most likely both enter the plant, for when the one is present in large quantity, the other exists in corresponding quantity. In wheat the average amount of chlorine is only 0.08 per cent. In the stems of plants which grow in soils containing much common salt, such as strand and marine plants, chlorine is very abundant. Still there is a doubt as to whether it is absolutely indispensable to the life of the plant,— Salm-Horstmar, LeyJhecker, Birner, Lucanus, Nobbe, and Siegert thinking that a minute trace is es- sential; while Knop takes a contrary view, as the result of his ex- periments with the maize plant. As far as agricultural plants are concerned, it is probable that chlorine, if indispensable, zs essential to plants only in minute quantity — buckwheat, vetches, and per- haps peas, requiring a greater quantity, and the foliage and suc- culent parts of a plant containing a considerable quantity, which may, however, be " not indispensable to the life of the plant." Strand plants require chlorine, but whether united to potas- sium or sodium is immaterial. Regarding the functions of chlorine, Johnson remarks that both Nobbe and Leydhecker found that buckwheat grew quite well up to the time of blossoming without chlorine; and that the use of it, according to these experimentalists, is to assist in transferring the starch-gran- ules which are organised in the mature leaves to the newer organs, and especially to the fruit. In the absence of chlorine, the terminal leaves of buckwheat became thick and fleshy, from extraordinary development of cellular tissue ; " at the same time they curled together, and finally fell off upon slight disturbance. The stem became knotty, transpiration of water was suppressed, the blossoms withered without fructification, and the plant prema- turely died. The fleshy leaves were full of starch-grains ; and it appeared that, in the absence of chlorine, the transfer of starch from the foliage to the flower and fruit was rendered impossible." Silica (Si 02)is a variable element of plants, and is "alwa3fs pre- sent in the ash of agricultural plants when they grow in natural soils." In wood-ash it ranges from i to 3 per cent, often 10 to 20, or even in the pine up to 30 per cent. Turnip-leaves contain 3 to 10 per cent, oat 11 to 58 per cent (especially in the stemj, lettuce 20 per cent, oak-leaves 31 per cent, and beech-leaves 26 per cent The cuticle of many plants contains a great amount of silica — this giving the stability of stem to many herbaceous plants, and the hardness of wood to arboreal species. The Cauto tree of South America {Hirtella silica) has the texture of soft sandstone, and speedily blunts the woodman's axe ; and in Trinidad the natives mix its ashes with clay to make pottery. The bark yields 34 per USES OF MINERAL INGREDIENTS OF PLANTS. 23 1 cent of ash, of which 96 per cent is silica.^ The ash of the well- known bamboo contains 70 per cent of silica, and the joints of the stem often contain concretions known as Tabasheer, which Russel and Smithson (Macie, the founder of the Smithsonian Institution) discovered to be a hydrated silica.^ The ash of the common " Dutch " or " scouring rushes " (so called because in Holland they are used to polish brasses) contains 97.5 per cent of silica. The actual amount of silica in the different British species of Eqnisetuin varies from 6.30 per cent in Equisetum arvense, to 23.61 per cent in Equisetum Telmateia. The ash of the straw of most of the cereals and grasses contains silica to the amount of from 40 to 70 per cent. Hence burnt straw is used to give a last polish to marble. After a hay-stack has been burned down, frequently little stony masses may be found among the ashes. These are composed of melted silicates. In the Characecz there is a curious variability of the substance which gives the hard incrustation to their thread- like leaves. In Chara transluceiis it is silicic acid, in C. vulgaris silicic acid and carbonate of lime, and in Chara hispida carbonate of lime solely. In the Carices and Juncacece there is also much of this substance. In all these plants the cuticle is richest in silica. It has also been found by Wottstein that the oldest parts of plants contain most silica. In the ash of the wood of a " Scotch fir" {Pinus sylvestris) 220 years old there was found 32.5 per cent, and in one 135 years old only 15. i. In the bark of the same tree, at the two ages given, the amount of silica varied from 30.3 per cent to 1 1.49 per cent. The leaves of pines which are destitute of silica in spring are rich in autumn. This rule about the oldest parts being richest in silica is not, however, without exception — the chaff of cereals and the seeds of Coniferee being richer in silica than the stem, leaves, or wood. Kindt, Wicke, and Mohl have also demonstrated that the hairs of nettles are highly silicious. The permanence of the bark of some trees has even been attributed, according to John- son, to the silica in it. The bast fibres of common hemp, manilla htm^{Mtisa textilis), aloe hemp {Agave Ainericatia), common flax, and New Zealand flax {Phormium tenax), all contain much silica. In jute {Corchorus textilis) some cells are partially incrusted also ; so that Wicke suggests that the durability of textile fibres " is to a degree dependent on their content of silica." From the great variability observed in the same plant as to the percentage of silica, it would seem in part to be an accidental ingredient of the vegetable kingdom ; and evidence is not wanting in the experi- ments of Sachs to show that it is not a necessary ingredient to the prosperity of all plants — maize, for instance. Plants have been grown successfully without silica by Sachs, Knop, Nobbe and ^ Wicke, Hinneberg's Journal, 1862, p. 143. Phil. Trans., 1790 and 1791. 232 USES OF MINERAL INGREDIENTS OF PLANTS. Siegert, Stohmann, Rautenberg and Kuhn, Birner and Lucanus, Leydhecker, Wolff, and Hampe, some of whom have shown that the amount of silica in a plant may be increased or diminished artificially. It thus appears that "very little will suffice their needs, and highly probable that it is in no way essential to their physiological development," and " that the notion attribut- ing the 'laying' of corn to a deficiency of silica in the straw is highly erroneous." The unqualified truth of the very generally accepted idea that the use of silica is to give rigidity to the stems of plants, and so enable them to bear the weight of the fruit, is embarrassed by the fact that the silica is not always found in those parts of the plant which on this idea most require it, and that the lower sheathing part of the leaf of most cereals and grasses conduces as much to the support of the plant as the stem itself. The idea that the stiffness of the straw depends on silica is not altogether true ; and the theory that silica applied to crops will strengthen the stem, and keep them from "laying," is founded on an erroneous idea of its function in plant-life, which function is not yet settled. Lithium (Li.), Fluorine (F.), and Tita7tium. (Ti.) — Salm-Horstmar considered that a minute quantity of these elements was necessary to the fruiting of barley, and the same observer considered that a trace of titanic acid is also a necessary ingredient of plants. Later observations rather go to demonstrate the fallacy of this idea ; but it is just possible, as Mulder has suggested, that exhaustion of soils is sometimes due to the exhaustion of some of the less abundant and usually overlooked ash ingredients. Rubidium (Rb.) has been found in sugar-beet, tobacco, coffee, tea, and grapes, and along with Casium (Cs.) is most likely present in many other plants. Probably they may help the growth of plants, yet Birner and Lucanus declare that when potash is absent they act as a poison on the oat-plant. Zitic (Zn.) — Alexander Braun and Risse show that zinc is an in- gredient of plants in the vicinity of zinc-mines, where the soil con- tains a carbonate or silicate of that metal. In the ash of Thlapsi alpestre, van calaminaris, Risse found 13 per cent of oxide of zinCj and in other plants from 0.3 to 3.3 per cent. It thus appears that the presence of this metal causes marked varieties in certain plantSj as witness the variety mentioned and the van calaminaris of Viola tricolor. Copper (Cu.), Arsenic (As.), Baryta (Ba.), Lead (Pb.), ajid lodint (I.), have all been discovered in the ash of plants ; but what use they serve, or whether essential to all plants (Iodine appear- ing to be essential to many algs only), is not certain, as indeed is also the history of the occurrence and use of the last ten USES OF MINERAL INGREDIENTS OF PLANTS. 233 substances mentioned, which, unlike the former five, can only be classed as accidental constituents of plants. Karl Miiller, in summing up the researches of Prince Salm- Horstmar on the food of the oat, defines the use of the different mineral ingredients in these words: "Without silicious earth, that plant cannot acquire sufficient strength to sustain itself erect, but forms a creeping stem, feeble and pale; without calcareous earth it dies even before the appearance of the second leaf; with- out soda and without potash it never attains a greater height than between 4 or 5 inches ; without phosphorus, though growing straight and regularly formed, it remains feeble, and does not bear fruit ; when iron is present in the soil it gives that deep-green tint so familiar to us, and grows rapidly robust ; without manganese it develops in a stunted manner, and produces few flowers." How far this simple generalisation is correct, the student will have been able to judge for himself from the facts already stated. Absorption of excess of Ash Ingredients by Plants. — That plants can take up more mineral ingredients than are indispens- able to them has been long ago proved by the experiments of De Saussure, and more recently by other chemists. Saussure found that the ash ingredients of some peppermint plants in their normal state were 40.3 per cent, but that under artificial cultivation this increased in 2^ months to 62 per cent ; so that it follows that the surplus was in excess, and accidental. It has also been shown that the ash ingredients of a plant may be increased artificially. These superfluous ash ingredients, Johnson shows, may be disposed of variously : (i.) They may remain dis- solved in and diffused throughout the juices of the plant; or (2.) exude from the surface as efflorescence, and be washed off by the rains, the latter appearance being repeatedly observed in the case of cucumbers and other kitchen vegetables. Saussure also found that " foliage readily yields up saline matters to water " if immersed in that liquid. By this treatment hazel-leaves lost in eight immer- sions of 15 minutes each jV of their ash ingredients. (3.) These insoluble matters may be deposited in crystals in the cells, or may incrust the cell-wall, and thus be set aside from the sphere of vital action, as in the case of cystolithes of sulphate of lime, &c., in many plants, which have been already noticed. (4.) Some plants absolutely excrete mineral matters, as is the case with Saxifraga incrustata found in lime soils, the leaves of which are " entirely coated with a scaly incrustation of calcium carbonate, mixed with some magnesium carbonate. At the edge of the leaf this incrus- tation acquires a considerable thickness." linger found that the undried leaves yield 4.14 per cent of carbonate of lime, and 0.82 per cent of carbonate of magnesia. The same botanist found that this excretion of carbonates " proceeds mostly from a series 234 HOW THE ASH INGREDIENTS EXIST IN THE PLANT. of glandular expansions at the margin of the leaf which are directly connected with the sap-ducts of the plant." ^ How the Ash Ingredients exist in the Plant.— This is not exactly known. In some plants {e.g., oat) much of the ash matter is in a soluble form ; and in the clover, the ash matter, according to Hellriegel, is more soluble in the young than in the old plant. Sulphates also may be absent from the plant, though present in the ash. Arendt found no sulphates in the lower joints of the stem of the oats after blossoming, though in the upper leaves at the same period there was present 7 per cent of sulphuric trioxide (SO3). There are many similar instances. To sum up the result of our inquiries regarding the use of the mineral ingredients of plants, we may say in a sentence that though the subject is yet involved in doubt, the use (i.) of the sul- phates is to produce the albuminoids and the sulphurised oils of the onion, mustard, horse-radish, turnip, &c. (2.) That the use of the phosphates is to elaborate the phosphorised oils ; and when found in the cereals, the explanation of their presence is, that " the soluble albuminoids which are formed in the foliage must pass thence through the cells and ducts of the stem into growing parts of the plant and into the seed, where they accumulate in large quantity." But as the albuminoids penetrate membranes with great difficulty and slowness in the pure state, potassium phosphate considerably increases the diffusive rate of albumen, and thus facili- tates its translocation in the plant. (3.) The alkalies and alkali earths are concerned in the formation of organic acids (Johnson). We are, however, yet in the dark as to why no vegetable cell can be formed without lime or potash ; or why magnesia, lime, or almost any other substance, is essential to the life of the vegetable organism. COMPOSITION OF THE PLANT IN SUCCESSIVE STAGES OF GROWTH. Professor Johnson, in his work on the chemistry of plants, de- votes considerable space to this subject, narrating at length the researches of Norton, Arendt, and Bretschneider, chiefly in rela- tion to the composition of the oat-plant. In a botanical work it is unnecessary to go at any length into this question, further than to refer the student to this treatise for details which may con- cern him as an agriculturist or a chemist. So far as the bo- tanist is concerned, the general 'facts may be summarised as follows : Plants alter in composition as they develop. The observers named divided the growth of the oat- plant into five 1 Sitzungsberichte der Wiener Akadam., 431, s. 519 {/frfc Johnson). COMPOSITION OF THE PLANT AT DIFFERENT PERIODS. 235 periods: the ist being i8th or 19th June; the 2d, between June 30th and July loth ; the 3d, July loth and July 21st; the 4th, between July 2ist and July 31st; and the 5th and last, between July 31st and August 6th, — when on an average of the different observations the grain had ripened. It was found that the total weight of the crops increases in the first three periods, then lessens. The total weight of dry matter increases through the whole season, but the water of the crop lessens during the fifth period only. The period of blossoming is the period of most active growth. " Afterwards the rate of growth diminished by more than one-half, and at a later period increased again, though not to the maximum." The proportion of volatile to non-volatile matters varies slightly with the growth, and it was found that " plants produce more amyloids and less albuminoids as they matured. In other words, the plant requires a change of diet as it advances in growth." The daily increase was most marked when the plant was " heading out," or getting into ear. The following table shows these facts in a graphic form. The quantity of each proximate element in the ripe plant is assumed as 100 : — Fibre Fat Amyloids Albuminoids Ash per cent. per cent. per cent. per cent per cent. ist period, 18 20 15 27 29 2d rr 81 50 47 45 55 3d " 100 85 70 57 79 4th ri 100 100 92 90 95 5th „ 100 100 100 100 100 gain during the period was as follows :- Fibre Fat Amyloids Albuminoids Ash per cent. per cent. per cent per cent. per cent. ist period, 18 20 15 27 29 2d '• 63 30 32 18 26 3d II 19 35 23 12 24 4th II 0 15 22 33 16 5th ,1 0 0 8 10 5 The migration or translocation of mineral ingredients from one part of the plant to another during the growth is very curious. For instance, it is shown that the growth of the stem, leaves, and ear, most probably takes place at the expense of the roots ; and that a transfer of amyloids probably, and albuminoids certainly, goes on from the leaves through the stem into the ear. Silica and chlorine do not appear to be subject to any noticeable change once they are fixed in the plant. Phosphoric pentoxide on the other hand, passes rapidly from the leaves and stem into the fruit in_ the earlier and later stages of growth. Sulphuric trioxidc migrates rapidly after the blossoming of the plant from the lower stem, which then contains none. "It is almost certain. 236 SOILS AND ROTATION OF CROPS. then, that sulphuric trioxide originates, either partially or wholly, by oxidation of sulphur, or some sulphurised compound in the upper organs of the oat." Magnesia is translated from the stem to the upper organs, where it constantly increases in quantity. Lijne is probably stationary ; and, as far as potash is concerned, it is probable that, with the exception of a decrease in the ears after blossoming, there is no transfer to any other part of the plant. SOILS AND ROTATION OF CROPS. From what we have said, the student will see how important a bearing this has upon practical agriculture. Indeed it lies at the basis of all scientific horticulture and agriculture, and on it is founded the theory of manures and the rotation of crops. If we could certainly know with the utmost exactitude what particular substance or substances every plant required for its nutrition, then all we would have to do would be to supply the soil in which it was deficient by means of manures, or suit every crop to the par- ticular soil, which by analyses we discovered was suited to its growth, from containing the substances necessary to the proper nutrition of the crop. Agriculture would become a science instead of a simple art, and from his laboratory the chemist would issue his directions to the farmer, who would perform mechanically what the science of his collaborateiir had found to be necessary to the growth of his crops or the nutrition of his exhausted lands. This is exactly what of late years has been attempted ; but the early dreams evolved by the enthusiasm which Liebig's researches a quarter of a century ago excited, have not grown into the substantial results which some at the first start imagined they would eventuate in. This is no doubt owing to our yet extremely imperfect knowledge of the subject ; but at the same time there is something deeper than this, and which the progress of science will not put out of the way. The sooner chemico-agriculturists recognise that the life of the plant is not altogether under the influence of mere mechanical or chemical forces the better. There is a vital force at work, which no combinations in the laboratory can ever imitate. At best the agricultural chemist can only give materials for this vital energy to work on ; and it is the inter- vention of this which has rendered the theories so carefully wrought out in the laboratory not always borne out by practice. Soils are, as we will have occasion to notice in another section of this work, dependent on the disintegration of the particular rocks in the district where found; and hence argillaceous, sili- cious, marly, calcareous, and loamy, according to the amount and character of the mineral ingredients of which they are composed. SOILS AND ROTATION OF CROPS : DIBLIOGRAPHY. 237 Vegetable matter (or Junmis) enters largely into the composi- tion of many soils, and has greatly altered their original compo- sition. That plants can subsist, however, on mineral ingredients alone, is scarcely capable of doubt. The first plants most probably did so to a great extent, for of course vegetable hiimus could not exist before the materials of which it is composed did. We have, however, now got to the limits of our department. To enter upon the subject of soils or their formation, manures, or any other of the endless questions which lie contiguous to or dovetail into our science, would be foreign to our plan, and belongs to the depart- ment of agriculture rather than to scientific botany.^ Having now considered, so far as is necessary, the question of the chemical constituents of the plant and of the soil, we are pre- pared for entering on a consideration of how these materials find their way into the plant in the process of Nutrition. 1 Those who wish to refer more fully to the facts of which an outline is stated, will find them in by far the best work on the chemical history of plants — Pro- fessor Johnson of Yale's ' How Crops Grow,' edited by Professors Church and Dyer (1869), and in the various works and papers so abundantly quoted there ; Boussingault's Economic Rurale, 2 vols. ; Bibra, Die Getreidearten und das Brod (i860); Liebig's Agricultural Chemistry (Engl, trans.), and Ernahrung der Vegetation ; Arendt, Das Wachsthumder Haferflanze (1859) ; Wolff, Die naturgesetzlichen Grundlagen des Ackerbanes ; Salm-Horstmar, Versuche und Resultate iiber die Nahrung der Pflanzen ; Schulz-Fleck, Der Rationelle Ackerbau ; Knop, Lehrbuch der Agricultur Chemie ; Mulder, Chemie der Ackerbrume ; Stockhardt, Chemischer Ackersmann (1855) ; Wolff, Die Ers- chopfung des Bodens durdieCultur (1856) ; Johnston's Chemistry of Common Life, and Elements of Agricultural Chemistry ; Falconer King, Trans. High- land and Agric. Soc. (1873) ; and the various papers of Hinneberg, Kohn, Aronstein, H. Schulze, Busse, Norton, Anderson, Voelcker, Peligot, Mitsclierlich, Stein, Schacht, Bretschneider, Grouven, Sachs, Unger, Gladstone and Diver, Knop, Salm-Horstmar, Cloez, Stohmann, Metzdorf, Birner, Lucanus, Nobbe, Schmidt, Topler, Hoppe-Seyler, Ritthausen, Bopp, Pierre, Gorup-Besanez, Cohn, Maschke, Kubel, Hartig, Daubeny, and others : in the various volumes for later years of Jahresbericht fiir Chemie, Hinneberg's Journal fiir Landwirths- chaft, Wilda's Centreblatt, Journal fiir Prakt. Chem., Versuchs Stationen, Annal. Chem. u. Pharm, Jahresbericht iiber Agricultur Chemie, Salsmiinder Bericht, Sitzungsberichte der Wiener Akad., Transactions of the Highland and Agri- cultural Society of Scotland, Trans, of the Roy. Agr. Soc. of England, Silli- man's Am. Jour, of Sc., Philosophical Transactions, Quarterly Journal of the Chemical Society of London, &c. &c. 238 CHAPTER V. THE FUNCTION OF NUTRITION. The organs necessary for and concerned in the nutrition of tlie higher forms of vegetable life are, we have seen, the root, the stem, and the leaf. We have also seen that the plant increases in size and is composed of various chemical ingredients, which in- gredients it must extract from the earth, air, or water, or from all three. Now the action of the root, stem, and leaf, in extracting these substances from the elements in which they are found, con- veying them to the plant, and placing them so that they conduce to the increase and prosperity of the individual, constitutes the function of Nutrttiojt. It is, in fact, the physiological action of the organs named in combination. Therefore, before dismissing this part of our study, let us consider this more as a whole than we have been able to do while mentioning the uses of the different organs concerned in it. Nutrition may be said to consist of seven different acts : i. Absorptions 2. Circulatio7i ; 3. Respiration, or the elaboration of the nutritive fluid by the contact of the air and the exhalation of carbonic acid (carbonic dioxide) ; ^ 4. Tran- spiration, or loss of water ; 5. Excretion, or elimination of sub- stances injurious to the plant ; 6. Assimilation of the nutriment ; and 7. — its result — the increase of the organs. In the most simple plants, such as Protococcus, which is com- posed of a single cell — and even in some like the Conferves, which are made up of simple rows of cells — each cell seems capable of absorbing and elaborating the nutriment necessary for its simple organism (p. 14). In lichens, again, though simple cellular plants, there is most probably a different physiological function subserved by the outside green layer and the rest of the structure of the plant ; but what this is we are yet entirely ignorant of. In the higher cryptogamia the case is different. Here the function of 1 Here it may be mentioned that though the newest chemical nomenclature, such as is given by most approved authors, is followed, yet when a word is consecrated by long usage we may use it, even though not perfectly correct from the stand-point of scientific purism. Thus, carbonic acid is usually now called carbonic dioxide (COj). ABSORPTION OF SAP BY THE ROOTS. nutrition is a much more elaborate operation ; and in the Dicoty- ledons, owing to various circumstances, it has been more carefully studied than in the Monocotyledons. We shall therefore, in the observations which follow, describe it as it exists in the former division of plants. The nourishment is absorbed from the soil in a state of solution ; from the root it passes into the wood, and thence into and through the stem and branches. From the stem and branches it flows' into the leaves, and thence into their paren- chyma, where it is subjected to the action of the air, evaporation, and other agencies which fit it for the nutrition of the plant, which previously it was not. In the first case it was crude sap ; 1 it is now, after undergoing this elaboration in the leaves, elaborated sa.-^. From the leaves the sap flows back again in the direction of the root through the bark, forming in its downward course the cam- bium (p. 89), out of which the young wood and the tissues gene- rally are formed. In the course of its downward path it deposits in various portions of the plant stores of nutritive material, which again in the spring the ascending sap dissolves and carries onward for the nutrition of other portions of the plant. Thus it passes in its downward route transversely, depositing stores of starch in the medullary rays of many plants ; so that, though its general course may be perpendicular and downward, yet it makes frequent trans- verse detours — " not indeed in determinate vessels, but in a definite path leading through the different parts of the plant." Having thus taken a glance, tout etisemble, at the functions of nutrition, let us consider it, in its individual phases, more in detail. ABSORPTION OF NUTRITIVE FLUID. In the preceding chapter we have seen that the various sub- stances composing the tissues of the plant are derived from the air, earth, and water — more especially from the first two. All those derived from the earth are found in the ash. Those from the air, being gaseous, are naturally not found in the ash, but are determined to be present through other and more delicate means. Of these latter elements, oxygen alone is taken into the plant in a pure state ; the rest are the result of certain chemical decomposi- tions going on in its tissues. All the materials which the plant requires for its nourishment must be taken up in either a liquid or & gaseous condition —nothing solid, no matter how minute its sub- division, can be taken up by the plant. It is, however, dubious, whether it is absolutely necessaiy for the nutritive substances to be in an inorganic form. On this there 1 Also styled the non-elaborated, ascending, or spring sap, or sometimes simply the sap. 240 ABSORPTION OF SAP BY THE ROOTS. has been no little controversy. On the one hand it is pointed out that plants can derive nourishment in soils where absolutely nothing but inorganic substances can exist. Thus plants have grown, no doubt in a very stunted condition, and have even flowered, in sand which had been subjected to a red heat, and, according to Humboldt's experiments, even in a soil composed of metallic oxides, red oxide of lead, &c. Sukkow grew "salad plants" in pounded fluorate of lime and baryta. In powder of coal and sulphur seeds germinate likewise very well. Boussingault grew plants to maturity in soils which had been deprived, by being subjected to a red heat, of every trace of organic matter. In practice the same has been' found true. In the interior of Peru and Chili rich harvests of maize are grown on soils of quicksand never enriched by manure ; and, according to Campbell, the soil of the cinnamon gardens at Co- lombo, in Ceylon, is " pure quartz, and white as snow." The oil- palms of West Africa grow in moist sea-sand ; and yet in nine years there was imported into England alone 107,118,000 lb. of palm-oil, containing 32,000 tons of carbon, furnished by a soil practically free from organic or carbonaceous matter of any sort.^ On the other hand it can never be doubted that all plants can- not live on inorganic substances, or even, as Ingenhouz and more lately Liebig taught, require them for their nutrition. Thus a great number of plants, and even whole orders, like the Loran- thaceae (Misletoes), are parasitic on other plants, and must de- rive their nourishment from the juices of such plants, and of course imbibe a considerable amount of organic matter. Again, fungi, many bog-plants, orchids, &c., derive their nourishment from the decay of animal or vegetable substances alone. Lastly, it is pointed out that most plants, if deprived altogether of organic nutrition — as when grown in sand deprived by heat of any such mat- ters— exhibit a stunted growth. Different plants, however, mani- fest in this respect widely different necessities. Firs, buckwheat, Spergula, Sarothamus, Erica, Calluna, &c., can flourish in a soil which contains a mere trace of inorganic matter. Others, like all the cereals, require for their proper growth a certain amount of organic matter in the soil. The plants which grow in the great primeval forests must of necessity grow in a soil composed almost entirely to the depth of many feet of nothing but mould, formed out of the shed leaves and decayed tissues of thousands of generations of forest-trees and other plants. In fir forests of this type, generally very few species of plants grow under the shade of the trees — a fact probably due to the absence of light and inorganic matter, required for the growth of many plants, and the presence of resins in the vegetable mould. It thus appears that both organic and 1 See Odling on Food of Plants, in Manchester Science Lectures for the People, 1871. ABSORPTION OF SAP ; RAPIDITY OF ASCENT OF SAP. 241 inorganic materials are required, and are capable of nourishing certain species of plants. From whatever source this nutritive fluid is taken into the plant by means of the root, from the medium in which these roots are placed, it constitutes the sap. The force of the ascent of the sap into the roots and up the stem is very great, though this varies accord- ing to the hygroscopic character of the soil. Hales's experiments made more than 140 years ago,^ which were mentioned when de- scribing the functions of the root (p. 139), are still our best authority on the subject. Without even the force of argument derived from these experiments before us, it will be at once self-evident to the student that the force of the sap must be great to raise it against the force of gravity to the top of a palm-tree 200 feet, or of a Se- quoia between 300 and 400 feet in height. Mohl, indeed, is in- clined to attribute the imperfect nutrition which the terminal shoots of such trees must latterly get, from the increased difficulty year by year of the sap ascending to such a great height, as one of the chief causes of their decay and death. The rapidity of ascent is also great ; but this varies with heat, cold, the amount of moisture in the soil, and the dryness of the air. The mean velocity Dr M'Nab has calculated to be .0047292 inches per second — a result which gives a velocity greater than Hales or Sachs calculated.^ The leaves assist by evaporation in the rapidity of the ascent. The leaves themselves are not, it may be mentioned, contrary to the common doctrine on the subject, organs of absorption of moisture from the air, though, if bathed in water, they will mechanically byendosmose absorb water.^ How- ever, while growing free in the air they only favour the plant in the way of moisture by arresting evaporation, not by directly absorbing moisture, hiter alia, it may be pointed out, as a proof of the all- powerful effect of the leaves in promoting the ascent of the sap, that if the shoot of a vine growing in the open air is put into a hot- house, the leaves will unfold, owing to the increased temperature, and immediately the sap will commence to rise, as it would have 1 Vegetable Staticks; confirmed and extended by Briicke (in Poggendorf's Annales, 1844, No. 10), Mirbel, Chevreul, Hoffmeister, and others. 2 Trans. Bot. Soc. Edin., xi. 29. * Bonnet found that plants of Mercurialis absorbed as much, and kept nearly as fresh, when their leaves were in contact with water, as the same plants with their roots immersed. The hairs on the under surface of leaves act like the hairs of the rootlets in absorbing moisture. Hoffmann (Scientific Memoirs, i. 46) proves that after every fall of rain or dew, the leaves ab- sorbed moisture, which, passing down into the tracheary vessels, &c., contain- ing air, displaced for a time the air usually found in these vessels. Leaves have thus some analogy with roots— an analogy still greater in aerial roots which serve the purpose of leaves, and even throw out leaf-buds. — See, on the ab- sorption of water by leaves, Cailletet, Ann. desSc. Nat. Bot., ser. 5, xiv. (1872). 242 ABSORPTION OF SAP : HOW ACCOMPLISHED. done had the leaves expanded naturally. All these facts confirm us in our ideas, derived so long ago from Hales, that the sap is active in proportion to the number of leaves on the plant. This leads us to ask, How is the sap absorbed by the roots? This question we partially discussed in chap. ii. (sect. ii. p. 138), when speaking of the functions of the root. We can now speak of it in more general terms, and from a wider stand-point. This we saw was done by endosmose (p. 36) in the delicate cellular portions of the roots. In cellular plants the absorption of fluids takes place by the whole surface of the plant : and in those which are rooted like the Algas, the root absorbs no nourish- ment in the same sense that the roots of the higher plants do ; it simply acts as an anchor. In the higher plants, only the young rootlets absorb ; if the young rootlets are kept from the soil or other nutritive medium, the plant will soon get sickly, even though the older roots are placed in a position to nourish the plant. Endosmose and exosmose can be seen if cellular tissue is laid in gum-water ; the cells will gradually empty of their proto- plasm, the gum being denser than the protoplasm inside. Again, if laid in water, they will, unless the cell-wall is very strong, burst, from the rapid absorption of water. In cells exist all the condi- tions necessary for endosmose, — viz., an organic membrane (the cell-wall), freely penetrable by water fluids ; and in the cell-con- tents on one side of this membrane, dextrine, sugar, &c. ; while on the other or outside, is the water occurring in nature, holding in a diluted solution certain saline substances. The result is that endosmose goes on with ease and rapidity. But if a root is put into food ready prepared for it — e.g., gum, syrup, &c. — the result is that nutrition is retarded rather than assisted by endosmose being prevented. Roots will absorb no insoluble material, no matter how minute it may be. For instance, if silica is so minutely pulverised as to be suspended in syrup, not 'a particle will be absorbed. Even charcoal, so finely divided as it is in gunpowder, cannot be absorbed, even though mechanically suspended in water. The water will be absorbed, but the charcoal will be left behind. De Candolle found that the colouring matter of logwood, an infusion of saffron, &c., would be absorbed. But this was not by healthy roots ; only by cut surfaces at the places where the plant had been wounded, and, accordingly, where the natural root-action of endosmose was not going on. Some substances are absorbed much more readily than others, even though these substances may be more fluid. Hence it is owing to this that plants have the power of selection. If the cells of the root are diseased, owing to the disturbance of the laws of endosmose, often more of some substance is taken up than would occur in the natural condition of the organ. The experiments of Trinchinetti are in opposition to ABSORPTION OF SAP : SELECTIVE POWER OF ROOTS. 243 those of De Saussure, in so far as they show that different sub- stances are not absorbed by different plants in equal relative quantities. For instance, Mercurialis annua and Chenopodmm viride absorbed much nitre and little salt (chloride of sodium), while Satureia hortensis and Solamcm Lycospersiciim took up much salt and little nitre. Again, from a mixture of sal-am- moniac and common salt, Mercurialis absorbed more sal-am- moniac, while Vicia Faba took more salt. Daubeny found that Pelargoniums, barley, and winged pea {Lottis tetragonolobus), though made to grow in a soil containing nitrate of strontia, absorbed none of the earth — at least none was found in the roots or stems when burned — thus confirming the experiments made by De Saussure on Polygo7in7n persicaria, which refused to absorb acetate of lime from the soil, though it freely took up common salt ; though, on the other hand, Gyde found that beans took up both lime and strontia without injury, if the substances were sufficiently diluted.! Pure water is absorbed more readily than when substances are dissolved in it. It is possible this is owing to the peculiarity that the plant can reject substances in solution and only take up water. Fungi have been observed in arsenical solutions. Now arsenic is a substance so fatal to vegetation that it is scarcely possible to believe that any of it could have been absorbed by the plants. Cereus variabilis, after having been watered for ten weeks with a solution of sulphate of copper, took up no copper ; and the same is true of Stratiotes aloides (water-soldier) and Chara vulgar- is, both of which refused to take up copper — even though, as in the case of the latter plant, it vegetated for three weeks in a solution of the sulphate of that metal.^ De Saussure considered that this selec- tive power was owing simply to the different degrees of viscidity in the substances absorbed or rejected. But even could we con- ceive any sieve so fine as the one he imagined the delicate root- lets to be, recent experiments have distinctly shown that the capacity of plants to absorb certain substances in preference to others does not run parallel with the fluidity of these substances. Poisons are sometimes absorbed by plants. This seems contra- dictory of the views enunciated in the preceding paragraphs. On the contrary, however, there is nothing in this to cause us to doubt the selective power of roots. It is probable that the effect of these poisonous substances is to deaden the selective power of the rootlets, and so cause them to take up substances they other- wise would not, or more than their normal quantity. It is well known that plants which grow side by side in the same soil take up different substances — as is seen by the different analyses their ' Prize Essays, Highland and Agric. Soc, 1845. 2 Vogel in Erdmand & Marchand's Journal, Bd. .x,\v. s. 209. 244 CIRCULATION: ASCENT OF CRUDE SAP. ash gives. This can only be explained in the light of the facts mentioned— viz., that roots have a selective power, and take up dififerent constituents in an unequal quantity from the same solu- tion ; for Liebig's idea, that the roots are mere sponges taking up all presented to them, and again rejecting what they do not re- quire, based as it was on Macaire-Prinsep's experiments, to be presently discussed, has not been borne out by late experiments and observation, though long a familiar doctrine among agricul- turists.i No doubt when the leaf falls, some substances are re- turned to the soil ; but this can only act in perennial, not in annual plants.^ It is not, however, very easy to examine the function of absorption, except when the plant is grown in solu- tions in glass vessels ; and even then it is so modified by various circumstances, such as evaporation, the different degrees of con- centration of the sap, &c., that a wide field, and one of immense scientific and practical importance, lies before the experimenter on this subject. CIRCULATION — ASCENT OF THE CRUDE SAP. The nutritive fluid having now entered the plant through the rootlets, commences its circulation under the name of the sap. It is, in fact, only the water of the soil in the vicinity of the root, with the inorganic materials there found dissolved in it. Here it describes two courses — viz., an ascending a.ri.6. a descendi7ig course j the ascending course to the leaves, where it is submitted to certain influences which fit it for the nutrition of the plant ; the descending one from the leaves, in a condition fitted for that purpose. Before, therefore, considering the descending sap, it will be necessary to describe the ascending one, and the processes it undergoes in the leaves (respiration and transpiration) before it becomes fit to descend and nourish the plant. Composition, &c. — The sap begins to ascend in the spring when the soil is warmed. It cannot, of course, ascend when the soil is 1 Bouchardat (Comptes rendus, 8th June 1846) also considered that roots would absorb anything presented to them in a liquid form ; but he also be- lieved that there were root excretions of a different kind in different plants. However, observations made by Cauvet in 1861 almost conclusively point out that he and others who adopt the doctrine of the non-selective power of roots and of root excretions were wrong, and that healthy roots would not absorb poisons, but if injured, they would do so. Nevertheless, if the plant survived the action of the poison, the leaves in which it concentrated died one after another. According to Liebig and Way, the roots do not find the materials of nourishment dissolved in the water of the soil, but excrete the carbonic acid which renders the substances soluble. — See p. 268. 2 Mohl, Vegetable Cell (Henfrcy's trans.), p. 69. CIRCULATION : ASCENT OF CRUDE SAP. frozen, because at that time the moisture in which the nutritive materials require to be dissolved is in the state of ice. At this season the sap is liquid, and more or less limpid, and generally tasteless or insipidly sweet, though analyses show that it has an. admixture of sugars, gums, albumen, and gluten, in addition to the salts which it holds in solution. The composition varies in dif- ferent plants, as might naturally be expected, from the varying materials each plant takes from the soil. Invariably, however, the crude sap is of low density, water forming its great bulk, in which inorganic matters are dissolved often to a very small extent. The density of the sap of the vine, for instance, at the time of its greatest abundance, is only, according to Briicke, i.ooi ; while that of the elm, according to Vauquelin's analyses, is not more than 1.003— i.ooo being taken as the standard of water. The proportion of the various substances dissolved in it increases as the sap ascends and the circulation goes on, on account of the supplies of starch, sugar, &c., deposited in the tissues of the plant during the preceding years being dissolved and taken up in the course of the circulation. The wood of all deciduous trees contains more or less of starch, and yields a sweet spring sap, produced, as in the case of the sugar-maple, from the transformation of this starch into sugar ; while ever- greens contain little or no starch.^ Accordingly the sap varies in density as it ascends. Knight, and afterwards Biot, found, for in- stance, that in a maple the density of the sap in the stem close to the ground was 1.004; at the height of 6 feet, 1.008 ; at 12 feet, 1.012. However, as the summer advances, the amount of these substances found in the sap decreases, and simultaneously its density. The amount of sap which flows may be judged when it is known that the cut stem of an ordinary-sized vine will "bleed " one pint in 24 hours, and a sugar-maple tree {Acer saccharinuni) 200 lb. in the course of a season — this amount of sap holding about 10 lb. of sugar in solution. In palms and some other tropical trees the sap ascends continuously all the year through ; but in all the plants of our northern and temperate latitudes it only ascends in the spring (or perhaps in some cases to a slight extent in the autumn), when it bursts the buds open, and then, the leaves expand- ed, the circulation goes on apace. Cold stops it; and hence a cold spring stops by this means the bursting of the buds, and thus checks vegetation. The effect of heat or cold is well seen in the flow of sap from a sugar-maple during the season when it is collected for the sake of its sugar. During warm dull nights the radiant heat of the sun is most rapidly absorbed by the dark rough surface of the tree ; then the temperature of the latter rises most speedily, and acquires ^ Hartig, Journ. ftir Prakt. Ch., v. 271 Johnson, 1. c.) 246 CIRCULATION : PATH OF ASCENT OF THE SAP, the greatest elevation— even surpasses that of the atmosphere by several degrees : the sap at that season is also most copious. On the contrary, on clear nights the cooling of the tree takes place with corresponding rapidity ; then the snow or surface of the ground is frozen, and the flow of sap is checked. From trees that have a southern sunny exposure, the sap runs earlier and faster than from those which have a contrary aspect. Sap starts sooner from the spiles on the south side of a tree than from those towards the north (Johnson). Sometimes the sap will commence to flow when the snow is on the ground. In that case the deep-seated roots must be sufficiently warmly placed to allow endosmose to commence, and the trunk sufficiently warmed by the sun to allow it to flow. Path of ascent. — Regarding this there are two rival theories — viz., one that it ascends in vessels (Malpighi, Duhamel, Trevir- anus, Link, &c., including all the older botanists), and the other that the vessels are reserved for the conveyance of air while the sap ascends through the cellular or wood tissue (Schleiden, Mohl, &c.) Accordingly, the vessels have been called air or sap or /)/;«- phattc v&sstls, in accordance with the opinion, as to their function, of the particular writer quoted. The truth may probably be found, as it is usually, somewhere midway between these rival theories. The outer and youngest layers of wood, and in stems not more than two years old the medullary sheath also, chiefly carry sap ; but the older and harder wood takes less and less share in convey- ing sap. Hence the duramen or heart-wood carries none ; while in soft-wooded trees like the poplar and willow the centre wood still conveys sap, as perfectly as does the albumen of hard-wooded trees. In spring, however, the whole plant gets so gorged with sap that the vessels are also filled with it ; it is onlyat this time that the sap flows from an incision in the wood. After the press of work is over, the vessels again resume their usual office of carrying air, and the plant settles down to its normal condition.^ Sachs has 'shown that though the sap in the parenchyma and that in the vessels are not invariably distinct one from another, yet in most cases the cellular tissue contains chiefly nitrogenous principles (sugar, starch, oil, &c.), and also organic acids and acid salts, which give a red colour to litmus paper ; while the vascular tissue contains a preponderance of albuminoids, and gives an alkaline reaction. This exceptional spring condition of woody plants in our climate is a normal one in certain tropical climbing plants called ^ ^ Link, Ann. des Sc. Nat., xxiii. 144 ; Vorles iiber Krauterkunde, vol. i. s. 116; Rominger, Bot. Zeit., 1843, s. 177; Mohl and Hoffmann, Bot. Zeit., 1850 ; Scientific Memoirs, ser. 2, vol. i. ; Schleiden, Grundziige der Wissen- schftl. Botanik, 2 Auft. Bd. ii. s. 505; HofFmeister, Flora, 1858, ss. 1-12 (trans, in Ann. des Sc. Nat., x. (1858) 5-19). CIRCULATION : LATERAL MOVEMENT OF THE SAP. 247 "Lianas," (p. 112, 136), especially in Phytocrene and certain species of Cissiis} However, in Coniferas, in which there are no vessels, the wood- cells must alone convey the sap. In these and other woody plants the sap can easily enter, owing to the numerous punctations or thin places in their walls. Indeed, Hoffmeister tries to demonstrate that the wood-cells are much more permeable than the cells of the parenchyma itself.^ Lateral movement. — When the sap arrives opposite the leaves, it sends off lateral branches, which direct a sufficiency of sap into the bundles of vessels, &c., composing the petiole, and from which it circulates by means of the ribs and veins all through the leaf, and finally passes into the parenchyma. The sap thus, though describing a general upright course, in reality takes a more or less zigzag path. At this time the bark is easily torn off. Autumn sap. — Occasionally, under exceptional circumstances, there will be an ascent of the sap for a brief period during the autumn, just before the plant has gone into the dormant condition its vital functions are in during the winter months. Leaves, before they fall, develop buds in their axils. These buds, therefore, sometimes stimulate another ascent for a short time, until it is stopped by the winter cold. In early-leafing trees (poplars, lin- dens, &c.) it is chiefly seen, and most frequently after a hot, dry summer, when the leaves soon fall ; when, if succeeded by plenti- ful rains and a warm autumn, the sap rises. Perhaps errors in determining the age of trees by the rings of wood may be made in this way, since the short autumn ascent will also form a thin layer of wood. This autumn ascent is not, however, by any means a general occurrence in our climate. After this fitful revival of circulatory life, the vital forces of the plant languish, and finally go into a state of winter repose. There is, however, always more or less of water in the stem of trees all the year round, ranging, as in the case of the beech, from 35 to 49 per cent — the minimum, however, being found during the summer months, the maximum in December and January. This water is owing to the fact that in the autumn and winter, so long as the weather is mild, the roots continue to absorb the nu- tritive f^uid around them. The leaves having perished, this sap is not elaborated, but deposits in the tissue its inorganic contents, which, undergoing transformation during the winter into starch, &c., are again, as we have already mentioned, redissolved in the spring by the ascending sap, to be carried on to aid in the nutri- tion of the plant. ' Gaudichaud, Ann. des Sc. Nat., 2d ser., vi. 138 ; Poiteau, Ann. des Sc. Nat., vii. 233. ' Flora, 1862 ; Nos. 7, 8, 9, 10, 11. 248 CIRCULATION: CAUSES OF THE ASCENT OF THE SAP. In warm climates there is a different state of affairs. In tropical countries there is little or no cessation of the circulation, on account of there being little, if any, difference between the different seasons of the year. Accordingly, many trees of such climates are without "annual rings" of wood. In palm-trees the juice is so rich in nutritive saccharine materials that it is boiled like that of the sugar- maple in order to extract the sugar. In certain tropical climbers we have already mentioned that the plant is gorged with sap all the year round, and that sap can be got from them at almost any time of the year. Hence travellers in tropical forests take advan- tage of this to quench their thirst. On this account some of these species (such as Cissus hydrophora) are known as the " water " or " Hunters' Lianas." Here a curious observation made by Gaudi- chaud ^ on this species of Cissus, and by Poiteau on another but unknown species of the same genus, may be mentioned. If the stem is cut across at one place only, very little sap issues from the two cut surfaces (the upper and lower). " It continues to mount rapidly in the upper part, in which we may be assured that the vessels are being emptied from the bottom to the top. The ascen- sion cannot be attributed to the roots, with which the upper part is no longer in connection, and the vessels are of much too large a dia- meter for capillary attraction to have any influence. But if we cut it at two different heights, so as to detach a fragment of the stem of a certain length, we immediately see a great abundance of sap flow from that extremity which is held the lowest down, consequently obeying the laws of gravity. Now previously the sap continued to mount very rapidly. This can be caused by no force which is placed beneath or at the sides ; it can only, therefore, be from some force situated above the second section, and drawing the liquid upwards." In the course of the ascent, the sap, as we have already intimated, changes rapidly in composition. The stem is the scene of busy chemical activity, and within this organic laboratory numerous physical, vital, and chemical processes are going on, the results of which are, that the sap mixes with and takes up the substances deposited during the previous year, and so changes its composition until it arrives at the leaf, when still further and more important changes take place. The method in which heat expedites and cold retards the circu- lation seems to be simply by the mechanical operation of contract- ing or expanding the cells and vessels. Causes of the ascent of the This is a subject of much in- terest and no little controversy. Here we see a fluid ascending, contrary to the laws of gravity. What,. then, are the causes that enable it to rebel against the laws of nature in order to fill its place 1 L. cit. CAUSES OF THE ASCENT OF THE SAP. 249 in the economy of nature ? On studying the matter closely, it will be seen that this cannot be explained by one set of causes alone, but by many, often widely different, and seemingly disconnected. These causes may be classified as follows : — 1. Endosinose.— This, the initial force, we have already dis- cussed (p. 36). 2. Capillary attraction. — This has a considerable influence on the ascent of the sap, and is the rationale of several familiar horti- cultural operations. For instance, this is the reason why gar- deners cut off the rootlets to " refresh " a plant when withered. The delicate cells of the rootlets have lost the power of imbibing moisture by endosmose, but the physical operation of capillary attraction, of moisture and nutriment through the open ends of the vessels still enables the plant to draw up sufficient to meet its wants, until it has recuperated itself and put forth fresh rootlets. When a " cutting " is put into the ground, the first moisture drawn up by it is through capillary attraction also. The horticulturist cuts the end which is to go into the ground in a slanting manner, not only for greater convenience in the mechanical operation of pushing it into the soil, but also that a greater exposure of the open mouths of the vessels may thereby be obtained, and the vessels not contract so easily. It is also by capillary attraction that a bouquet is nourished when the cut ends of the flowers are put into water. When the vessels are cut across in this manner, then, and then only, will colouring matters enter the plant along with the water in which they are held in suspension or solution ; and accordingly, advantage has been taken of this to trace the course of the sap. Experiments undertaken on plants in which the sap enters in this unnatural manner are, however, not to be implicitly relied on. Capillary attraction is well seen in the continuous ascent of oil in wick when at the same time the oil is withdrawn by supporting the flame at the other end. Something very nearly the same is •seen in plants — the leaves, in this case, by their evaporating the drawn-up liquid, acting the part of the flame in the wick of the lamp. 3. Evaporation by the leaves. — In the course of the spring ascent of the sap, a time will come when endosmose will no longer act so readily, the equilibrium of the contents of the cells and the entering sap being restored, and when capillary attraction ceases to operate also. Yet we see a plant, after its full size has been attained, still drawing up moisture from the soil, as exemplified in the "Lianas" and suchlike plants (p. 112, 136). How is this ? We answer, that the leaves, by exposing the sap to the air over an extended surface, cause much evaporation, as we shall presently see, and this evaporation acts as a vis e fronte to draw up more sap to supply that lost by this means, just as the water 250 CAUSES OF THE ASCENT OF THE SAP. entering by endosmose to supply the place of that transferred to those above them is a vis a tergo. There are thus tw o forces at work at either end of the plant, in addition to the capillary attrac- tion in the middle assisting in drawing up the sap. The one is the root, which pu7nps it into the plant by means of endosmose ; the other is the leaves, which draw tip this pumped -in fluid. It is seen that the root attracts when the leaves do not, by the experiment of the sap of the vine flowing more forcibly when the root is transferred to a warmer temperature.^ The sap flows then not only from the cut stem of the bleeding vine, but also from the most minute ramifications of the root. Even when there are leaves, the action of the root is also frequently necessary. This is shown by the leaves of NytnphcBa alba, the white water-lily, and other plants, drying up when the stem is cut across, though placed in water ; but if placed in water under similar circumstances, with the fibrils of the roots uninjured, the plant will remain fresh.^ Yet the leaves, when even a small number only are left, can lift the fluid up to their level, as shown by the fact that pyrolignite of iron will rise in enormous quantities in the stem to the leaves if the extremities of the plant are placed in it.^ Capillary attraction has, however, much to do with this. The effect of the leaves in attracting the sap is also shown by the fact, that as soon as the buds expand the ascent of the sap is rapidly increased, and by the experiment of the sap commencing to ascend if the bud is forcibly opened by being put into a hothouse ; it is also shown when a graft has a different time of leafing from the stock on which it is grown, the graft in this case regulating entirely the season of the flow of the sap, and thereby influencing and controlling the habits and life of the stock. Dassen in Frorieps Neuen Notizen, Bd. xxxix. s. 129. 2 The Nymphseacese grow larger, more abundant, and flower earlier, when grown in warmish water. In unusually hot summers, when the water in which they grow is diminished, or even altogether dried up, they grow with undimin- ished vigour, standing erect, though whether any change of structure takes place in the stem and peduncles to suit the new condition of life has not been ascertain- ed. The stomata being only on the upper surface of the leaves, there is a curious provision to prevent the leaves being submerged by any increase of water in the pond or lake in which they grow. This consists in the stem not being straight, but bent ; so in the case of such an emergency as the pond being flooded, it can straighten itself, and thus still keep its leaves floating. I question, however, if Mr Britten of the British Museum, to whom (Field Magazine, iii. 46) we are indebted for these facts, is right either in his facts or his explanations of them, when he says that fluid will not ascend in the stem on account of its being cellular and filled with air. Lecoq says that after the young plants are furnished with their primordial leaves they float about, following the course of the stream, entirely unattached to the soil ; and the same fact has been observed in A^. iuberosa, a North American species. s Boucherie, Comptes rendus, t. ii. (1840) 897. CAUSES OF THE ASCENT OF THE SAP. 4. The waving of the tree or other plant by the wind, Mr Her- bert Spencer has recently shown, assists mechanically in causing the ascent of the sap, by alternately compressing and relaxing the vessels.^ 5. Diffusion of liquids.— Th.\s assists throughout in aiding the ascent of the sap, especially in conditions when it could not be accomplished either by the attractive power of evaporation of the leaves, or by capillarity. This is accomplished in virtue of the power which certain liquids have to pass through each other. The late Thomas Graham named the thin, readily diffusible liquids, such as the saccharose, glucose, and other such acids, and the ordinary salts, "crystalloids ;" and from their gluey nature, the other less easily diffusible ones, like starch, the gums, gelatine, &c., " colloids." Now the " crystalloids " pass through and diffuse themselves among the " colloids," hence assisting in carrying for- ward the sap. To these primary causes maybe added the variations of tempera- ture, especially in the spring, causing the vessels to alternately expand and contract, and so force up the sap, and the imbibition of the walls of the cells and vessels, owing to the porosity of vege- table tissues, and we have the most patent causes of the ascent of the sap. Boehm's idea,^ that the sap ascends by atmospheric pres- sure, is not in accordance with known facts, and may therefore be at once dismissed from discussion. The porosity of vegetable tissues is, however, only in reality a modification, though an important one, of capillarity, when a portion of parenchyma is subjected to great dryness, so that the contents would be evaporated. This, however, probably never in reality occurs, if the plant is in a healthy state ; for instantly, by this modification of capillarity, the cell-wall of the dry cell would imbibe the juice from the neighbouring ones which are full, and simultaneously endosmose and exosmose would com- mence, and the sap accordingly ascend. It is thus a power- ful secondary cause of the ascent of the sap, though probably Hoffmeister overestimates its influence when he considers it as one of the chief causes of the ascent of the sap in woody bodies. Assuredly Unger exaggerates its importance when he declares that 1 Trans. Linn. Soc, xxv. (1866) 405-429. 2 Sitzungsberichte der wiener Akad., &c. (1864). For a fuller description of the physical and physiological causes of the ascent of the sap than our space will admit of, the student is referred to Sachs' Experimental Physiology of Plants (either in German or French) ; Johnson's admirable treatise, already referred to and quoted ; Halher's Phytopathologie (1868) ; Schumacher's PhysikderPflanze ; Dutrochet's various works ; papers by Boehm in Sitzungs- berichte, &c., 1863; Fr. Schulze in Karsten's Bot. Untersuch. ii. ; Knight's papers on Vegetable Physiology ; Herbert Spencer's Principles of Biology, &c. 252 CAUSES OF THE ASCENT OF SAP : RESPIRATION. sap does not ascend within cells or vessels, but simply by imbibition through their walls. We have thus briefly but comprehensively given a summary of the phenomenon of the ascent of the sap, and the causes which are either conducive to this ascent, or are supposed to conduce to it. In reality, however, the cause of the ascent of the sap is by no means placed beyond a doubt, and, like a hundred other questions in vegetable physiology, is still open to farther examination. For instance, it seems one of the easiest things in the world to show how endosmose can go on in the plant in the vv'ay we have de- scribed. The fact is, that the stores of organic compounds, especially starch, are not contained in the wood-cells through which the sap chiefly ascends, but in the pith and medullary rays, or in the rind of the root; while in various monocoty- ledons, which, like the palms, lay up a store of sugar, gum, starch, &c., these substances are deposited in the parenchymatous cells of the stem. Therefore, though we can account for the sap entering the delicate fibrils of the root, we must coincide in Mohl's opinion that the method in which it reaches the wood-cells and vessels, and that in which the motion is imparted to it, notwithstand- ing the various explanations offered, are at present among the unsolved questions of Phyto-Physiology. No doubt we can account for the leaves attracting the sap by means of endosmose, on account of the thinner sap coming, in accordance with the physical law already described, to take the place of the thick sap concentrated by evaporation in the parenchyma of the leaf; but we cannot explain by endosmose why the ascending sap will ascend through the wood and vessels, and not by the bark, or why the descending sap takes a contrary course. RESPIRATION. Perhaps this is scarcely a correct word to apply to the pheno- menon of the plant decomposing the atmospheric air, retaining certain portions to build up its tissue, and exhaling others by means of its leaves and green portion under the action of light, while it pferforms- a contrary operation in darkness — in fact, a double respiration. The plant has no organs corresponding to the lungs or gills of the higher animals, but still the term is convenient as expressing an operation analogous to, if not homo- logous with, that performed by animals. The composition of atmospheric air is, nitrogen 79, oxygen 20, and a little carbonic acid, which is a compound of carbon and oxj'gen (CO2). It is, however, in very small quantity. Nevertheless, it has been calculated that, though it only forms i,ooo,oooth part of the RESPIRATION : IN LIGHT : IN DARKNESS. air, there are in the atmosphere 138,616,075,892 tons of carbon. This is being continually imbibed by plants during the day, and exhaled by animals, while volcanoes, decomposition of organ- isms, &c., are continually supplying it to the atmosphere. The stomata, and the epidermis when it is not too thick or indurated, allow the air to enter. The young branches, scales, twigs, &c., all act like leaves, absorbing air which ramifies through the plant probably by means of the spiral vessels, and into cellular passages. This operation consists essentially in taking in CO2, decomposing it under the action of light, sending out the O., while the carbon is retained for the purpose of assisting in building up the tissues. The chief agent in this decomposition of CO2 is chlorophyll. That O. is being given off can easily be seen if a few leaves are put into water, and the vessel covered over with a corked funnel. In a short time, under the action of sunlight, bubbles of oxygen will rise until the funnel is full. Then take out the cork, and the escaping oxygen will revivify a spark, or even cause a blown-out taper to burst into flame.^ In darkness the plant absorbs O. and gives out CO2, but in smaller quantities. This CO2 is probably derived from the com- bination of the O. with the carbon of the plant. Dumas and other chemists have, however, asserted that it is only the CO2 drawn from the soil in the sap escaping from the plant undecom- posed during the absence of sunlight. Certain experiments by Unger and others also show that probably the air is not alone the source of the carbon in the plant. The amount of O. absorbed in different plants in twenty-four hours varies from ^ to 8 times the volume of the plant. All parts of the plant, — such as the root, woody stems, flowers,^ buds Phanerogamia without chlorophyll, such as Orobanches, Motiotropa, Cytmus, Rafflesia, &c.,'^ fungi,^ &c., — not coloured green, give out CO2 in like manner, v^hether exposed t6 the light or not, though in varying quantity. Germinating seeds, in like manner, take in O. and give out CO2. It is probable that this is the reason why the vitality of seeds can so long remain ^ This method of demonstrating the emission of O. by the plant is, however, owing to the leaves being in a condition unnatural to them, liable to objection. It can be, therefore, equally well seen, and more naturally, if the somewhat more difficult method of experiment, on the leaves or the branch in connec- tion with the plant, adopted by Boussingault (Economic rurale, i. 61), or by Rauwenoff, Vogel, and Witter (Mem. Acad. Munich, vi. (1851) 265-345), and others be adopted. 2 Saussure, De 1' Action des fleurs sur I'air ; Ann. des Chim. et de Phys., xxi. (1822) 279-303. Garreau, Ann. des Sc. Nat., xv. (1851) 5-36, and xvi. (1851) 271-292. * Lory, Ann. des Sc. Nat., viii. (1847) 158-172. " Grischow, Physikalisch-chemische Untersuchungen iiber die Athmungen (1819), ss. 160-163. 254 RESPIRATION : ANOMALOUS ACTION OF FUNGI. dormant if they are buried in the ground and thus kept from air. It is perhaps somewhat theoretical, however, to attribute unhealthi- ness to places where there are many flowers, on account of their absorption of O. and disengagement of COg. Professor Kedzie, of the Michigan (U.S.) Agricultural College, analysed volumes of air talcen at noon from different parts of the College greenhouse, containing 6000 plants, after it had been closed for twelve hours. He found the COg amounted to 1.39 in 10,000 parts. A similar analysis of the air taken before sunrise indicates the CO^ to have increased to 3.94 in 10,000 parts. Hence the accumulation of CO2 was greater in darkness or during night than during the day — a fact in accordance with previous observation. However, ordi- nary country air outdoors contains four parts of CO2 per 10,000 ; so that, even with all the plants in it, the air of the greenhouse was actually purer than it, and the emission of CO2 was barely sufficient to counterbalance the production of oxygen during the day. This being the case where 6000 plants are collected, the harm done by a dozen or two in a bedroom must be inappreciable. The behaviour of fungi is somewhat peculiar at all times. Sachs, for instance, thinks that they induce a marked exhala- tion of ammonia at the surface. Borscow^ even affirms that the production of gaseous ammonia is a characteristic of the whole order, or at least of the Agarics — the quantity of gas exhaled being in proportion to the vital activity of the plant, but having nothing to do with its weight. It is equally without relation to the production of CO2 as a result of respiration. Wolff and Zim- mermann^ object to these conclusions, and believe the small traces of ammonia they found in their experiments to be only a product of decomposition of the tissues, but a product which begins to appear immediately the vital functions of the organisms are slackened. With these conclusions we are inclined, from experiments made by us, to coincide. It is also almost certain that the traces of hydrogen which Humboldt considered fungi disengaged were only accidentally present in the air, having only been found in one case {Ama7iita imiscai'id), and never confirmed. The CO2 given out at night has been thought to be taken up by the roots mixed with the sap, though how the CO2 can be taken up in this manner when the sap is not ascending, as is the case in our latitude for about one half of the year, is somewhat difficult to understand. The root, moreover, has not the power of absorbing much CO2, as the experiments of Corenwinder prove. The respi- ration during the day has been called the diurnal or chlorophyllian respiration, chlorophyll being the agent chiefly engaged in caus- 1 Mdlanges Biologiques tirds du Bull, de I'Acad. Imp. des Sc. de St Pdtersb., viii. 12. 2 Bot. Zeit., 1871, Nos. 18 and 19. RESPIRATION : EFFECTS OF LIGHT AND HEAT. ing the decomposition of CO2 ; wiiile to the second has been given the name o{ nocturnal or general, because it is common to all the organs of the plant, even to the leaves in the absence of light.i We may say, with Garreau and Sachs, that is the true respiration, the other being more an act of nutrition than true respiration, as we understand it in the higher animals. It has been supposed by some physiologists that under excep- tional circumstances — such as a clouded sky, &c. — plants even during broad day will inhale O. and give out CO2, or at least form it, only to be speedily decomposed by the action of chloro- phyll. But the experiments on this subject are too contradictory to allow us to form any stable conclusions regarding this important point.- The oxygen disengaged from plants under the action of sunlight varies in amount in accordance with the amount of light the plant is exposed to, and decreases in the shade.^ Plants, however, which, like Coniferae and others, grow naturally in the shade, are less sensible than others to light. Plants flourish in the dark shade of the dense primeval forests, and it is seen from the bright green of the leaves that they decompose CO2. Heat has also some effect on the evolution of O. by water-plants. Thus in certain experiments with the feather-foil {Hottonia palus- tris), Heinrich* found that if the plant was placed in common water at a temperature of 2°.7 Cent.— 36°.86 Fahr. — in full sunlight, no evolution of gas took place, but at 5°.6 C. a regular evolution com- menced. The most active period was when the water was at 31° C. At from 50° to 56° C. the gas ceased to be formed, but the leaf resumed its activity in cooler water. If the leaves were exposed to a temperature of 60° C. for ten minutes, their power of decomposing COg — and we suspect of performing any other functions too — was destroyed. The amount of O. exhaled also varies under illumina- tion by different rays of the spectrum : under red there is none set free ; in red and orange, 24.75 ! i^i yellow and green, 43.75 ; in green and blue, 4.10 ; in blue, i.o; in indigo, o, — the light acting according to the intensity of its illuminating power." 1 Mr Pepys jDrobably stands alone in his belief that the evolution of COj is only in an abnormal state of the plant (Phil. Trans., 1843, 339), tliough Draper maintains that plants, like animals, absorb O. and exhale CO2 — a deduction founded (in our opinion) on data too imperfect to admit of its being seriously discussed. 2 For a discussion of the question, see Garreau, 1. c. ; Ed. Robin, Comptes rendus, 14th July 1851 ; and Mfene in Richard, lib. cit., 149 ; Traube, Monats- bericht, &c., 1859, ss. 83-94 (Bull. Soc. Bot. Fr., 1859, 62, 63) ; and Sachs, lib. cit. : while the contrary view is taken by Corenwinder, Mdm. de la Soc. des Sc. de Lille, 1863; and Ann. des Sc. Nat., 1864, 297-313. * Though, curiously enough, Prillieux has shown that tbe viridescence of leaves is more rapid in diffused light than in the direct light of the sun. Journ. Chemical Soc, Nov. 1871. ' Draper, On the Forces which produce the Organisation, of Plants, Appen- 256 RESPIRATION : YOUNG LEAVES AND GREEN FRUITS. Different species of plants vary also in their power of decom- posing COg. Probably this is not related to anything in the con- stitution of the particular plants, but only to the form of their leaves. Thus Saussure found that very thin and particularly laciniated leaves exhaled more O. than others which exposed less surface to the atmosphere in proportion to their bulk. Fleshy leaves consume less O. and disengage less COg than other leaves. In Saussure's experiments with 57 species of plants, the apricot and beech consumed most O. in darkness, and the Agave Americana (American aloe) and Alisma plantago (water-plantain) — the one a fleshy, and the other a marsh plant — least. There is in general no fixed relation between the number and size of the stomata and the amount of gas disengaged,^ though in some trees with a dry and coriaceous tissue there is a relation of this sort. Very young and tender leaves disengage little or no O. ; but coriaceous and dry ones do in youth — hence they are soon con- solidated. Fruits while green exercise, though in a less degree, the same respiratory functions as leaves ; but as they ripen, this power gets gradually weaker and weaker, until finally, after they get ripe, it is entirely lost. Leaves cannot decompose pure CO2 unless it is rarefied ; and when it is mixed with nitrogen or oxygen they are equally incapable of performing that operation. The elimination of O. from growing plants is a chemical necessity when we know that the plant lives for the most part on oxygen- ated food. Hence, supposing starch to be formed by a plant from CO2 and water, the following formula will represent the extrication of 12 atoms oxygen : — 6 CO2+S H20=C6 05+120 (Johnson). When plants are continuously kept from light, their nutrition suffers ; they become sickly, weak, and etoliated. As seen in the case of a potato kept in a dark cellar, they form shoots at the expense of the nutriment stored up in the older parts, these shoots being even of a larger size than similar ones formed under the action ot light, but weak and soft. The leaves do not increase in size, do not become green, and the normal qualities of the sapS are altered, bitter milky plants remaining sweet, &c. Some plants will exist dix, 177. Pfeffer (Arbeiten der Bot. Instit. in Wiirzburg, Cahier I., 1871) con- cludes that ' ' the rays of the spectrum perceptible to our eyes are the only ones which can become the cause of the decomposition of CO^— the rays endowed with the most considerable illuminating power (the yellow rays) exerting them- selves an influence equal to that of all the others taken together. The most refrangible rays possess a much less marked action. To each spectral colour there belongs a certain degree of activity in the phenomenon of assimilation— a degree which remains the same whether the rays act isolatedly upon plants, or whether their action is combined." See also Rarentzky in Bot. Zeit., 1872. No. 13. 1 Duchartre, Coniptes rendus, xlii. 37. EFFECT OF POISONOUS GASES ON PLANTS. 257 for months in this sickly condition, but they cannot bear it perma- nently (v. Mohl). If, on the other hand, more than the normal quan- tity of CO2 is supplied to the plant, it will flourish and increase its bulk greatly, even to an extent double that of the carbon contained in the inhaled CO^} On the contrary, all the functions of the plant become paralysed if placed in air containing no oxygen — e.^., nitrogen. According to Dutrochet,^ the unfolding of the leaf-buds is checked, resulting in them finally rotting; and the leaves no longer turn towards the light, or exhibit the alternate movement of folding and opening. Even single organs cut off from oxygenated air, like roots buried too deeply in the earth, decay and die. Accord- ing to Saussure's experiments, a Cactus, one of an order usually very retentive of life, died in five days in non-oxygenated air. Yet the experiments of Messrs Gladstone^ show that plants remained green and in good health during fifteen days in pure hydrogen, during almost three weeks in nitrogen, and even during four weeks in pure carbonic oxide (CO) — a gas eminently deleterious to animals which breath it. Boussingault* considers that he had detected marsh-plants exhale an exceedingly small quantity of this carbonic oxide ; but the latest researches, those of Cloez,^ give decisively negative results : so that this, like many other assertions we have touched on in this chapter, must receive the Scotch verdict of no^ proven. Uitder the actio7i of actively poisottous gases — such as sulphur- ous acid, hydrochloric, chlorine, and nitrous acid gases — the plant disorganises as if under the action of an irritant poison ; while under the action of sulphuretted hydrogen, cyanogen, carbon dioxide, and ammoniacal gas, they droop and decay.'' The action of sulphurous acid seemed toconsistiii itsbeingconvertedinto sulphuric acid by oxidation, and so attacking the tissues of plants. Coal-smoke injures plants chiefly by clogging up the stomata, and so impeding respiration and transpiration. Oxygen, as we have seen, is the only gas which is taken into the plant in a pure state ; the rest are in a compound form. For instance, the substances which give nitrogen are taken up by the roots, and not ^ by the leaves.^ Nitrogen, it appears probable, from 1 Saussure, Recherches, &c., 226. 2 M^moires, &c., i. 361, 483. 3 Philosophical Magazine, Sept. 1851.' 4 Comptes rendus, liii. (1861) 882, 883; and Ivii. (1863) 412-414. 5 Ibid., Ivii. 357. 6 See the extended observations of Christison in Ed. Med. and Surg. Journal, xxvii. 356; and those of Livingstone and Coldstream in Edin. New Phil. Journ. 1859, and Trans. Bot. Soc. vi. 391 and 325 (on the effects of anECSthetics on sensitive plants). 7 Comptes rendus, Nov. 28, 1853 ; Ann. des. Sc. Nat., ser. 4, t. i. and ii. (1854). and t. vii. (1857). 8 Ville (Comptes rendus, xxxi. 678) tries to prove the contrary— viz., that it is absorbed by the leaves from the atmosphere. R RESPIRATION IN WATER-PLANTS. theresearchesof Boussingault, Liebig, Lawes and Gilbert, and Pugh, is derived, not from the atmosphere, which it enters inlo the com- position of to the extent of J, but from ammonia — ammoniacal salts being found in abundance in the ascending sap of the maple, birch, &c. Hence the value of guano and other manures containing ammonia. The universal diffusion of water will give hydrogen, while carbon and oxygen are supplied both from this and from the sources already indicated. In Wate7'-plants. — The air dissolved in water acts on water- plants not through the stomata, as in land-plants — these being wanting on the surfaces of aquatic plants exposed to water — but through their cuticle. They send out oxygen by both the upper and lower surfaces of the leaves (Duchartre). Water-plants get etoliat- ed in darkness ; yet, according to the experiments of Cloez and Gra- tiolet, no CO2 is sent out under the action of darkness, though the decomposition of that gas is, as in terrestrial plants, affected under the action of light. Nevertheless — as shown by their experiments, and those of Heinrich, already quoted (p. 255) — a certain elevation of the temperature of the water is necessary for this phenomenon. The salts and the air which in common with CO2 are found dissolv- ed in natural water, are indispensable to the duration of the pheno- menon. The gas produced contains, in addition to the oxygen, a certain quantity of nitrogen, the result, possibly, of the decomposition of the substance of the plant itself, and which probably the nitrogen of the air dissolved in the water is destined to replace. Ammonia, however, and ammoniacal salts, when dissolved in water, even in minute quantities, hasten rapidly the death of aquatic plants. They only absorb COg by the upper surface of their leaves. The oxygen disengaged in these plants circulates all through the in- tercellular passages (p. 15) — according to the experiments quoted — " constantly from the leaves to the roots," a fact not supported by Duchartre's observations, he having found it given off by the leaves, as in terrestrial plants. Plants are thus the scavengers of the atmosphere, removing the carbonic acid exhaled by putrefying matter, volcanoes, manufactures, &c., and giving out instead of this gas — so poisonous to animal life — oxygen. Water-plants perform the same office to water — viz., oxygenating it. The amount of CO2 exhaled at night is small compared with that taken in by the plant during the day.^ As carbon, hydrogen, oxygen, and nitrogen — the only four ele- ments absolutely essential as the proper food of plants — all exist in the atmosphere, it follows, from the power of the plant to absorb 1 On the general question of the diffusion of gases in plants, see N.J. C. Milller in Pringsheim's Jahrb., Bd. vi. vii. ; Van Tieghen, Ann. des. Sc. Nat., 5" s^r., ix. 269 (abstract in Annals of Nat. Hist., 1872, 150) ; and Barthclemy, Comptes rendus, Ixxii. TRANSPIRATION : EVAPORATION. air and water, that a good deal of the food of the plant may be de- rived directly from the atmosphere. Some plants, like the " Epi- phytes " (various orchids, &c.), derive their nourishment from the air ; while others, like some of the Sedums (e.g., Seduvi Telephimn, or " livelong "), can live for a summer with their roots severed from the soil. The plants that germinate on a barren volcanic island raised above the water, or which grew upon the earth for the first time, before the soil had formed by the disintegration of rocks, or the decaying animal or vegetable matter had formed a mould, must have obtained their nutriment from the air alone. In a similar manner a seed which has been grown in powdered flints, and watered with rain-water only, will be found after some time to have increased to fifty or a hundred times its original weight. Plants have been frequently flowered— and even fruited — with no other nourishment than that derived from rain-water, showing that in this fluid were all the necessary nutrient substances. TRANSPIRATION. Simultaneously with respiration there is a continuous transpira- tion of watery fluid going on from the leaves. The cells in the leaf are surrounded by intercellular spaces and canals full of air, so that they may be said to be surrounded by an atmosphere ; into these spaces the vapour from the watery contents of the cells passes, from these into the chambers beneath the stomata, from which it escapes either by the mouths of the stomata or by the invisible pores on the surface of the epidermal cells.^ The result of this evaporation is that the watery sap is thickened, and, combined with the action of the air upon it, is fitted to commence its downward course, and to nourish the plant in its descent. In some cases this water is given off in the form of invisible vapottr — in other cases, in the form of drops which can be easily seen by the naked eye. Evaporation. — That the amount of watery matter exhaled from leaves in the 'form of vapour is great, may be gathered from the following statements. Hales found that a sunflower {Helianthus amttcus) only three and a half feet high, and with 5616 square ^ De Candolle attempted to distinguish the exhalation by the stomata, and that by the invisible pores of the epidermis, which takes place in parts of the leaves where there are no stomata. The first he called aqueous exhalatiott, the second insensible deperdition. As both are going on simultaneously, the distinction is scarcely tenable. It is also probable that the air-circulation in the plant changes the composition in different parts of the plant, owing to cer- tain elements being absorbed from it by the sap, according to its requirements. 2 6o TRANSPIRATION: EVAPORATION, ' I inches of surface exposed to the air, exhaled at the rate of 20 to ! 30 ounces avoirdupois every twelve hours — seventeen times j more than a man does ; a vine vs^ith 144 square inches of surface I exposed to the air, exhaled in the same period at the rate of five or | six ounces ; and an apple with 132 square inches exposed, perspired at the rate of nine ounces. Knop found that between the 22d May and 4th September a maize plant exhaled thirty-six times its weight of water. Lawes observed that most of the common agricultural | plants — wheat, barley, peas, beans, clover — exhaled during the five 1 months of growth more than 200 times their dry weight of water. ' I Still more extraordinary is the transpiration of the "cornelian l| cherry " {Comics mascula), which exhales in the course of twenty- j| four hours water which is equal in weight to twice that of the M whole shrub.^ It has been calculated (by Dresser) that an acre of ■ cabbages, planted in rows 18 inches apart, and 18 inches from I each other, would transpire in the course of twelve hours no ■ less than 10 tons, 4 cwt., 3 qrs., and 11 lb. The degree of light, I v^armth, and dryness of the air also affects the amount of fluid w exhaled. The temperature and chemical composition of the soil, mi and the age and texture of the leaf, have also to be taken into H account. If the air is full of moisture, little or none will be ^ exhaled; but if it is in a contrary condition, then much fluid 'l| will be given off by the leaves. 1] The amount exhaled also varies in different species. In an | { elaborate series of experiments conducted by Dr W. R. M'Nab ' on the bay laurel [Prunus Laiirocerasiis), the following among other results were obtained. In the leaves of this plant was 63.4 ^ j per cent of water; the amount of water which could be removed | by the leaves in the sun was 5.8 per cent, though by action of cal- cium chloride and sulphuric acid about the same quantity could . j| | be removed. The rapidity of transpiration in sunlight in one hour was 3.03 ; in diffused daylight in one hour, 0.59 ; in darkness in \ one hour, 0.45 per cent. It was also found that while in a saturated 1 atmosphere iii the sun, 25.96 per cent of fluid was exhaled in one ' hour, 20.52 per cent was transpired in a dry atmosphere in the same period. However, when the plant was transferred to a satu- rated atmosphere in the shade, no fluid was transpired in an hour, though in a dry atmosphere 1.69 per cent was given off in the same period. The under surface of the leaf also transpired up- wards of twelve times as much as the upper surface." It has been found by various experiments, chiefly by Unger^ and Sachs, that the amount of water evaporated from a leaf is about from 2^ to 3 1 DuhEimel, Phys. des Arbres, i. 145. ji 2 See his interesting and valuable paper in Trans. Bot. Soc. Edin., xii jj (1871) 45-65. i I ^ Anat. u. Phys., s. 333. TRANSPIRATION : EXHALATION IN THE FORM OF DROPS. 261 times less than would be evaporated from a surface of water of the same space. There is also in each plant a maximum and a mini- mum of transpiration, the first being about 2 p.m., the second during- the night. This transpiration in leaves acts chiefly through the stomata — transpiration taking place, however, in parts deprived of these, though much more slowly. Garreau and Unger found that the amount of transpiration from the two sides of the leaf was in an exact ratio to the amount of stomata on these surfaces. For instance, the stomata on the upper and lower surfaces of the leaf of Belladona are as 10 to 55, and the quantity of transpiration by the two surfaces is as 48 to 60. In the dahlia, the relative number ot stomata on the two surfaces of the leaf is as 22 to 33, and the amount of water transpired is as 50 to 100, — and so on.^ The amount of moisture taken up by the root is usually in about exact proportion to the amount of water given off by the leaves, or in the proportion of about 100 to 97.8 ; but, as familiarly seen in M^arm sultry days, the ratio will be occasionally disturbed — more tran- spiration than absorption going on — the result of which is, that the plant droops and gets " wilted " looking, and eventually dies, unless the balance is again restored. This transpiration is thus one of the primary causes of the ascent of the sap (p. 249). Ever- greens do not " bleed " when cut in the stem in the spring, like the vine, maple, &c., because the continual transpiration going on by their leaves enables them to get clear of their superfluous moisture. In the air the moisture transpired falls again in rain, after being saturated with the gases deleterious to life, which it washes out of the atmosphere, and again nourishes the plant. Thus it has been calculated that the water raised into the air by evaporation is again condensed, and again evaporated, ten or fifteen times in the course of a year. In a IVardzan case^ which is closed in on all sides, a small amount of moisture suffices — the transpired water being again and again used over, the only consumption occurring being that absorbed into the tissues. It shows the whole economy of vegetable life on a small scale. Exhalation in the fortn of drops. — During the night many leaves exude drops of water, which accumulate at the points and serratures. In some cases, these drops are only the insensible evaporation condensed by a fall of the temperature. But it is dubious whether this exhalation is always of the same nature as that just described, and not a true excretion of water. Trin- 1 Ann. des Sc. Nat., xiii. (1850) 321-346. See also Barentzy, Bot. Zeitung, Feb. 1872. * Ward, On the Growth of Plants in closely-glazed Cases, 1842. 262 EXHALATION IN THE FORM OF DROPS. chinetti ^ has even described little glands (glandulse periphylla;) at the spots where the excretion takes place ; and the fluid secreted by them, though at first limpid, contains organic sub- stances which pass into fetid decomposition. In a few cases this fluid has an odour resembling that of the plant. In some of the order Aracece (particularly in Calla JEthiopica, Anwi Colocasia, &c.), water is evacuated in great quantities from the point of the leaves. In Calladhtin distillatoru7n, the colossal leaves give off each about half a pint each night. In this latter plant, as in Arum Colocasia, the water flows from an orifice in the neighbourhood of the point of the leaf, upon the upper surface, in which terminates a canal running along the border of the leaf ; while smaller canals, running along the principal nerves, open into this.^ Even in dry dewless nights, when no moisture is on the surrounding vegetation, there may be noticed drops of water depending from the tips of the branchlets of Equisetuvi umbrosum, {E. pratense, Ehr. — one of the " horsetails "). The water secreted in the pitchers of Nepenthes, Sarracenia, Cephalottis, and other pitcher-plants, is most probably of the same nature as the above. That in Nepenthes contains only 0.27 — 0.92 per cent of solid matter, consisting of citric and malic acids, chlorine, potash, soda, lime, and magnesia.^ The liquid often collected in the flowers of Coryanthes, one of the orchids, is clear and somewhat glutinous in appearance, with a specific gravity of 1.062, neutral to test-papers, becoming milky by concentration on the water-bath, and finally yielding a transparent gum insoluble in alcohol. In 100 parts, there are 98.51 of water and volatile oils, and 1.49 of non-volatile residue, thus proving that this liquid is something else than pure water.* The water evaporated from the leaves contains also a very small amount of organic matter. It is probable that really no injurious substances are excreted by the leaves by either mode of transpiration ; the case quoted in support of the opposite opinion — viz., that the leaves died when the transpiration was prevented by being smeared with oil — being equally capable of being applied in support of the doctrine that death ensued on account of the leaves being deprived of air by this means. It would be wrong, however, to regard even transpiration as a mere physical act, like ordinary evaporation. This is proved (i) by the fact that not only water, but a very minute quantity of 1 Linnea {fide Mohl), Bd. xi. s. 66, See also Rainer Graf in Flora, 1840, P- 433- 2 Mohl, lib. cit., p. 100 ; Gartner, Beiblatter zur Flora, 1842, s. i. ; Schmidt, Linnea, Bd. vi. s. 65. Volcker in Ann. of Nat. Hist., 2d ser., i. 178; Phil. Mag., xxxv. 192. 4 Buckton in Nature, 1870, p. 34. CIRCULATION : THE DESCENDING SAP. 263 organic matter, passes off at the same time ; (2) that much less water is transpired when the cells are in active health than when their vitality is in any way affected.^ CIRCULATION — THE DESCENDING SAP. The sap has now undergone certain changes in its upward course and in the leaves. From a crude liquid incapable of nourishing the plant,^ it has become by admixture with the starch, sugar, &c., in the stem, a highly organised fluid, and by evaporation from contact with the atmosphere, thick and con- 1 We have not in the text referred to the observations of M. P. P. Dehdrain — not being altogether satisfied with some of his results, or the accuracy of the methods by which they were arrived at. They are, however, too important to be altogether passed over. He proposes to demonstrate the three following points : ist, The evaporation of water from leaves proceeds under conditions very different from those which determine its evaporation from an inanimate body, for it continues in a saturated atmosphere. 2d, This evaporation is entirely determined by light. 3d, The rays of light which are efficacious for the decomposition of carbonic acid by the leaves are also those which favour evaporation. A leaf of wheat was fixed in an ordinary test-tube by means of a spht cork. This tube was exposed at intervals to the action of the sun, and subsequently weighed, when it was found that during each equal period of half an hour the tube (without the wheat-leaf) had increased in weight by almost exactly equal increments, although the air in the tube had become completely saturated, and a considerable quantity of moisture had condensed. Under similar circumstances no increase of weight was found, if, instead of the wheat-leaf, a wick of cotton was inserted in the split cork, one end of which was immersed in water. The quantity of water emitted varies con- siderably with the species of plant and the age of the leaf ; but the most efficacious agent in determining the evaporation is light. In bright sunshine leaves of corn gave off, under long exposure, from 70 to 108 per cent of their o\vn weight of water ; in diffused light, from 6 to 18 per cent ; in total dark- ness, from 0.6 to 2.8 per cent, being very little influenced by temperature. Even when the tube was surrounded by ice the? leaves gave off an increased quantity of moisture, probably in consequence of the more rapid condensation. Further experiments with coloured solutions showed that the blue or green rays which decompose chloride of silver, but are without action in the reduc- tion of carbonic acid, also do not facilitate evaporation ; while the red and yel- low rays, which have little photographic power, but have a powerful action in decomposing carbonic acid, have also great influence in promoting evapora- tion. The series of experiments showed an exact proportion between the quantity of carbonic acid decomposed and the quantity of water evolved. M. Dehdrain also confirmed an old observation of Guettard, in 1848, that the upper hard and smooth surface of leaves has more power in decomposing carbonic acid (and hence also in evolving water) than the under surface. — (Comptes rendus, 1869 ; The Academy, 1869, p. 46.) * This has been repeatedly proved by a variety of experiments. Those who are interested in the matter will find some such described by Hanstein, Wird das Saftsteigen, &c. (Sitzungsberichte, &c., 1864). 264 CIRCULATION : THE DESCENDING SAP. centrated. It is now prepared to subserve its function in the vegetable economy by nourishing the plant. To do this, how- ever, it must descend — and descend accordingly it does in a slow stream continuous with the ascending one. The path it takes is through the cellular layer of the bark and the liber, right down to the root, forming — in fact giving birth to — the cambium layer, from the inner surface of which the annual layer of young wood is formed, and from the outer surface of which the liber receives its annual increase (p. 89). Apply a ligature very tightly to the stem, and by this means the upward course of the sap through the wood, and the downward course of the elaborated sap through the bark, are demonstrated. Very soon a swelling will form above the ligature, showing that the sap is stopped in its downward course in the bark ; while no swelling takes place below the ligature, showing that the pathway of the ascending sap is beyond the influence of the ligature — viz., within the wood, not within the bark. This can be even better seen if, instead of a ligature, a ring of the bark be cut out. Then the part of the stem below will cease to increase, and, in, the case of the potato-plant, no tubers will be produced ; while in the portion above the wound, much thicker layers of wood will be formed, more fruit will be produced, and this fruit will ripen sooner than in ordinary cases : in fact, all the advantages which the whole stem would have derived from the descending stream of nutritive sap will go to that portion above the wound, simply on account of the sap being unable to descend, the bark througji which it would have done so being destroyed. This operation of cutting a ring of bark from a tree is known to gardeners as girdling, and is taken advantage of to increase the produce, and, as in the case of vines, the size of the fruit produced above the wound. It has also a tendency to cause new (adventitious) roots to be produced — these roots (originating from the vascular tissue) usually springing from the protuberance or callus, as it is called, or just above it. In endogenous plants, the roots, according to Hanstein, are formed for the most part, if not entirely, at the base of the cutting, and not above the girdled place. The same result is seen in some exogens, in which the vascular bundles are not confined to the exterior of the stem, but pass into the pith (e.g., Piper viedium, Amaranthus sangtcineus, &c.) The sap having ascended up to the leaves, from which it is conveyed downward, it may be asked, Is there anything which corresponds to the absorbents, or to the capillaries of the higher animals, found in plants ? To this question Mr Herbert Spencer,' supported by Dr Pettigrew, has answered in the affirmative. He described, as being found in the leaves, masses of " irregular and 1 Principles of Biology, i. 559. CIRCULATION : THE DESCENDING SAP. 265 imperfectly united fibrous cells, such as those out of which the vessels are developed " — forming club-shaped masses, occupying the intercellular spaces between the ultimate venous network of the leaves, into which network they also open. Some of them, how- ever, open outwards towards the air. " They are also found in the root and body of the turnip, in the simpler form of fenestrated cells, with their ends bent round so as to meet. If this is so, then there is direct communication between these club-shaped masses and the vascular tubes found in the stems, branches, and roots— in fact, a system of absorbents and capillaries in one." Pettigrew therefore considers that the circulation goes on in the form of a set of siphons. Without, however, denying that such a system of absorbents does exist, we must warn the student that this doctrine is not generally held, and that we are not aware of any botanist who has yet been able to see these absorbents ; after repeated efforts, we have failed to demonstrate them. Moreover, they are not found, according to Mr Spencer, in all leaves, though in many stems, &c., taking on the function of leaves. At all events, whether we believe in this or not — and the tempta- tions to do so are captivating — there can be little doubt that the sap descends after being elaborated in the leaf; and the next question is, Does the descending sap travel in any definite canals, or simply by eiidosmose or exosinose ? To this question we may answer that it is now generally believed that there are certain definite conducting tissues in or about the bark through which it descends. These are : i. T\\& Celliilce clathratiz, or " cribriform cells or tubes " — the vasa propria of v. Mohl — which we have already described (p. 43). They form a system which accompanies the fibro-vascular bundles in every part of the plant; and in the liber their existence is even more general than the laticiferous vessels, and even the liberian fibres themselves. 2. Nagli has de- scribed as lying outside of the cambium, and very like in form to the cells of that layer, but altogether distinct from it, a series of thin- walled delicate cells, which he has called the cribriform cells. 3. The cellules conductrices of Caspary (p. 13), which are an essential element of most of the woody bundles, and contain mucilaginous or albuminoid contents, and often replace the cribriform tubes, are believed to assist in conveying the descending sap. These dif- ferent tissues, owing to their thin walls, or, as in the case of the cribriform cells (or tubes), the openings in the walls, are pecu- liarly suited for conveying the sap downward, and distributing it to the cambium. The contents of all these vessels or cells named are alike in this respect, that they are rich in nitrogenous materials — more or less mucilaginous, and very thick. Hanstein's researches have left little doubt that their function is the convey- ance of this nutritive sap, though Schacht has taken exception 266 CIRCULATION : THE DESCENDING SAP. even to the expression " descending sap " — considering tliat it is simply an exchange of sap between the different cells by means of endosmose ; a view which it would be about equally difficult to prove or disprove. Notwithstanding the various experiments detailed above, the descent of the sap through the bark has been denied by Herbert Spencer, who considers that its course is through the young wood — an idea not remarkable for its intelligibility.^- Schleiden (and others both before and after him) has even denied — and what is still more singular, attempted to support his denial by proof — that the sap descends at all, explaining the increased growth above the "girdling" by an artificial interruption of the upward current of crude sap, " in consequence of which the sap contained in the upper part of the plant must soon become greatly concen- trated and potential for development." ^ To such an idea the best reply is the characteristically sarcastic but not less unanswerable one given him by Hugo v. Mohl : " When we can succeed in fat- tening an animal by depriving it of a portion of its accustomed food, this explanation may be received as satisfactory." Notwithstanding the crotchets of the botanists referred to — Du- petit-Thouars, Turpin, Schleiden, Hdrincq, &c., who, to support some theories of their own, have either denied the circulation of the sap z« toto or partially — there can be but little doubt that few facts are better established in vegetable physiology than that the sap ascends from the root to the leaves, and again descends in an elaborated condition from the leaves towards the root. There may be occasional exceptions, as in cereals, when the plants, as they approach maturity, lose the power of elaborating nutriment by their leaves — the flowers, &c., subsisting by the nutriment stored up in the stem ; or as in the case of biennial root crops, when in the first year the nourishment is stored in the root, and in the second rises upwards to nourish the plant. That the elaborated sap also sometimes ascends is proved by the fact that "unde- veloped buds perish in most cases where the stem is girdled between them and the active leaves." In these exceptions the vascular bundles, as in the instances previously mentioned, pass into the pith. Still the broad fact remains the same, that though nutriment can be transferred by means of the sap to whatever part of the plant requires it, yet the general course of the sap is up- wards and downwards. 1 Principles of Biology, i. 550. ^ Grundzuge, &c., Auf. 2, Bd. ii. 513. SECRETIONS AND EXCRETIONS : ROOT-EXCRETIONS, 267 SECRETIONS AND EXCRETIONS. It may be asked, Does not the elaborated sap, in the process of forming the substances necessary for the nutrition of the plant, also form some substances which are not necessaiy for nutrition, or are ev^en injurious to it, and which, therefore, must be excreted from the organism ? After the descending current has reached the root, is there no refuse ; and if there is, where does this refuse go to ? — is it absorbed in the sap of next year, or thrown out of the plant altogether? This idea has been held, and is yet to a small extent maintained, bysome botanists, and by the majority of agriculturists, though, as we have already hinted, on very feeble grounds. Root-excretions. — It has been pointed out, in support of the ex- creting power of plants, that there frequently appear on the surface of roots substances which swell up in water, and which enable the particles of earth to cling to them. It has also been pointed out that certain plants do not prosper in the vicinity of others — in a word, that these plants have " antipathies " to others. This subject we have already mentioned casually when describing the functions of the root (p. 141) ; and as it is one which has excited no little controversy, we may devote a few more paragraphs to it in this place. By the advocates of these antipathies of certain plants it was believed that particular plants emitted certain fluids or other substances from their roots, which corroded.'or in some^way poisoned, the roots'of particular species growing in their vicinity. The idea was long entertained, chiefly through agriculturists observing that particular crops would not prosper in ground which had been occupied by others, and vice versdj or that certain plants would not prosper if growing side by side. It is owing to the observations of Macaire-Prinseps,^ undertaken at the instigation of De CandoUe, that this idea has taken ground among vegetable physiologists. He seemed to have found, by the most positive experiments, that certain plants gave off chiefly during the night certain substances, different in each case according to the kind of plant examined. For instance, in Lactucece (lettuces) and the poppies the excretion was opium - like, that from Euphorbice (spurges) acrid, that from Leguniinosce (bean and pea order) mucilaginous, &c. ; and that even if the plant was made to imbibe certain substances foreign to it, these substances would be afterwards rejected. Finally, he considered it proved that while some plants would prosper in the water (or soil) into which these excretions had passed, others would not grow at all. From these experiments De Candolle and his followers drew the conclusion that these root-excretions were analogous to ^ Mdm. de la Soc. de Phys. et d'Hist. Nat. de Geneve, v. 282-302. 268 ROOT-EXCRETIONS. the urinary excretions of animals ; and that as animals cannot live upon their own excretions, so neither could plants. Hence cereals could not be long uninterruptedly cultivated in the same soil. However, subsequent experiments undertaken by other physiologists^ showed either a perfectly negative result, or that Macaire-Prinseps had proceeded without much circum- spection— only wounded or irritated roots yielding anything in the shape of excretions. It would be tedious, even if space permitted, to go into these experiments in detail. Suffice it that this is the result arrived at, and that at best the question of root- excretion is not proven. The true theory of rotation of crops, as already mentioned (p. 141), lies in the selective power of roots, and in the fact that certain crops can grow on soil after others, owing to the different media they extract certain essential nutritive substances from. For instance, leguminous plants (like beans, peas, tares, &c.), prosper after cereals (wheat, barley, oats, &c.), from the fact that the first order of plants derive their nitrogen from the air, and the other from the earth ; the one exhausts, the other improves the soil. While denying the power of the roots to secrete (and excrete) substances either beneficial or prejudicial to other plants, we cannot shut our eyes to the fact that roots exert chemical influences on certain hard bodies which it is difficult to see are not produced by some excreted substance. Gazzeni, according to v. Mohl, saw this in clover, and Trinchinetti^ saw a root of Nepeta Cataria grow through the midst of a peach- stone. Moreover, Trinchinetti observed that a decoction of humus underwent fetid putrefaction when left to itself; but when the roots of living plants were placed in it, this did not take place. Gardeners have noticed that the debris of horn gets consumed much more slowly in earth not covered with vegetation than in similar ground in which grow plants, the roots of which penetrate in every direction (Martins). It is also probably owing to the secretion of a free acid that the roots of Colocasia afitiqjiorjim have the property of keeping water from putrefaction. Schacht, indeed, informs us, that in Madeira even the petioles of this plant put into water will keep it sweet for some days. This is probably done by means of the excretion of a free acid — most likely acetic — "or of a substance which is converted into an acid in the air." Bec- querel even goes so far as to declare that there is a free acid excreted from not only the roots, but from the bulbs, tubers, buds, and leaves. The roots of some plants seem to have a corroding in- fluence on marble (as proved by numerous observers, and more recently by Sachs), and lichens will dissolve the limestone they 1 See Bracconet, Ann. deChim. etde Phys., Ixxxii. 27 ; also Meyer's Jahres- bericht, &c., 1839, s. 5. 2 Sulla facolt^i assorbente delle radici, 57. LEAF-EXCRETIONS. 269 gro\y upon, all of which points to the secretion of an acid of some kind, unless, indeed, this is owing to the CO2 dissolved in the water. Of the numerous hypotheses which have been framed on this subject, the student had better remain ignorant, since these are entirely unsupported by aught but the vivid imaginations of their manufacturers — voces et prceterea nihil. Leaf-excretions— Thtrt are, however, certain excretions in the plant, though not given off by the root, but chiefly by the leaves and the epidermis generally. Of this nature we are inclined to regard the resinous substance seen on the buds of many plants, the sugary substances which cover the sycamore-leaves in the course of summer, the fragrant resinous substance covering the leaves of Ceanothus velutimis {the Cinnamon laurel) of North- West America, the saccharine excretion of orange-trees, the gummy matter on Lychnis Viscaria, &c., the resins of firs, pines, and other Coniferse, the sugar (pinite, p. 215) given out from the bark of the sugar-pine {Finns Lajnbertiafid), the M'ax of the leaves and stems of the candleberry myrtle {Myrica ceriferd), and the layer of wax ' which covers the wax-palm {Ceroxy'lon andicola), and probably flows from the base of the leaves. Of a similar nature are pro- I bably the excretions given out by the hair-like structures on the leaves of Drosera (p. 61), and the acrid substance on the hairs of the chick-pea {Cicer arietinuin), the gummy secretions of Primulacese, Sileneae, &c. — -these last being found only on particular plants, and serving special and not general purposes.^ The gyration of the contents of the interior of many cells (p. 20), and the cyclosis observed in the milk-vessels (p. 44), are also minor local circulations, each being a sort of imperium in imperio. Nothing of the nature of a true or general nourishing fluid can, however, be supplied by the latex of the milk-vessels, as supposed by some physiologists (De CandoUe, Schultz, &c.), v^^ho have even 1 On the subject of excretions the student is referred to the following works, in addition to those already quoted : Duhamel, Physique des arbres, i. 86-87 \ Brugman's De mutata humorum in regno organico indole (1789) ; Plenk, Phy- siologie ; Humboldt, Aphorism a. d. chemisch Physiologic der Pflanzen, 116 ; Cotta, Naturbet. uber Bewegung d. safts; Boussingault, Ann. de Chim. et Phys., 1841, 217 ; Unger, tiberd. Veget. v. Kitzbiihel, s. 149 ; Meyen, Physiol., ii. s. 530 ; Guillemin, Archiv. de Botanique, i. 398 ; Moldenhawer, Beitrage zur Anat. der Pflanzen 320; Gyde, Trans. Highland and Agr. Soc, 1845-47; Schleiden, lib. cit. ; Schultz, Die Entdeckung der Wahren Pflanzen nahrung ; Mohl, Vegetabilische Zclle, and trans, by Henfrey ; Chatin, Comptes rendus, XX. (1845) 21 - 29, &c. ; Roche, De Taction de quelques composes du r^gne mineral sur las vdgdtaux ; Cauvet, Etudes sur le r61e des racines dans I'absorp- tion et Texcrdtion, 1861 ; Sachs, Handbuch, &c. ; Bracconet, Ann. de Phys. et Chem. (1839), kxii. ; Unger, Ann. des Sc. Nat., viii. {1838); Meyen, Neues System d. Pflanzen Phys., ii. s. 529; Walser, Untersuch. iiber die Wurzel Ausscheidung, 1838, &c. I 270 GYRATION : CYCLOSIS OF LATEX : ASSIMILATION. been inclined to look upon it as the descending sap. Did the latex serve so important a purpose, we might be certain that it would be much more universally distributed throughout the vegetable kingdom. On the contrary, it is only found in a few orders, and has not even the same properties in all, being poison- ous in some, nourishing or innocuous in others. TrecuP looked upon it as a deoxidised fluid, analogous to the venous blood, which in passing into the vessels proper gets oxidised like the arterial blood. Hence he called the laticiferous vessels vetwus, and the vessels proper arterial vessels. It is, however, just possible, from the researches of Hanstein and Favre, that in the plants in which the latex is found it may serve some minor purpose in nutrition. There is, however, no doubt but that it is not a true or universal nourishing fluid which is organisable, the elaboration of that being confined, as we have seen, to the leaves. We are not, however, authorised, in the present state of our knowledge, to coincide with the ingenious theory of Sachs, that there are in plants two nutritive fluids, — one rich in nitrogenous materials which supplies the cam- bium ; and the other which forms the non-nitrogenous materials such as starch, inuline, sugar, &c., traversing as its pathway the bark, the pith, the periphery of the tubers and the parenchyma generally. Without going into details, we may see that this idea is contrary to some primary facts, and is held by but few botanists. ASSIMILATION. The sap has ascended to the leaves ; there it has been elaborated ; and finally the sap, so elaborated, has descended in a condition fit for the nutrition of the plant, the result of which is the growth of the tissues. Here, again, we are brought face to face with one of the most important, but at the same time most difficult, pro- blems in all vegetable physiology. At the very outset it seems difficult to imagine how materials all soluble in water, as the primary nutritive substances of the plant must be, can form substances like lignine, &c., perfectly insoluble in the same liquid ; and finally, how all the varied substances — oils, acids, salts, &c. — found within the cells, can be formed from the same set of materials. We see that there is one point of agreement in all plants — viz., that all produce a series of neutral hydrates of car- bon, out of which all the solid materials of plants are formed, and also the proteine substances which take so active a part in cell- development. We can easily see that all these materials are formed by some series of chemical changes within the plant ; by the reaction of various of these substances — either in their ^ Ann. des Sc. Nat., 1857, vii. 288-301. ASSIMILATION OF NUTRITIVE MATERIALS. 271 primary or secondary states — on one another : the result of which combinations we see in the cell-wall's incrustations and the cell- contents. For instance, cellulose, out of which the walls of the cells — the ultimate microscopic elements of all the tissues — are composed, in chemical composition is C, H, and O ; in other words, it consists of carbon and the elements of water. If, then, the CO2 taken in by the leaves is decomposed, carbon and the water (H and O) taken in by the roots remain ; so that we have thus the exact elements of cellulose supplied to us. We can see that every facility for these chemical reactions is found in the ever changing and interchanging of the cell-contents by means of exosmose and endosmose ; for if this law is true, they can never be for one moment at a stand-still : even were the plant filled with a liquid of uniform consistency, in a short time evaporation at some particular part would determine the commencement of endosmose and exosmose. As Mohl has pertinently observed, re- markable changes must occur in cells like those, for instance, of the leaves which have ammonia derived from the soil on one side of them in the ascending sap, and COg derived from the atmo- sphere on the other. We can see — as Richard has pointed out — that three processes at least are concerned in forming the sub- stances which the plant is composed of — viz., (i) a chemical action, by which the primitive elements of the plant — C, O, H, and N — are isolated and absorbed by it ; (2) an orgatiic or physiological action, by which the elements combine to form immediate princi- ples; and (3) 2. physical 2s:\\ovl, through which inorganic materials (metals, alkalies, sulphur, silex, &c.) which are found in the ash of plants are allowed to penetrate into the plant and form a com- ponent portion of it. Summing up our knowledge of the distribution of these sub- stances in the tissue, it may be said that (i) the cambium and the tissue which are formed from it are rich in nitrogenous principles ; (2) the parenchymatous tissues contain about all combinations of carbon and hydrogen, and their contents are starch, inuline, dex- trine, and sugar, resins, oils, colouring materials, organic acids, crystallised salts, &c. — the cortical cells secrete alkaloids (strych- nine, morphia, quinine, &c.) and caoutchouc ; (4) indurated cells — i.e., those thickened by internal deposits — contain air, lignine it- self being a product derived from cellulose; (5) combinations are not formed in the epidermis in general ; (6) cork, which does not long remain in a living state, is equally derived from cellulose. One parenchymatous cell labours for the benefit of another ; hence, as we shall see by-and-by, the little cells of the anthers prepare the substance which is in due course utilised by the larger cells, which generate the pollen-grains. The endosperm furnishes the necessary nourishment which the embryo requires. The cotyledons 272 ASSIMILATION OF NUTRITIVE MATERIALS. in their turn do the same good office for the young plant before it ha:s taken root in the ground and can nourish itself from the soil. The parenchymatous cells which surround the reservoirs of resin transform starch into a substance which gets brown under the ac- tion of iodine ; this again is changed into essential oil, which in its turn becomes resin (Schacht). Yet after all, we are not one whit nearer the question of how each of them, or out of what materials each of them, is formed. In the secret recesses of the plant are chemical processes going on that we cannot do more than guess at. We know such must be going on, and in some cases we can reasonably enough pretend to say what they must have been from seeing the result ; yet until we know how and in what stage and quantity each substance is brought into contact with the others, we are only vaguely groping our way in a thicket of conflicting hypotheses. Some of these processes the chemist may be able to demonstrate in his labora- tory ; but still chemistry will not enable us to explain all— for light, shade, and other imponderable physical agents, have their share in regulating these processes ; and above all, the vital principle which takes no share in the mere operations of the laboratory presides over those within the living plant. Indeed, in all the questions of assimilation, of only one thing can we be certain, and that is, that carbon and water remain in the plant, and are applied to the building up of its structure. Even that it is by the decomposition of CO2 that O is given off is by no means perfectly certain. For has not Mulder, an eminent Dutch chemist, even broached the opinion that O is set free from the decomposition of an organic sub- stance previously formed, and that the plant does not decompose CO2 because of its chlorophyll, but while the chlorophyll is forming ? Draper has even doubts whether nitrogen is not also given off, though it is now very generally admitted, as we have taught, that 0 is given off under sunlight ; but again, in addition to the hypothe- ses given, there is another — that it may be due to the decomposition of water. Again, we are not one degree surer as to what combina- tions the absorbed nutriment first enters into. At every step we meet with difficulties insolvable in the present state of our know- ledge. The process of assimilation is a threefold one — chemical, physical, and physiological — and is much too complicated for us, with our present means of research, to follow. Everywhere we are met by abundant crops of hypotheses, without any facts to sup- port them, and with theories in the presence of which facts fare but indifferently. Assimilation is essentially a question of organic chemistry, and there the botanist is glad to leave it. In a word, the author would best perform his duty to his readers if, following the example of his distinguished teacher, M. Duchartre— he at once informed them that so little is known about assimilation. THE INCREASE OF THE PLANT. and that little so imperfectly, that the limited space of a student's text-book is better occupied with matters regarding which we can speak more confidently and satisfactorily. THE INCREASE OF THE PLANT. In whatever way the ultimate materials out of which the organs are formed are derived from the descending fluid, the invariable re- sult is the nutrition of the plant, and the consequent increase of its bulk by the increase of the individual organs composing it. The nutrition of the plant is a twofold act. It consists, firstly, in keep- ing up the organs in their integrity ; and secondly, in increasing these, and thereby the whole plant. The way this is done is best seen in the stem of Dicotyledons. Here, as we have already seen, the stem is annually increased by layer after layer of wood being laid down, one over another, around the pith as the central object. If we examine the stem during the winter, we will find between the bark and the wood a cellular layer without green matter in it. This layer we already know as the cambhmi. In summer, when the sap descends, this gets gorged with the nutritive fluid, and at this time it is easy to separate the bark from the wood. The cells of this cambium are regular in shape, with thin transparent walls. If the bark is raised and the cambium rubbed off, no new wood is formed. However, if nothing interferes with its natural growth, insensibly in the pro- gress of growth some of these cells are elongated, their walls be- come thicker, and they then present the character of fibrous tissue. About the same time, a certain number of the cells scattered in the midst of the former augment in diameter and in length ; the thin walls show transparent punctations, either in the form of transverse lines or in scattered "dots," and thus get converted into barred and punctated vessels (p. 49). These form bundles united by cells, and so form a layer of woody matter exactly the same as the one before it, which it covers over. Some of the outer vessels branch and form a new coat of liber, thus giving the increase to the bark. All the newly-formed fibres and vessels take the same character as those over which they are superimposed. For in- stance, if cells are in contact with dotted cells they become dot- ted— if in contact with barred ones they have similar transverse markings, — and so on. Hence Duhamel said that " vessels produc- ed vessels, and cells produced cells." The rest of the process has ' en described in describing the development of the stem (p. >)■ This is the increase in diameter. There is, however, another increase, to which attention was first called by Link and Dutrochet, ■ind which they styled the lateral increase. Like the first, it con- s I 274 THE INCREASE OF THE PLANT. tributes to the increase of the thickness of the stem, but in a differ- ent way. After the vascular bundles have once formed, either in the bark or the wood, they have a tendency to divide into two by the formation of cellular tissue in their middle ; these two again in- to four, — and so on by the same means until at the end of the year perhaps twelve woody bundles will be found at the base of the same ; next year there may be twenty-four, — and so on. Now all this contributes to increase the diameter of the stem by pushing out laterally as it were — quite different in character, though in final result the same, from increasing the thickness by the formation of layers of superimposed wood. The increase in height of the dicotyledonous stem has been al- ready described (p. 76) as being effected by the growth of the ter- minal bud, which in the newly-germinated plant is the plumule. This is composed of an axis and of rudimentary leaves. As the axis elongates, the leaves expand and gradually take the characters they are destined to assume. At each " node " the year's growth terminates with the terminal bud, which is next year in a similar manner to cai-ry on the growth. At the same time, it increases in diameter in the manner already described — each year a new coat of wood covering that formed the year before. The axis is there- fore a series of very elongated cones, composed of the woody layers placed one upon the other. The summit of the innermost cone is arrested at the base of the second node or year's growth, that of the second at the third, and so on in succession with the others. It is then at the base of the trunk that the number of woody layers corresponds to the number of years of the plant. Thus, for example, a stem ten years old shows at the base ten woody layers, at commencement of second year's growth nine, eight at the third, and so on until there is only one at the summit. It is owing to this that the trunks of Dicotyledons are somewhat conical — in a word, " the number of woody layers being gradually more in number as we get from the summit to the base " (Richard). In endogefious stems we are not so well acquainted with the course the sap takes; but it probably ascends and descends in the isolated woody bundles, the cellular tissue also taking part in this function. Their increase we have already described (p. 95). In acrogenous stems the course of the sap is most likely also in the woody bundles. In herbaceous Dicotyledons, in which the woody bundles often remain separate, the course is similar. In ferns, Hoffmann considered there were no channels for the descent of the sap — the fluid simply ascending and diffusing itself through the substance of the plant in its pro- gress.^ Finally, it might be remarked that though we are enabled to see the cambium best in exogenous stems, it is also found in endogenous and acrogenous ones ; in the former, in the interior of 1 Taylor's Scientific Memoirs, vol. i. THE INCREASE OF THE PLANT. the woody bundles — and in acrogens, round them. In these stems, however, the cambium soon lignifies, and the increase is probably carried on at the upper ends of the bundles by means of unhardened cambium cells. We are, however, still much in the dark in regard to these questions. In Monocotyledons there is, in the vast majority of cases — espe- cially in those with woody stems — only a terminal bud which car- ries on the growth. If this is destroyed the plant dies. However, in a few cases, as in the screw-pine, &c., lateral buds are developed, and from them spring branches. Now we see that this assumed method of increasing the plant by producing the annual layer of new wood is exactly in accordance with what we have already been taught regarding the growth of cellular tissue, and is in all likelihood the right one. Du Petit- Thouar's (or rather Lahire's) theory ^ of the young wood being merely the roots of the bud, which he looked upon as a young plant rooted in the stem, is so entirely erroneous that it is aban- doned by nearly all scientific botanists ; and ranking as it does among the other abandoned theories of the production of new wood, need, in common with its companions in misfortune, have no further space wasted on it.^ To trace the growth of new tissue is much more difficult than most other researches in vegetable anatomy or physiology, where we can have the object under examination under our own eyes. Here all is concealed, and great care is requisite to avoid errors, I as the numerous futile attempts of former operators have abund- antly proved. A curious fact mentioned by Dutrochet would at first sight seem I to militate against the rationale of nutrition as explained in the fore- going pages. A number of stumps of firs {Abies fiectinata and A. excelsa chiefly) which were cut down within a few feet of the ground, produced annually each a*new though very thin layer of wood, without the intervention of any leaves on the stump to elaborate the ascending sap. In reality, however, this was not so ; for on closer examination it was found that the roots of these stumps were ingrafted on the roots of some trees of the same species growing in the immediate vicinity, the result of which was, that the leaves of these trees in all likelihood supplied the elabor- I ated sap out of which the annual layers of wood were formed on the leafless stumps.' 1 Adopted and extended by Goethe, Gaudichaud, Trecul, and others, * This vertical theory of the formation of wood, as, in contradistinction to the horizontal theory adopted in these pages, it has been called, is supposed to account for the growth of plants in an upward direction, and by the presence in some pines of adventitious roots which descend into the soil. » Similar facts have been stated several times since. For instance, at the 276 THE INCREASE OF THE PLANT. Finally, before leaving this subject we may point out an essen- tial difference between the nutrition of plants and that of animals. In animals, every particle of the structure is in course of time renewed by interstitial nutrition ; while in the plant, the parts, once formed, are never renewed in this manner, but either die and fall, to be replaced by similar organs next year, or remain unchanged, cease to be nourished, and therefore soon lose their vitality, while new parts are continually found to take their place' — these in their turn to be replaced by others. Whether the plant increases at a greater rate during the day or night has long been a subject of controversy,^ and is still sub judice. The latest researches on the subject are those of a Dutch botanist, Dr W. P. Rauwenhoff, made chiefly on Bryonia dioica, Wistaria Chinensis, Vitis orientalis, Cucurbita Pepo, and Dasylirium acro- trichu7n. He found, as a general result of his observations, that (i) the stem increases most during the day, less by night ; (2) that, however, during certain periods the nocturnal increase is greater — and as this is found in plants of very different natures and de- velopments, it indicates some general action the nature of which is not precisely known ; (3) the elongation of the plant is quicker in the afternoon than in the morning, though at certain intervals the opposite is true {e.g., in Cticurbita, from loth June to loth July), yet zs. 2. general covlxs^ the increase in length is greater in the after- noon ; (4) the ratio of increase differs in different species ; and (5) it usually corresponds to an increase or diminution of temperature, being greater when the temperature is higher, and vice versd — as might have been presaged from what we know of the effect of the same agent on the flow of the sap.^ meeting of the Scottish Arboricultural Society in 1873, Messrs Robertson and Sadler exhibited a stump of a larch-tree which had been felled about thirty years ago. The stump had continued ever since to increase by additions of wood to the outside, while the central part had decayed. It was found, on tracing the roots proceeding from the stump, that some of them had got in- grafted into the roots of another larch growing about three feet distant. 1 Ventenat, Bulletin de la Soc. Philom. , 1795 ; Meyer, Verhand. des Vereins zur Befurdnung des Gartenbaues in den Preussischen Staaten, 1828 ; Meyer, Linnea, 1829; Munter, Bot. Zeit., 1843; Mulder, Bijdragen tot de Natuur- kunde Wetenschappen, iv. 1829 ; De Vriese in Van der Hoven, and De Vrieses Tijdschrift van nat. geschiedenis en Physiologic, iii. 1836 ; and in Neder- landsch Kruidkundig Archief, iii. ; Hartig, Tijdschrift, ix. 1842 ; Karsten, Bot. Untersuch., 2d part, 1866 ; and Martin and Qu^telet in various papers. 2 Verslaegenen Medeelinger der K. Akad. Van Wetenschaffen (2d ser.. Sect, of Nat. Sc.), ii. 134-161 (1869). SECTION III. REPRODUCTION CHAPTER 1. GENERAL REMARKS ON THE FLOWER AND FLOWERING. "The fructification is," in the words of Linnaeus,^ "a temporary part of a vegetable destined for the reproduction of the species, terminating the old individual, and beginning the new." The aim and end of a vegetable existence is to produce flowers, and from them and by them fruit and seed, so as to continue and re- produce the species. To use the language of the famous Roman naturalist, " Blossoms are the joy of trees, in bearing which they assume a new aspect, vying with each other in luxuriance and variety of colours." The part of a plant concerned in reproduction is the flower, which, in a perfect state — z. when possessing all its normal parts, — consists of (enumerating from without inwards), i. iht calyx, com- F'g- I39-— A, Flower of Tulip with the external parts removed, showing the six sta- mens (x) surrounding the pistil (/). B, Single stamen enlarged, showing anther (a) and the filament or stalk (/). C, Pollen-grains enlarged, one of them discharging the fovilla. posed of the sepals; 2. the corolla, composed of the petals; 3. the stamens, each composed of filametit and anther; 4. the pistil, of one or more carpels, styles, and stigmas, — the whole supported on the termination of the pedimcle or flower-stalk, which corresponds to 1 Phil. Bot., 52. 28o GENERAL REMARKS ON THE FLOWER. the petiole of the leaf (figs. 139, 140). The calyx and corolla are, however, often wanting, singly or both— the only parts of the A B c Fig. 140. — A, Pistil of the Apricot. B, Pistil of the Orange. C, Flower of Valerian, cut vertically, a Ovary, containing the ovule or ovules ; b Style ; c Stigma ; d Stamen. flower essential to the production of fruit and seed being the stamens and pistils ; and even these may not be found on one plant, or in each flower on a particular individual plant. It may happen that the stamens are alone found on flowers on one part of a plant, while the pistil is alone found on the flowers on another part ; or quite as commonly the whole of the flowers of one individual plant of a species may have only siaminate flowers, while another may have only pistillate flowers : in other words, ona having only stamens, the other only pistils. As the union of both organs is necessary to the production of seed, the contact of the essential portions is accomplished by means which we will explain when considering the physiology of repro- duction. The calyx or outer covering, and the corolla or inner one (generally bright-coloured), are not essential, and are often entirely wanting. But no seed can be produced without the aid of the stamens and pistils. The seed produced, the functions of the plant have ended, so far as its aim of life is concerned ; the seed falls into the ground, or other medium in which it is to vegetate ; it germinates, grows up, produces leaves, then flowers ; then this flower performs certain functions, necessary to fertilise certain parts within the flower which produce the fruit — the fruit contain- ing the seed — this seed again reproducing and continuing the species ; and so the cycle of life goes on. All the other functions of the plant are only subservient to reproduction. After the flower GENERAL REMARKS ON THE FLOWER. 281 has arrived at that stage at which it may produce seed, the sub- sidiary corolla fades, while the lower portion of the pistil swells and becomes the fruit, contained in which are the seeds. We have said that all the above-named parts of the flower may not be present in every flower, and have instanced cases of varia- tion. If all the essential parts — viz., the stamens and pistils — are present, then the flower is said to be hermaphrodite j if only sta- mens or pistils, it is tmisexiial — the terms staminate and pistillate being applied to the particular kind of organs, stamens or pistils, found in such unisexual flowers. Again, a plant is said to be (i) jnojicEcioiis'^ when the stamens are on one flower and the pistils on another flower of the same individual plant. Such a plant is the maize or Indian corn {Zea Mays), where the staminate flowers or " tassels," as they are commonly known to the farmer, are at the vig. 141.— Flowering plant o( Carex areiiaria {c). a Female flower; i Male flower. summit of the stalk, while the pistillate flowers or "silk" are lower down. The hop, and various species of Carex (fig. 141), 1 fioTOs, one ; oikos, habitation. 282 GENERAL REMARKS ON THE FLOWER, also afford examples of monoecious plants. Again (2), dioecious^ plants are those in which the stamens are on one individual plant and the pistils on another {Ex., hemp {Cannabis saliva), Aucuba Japonica, &c.) ; (3) polygamous ^ flowers, in which the same species may have staminate and pistillate or hermaphrodite flowers on each plant, or on two or even three different plants. In various species of Viburnum, Hydrangea, and even in certain monstrous states of the whole cluster, owing to cultivation, as in the garden guelder rose [Viburnum Opulus), Gray has shown that in the blos- soms occupying the margin of the cyme both the stamens and pistils may be wanting. Such flowers are called neutral, being neither staminate nor pistillate. It occasionally happens, also, that the marginal or ligulate flowers of some of the " composite " flowers {e.g.). Coreopsis, may-weed {Maruta), and sunflower, may be neutral. Hemaphrodite flowers are the more common of the category, the rarity of the other kinds being in an inverse ratio to the order in which we have mentioned them. Various signs are used by descriptive botanists to express the character of a flower in the above respects. The following are the principal ones used : for staminate flowers, the astronomical sign of the planet Mars $ or J (the sign of the earth) ; for pistillate ones, the sign of the planet Venus $ ; while for hermaphrodite flowers the two signs are united as follows, ^ The following synopsis gives a precis of the conditions we have mentioned, with a few minor terms : — A. Complete Flowers [in four verticils]. L rioral Envelopes (perianth or perigone). 1. Calyx, ist verticil composed of Sepals. 2. Corolla, 2d verticil composed of Petals. II. Sexual or Reproductory Organs. a. Considered in reference to themselves. 1. Andrcecitivi. 3d verticil formed of Stamens. [Also of filament, anther, and pollen.] 2. Gyncecium (pistil), 4th verticil formed of Carpels. [Also of ovary, ovules, style, and stigma.] /3. Considered in reference to their functions. The inflorescence being in one flower, renders this flower Herma- phrodite. B. Incomplete Flowers. I. Those wanting the Perianth. 1. Wanting the corolla, the flowers are /i/c/a/o//^ (monoperianthous or monochlaniydeous). 2. both caly.x and corolla ,, Naked. 1 Suo, two ; oi/co?, habitation. 2 TToAi/?, many ; and ■yo/ie'iu, I marry. GENERAL REMARKS ON THE FLOWER. 283 II. As concerns the Sexual Organs. 1. When the stamen is alone present the flowers are Staminate or male. 2. pistils are ,, ,, Pistillate or female. 3. When there are staminate and pistillate flowers on the same plant the flowers are Moneecious. 4. When there are staminate and pistillate flowers on different plants Dicecious. 5. When unisexual and hermaphrodite flowers are on the same plant, the inflorescence of the plant is said to be Polygamous. 6. When the stamens and pistils are entirely wanting Neutral. Flowers generally grow from the axils of little leaves called bracts, and though they are generally at the end of peduncles, when they are called pedunculated, yet this flower-stalk may be wanting ; in this case the flower is styled sessile. This peduncle is apparently a branch, at the summit of which the parts which it supports are united in the form of appendages to the axis, which is their support. This summit, to which they are all attached, and which is usually more or less expanded, is called the receptacle, to- rus, or thalamus. The calyx, corolla, stamens, and pistils are, notwithstanding their varied forms and functions, only modifications of one another, and all are, again, only modified leaves. So that not only in the arrange- ment of the parts of the flower, but in their character also, the organs of reproduction are modifications, for a particular purpose, of those of nutrition. The flower is in reality terminated by a bud and shortened branch, the axis of which is not elongated further, but has its leaves (viz., the sepals of the calyx, the petals of the corolla, and the stamens and pistils) arranged in the form of a rosette, like what we see in the leaves of many plants — e.g., the house-leek. The four circles of the parts of the flower appear to be simply ver- ticils, like the verticils of leaves. Yet when we carefully 'examine the arrangement of the floral organs, we will find that, like the leaves, they are arranged in a spiral, closely crowded together, but nevertheless, with the component members of the verticils, plainly alternating one with another. To this law of the alternation of the sepals of the calyx with the petals of the corolla, and these again alternating with the stamens, and the stamens with the pistil or divisions of the pistil, there are very few exceptions. Such an exception might seem to be found in the tulip, where there are six stamens opposite the six faces of the segments of the " perianth," or gay-coloured, corolla-looking, outer covering. This is not, how- ever, really the case ; for in this plant, and indeed in most mono- cotyledonous " flowers, " the calyx is alone present, the place of the corolla in the tulip, for instance, being supplied by the gaudy- coloured calyx. HQwever, some botanists take another view, and 284 PEDUNCLE. say that in monocotyledonous plants there are both calyx and corolla present, but that the calyx consists of three sepals, the corolla of three petals, and that the androecium or staminal whorl is in reality also in two verticils, each of three stamens. Hence in this manner it is explained how in such plants we find the stamens opposite to instead of alternating with the segments of the whorl of floral organs next to them. In the great division of di- cotyledons, again, instead of having the floral organs in three, or multiples of three, as in monocotyledons, five and multiples of five is the rule. There are, however, numerous exceptions, as we shall see by-and-by. PEDUNCLE AND BRACTS. Before commencing to consider at length the various parts of the flower, and the way these flowers are arranged on the stem, it may be well to describe certain supplementary or variable parts connected with it — viz., the peduncle, and bracts and their modifi- cations. Peduncle. — The peduncle or flower-stalk, when present, is a veritable branch of the axis (axophyte), and may be either simple Fig. 142.— Plumose peduncles of the Wig tree {Rhits Cotiniis, L.) pd Fertile peduncles ; /r Fruits ; peC Sterile peduncles, branched and plumose. or branched. In the latter case the branches are called pedicels. As we shall see when discussing the inflorescence, there may be primary, secondary, and tertiary axes; and, in reference to its PEDUNCLE : RECEPTACLE. 285 position on the main axis, it may be axillary or tcrmmal—i. e., it may arise in the axil of a branch or at the end of a branch. Some pedun- cles, as in certain species of Solammi, come off opposite to leaves ; but when speaking of the scorpioidal inflorescence, we shall return to this. Finally, peduncles may be unifloral, bifloral, trifloral, or multifloral, according as they bear one, two, three, or more flowers. In shape the peduncle varies, being cylindrical, com- pressed, and grooved. In the Q.2Ls\s.t.yN {Anacardhcjn occidentale) it is the large succulent coloured expansion on which the nut is supported ; while in Vallis7ieria, &c., it is spiral ; and in Alysstcm spiiiosum it is spiny. Peduncles may often branch, the branches being very numerous, and yet produce no flowers at their termina- tions, as in the case of Rhus Cotiniis (fig. 142). Receptacle. — This is the summit of the peduncle on which the floral organs rest, or to which they are attached — hence the name ot Thalaimis (bed) some- times applied to it. In shape it may be coni- cal {Rammcuhcs, Helle- bore), flattened {Cerasti- ntn),or,2iS in Nelumbium, dilated into a large top- shaped body nearly en- closing the pistils, each in a separate cavity. In Myosurus the peduncle terminates in an elon- gated form, which in certain stagesof the fruit cause's the peduncle to look likeamouse's tail — hence the familiar name applied to the plant ; while in the strawberry it is the expanded suc- culent receptacle which forms the well-known " fruit " — the real fruits, however, being only the minute carpels, famil- iarly called " seeds," at- tached to the surface of this swollen receptacle. Fig. 143. — Dorstenia Conirnyerva. in flower, showing also the "nodose" is used medicinally as a diaphoretic ; mersed in the receptacle. a Entire p ant rhizome, which b Flowers im- immersed In Dorstenia the flowers are in an expanded receptacle (fig. 143). It occasionally happens that we find in plants — for example. Solatium Gtmieense, Lamk. — the peduncle arising apparently not from the axil of a leaf ; but in 286 RECEPTACLE : GONOPHORE : ANTHOPHORE. the case of such an extra axillary peduncle, we find that in reality it is adherent to the axis for some distance, and only becomes free at the place from which it seems to spring. A less abnormal case is that in which the peduncle is united along the median line of the leaf from the axil of which it springs. Examples of these epiphyllous inflorescences are afforded by Dulongia acuminata, and notably by the remarkable Japanese shrub, Helwingia rtisci- flora?- In a Diosmaceous American plant of the genus Erythro- chiton {Hypophyllanthus), the peduncle adheres to the under sur- face of the leaf, such an inflorescence being called by Planchon, who described this singular exception to the ordinary rule, hypophyllotis. It not unfrequently happens, as in the pinks, and markedly in Silene, that there is a considerable distance between the calyx and corolla, by the development of the internode between them ; so that a stalk on which the rest of the flower is borne is formed within the calyx. Again, in Gentians the fruit is borne on a stalk by the formation of an internode between the stamens and pistil. This kind of stalk is called a stipe, and the organ or set of organs thus elevated is said to be stipitate. If it elevates the petals, Fig. i/^^.—Passi/fora Loiedoniatia, Hort, entire flower, d d Numerous coroUine filaments ; e e Stamens ; / Pistils borne on the gonophore. stamens, and pistils, it is called the anthophore (flower-bearer), as in Sap07iaria officittalis (fig. 145) ; the gojiophore when it supports both stamens and pistils, as in the passion-flower (fig. 144), Capers, 1 Of W, Dans, Osyris Japonica of Thunberg ; see Decaisne in Ann. des. Sc. Nat. vi., 1836, p. 65-76, pi. 7. GYNOPHORE : BRACTS. 287 Magnolia (fig. 146), &c. ; and the gyitophore, gynobase, or caro- phore when, as is most common, it bears the gynoecium alone. The stalk, which sometimes supports each simple pistil or carpel of the gynoecium, as in Coptis, is called a thecaphore} This does not, however, in reality belong to the receptacle at all, but to the pistil itself, and is homologous with the leaf-stalk.^ Bracts. — In many plants the flowers spring from the axils of leaves (floral leaves) differing in no appreciable degree from ordinary leaves. But in others the leaves from the axil of which the flowers rise have a regular gradation from ordinary leaves up to what are called bracts — these bracts being, however, veritable leaves, which, as they ascend the stem, change their form and col- oration, until the uppermost ones not unfrequently assume the appearance of petals. In being entire or divided, bracts also ape the nature of leaves. In position they likewise affect the charac- ter of leaves, being alternate, opposite, or verticillate. Though ordinarily they have the same phyllotaxis as the leaves of the plant on which they are found, yet it will occasionally happen that a different arrangement will present itself. For instance, in Cam- panula erinus the leaves are alternate and the bracts opposite. ^ Under the special name of Podogyne, Mirbel has described a long narrow extension of the base of the ovary in Astragalus galegiformis and a great num- ber of other LeguminoscB ; but to apply a separate name to a thicker or thinner portion of the same organ, and then a separate name to the organ (or in the case of a fruit) so shaped, is the rcductio ad absurdum of name-making. * Gray, lib. cit., 267. Fig. 145. — Longitudinal section of Saponaria officinalis, L. (Soapwort), with a semi-double flower, j Calyx ; c c Petals furnished with appendages or lamelte a ; si Styles ; ov Ovary. The corolla, stamens, and pistils borne on the anthophore. Fig. 146. — Magnolia grandiflora, L. Mass of pistils or carpels of pistils, p, supported by a large long gynophore (a). 288 BRACT : BRACTEOLES : INVOLUCRE. Fig. Occasionally these bracts will attain a great development, and a pnlhancy exceeding that of the flowers themselves. This is seen in the bracts of Salvia fulgens, Atjtherstia nobilis, Poinsettia fiul- cherrima, Bougainvillea spectabilis, Musa coccinea, and various of the Bromeliaces or pine-apple order. The linden supplies an ex- cellent example of the nature of a bract. In fig. 147,/ is the nor- mal leaf, and b the bract of a linden {Tilia platyphylla. Scop.) ; pd the peduncle, bearing the two fruits fr, attached in its inferior por- tion pd' to the midrib of the bract. (The student's attention may also be called to the fact that the two sides {a a') of the normal leaf of the lime are unequal.) In some species the stem above the place from which the flower arises bears several bright-coloured bracts, ga- thered into a terminal tuft (coma), as seen in Salvia Horminum, Lavandtda Stcechas, Ananassa sativa (pine-apple), &c. Accordingly, in such plants the bracts have no flower-buds in their axes. In Barleria and Exoacantha the bracts are transformed into spines, and in Bauhinia into tendrils. Bracteoles. — Suppose, now, that in addition to the bract, as ^ figured in Tilia, there was another smaller one inside of it, and at the base of the ramifications of the peduncle {pedicels), this would be called a bracteole, or little bract. Involucre. — We have seen that a flower or a flowering branch may spring from the axils of a bract. Now, if a stem terminates by a number of peduncles, or by flowers very close together which seem to end about the same level, the bracts will be equally arranged around the same point, and will form an envelope sur- rounding its base : this is an involucre. There are two kinds of involucres : i. In composites. In this order of plants a great number of small florets are placed together, and at about a com- mon level on the summit of an expanded peduncle (as is seen in the daisy, dandelion, &c.) ; hence the older botanists called such plants composite plants, and the name has been applied to the great order Compositas (figs. 148, 150). All these florets are en- veloped by a number of bracts, to which L. C. Richard applied the name of Periphoranthium, Cassini that of Pcriclenium, and 147.— Leaf and fruit of Linden [Tilia ^latyj>hylla), with bract. INVOLUCRE. 289 Linnaeus, first of all, that of the commo?i calyx. The term in- volucre is now more commonly used. This general involucre Fig. 148. — Aiithemis rigescens, W., one of a group of flowers called " Compositae," or " composite flowers,"cut in a longitudinal section to show the numerous flowers of which the capitulum is composed (nat. size). Fig. 149. — Flower or capitulum of a Thistle (Car duns pyc- nocephalus, D. C. ) , entire, with the im- bricated involucre. of compositae presents, however, various forms, which have been used by systematic botanists to furnish characters for the division of this extensive order into smaller groups. For instance, it is often (a) scaly J in other cases the bracts are ((3) superimposed and Fig. 150. — Capitulum or flower-head oi Erynginm campestre, in longitudinal section, showing the large involucre. imbricated (fig. 149) ; (y) in HeMinthia echi'dides, Geert., Senecio (groundsel), &c., the involucre is surrounded at the base by a row of bracts like a calicula around a calyx, hence such bracts have been styled caliculatedj (S) lastly, there may be a single verticil of bracts with their edges, when they come in contact with each other, united so as to appear like a gamosepalous calyx (p. 304), as in species of Buplevrum, Lavatera, &c., such bracts being called gamophyllous, in contradistinction to the opposite case of polyphyllous bracts. The bracts of an involucre may, like ordinary leaves, be terminated by spines, hooks, &c., as seen in thistles {Carduus), Burdock {Arctium Lappa), teasel {pipsacus) — \\As 1 290 INVOLUCRE : CALICULA, character in one of the last-named genus, the fuller's teasel (Z>. fullo7tmn), having caused it at one time to be used in card- ing, &c. 2. In Ujnbellifei'cs, a large order to which the hemlock- like plants belong, we find the second division of involucres. In this order we find a general involucre (the collerette of the French botanists) round the main, and several little involucelles around the base of each secondary umbel or umbellule {Ex., the carrot). In some plants of this order (^Angelica, Scaiidix, Charophylhim, &c.) the involucre disappears, and only the involucelles remain. In a few {e.g., Pastinacea sativa, L.) it is reduced to one or two bracts; while in a third set they fall off entirely, leaving the umbel naked {e.g., Pimpinella Anisiim, L.), the fennel {Fcenicuhun officinale, AIL), &c. Though involucres generally surround several flowers (in which case they are plurijloral, yet instances are not wanting in which there is only a single flower surrounded by an involucre. Such a case of u7iifloral involucres is exhibited in Nigella damascena, L. In the common hepatica {Anemone Hepatica) the involucre looks very like a calyx, and indeed has been so described by some botanists, though it is usually styled a calyciform involucre. It, however, by insensible degrees, graduates into the ordinary pluri- floral involucre, seen in various other members of the same genus and order. Calicula. — Occasionally we have at the base of the calyx several bracts in union, the divisions being either the same number as the divisions of the calyx, and alternating with them, or a different number. Fig. 151, showing an entire flower of an Indian straw- berry {Fragaria Indica, Andr.), gives an example of the first case. In this plant the calicula is much larger than ' the calyx itself. Our common strawberry, as well as the allied genera, Geum, Potentilla, &c., possesses an analogous calicula, but much smaller, and apparently, on first sight, differently arranged. The second form of calicula — viz., in which the divisions of the calicula are generally in number different from and non-alternating with the divisions Fig. isi.-Entire flower of Fra- of the calyx— is sccn in the mallows garia Indica. s s s Calyx ; i i i i i ^nd the greater number of the genera Bracts forming a calicula (x/i). ^j. ^^^^^ MalvaCCce. In thcSC plants the divisions of the calicula are rarely equal to the divisions of the calyx, and are sometimes free, sometimes united one to another in such a manner as to appear like a second gamose- CUPULA : SPATHE. 291 Fig. 152. — Entire flower of DiantJncs barbatns, L., with an imbricated caliculaof six bracts (i/i). palous calyx. The latter kind of calicula is frequently styled by descriptive botanists regular or calyciform calicula j but, strictly speaking, the term would be more applicable to the first kind. Among the pinks {Dianthus), and especially in Dianthus barbatus (fig. 152), we find an imbricated calicula. In the figure it will be seen that the calicula is composed of six bracts, rather expanded inferiorly and attenuated superiorly, arranged in three pairs, which overlap each other. In the ordinary cultivated garden pinks, a curious monstro- sity is often seen ; the bracts become numer- ous, and overlap each other in many pairs, while at the same time the flower becomes badly developed, or atrophied.^ Cupula? — This form of bract is familiarly seen in the acorn of-the oak. The cup, which surrounds the gland or acorn, is an involucre of little bracts, which, after having covered many flowers, remains, and accompanies the fruit, which it either partially or entirely covers. This cupula only covers the female flowers. The " scales " of the cup, which differ in form in different species, are the bracts. In the species figured (fig. 153), the cups are, on account of their richness in tannin, used for dyeing black. In the chestnut, as well as in some of the " overcup " oaks, the cupula quite surrounds the fruit, when it is said to be pericarpoidal — i. e., having the appearance of a pericarp or wall of a fruit. Spathe. — Hitherto we have only spoken of bracts as seen in Dicotyledons ; the remain- ing four which we shall de- scribe are found among the Monocotyledons. This is the large sheathing bract which surrounds the flowers of vari- ous monocotyledonous plants, and may be either composed of one Dract {uuivalvularox moiiophyllous) or of two (bivalvular or diphyl- lous). Palms Arace^ (fig. 154), i,-is, Narcissus, &c., all show ex- cellent examples of the spathe. ' Duchartre, 1. c, p. 452. 2 Little cup. Fig. 153 —Gland, Qiiercns ^Egilops, L., surrounded on the lower portion by a cupula of foliaceous bracts, cp (nat. size). 292 SPATHELL.E : GLT^mE : GLUMELLA. Spathellcp are the little spathes surrounding each subdivision of the general inflorescence, surrounded by a common spathe, as in the palms. The spathe may present great differences in form, in dimensions, Fig. 154. — Aniin vtaculatnm (Cuckoo-spit), one of the Araceae, showing the spathe (a) and the spadix (V). in coloration (being either herbaceous or of bright colours), in consistence {foliaceoics, thin, dry, scariaus, or completely woody, 3& in some palms), or it may contain one, two, three, or a number of flowers {tmijloral, bifloral, trifioral, and imelti/loraf). In some palms, when it may reach a length of more than 20 feet, the spathe may embrace as many as 20,000 flowers. The spathe frequently (as in the case of palms, Pothos, Typha, &c.) becomes caducous after the flowers which it protects in the young state have become developed. Glttme and Glumella. — By most authors these are considered -of the nature of bracts, and are seen in grasses and Cyperacecc, where GLUME AND GLUMELLA. they play a part analogous to that of the perianth of many other monocotyledonous plants (figs. 16S, 169). The flowers of grasses are attached in distichous order on a common axis in little groups called spikelets, which in several genera consist of but a single flower, and which are distributed along the stem in various ways (fig. 170). The common rye-grass {Lolhi7H perenne, L.) supplies a good typical example of the way these spikelets are arranged on the common axis. Each of these spikelets is enclosed within two bracts, placed opposite one another, but attached, the one a little below the other. This common envelope constitutes the ghcmes?- Again, each floret is enclosed within its own proper envelope or scales, which has been called a glwnella? The two leaflets or palece of this glumella are unequal in size. The exterior one is (fig. ■ 155) the largest, and is ordinarily green and firm, and provided with a median nerve, and lateral symmetrical nerv- ules of unequal number. Accordingly, it has been called hnparinerved palea. The one next to the axis is, on the other hand, thin, dry, translucent, smaller, and placed a little higher up, and shows, in the opinion of Schleiden, Duchartre, and other bo- tanists, that the glumella is not, as Robert Brown thought, " a floral envelope, comparable to what is seen in the flower of phanerogamia in general," but only two leaflets, which bear the relation of brac- teoles to the bracts which form the glume. This internal palea, on account of the two symmetrical nerves which are seen in it, has been called the pari- nerved palea. Finally, the singular floral structure of the gramines is further complicated by the pre- sence of an interior circle, composed of rarely three, pig. 155.— Part but often of two, little scales, situated a little in front °^ ''°^^er of of the external palea; these are (fig. 155, sq) the nalTaiel^wfth paleolcB, squaimilcE, glumellula:, or lodiciilce (De removeTtolho"^ Beauv.) Many botanists are inclined to look upon sq, the 'lodicute these as the true perianth of grasses (Duchartre). styie'^"aTnfhers'^ Ordinary bracts frequently fall off when the bud in their axil expands ; and in some Boriganaceae, and in most of the CruciferEe, 1 Of Jussieu (ghcmes, Latin) ; the calyx of grasses and cyperace^ of Linn^us ; the Upicene of Achille Richard ; the b0.le (French) or tegmcn (Latin) of Palisot de Beauvois ; peristachyum of Panzer ; the perianthclium of Petermann. 2 By Link, Mirbel, and others; Linnceus called it a corolla, and Robert Brown, who looked upon it as a true floral envelope, gave to it the name of p'erianth ; De Candolle and his followers named it the perigonium, while De Beauvois named it the stragulutn (stragule). I 294 FLOWERING. they are entirely wanting, sucli inflorescences being termed ebrac- teated. The outer bracts of involucres do not generally produce flower-buds, but, as in the case of the " hen and chicken daisy," this may occasionally happen ; and it may also occasionally happen that, as in the case of viviparous flowers, the axils of the bracts, instead of giving rise to flower-buds, produce leaves instead — such a mon- strosity showing, amid many other proofs, that the flower-bud is only a metamorphosed leaf-bud. We will now consider each of the floral whorls more in detail ; but before doing so, we may profitably discuss the nature of the operation known as flowering. FLOWERING. Flowering an exhaustive process. — Flowering is directly anti- pathetic to nourishment — plants, as a rule, flowering in a ratio inverse to that of their luxuriance of growth. Take, for example, maize or Indian corn. For its successful cultivation, a mean summer temperature of 65° Fahr. is requiicd, with a mean 2° higher in July. In southern latitudes the warm spring develops the juices of the Indian corn too rapidly; and accordingly it runs to leaf and stalk, to the neglect of the seed. In the West Indies, for in- stance, it rises 22 feet in height, but produces only a few grains at the bottom of a spongy " cob " too coarse for human food. In the Southern United States the corn grows to the height of 15 feet ; but the produce is much less than in the Northern States, where the stalk is only from 7 to 10 feet. Hence, in order to make a tree or bush bear fruit, it must be pruned, otherwise the nourishment which was necessary to produce the flower goes to nourish the luxuriant growth of wood and leaf. Again, the gardener girdles a tree in order to make it bear fruit more luxuriantly ; in other words, he cuts off a ring of bark, by which the descending (elabo- rated) sap is kept in the branches above the "girdle" — the result being that these branches bear fruit abundantly, while the shoots below do not blossom, but send out leafy branches. For a similar reason, as Gray remarks, the flowers of most trees and shrubs which bear large or fleshy fruits are produced from lateral buds resting directly upon the wood of the previous year, in which a quantity of nutritive matter is deposited. So, also, a seedling shoot which would not flower for several years, if left to itself, blossoms the next season when inserted as a graft on to an older trunk, from whose accumulated stock it draws. Accordingly, the student must see that flowering is an exhaustive process, requiring as it does such a large amount of nourishment ; yet if the plant is placed in too rich soil, it either rots or runs off to leaf without bearing flowers. Animals flower within a few weeks of the time FLOWERING. the seed is placed in the soil, and so soon exhaust themselves. Biennials, again, soon exhaust the supply of nourishment stored up in the roots ; while shrubs and trees do not flower until they are strone enoueh to bear this strain on their constitution, and hence are perennials. Linnteus remarked that however hardy a biennial might be before flowering, it perishes at the approach of the suc- ceeding winter ; nor can artificial heat preserve them. This is attributed to exhaustion of the vital forces by flowering. Several perennial or even shrubby plants of hot climates, become annual in our gardens — e. g., Tropceohtvi or Indian cress, Mirabilis Jalapa, &c. On the other hand, some biennials flower and fruit their first year, and thus become annuals — as, for example, accord- ing to Thilo Irmisch, is often seen in Melilotus dentata and Echinospermum Lapptila. According to Duchartre, the black henbane {Hyoscyamus niger), which is normally a biennial, has been known to become annual ; and these individuals have been described as a distinct species under the name of H. agrestis. The age of a plant has also an effect on flowering, and some plants have a predisposition to flower early. For instance, the " Bengal roses " {Rosa seinpervirens and hidica) flower before the seminal leaves have died away.^ Feebleness of constitution, also, sometimes assists in causing the plant to flower, while excess of vigour in- jures it in this respect. Hence plants brought from a distant country will often flower immediately after a sea voyage, though not for a long time again. Gardeners take advantage of this pecu- liarity, and by arresting the vigour of a plant secure flowers, when otherwise they would not have been produced. If a tree, especi- ally of a late-fruiting variety, bears an excessively abundant crop of fruit one year, it will often bear none the next year. This peculiar- ity is equally seen among wild as among cultivated plants. On the other hand, if no fruit appear one year, the tree will accumu- late strength, and most probably bear abundantly next season. How exhaustive a process flowering is we see in biennials like the turnip and carrot. The edible portion of both these plants contains the store of nourishment accumulated for the nutrition of the flowering plant. After the plant has flowered, we see that it has quite exhausted this store in addition to what it had taken up directly from the soil. The farmer accordingly, unless he wishes to obtain seed, takes his " root crops " out of the soil before they have flowered. Again, the bamboo, a gigantic grass of intertropi- cal countries, after attaining a height of 60 or 70 feet, flowers and 1 Early flowering sometimes occurs as exceptional cases in plants. For in- stance, in the ' Gardeners' Chronicle,' 1873, P- 213, is figured a cocoa-nut palm from Bengal producing flowers of both sexes while still in the seedhng state, though these trees do not naturally produce their flowers until they have attained some age and size. 296 FLOWERING. fruits, and then perishes. The sugar-planter is also well aware of this, and cuts the canes before they flower, otherwise the sacchar- ine juice would be consumed in supporting the strain on the plant's constitution. We see a practical application of these facts in the horticulturist being able to convert annuals into biennials, or even to prolong the life of the plant indefinitely, by not allowing it to seed ; but if once the plant is allowed to seed, whether this maybe in the first or second year, the result is the same — the plant's exist- ence is over. For example, the common garden larkspur has given origin to a double-flowered variety, which of course bears no seed, and has therefore become a perennial instead of an annual. The common mignonette {Reseda odoratd) can thus be converted into a perennial by preventing its seeding. Cabbage-stumps planted for seed, it is also affirmed, may be made to bear heads the second year by destroying the flower-shoots as they arise ; and if the pro- cess is continued year after year, the result will be that an annual plant, as the cabbage naturally is, will be converted into a kind of perennial. Again, the Agave Americana, or " century plant," so called because in our conservatories it only flowers about once in 100 years,^ flowers in the warm climate of its native Mexico when only 5 or 6 years old; but the process is so exhausting, that to nourish the large flower, the juice (fermented under the name of "pulque " and " mescal ") is exhausted, and the plant perishes 'kfter flowering and maturing its fruit. The large Talipot palm (Co- rypha), which grows to a great height, bears immense clusters of flowers, and produces a great crop of nuts. The effort of so doing is, however, too much for it, and the tree perishes after the first season. Flowering, therefore, differs from the production of foliage in so far that it consumes the stored-up products of the plant without giving anything in return. Instead of taking CO2 from, it gives back CO2 and water to, the air. The flowering is the most exhaustive of the reproductive processes, though fruiting is also somewhat exhausting. In the fruit and seed, however, the nutri- ment is stored up in a concentrated form for the future use of the new individual in the seed — viz., the embryo plant. Flowering is also accompanied by an evolution of heat considerably over the normal temperature of the plant, owing to the fact that "when carbon is consumed as fuel, and the oxygen of the air converted into CO2, an amount of heat is evolved duly proportionate to the quantity of carbon consumed, or of CO2 produced " (Section IV.) A ^period of rest is needed. — If a plant leafs too luxuriantly, or is grown in too rich a soil, there is , often no seed produced. Hence Northern trees transplanted to the tropics often do not flower; 1 This is a somewhat arbitrary popular generalisation. The truth is, that it only flowers once in a great number of years, generally once in 50 or 60. FLOWERING. 297 and transplanted trees generally flower the first year after their transplantation, though not a second time until after a long inter- val, because during the first year there has been a check to their growth, owing to the transplantation. However, if the tree is not injured or checked in transplantation, the contrary fact is true. A period of rest is required after flowering. This season of rest is supplied by the dead season of winter and autumn, in which latter period most of the trees and shrubs, and other perennial plants of temperate climates, form the flower-buds for the ensuing year. In the tropics, again, the dry season supplies the necessary season of rest. In the Canary Islands, the growing season is from November to March — the mean temperature of this season, corre- sponding to our winter, being 66° Fahr. ; while that of the summer (April to October), when it seldom rains, is as high as 73° Fahr. During this season the soil is baked like a brick, and with the exception of the succulent plants, vegetation almost disappears. Thus the dry season brings a period of repose to plants, just as the cold season does in our climate — " the roots and bulbs lie dor- mant beneath the sunburnt crust, just as they do in our frozen soil. When the rainy season sets in, and the crust is softened by moisture, they are incited into growth under a diminished tem- perature, just as with us by heat ; and the ready-formed flower- buds are suddenly developed, clothing at once the arid waste with a profusion of blossoms. The vegetation of such regions consists mainly of succulent plants, which are able to live through the drought and exposure ; of bulbous plants, which run through their course before the drought becomes severe, then lose their foliage, while the bud remains quiescent, safely protected under ground until the rainy season returns ; and of annuals, which make their whole growth in a few weeks, and ripen their seeds, in which the species securely passes the arid season." — (Gray.) Heat is one of the most powerful of the exterior influences ex- erted on flowering. Each species has a mean temperature or a su7n of degrees necessary for flowering. Thus Gasparini has, in a table from which the following examples are culled, given the following as specimens of the mean heat required for the flowering of certain plants : — Fahr. Fahr. Robinia, . 57°2 Hazel, . . 37°4 Peach, . . 4i°oi Apricot, almond, 42°8 Cherry, pear, &c., 46°4 Lilac, , . , 48°2 Barley, wheat, 6o°8 Chestnut, . 62°6 Vine, . . 64°4 Maize, olive, &c., 66°2 It is not easy to give the sum of degrees of heat necessary for the flowering of all plants in regard to which calculations have been 1 The degrees Centigrade are not reduced to the hundredths of a degree. 298 FLOWERING. made, as different writers take different methods of calculating it. In the same country and the same year, a plant often flowers late or early, according to the degree of heat it is subjected to ;^ while the same species growing in different countries opens late or early, according as the country may happen to be north or south, or be hot or cold. Schubler says that each degree of latitude in- fluences the time of flowering of a particular species a quarter of a day ; and this difference of time in flowering has, of course, an equal influence on the fruiting of the species.^ Dryness also affects flowering in this respect, that wet increases the foliage, and therefore acts indirectly in moderating the flower. Hence Britain and other equally damp countries — particularly the " Emerald Isle" — are specially distinguished for the green luxuriance of their vegetation, in comparison with dry countries. The gardener can accordingly take advantage of these facts to vary the influ- ences under which he desires to place the plants in his conser- vatories, according as he wishes to obtain early or late flowers and fruits. " Forcing," for instance, is only an application of the foregoing principles, and consists in a skilful alternation of the periods of repose, by subjecting a plant to heat in a hothouse at one season, and cold in a frigidarium at another. The cultivator thus gives plants an artificial season of rest by the application of cold ; and then by the influence of heat, light, and moisture, causes it to grow at a season when it would have been quiescent. Thus at will he retards the periods of flowering and of rest, so as in time to completely invert them. Lastly, each plant flowers at particular season, and opens and closes at particular hours ; but this we shall have occasion to discuss in subsequent pages — (Section IV.) 1 See the very instructive reports on this subject, so far as regards the flowering of plants in the Edinburgh Botanic Gardens, by Mr James M'Nab, in Trans. Bot. Soc. Edin. (passim). 2 See for further discussion of this question the subject of Phyto-geography. 299 CHAPTER 11. THE PERIANTH, OR FLORAL ENVELOPES. In a perfect flower there are four whorls of organs— viz., the pistil, the stamens, the corolla, and the calyx. The Calyx'^ is the most external of the four, and, in common with the corolla, con- stitutes the Perianth or Perigone^- or envelopes which surround the essential reproductive organs — viz., the stamens and pistils — and, like the corolla, may be either absent or present. In Dichlamy- deous ^ plants, both calyx and corolla are present ; in Monochlaviy- deous'^ only one, the calyx, remains; while in Achlamydeoiis^ plants, both calyx and corolla are absent. The segments of the calyx in most cases alternate with the segments of the corolla. CALYX. The calyx is composed of leaf-like divisions called sepals^ — these sepals being either coalesced with each other wholly or in part, or distinct. Form and Nervation of Sepals. — In appearance the sepals are not unlike the scales surrounding buds. In shape they vary little. They are generally more or less ovoid, entire, or slightly dentate or crenulate, and rarely^ deeply divided. To the forms and divisions of the margins of sepals, the terms used in the descrip- tion of leaves are also applicable, so far as necessary. Thus sepals may be winged, obtuse, lanceolate, cordiform, &c. ; and their varieties in shape are occasionally used as characters for species. The nervation of sepals is usually simple, and corresponds to that of the leaves of the species of plants to which the calyx belongs. In Dicotyledons, the venation of the sepals is accord- ingly usually netted, and in Monocotyledons parallel, the paren- 1 Calyx, a cup ; plural calyces. I prefer using the Latin plural rather than the barbarous English " calyxes." ' irepl, around ; ai/flos, flower : irepl, ydi^os, reproduction. " !t9, twice ; x^^f*"?. a covering. * ii-ovo%, one. ^ a, privative. * Sepio, I enclose ; also called foliola, phylla, or calycine leaves. ^ As in Perganum Harmala (Syrian rue). 300 PAPPUS OR AIGRETTE. chyma being- placed between the vascular bundles, and each side covered with an epidermis, differing in no appreciable manner from the corresponding tissue in the leaves. Each sepal is usually sessile, but in -a few cases {Trop(xolum or Indian cress, fig. 182) it is prolonged into a spur {calcar), or enlarged so as to form a hood or helmet {galea), which covers up the flower like a cowl Cas in Aconite or " Monk's-hood "). Sometimes in the violet and mouse -tail {Myosurtis minimus) each sepal posesses a peculiar appendage, arising from it just where it is attached to the receptacle, and prolonged downward along, but without ad- hering to, the peduncle. Pappus or Aigrette. — In the order Valerianacea, and in most compositcB, the calyx is reduced to a tuft of hairs called z. pappus, (fig. 156, V) in which, at first sight, it seems difficult to recognise the Fig. 156. — Carlina subacauUs, one of the Compositse, distinguished by the large de- velopment of the scales of the involucre. Fruit, b, terminating in a pappus ; a Tubular floret surrounded by its aigrette-like calyx (pappus) ; c Magnified view of one of the " hairs " of the pappus. calyx at all, until we find certain plants, where we can trace all gradations between the ordinary form of calyx and the pappus, as may be seen by examining Caillardia picta, Catanaitche coerulea, and Scabiosa atro-purpurea — the first and last of these plants presenting the two extremes, and the second - named one the medium between the forms of calyx. Each " hair " of this tuft- like calyx or aigrette may be either simple or plumose (fig. 156, c) by the presence of secondary barblets along its side. MORPHOLOGY OF SEPALS: DURATION OF CALYX. 30I Mode of Insertion of Sepals. — They are generally attached to the receptacle horizontally, leaving, when detached, a cicatrix shaped like the arc of a circle or a horse-shoe. In the mode of insertion of the sepals there are, however, several minor modifications, though none are of any very great importance. An examination of the calyces of Cytistcs hypocistis, Pe largo jiitun, Erisma violacea, uAAov : also called mo7iosepalous zxid gamophyllons. 304 CALYX : REGULARITY : COLOUR, ETC. may be two, three, four, five, or a greater number of divisions. It is cleft wlien the sepals are united for almost half their length (fig, 164), the termination fid being used to express this kind of division ; thus a calyx is said to be bifid, trifid, q^iadrifid, qidnquefid, imdtifid. Sec. Thirdly, when the sepals are almost united through their entire length, they are said to be dentate ; and, according to the number of divisions, are said to be bideniate, tridetUate, quadridentate, quinquedentate, &c. Lastly, as in the honey- suckle, and most Umbelliferas, the superior margin may be entire. In a gamosepalous calyx we distinguish three parts — viz., ist, the base, or the part which is soldered together; 2d, the tube; 3d, the upper portion, or limb or lamina, formed by the free portion of the sepals ; 4th, and lastly, the throat, or that portion represented by the line of separation between the tube and the limb. Hence in describing species the tube is said to be cylindrical, com- pressed, angular, short, or longj the limb bidentate, bifid, bipartite, entire, &c. Viewing the gamosepalous calyx as a whole, it may be ttcbular (as in most LabiatcB), cylindrical, angular, cupuliforjn (as in the orange), urceolate (as in the Silene i?ifiata), &c. Regular or Irregular Dialysepalous Calyx.— When all the divisions of a dialysepalous corolla are equal in size (as in the wallflower), it is said to be regular. When the contrary is the case, or when the sepals are united at different heights on the receptacle, or follow in their arrangement no certain law, then they are said to be irregular. Regular or Irregular Gamosepalous Calyx. — When the divisions are all equal among themselves, or inserted at the same heights— by each portion of their united base — upon the receptacle, a gamosepalous corolla is said to be regtdary and even though such conditions do not exist, still, in botanical language, such a calyx is said to be regular, provided such irregularities fol- low some uniform law. If the contrary conditions are present, the calyx is irregular (fig. 163). It may, however, happen, that even though the sepals or divisions of such a gamosepalous corolla may be equal, and attached at the same height and at equal distances on the receptacle, it must be irregular if they are 7iot all utiited together at the same height (Payer). Colour of Calyx. — It is in most cases of a more or less intense green ; but there are numerous instances in which it is otherwise — e.g., yellow in the Indian cress, red in the pomegranate {Punica Gratiatum), Salvia splendens, and fuchsia, though in the latter plant it is occasionally white. Such coloured calyces are called petaloid, from their likeness to the petals of the corolla. Peculiar Calyces. — In the Australian EticalyptJts} or gum-tree, 1 ev, well ; and KoX-awna, I cover : hence the term ealyptrate, applied to such a calyx. calyx: peculiar: absence or presence. 305 the calyx is in the form of an operculum, under which the stamens are placed as under an arch. At the time of flowering, this calyx gets constricted round the base, and, after being raised by the elasticity of the expanding stamen, drops off. In the North-West American 1 Eschscholtzia, now so familiar a plant in European gardens, the calyx is composed of two sepals soldered together by their free extremities, so as to cause it to resemble the extinguisher of a candle. The development of the flower forces up the calyx, by detaching it from its base; it then falls off, and allows the petals to expand. Very similar peculiarities of the calyx to what we find in Eucalyptus are seen in other members of the order to which it belongs (Myrtaceae) — e.g., in Calyptranthes of tropical America, Syzygium of tropical Asia and Africa, or in the" flower- buds of the common clove {Caryophyllus aro7naticus). Absence or Presence. — If there are two floral coverings present in a flower, then we may be certain that the outermost one is the calyx ; but if the flower possesses but one covering, then opinion is divided whether this should be considered a calyx or a corolla. Thus, in the order Ranunculaceas, some of the anemones, cle- matis, &c., noted for their beautiful flowers {e.g., Clematis lanu- ginosa, &c.), owe their beauty to coloured sepals. A whole series of dicotyledonous plants, which Jussieu called ApetalcB, have the calyx as the sole floral envelope — e.g., nettles, Chenopodiacese, &c. In the Amentaceae willows (fig. 162), ash (figs. 163, 164), beech, alder, oak, &c., the calyx is even wanting, and is replaced by scales of the nature of bracts. One of the most extraordinary of these is 165. 166. 167. 168. 169. 170. Figs. 165-170. — ^Various flowers showing stamens and pistils. Fig. 165. — Naked flower of the ash. Figs. 166 and 167. — Staminiferous and pistillate flowers of the willows. Fig. 168. — Flower of a Crzr^jr (Sedge), showing the "perigynium" or covering of the pistil, which is borne on a glume. Fig. 169. — Staminiferous flower of the same plant, consisting of a glume, and 3 stamens with innate anthers. Fig. 170. — Spikelet of a grass. the North American "Dutchman's pipe" {Aristolochia Sipho). The calyx forms a " long and thick tube, bent into the form of a siphon, swollen at the base, contracted at the throat and orifice, round which is spread out a limb almost circular, and feebly three- 1 California is commonly given as the peculiar country of this species {E. Californica). I have, however, seen it growing on the Pemberton Portage in British Columbia, more than seven degrees of latitude north of the Californian boundary line. U 3o6 USES OF CALYX : COROLLA : PETALS. lobed" (fig. 171). Duchartre has called attention to the fact that certain Dicotyledons which at first sight seem to possess a corolla outside their coloured petaloid en- velope, do not in reality do so. An example of such a plant is afforded by the Marvel of Peru {Mirabilis Jalapd). What is usually taken for a calyx is in reality an involucre enclosing a single flower. In Mi'ra- bilis triflora, Benth.,^ a similar in- volucre envelops three flowers ; six in Oxybaphusj and in Abronia, another genus of the same family (Nyctaginacese), this calyx-like in- volucre is situated at the base of a group of numerous flowers.^ Fig. 171.— Entire flower of Arhiolo- Use.— The use of the calyx, when chia Sipho, L'Herit. ov Inferior ovary present, is mOSt probably for the °^ ■ ' protection of the more delicate organs within ; but when it is entirely absent, or, as in the case of the vine, very minute, we are led to hesitate before bringing the doctrine of "final causes" to bear upon this part of vegetable organism. In many cases, when it remains green, it assists, by performing the function of a leaf, in the nutrition of the plant. COROLLA. When the perianth consists of two whorls, then the innermost is called the corolla (plural, corollcB). This floral envelope, ■which is usually bright-coloured, and constitutes the most conspicuous part of the flower, is made up of leaf-like organs — equivalent to the sepals of the calyx — called petals,^ each petal being either distinct from the others, or they are coalesced either wholly or in part, so as to constitute one continuous circle, just as we have seen the sepals in many cases are. It is wanting in the apetalous or monochlamydeous Dicotyledons, and most probably in all the Monocotyledons. Petals. — The petals are leaf-like organs, so far as the shape is concerned, though, as a rule, they are brilliantly coloured. Each petal may be divided into two parts — viz., i, the limb, or expanded upper portion, which is usually coloured ; 2, the unguis, or claw, 1 Quamoclidion, Choisy. 2 What is sometimes called the Epicalyx (em, upon, cafyx) on the mallows and other plants, is, in reality, an involucel (fig. 161). Petalum (Latin), from the Greek Tri7aSov, a coloured leaf. PETALS : NUMBER. which is the lower narrowed portion by which the petal is at- tached to the receptacle. It occasionally happens that the unguis is either imperfectly marked or entiVely absent; in this case the petal is sessile (Ex. Ranunculus). In regular symmetrical corolte the petals are symmetrical throughout, both as to their own parts and to their neighbours'. In Hellebortis odorus the five sepals are large and petaloid, while the eight to ten petals are very small, pyramidal in shape, hollow, four-sided, and each with a long claw \ungjiiculate\ In Eranthis hyenialis (winter aconite) we find a very similar arrangement ; while in Nigella arvensis (Devil-in-the-bush) the petals are reduced to from five to ten singular, very unpetal- like bodies. In Aconite the petals are represented by two peculiar arched organs ; while in the mignonette {Reseda odoratd) each petal is concave on its internal aspect, while on its external surface is a crest composed of a number of filaments of unequal length crowded together. In Magnolia, Calycanthus floridus, and more familiarly in certain species of water-lily, &c., there is a striking transition from the calyx to the corolla, and the converse. Petals, we thus see, are, tnorphologically, only modified leaves ; and accordingly, the same terms are used to describe them. Thus petals may be dentate, lobed, crenulate, laciniate, &c. Usually there are in each petal three principal nerves — a median and two lateral ones — but there are variations, which are curiously connected with the mode of insertion of the petals. For instance, if the three nerves enter the claw at the point of insertion separately, then the petal, on falling off, leaves on the receptacle a horse-shoe-shaped mark. On the contrary, if they enter the petal in unison, then the scar left at the place of insertion is rounded.^ In a gamopetalous corolla the thickened nerves at the lines of union of the margins of contigu- ous petals point out the number of petals which enter into such a corolla. Number. — The number of the petals, like that of the sepals, varies. Sometimes they are very numerous, and disposed in a spiral ; and more often they are few in number, and arranged in one, two, or a greater number of verticils. If there are two ver- ticils, then the interior one alternates with the exterior one — i.e., the petals of the interior verticil are placed in the intervals be- tween the petals of the exterior one. In Sauvagesia erecta there is an exception to this rule. Here we find the interior verticil superi7nposed on the exterior one — i.e., its petals lie not on the intervals between, but on the petals of the exterior verticil. If there is only a single verticil of petals, then the petals alternate with the sepals in the same manner that the interior verticil alter- nated with the exterior one. This law also finds an exception. In Garidella nigellastrum, and some Ternstroemiaceas (e.g., Tern- 1 Payer, Elements, 162. 3o8 ANATOMY OF PETALS : ETC. strannia fiediaicnlans), the petals are superimposed on the sepals which are placed exactly under them. Anatomy of the Petals. — As the structure of the sepal was only that of the leaf modified, so in like manner the anatomy of the petal is only a modification of that of the sepal. A delicate epidermis, superiorly and inferiorly, covers a parenchyma made up of loose, large, thin-walled cells, through which ramify the nerves, composed of a few tracheary vessels, which in their ultimate ramification are reduced to a single exceedingly delicate tube. In the petals of some plants — the black henbane {Hyos- cyamus Jiiger), for instance — the nerves are well marked, and of a purple or other colour, different from that of the rest of the petal. Weiss and others deny that stomata are, as usually stated (p. 54), wanting on petals ; and maintain that, on the contrary, though usually very few, examples are not wanting in which they may be found abundantly. If found, they are very indistinctly marked, and confined to the foliaceous petals, or in the coloured ones to the exterior aspect, which corresponds to the under sur- face of the leaf. On the interior face there are certainly none, and many plants entirely want them. The epidermal cells are often raised in lines or papillae, which give the velvety appearance to the petals of certain plants, such as the pansy (fig. 33) ; while throughout the parenchyma of the petals of scented flowers are little reservoirs of the odoriferous essential oil, which are even visible to the naked eye, as in the case of the orange and citron flowers. In a few rare cases, hairs are scattered over the surface of the petals, or they are hollowed into little fosses or pits. On the whole, the substance of the petals is much more delicate than that of the sepals, or other foliar organs of the plant, though"" they occasionally become fleshy {Rafflesia), or hard, stiff, and dry {Xylopia, &c). Corolla, Dialypetalous ^ and Gamopetalous.^ — Like the calyx, the corolla may be dialypetalous or gamopetalous, according as the petals are distinct from each, or are united to a greater or less extent — in the latter case the term used to express the extent of coalescence of the sepals being employed to describe the same characteristics in the corolla. In fig. 172 of the tobacco, we have a gamopetalous corolla; in fig. 173, representing a species of rose, the dialypetalous form. Dialypetalous Corolla. — In this corolla, the number of petals, like the number of sepals in a dialysepalous calyx, may vary. In the genus Circcea (enchantei"'s nightshade) there are two petals, and the corolla is accordingly called dipetalons j in Cncorum iri- coccutn there are three {tripetalons) ; in wallflower four {tctra- petalous) ; in flax and pinks five {pentapetalous). In like man- 1 Sometimes called Polypetalous. ^ Sometimes called Monopetalous. COROLLA : DL'VLYPETALOUS AND GAMOPETALOUS. 309 ner the terms hexa- hepta- octo- ennea- and deca- petalous are used to express the presence of six, seven, eight, nine, and ten petals in a corolla, though in general, when there are more than five, the word polypetalous is used. Though the petals are to all intents and pur- poses leaves, yet in the dialypetal- ous corolla there are some peculiar forms, as witness the Aconite and Hellebore, already noticed, or Del- Fig. 172. — Entire expanded flower of Tobacco (Nicotiana Tabacu}n,lj.) iCalyx; c Tube of corolla ; c' Throat ; c" Limb (nat. size). Fig. 173. — Open flower of Rosa arvensis, Huds. c cc c c The five petals of the corolla ; e The numerous stamens ; / The pistil ; pd The peduncle or support of the flower. phinium, in which (as in D. Ajacis, the common larkspur) the petals are two combined into one, — this single petal being length- ened into a spur within that of the calyx — this calycine spur being often as long as the rest of the flower. The petals may be also straight, inflexed (as in UmbellifercC, fig. 174), reflexed, &c. ; and, like the sepals, their arrangement and symmetry, or the want of it, may give rise to a regular or irregular corolla — the various forms of flowers which Tournefort took as the basis of his classifi- cation of plants being dependent on the arrangement and form of the petals. A. Regular Dialypetalous Corolla. — Un- der this head we may notice three chief forms of corolla, i. The .r««7.r;« corolla st^inr/&r?eTp"ei'. (fig. 182), in which there are four petals, ais, owmg to the strongiy- <,_^„__„,l :„ tu r r 1 marked median line being arranged in the form of a Greek cross. Ex. prolonged to the apex of Wallflower and the other members of the P^f?'- . '^'"^i"' .,.u_i-. 1 /- •!- forms a ridge mteriorly, a Whole order Cruciferas. 2. Rosaceous (fig. furrow exteriorly (5 times 187), in which there are five and sometimes four large, very short-clawed petals spread out in a circle. Ex. Fig. 174. — Flower of the common P'ennel (Fecnicu- 3IO REGULAR AND IRREGULAR DIALYPETALOUS COROLLA. Rose, Strawberry, cherry, and other members of the order Ros- aceai. It is the form of corolla which occurs most frequently • among dialypetalous corollas. 3. Caryophyllaceotcs, in which there 175. 176. 177. 178. Figs. 175-187. — Various forms of calyx and corolla. are five long-clawed petals attached to the bottom of a tubular or gamosepalous calyx. Ex. Pink, and the other members of the order Caryophyllacese (fig. 183). 4. Liliaceous, characteristics of the lilies. Here we find the claws of the segments of the perianth erect, and gradually spreading towards their summits. B. Irregular Dialypeialous Corolla. — One of the most remark- able is the Papilionaceous or Butterfly ^ corolla, so called from its resemblance to that insect. It is characteristic of the Papilio7iacea: or Leguminosce, the order to which peas, beans, vetches, whin, &c., belong. The corolla of any of these plants will show the following arrangement of the petals (figs. 188, 189, 190) : i. Superiorly is an undivided petal, generally larger than the others, called the vcxil- luiii or standa,rd. 2. At the sides are two others of equal size and 1 Papilio, a butterfly. IRREGULAR DIALYPETALOUS COROLLA, 3" shape, called the alee or wings. 3. Lastly, inferiorly are two others, symmetrical in form and size, which are often coalesced the one A B L Fig. 188. — Flower of a leguminous plant {^Lathyms latifolins). A, Entire and in por- tion ; B, The vexillum. or standard ; C, One of the alse or wings ; D, The carina or keel. with the other, either in part, or, as in fig. 185, D, altogether by their inferior border, in the form of a boat, or of a vessel with a keel — Fig. 189. — Longitudinal section (magnified) Fig. igo. — Diagram of the of the flower of a leguminous plant of the genus flower of Tetragonolohis, one Coronilla. of the Leguminosx. hence called the carina or keel of the papilionaceous corolla. In the common haricot {Phaseolus vulgaris), the keel is curiously twisted into a spiral form like a snail's shell. In Trifolium resu- pinahim, the positions of the parts mentioned are inverted — the standard being at the lower and the keel at the upper part of the corolla. In Amorpha we find both keel and wings have dis- appeared, leaving the corolla unipetalous. This is occasionally seen as an abnormality in other Leguminosze. Hence Moquin- Tandon considered that the standard was the only petal " rformal and regular to the papilionaceous corolla." In the keel of Legu- minosse the stamens and petal's are placed. 312 GAMOPETALOUS COROLLA : SCALES. Under the term anomala are sometimes classed a variety of forms of corolla which cannot be conveniently placed under any of the foregoing heads. Among these may be mentioned the corolla of the mignonette, which we have already had occasion to refer to, and that of the garden balsam {Balsatnina hortensis), Lopezia racemosa, Polygala vtdgaris (milkwort), and Pelargonium grandiflorum. Our space will only permit us to notice that of Lopezia. Here we have a calyx of four sepals which present nothing abnormal ; the corolla is made up of four petals, of which two are large with oval limbs, while the other two are small, nar- row, bent at a third part of their length, with a swelling at the " knee : " finally, there is a third little petal remarkable for its elastic claw, which is bent and hollow. This petal M. Duchartre, however, sees good reason for considering only a stamen trans- formed and petalised. Gamopetalous Corolla. — Here the petals may, like the sepals in the gamosepalous calyx, be either coalesced by their entire length, or only by a part. Hence, like the calyx of a similar nature, the same terms used to describe the margin of leaves are applied to describe the extent of union of the petals in this kind of corolla — the gamopetalous corolla being looked upon for the sake of convenience, like the gamosepalous calyx, as a single organ. We might, however, remember that in both cases we are not dealing with a single organ, but with several in union ; and that th'e spaces left between the non-coalesced sepals or petals are of an entirely different nature in their origin from the divisions in the margins of leaves. It is unnecessary to repeat these terms, which are the same as for the leaves or the sepals (fig. 191). As in the gamosepalous calyx, there may in the gamopetalous corolla be distin- guished,— I, the tube J 2, limb; 3, throat. The form or character of these parts is used in describing the forms of corolla. Thus the tube may be long, swollen, cylindrical, afigular, &c. ; the limb plain or concave, with 2, 3, 4, or 5 lobes or segments ; the lobes being in their turn obtuse, oval, roimdcd, lanceo- late, cordate, &c. ; while 'the throat may be bare or furnished with hairs, glands, and appendages of different kinds. Scales {squama:, fornices). — Though in reality in the majority of cases there is no marked distinction between the throat and the tube, yet it is in the throat where most frequently are found Fig. 191. — Flower of Pimpernel (/4 nagallis arvensis), with a quinque- partite corolla c ; s Calyx. UNION OF STAMENS WITH COROLLA. Fig. 192. — Flower of Brookweed {Satitohis Valerandi) in longitudi- nal section, e' Scales ; e Devel- oped stamens ; Placenta, with ovules. the various appendages of the interior of the corolla— such as the tufts of hairs, the prominences known as scales, &c. Thus, in Samolus Valerandi (the common brookweed) we find scales which some botanists look upon as imperfectly-de- veloped stamens (fig. 192, e). Other Appendages of Corolla.— In the genus Silene (and notably in Silene pendula), and many other Caryophyl- laceae, at the inner side of the point where the limb of each petal meets the claw, there is a little (usually two- lobed) upward projection or lamella, generally twisted, as if the claw was continued in this direction. The re- sult is that, when the petals are all in position in the corolla, there is 2.corona or crown round the orifice of the tube formed by the five lamellae in union. Something similar is seen in the oleander {Nerium Ole- ander)— in this case the corona being formed by a series of fringed lamellae attached to the petals. In the Narcissus poeticus, and still more markedly in the " hoop-petticoat " species {N. Bulbocodium), there is a corona composed of a single piece ; but whether this is to be looked upon merely as an appendage to the corolla, or as iden- tical with the scales (p. 312) already spoken of, is still a subject of dispute among botanists who have made a study of the morphology of these organs. The scales in the borages^ (fig. 194), the ap- pendages we have already spoken of as existing on the petals of Lychnis, Silene (at the line of junction of the limb and the claw), and the petaloid bands fixed on the lateral nerves of the five petals of the corolla Cii Hydrophyllum and Phacelia, are considered by Payer to be also of this nature. Union of Stamens with Corolla, — We shall have occasion, while in the next chapter speaking of the androecium, to describe the connection of the stamens with the different parts of the perianth. In the mean time, we may mention that, as a rule, the stamens in the gamopetalous corolla are attached to the corolla, or in other form have their extremities so blended with the substance of the corolla as to seem to rise out of it (fig. 193). To this rule there are, however, exceptions. For instance, in the order Plum- baginaceas, the corolla in the genus Plumbago (leadwort) is gamo- petalous, but the stamens are not attached to it ; while in the sea- pink {A rmeria) a.nd sea-lavender (Statice) the five petals are united at their base only to a small extent, and the stamens have only a slight connection with them, and then only at the point of union 1 All the European species, Echiiim and Pulinonaria excepted. 314 REGULAR GAMOPETALOUS COROLLA. of the claws. In the whole heath order (Ericaceae) the stamens are also independent of the corolla. Let us now examine briefly a few of the more marked forms of gamo- petalous corollas. Like the dialy- petalous corolla, the gamopetalous one may be regular or irregular, and from identical causes to those which render the gamosepalous calyx regular or irregular. A. Regular Gamopetalous Cor- olla.— This class is rather more varied in forms than the corre- sponding dialypetalous corolla. For instance, the following forms are well marked : i. The Campa- nulate or bell-shaped corolla (fig. 184). Ex. Harebell {Campaimla), Convolvulus, Sec. 2. Infujidibuli- form or funnel-shaped (fig. 169). Ex. Tobacco. 3. Hypocrateri- Fig. 193.— Flower of the Tobacco form (or hypocraterimorphous) {Nicotiana Tabacum \. ) op^^^A^ c or salver-shaped. Ex. Primrose, Corolla; oz/ Ovary; J/ Style ; Stigma. „ . _ ' . „ . bynnga, jasmme (fig. 181). 4. Rotate or wheel- shaped. Ex. Forget-me-not {Myosotis) and potato (fig. 180). 5. Stellate or star- shaped is perhaps only a modification of the rotate form. Ex. Galium or bed-straw, or the common Borage {Borage officinalis) (fig. 194). 6. Globose or globe - shaped (urn - shaped), of which the terms ovoid and urceolate are only modifications. Examples of all these shapes may be found in the different species of heath (fig. 176). 7. Lastly, we may note the tubiilar corolla, seen in the inner flowers of the capitula or heads of flower of Compositae, such as the thistle, dandelion, daisy, &c. (figs. 195 a, 178, 179).. Fig. i94.-Flower of the com- B. Irregular Gamopetalous Corolla. mon Borage (Borago officinalis, — The forms of this class are much L.), with stellate corolla ; ec Five . , . i i . scales at throat ; t' Stamens. less numerous, but are morc clearly marked, than the preceding ones. We may distinguish the following : i. The Labiate or lipped corolla, distinctive of the whole order Labiate, " when in a four or five lipped corolla the two or three upper lobes stand obviously up like an tipper lip^ from the two or three lower ones or imder 1 Sometimes called the galea or helmet. REGULAR GAMOPETALOUS COROLLA. lip."^ When, as in the dead-nettle {Lamium), bugle {Ajuga), and most of the common Labiaice (fig. 177). the two lips of the corolla are wide apart, the corolla is said to be ringent (grin- ning) or wiilabiate (one-lipped, the upper one being out of all proportion to the lower one) ; while if, as in the snapdragon {Aniirrhmujn), they are in contact, or closed by a projection from the base of one of them called a palate, the term personate (masked) or bilabiate (two-lipped) is applied to the corolla (fig. 175). In the snapdragon the base of the corolla is somewhat pro- tuberant or saccate (fig. 186), and in the toadflax {Linaria) this protuberance extends into a spur, which is common in various orders {e.g., violet, fumitory, &c.) ; while in the larkspur the whole five petals are thus calcarate or spurred. In the toadflax is occasionally a monstrosity, in which not only one, but the whole five petals of the corolla are thus spurred. In 1742, Linnaeus found such a plant near Up- sal, and was so astonished at the monstrosity exhibited by it, which he considered due to an accidental fecundation by another plant, that he called it by the name peloria? The name is now applied to this kind of mon- strosity in different flowers, and in the case of irregular flowers like the toadflax, may be looked upon as an effort of the plant to bring back the flower " to a singular abnormal state, of regularity." 2. The ligulate flowers of the exterior part of the heads or " capitula of composite " plants like the dandelion, chicory, daisy, &c. In the interior of the inflorescence of these plants, we find tubular flowers (fig. 192, d) ; but towards the circumference the flowers are irregular in shape, one side of the corolla being prolonged into a ligula or strap-shaped ^ a form (fig. 195 by Fig. i9S.-L;gulate (b) Finally, there are forms of corolla which and tubular (a) flowers of it is impossible to class under any of the ^ <=°-"P°^"- p'^"'- divisions given, and which have therefore received the some- what vague title of anonialcE. Among these anomalous corollce is that of the folks-glove {Digitalis purpurea), which is shaped 1 Sometimes called the labellum, though this term is usually reserved for one of the divisions of the perianth in Orcliidacem and a few other orders. 2 TTe'Awp, monster (Amoen. Acad., i. 55, t. iii. i (1744). 3 Sometimes, especially by the French botanists, the term flosculus (fleuron) is given to the tubular flowers, and semi-flosculus (demi-fleuron) to the ligu- late ones. 3l6 COLOUR AND DURATION OF THE COROLLA. like the finger of a glove — hence the name. Such a form of corolla is sometimes called digitatiform. Among other peculiar ones may be mentioned the corollas of the mullein {Verbascum), the Veronica or speedwell, the Lobelia, the Stylidijim, &c. We find the corolla, like the calyx, not always equally developed in all the flowers of the same inflorescence. A marked example of this we have already had occasion to notice in the Composite, where the inner flowers are regular, tubular, and quinqueden- tate ; while the marginal ones are irregular, one part of the corolla being much developed in the strap-shaped prolongation character- istic of these ligulate flowers. An identical arrangement is seen in the Dahlia. Colour of Corolla. — The calyx is usually green, while this colour is only exceptionally found — as in Hoya viridifiora, Geno- lobus viridiflorus, &c. — in the corolla. Black is a colour which really does not obtain in the corolla, what is usually so called^ being only a purple-red, blue, or deep brown ; while, as a rule, the colours of the corolla are of a gay character, or are blended to- gether in that inimitable manner which gives the beautiful variety to flowers. This subject we will have occasion again to refer to more in detail — (Section IV.) Duration of the Corolla. — Corollas, like calyces, may be classed according to their duration, as caducous^ decidtiotis, and viarcescent. In the first case, the corolla falls off soon after the opening of the flowers (Ex., Papaver A7-gcmone, flax, various species of Cistus, Cereus, &c.) ; in the second, which is by far the most common case, the corolla falls after the fecundation of the ovules or young seeds; while in the last division the corolla remains in a faded condition after the process of fecundation has been completed and the fruit has commenced to mature {Ex., some species of Eiica or heath, various Cucurbitacece (gourds), &c. In the greater number of flowers, however, no sooner have the anthers discharged their pollen on the stigma, and the pollen-tubes penetrated through the tissue of the pistil to the ovules, than the corolla begins to fade, and soon after drops off. This is the reason why double flowers, in w^hich the essential reproductive organs have been transformed into petals, last longer than single flowers. Use of Corolla. — Though in general the floral envelope which most prominently attracts the eye, the corolla is probably, physio- logically, the least important of the floral whorls. It is in general too delicate to serve as a protection to the essential organs within it, unless, indeed, as in the vine, the calyx is so small that it has to supply its place in this respect. There is, however, little doubt ^ For example, in Pelargonium tricolor and Vicia Faba. PERIANTH OF MONOCOTYLEDONS. that when it secretes honey or other sugary liquid at the bottom of the tube, by attracting insects to it— which, in their turn, convey the pollen from flower to flower— it serves a highly im- portant purpose in the economy of nature. This subject has of late years attracted so much attention that we shall, at the proper place, enter into a somewhat full outline of the recent researches on this question of the use of the corolla— (Chap. IX.) PERIANTH OF MONOCOTYLEDONS. The perianth of Monocotyledons, when they possess any floral envelopes, differs very considerably from that of Dicotyledons. Usually the segments of it are three in number, or some multiple of three — very commonly six — and are often gaily coloured, as in the tulips, lilies, &c. When the latter number are present^ — as in a tulip, for instance — the petals are arranged in two whorls. The question now arises, Is the exterior whorl a calyx, and the interior one a corolla? The older botanists, whenever they saw a covering exterior and green, called it a calyx ; but we now know that colour is no test whatever of the nature of the perianth. The greater number of modern botanists, from a study of the nature of this perianth in Monocotyledons, and from the fact that, as a rule, the segments of it do not alternate with the whorl of stamens, have concluded that it is not a corolla, but a calyx ; and that even when more than one whorl is present, the position, nature, and colora- tion of the segments, and their tendency to unite by their base to form a single tube, still lead us to look upon the monocotyledonous perianth as a calyx in two whorls.^ It ought not, however, to be denied that some eminent botanists are inclined to allow two coverings, and point out that in some plants the position and coloration of the two whorls give ground to this belief in two series of floral envelopes being present in at least some Monocoty- ledons. For instance, in the Virginian day-flower^ {Conmielyiia Virginicd), and other species of the order CommelynaccEe and Alismaceas, the three exterior segments of the perianth are foliace- ous, and have all the characters of a calyx ; while the three interior ones are larger, more delicate, and are brightly coloured, thus presenting all the characters of a calyx. In Alisma Plaiitago ^ In the IridacecB and other orders we find the stamens inserted on the coloured organ which we consider a calyx, — a startling proof that it is really so ; for though we often find the stamens united with the corolla, yet never do we find them inserted on that floral envelope, but either on the receptacle, like the petals, or on the calyx. * So called because the flowers expand for a single morning, and are re- curved on the pedicel before and after that period. 3i8 PERIANTH OF MONOCOTYLEDONS. (water-plantain) we find the same characteristics in the perianth. Opinion being so equally divided, De Candolle proposed to style the floral envelope of Monocotyledons the Perigonium'^ — an unnecessary term, as the phrase single or double perianth equally expresses its character, without committing ourselves to an opinion regarding its nature. In Orchidaceas the flower is very irregular. The perianth is composed of six segments in two sets — an exterior and an interior one — both sets being, however, of the same texture and petal-like appearance. The upper or posterior segment of the interior whorl (but which, by the tvs^isting of the ovary or stalk, commonly appears the lower or anterior one) differs in shape and direction from the others, being often spurred and appendaged, and is called the labelbim or lip. In Paxtonia and Isochilus the labellum does not, however, ^differ from the other segments of the perianth. The structure of the perianth of orchids is, however, so intimately con- nected with the very peculiar structure of the whole of the flower, that I consider it would be more instructive to the student to reserve the description of it until we have occasion to notice the extraordinary mode of fertilisation prevailing in the order — (Chap. IX.) In Zingiberacece and CannacecB (or Marantaces) there is also a labellum ; but this is not a part of the perianth proper, but ap- pears to result from transformed and reunited stamens, on which account Lestiboudois has given the name Sy7iema to it. 1 The segments being called Tepals. CHAPTER III. THE ANDRCECIUM,! OR STAMINAL WHORL. This constitutes the third whorl, and in a perfect flower is placed next to the corolla. It is made up of stamens, which are either free, or variously united among themselves or to other floral organs. They develop the ;pollen cells or grains by means of which the young seeds or ovules are fertilised, so as to be enabled to produce the embryo or young plant within the seed. The stamens are thus organs essential to the reproduction of the species. STAMENS. A stamen ^ is made up of the filaiiient and the anther — in other words, of a stalk and a head (fig. 196). The anther is composed of two sacs or theccE, which contain the pollen. This pollen is a dust-like substance, which, on microscopic examination, is found to consist of a multitude of either single cells or of several cells in combination. Finally, the filament is generally long and slender, supporting the anther, though sometimes it is wanting, in which case the anther is sessile. Number of Stamens. — The number of the stamens varies from one to a great number. From the number of the stamens Linnaeus, in the celebrated clas- sification of plants which bears his name, formed the first eleven or twelve classes ; and the terms which he 1 Or androcium (Roper), from ainjp, a man or male, and dlxos, a habitation ; it is sometimes spelt andrcecimn. The stamens were the " chives" or "capil- limenta" of the older botanists, who named the anthers apices (Blair's Botanik Essays, p. 29, 1720); but as late as 1682, Grew styled the androecium "the seminiform attire," while the perianth was "the florid attire." — Anatomy of Plants, p. 171, * Stamen, a thread. A B Fig. ig6. — Stamens of Lilium snperbuvi, L. A, an The an- ther, ready to discharge the pol- len ; Jl Filament. B, «« The same anther opened and com- pletely emptied of pollen, and so almost horizontally placed in the filament Jl. 320 NUMBER 01'" STAMENS. applied to these classes are still retained in descriptive botany to express the number of members of the staminal whorl. Thus, when there is only one stamen, the plant is monandrous,'^ — Ex. the mare's-tail {Hippuris vulgaris) ; when two {veronica) diandrousj ^ t\\vtt, iriafidrous^ (Iris, grasses) ; tetratidrous'^ when four {Del- phinium); pentandrous^ when five {Aquilegid); hexandrous^ when six (lily, tulip) ; heptandrous ^ when seven (horse - chestnut) ; octandrous^ when eight (heaths); enneandrous^ when nine (rhubarb, laurel) ; decandrous when ten (saxifrages) ; dode- candrous'^^ when twelve {Asarum). When there are more than twelve, and up to twenty, and the stamens are inserted on the calyx, the term isocatidrous {Ex. Mignonette) is applied ; when they are inserted on the receptacle, and are more than twenty, then the stamens are said to ht polyandrous^^ {Ex. Poppy, Ranun- culus, &c.) If below twelve in number, the general term definite'^'^ is frequently applied to them ; but if more than twelve in number, they are vaguely said to be indefinite, and are indicated by the sign 00. The stamens may either be the same as, or different in number from, the other whorls of the flower, particularly the corolla. For example, in the vine, carrot, Erodium {" heron's bill "), the number of the stamens is the same as the number o' the divisions of a gamopetalous corolla or Isostemonous'^^. 0 the other hand, they may be Anistejnonous,^^ or different in number from the divisions of the corolla. These anistemonous stamens resolve themselves into two divisions — viz. : (a) Those which are ineiosletnonous^'' or less in number than the petals ; and (/3) those which are polysiemonous^^ or more than the petals in number. The Pelargonium supplies an example of the first, while the Geratiijim is an example of the second case. In the Geranium the stamens are exactly double the number of petals, or Diplo- stemonous.^^ Finally, to show what variety exists in these rela- tions of the stamen, it may be mentioned that all these three numerical varieties may, and frequently do, occur in one order. It may occasionally happen, as a teratological change, that all the stamens in a hermaphrodite flower are suppressed {Meiotaxy); while of course this occurs naturally in a pistilline flower. There may, on the other hand, not only be an increase in the number of stamens, but an increase in the number of whorls, especially in I (Aovos, one ; avrjp, man. ^ Suo, two. •* rpei?, rpia, three. 4 TcVpa, four. * irevTe, five. ^ ef, six. orrd, Seven. 8 oKTw, eight. " kvvia., nine, Sexa, ten. II SwSeKa, twelve. 1^ eiKocToi, twenty. rroAus, many. 14 In this case the flower is sometimes styled oligandrous (oAiyos, few), and in descriptive writings is marked by the sign °°. 1^ icros, equal ; and or^nuf , a stamen. i" ai'io-o?, unequal. I'' /aeiwi/, less. TToXus, many. i" SittAoos, double. RELATIVE LENGTH OF THE STAMENS. 321 cases where the number of the circles of stamens is naturally large (this constituting Pleiotaxy). Lastly, Dr Masters notes that an increase in the number of the stamens frequently accompanies a corresponding alteration in the other whorls. Relative lengths of the Stamens. — All the stamens in a flower may not be of the same length — some being long, while others are short. In some cases there is almost a regularity in this, as in Oxalis (sorrel), where the ten stamens are alternately longer and shorter. On the basis of the relative lengths of the stamens, Linnaeus founded two of his classes ; and the names he applied to these classes are still used to designate the peculiarity in the staminal whorl which suggested the designations. Thus, when a flower contains four stamens, two of which are evidently shorter than the others, it is styled didyiiamoiis} Nearly all the thyme and dead-nettle order (Labiatas), the toadflax {Linarta vulgaris), the snapdragon {Antirrhinuni), and most of the Scrophulariacese (fig. 200), are of this nature. On the contrary, when there are six stamens on the flower, of which four are longer than the other two, the term tetradynamotis"^ is given to this variation. The whole order Cruciferse (wallflower, &c.) is distinguished by this among other characters. Among plants with five petals and ten stamens {e.g., Dianthus, Silene, &c.), five of the stamens are placed opposite to the petals, and differ much in length from the other five in the second whorl, which are alternate with the petals. Finally, in some flowers, like the lily, tulip, &c., the stamens are all of equal length. This subject of the relative lengths of the stamen has of late years assumed great importance, from the interesting observations of Darwin in regard to the different fertilising powers which the 197. 198. 199. 200. Figs. 197-200. — Showing modes of union, &c., of stamens. long and short stamened ■ flowers of the primroses, &c., possess. This subject of dimorphic and trimorphic plants we shall have occasion to speak about at greater length when discussing the various modes in which plants are fertilised (Chap. IX.) Regularity and Irregularity of the Androecium. — Like the calyx and corolla, the staminal whorl may be regular or irregular. ^ ivo, two ; Surajiis, greatness. - rerpa, four. 322 SITUATION OF STAMENS IN REGARD TO PETALS, ETC. Thus it is regular when all the stamens are of the same length, and inserted on the receptacle at the same height and at equal distances ; when the contrary is the case, then it is irregular, unless, indeed, these irregularities follow some uniform law. Thus, in the white water-lily {Nymphcea alba), the stamens being in a spiral, are inserted gradually nearer and nearer the centre : they are also gradually smaller and smaller, and. the distance which separates them varies ; yet the androecium is still regular, because these irregularities of size, insertion, and distance follow a uniform law.^ Situation in regard to Petals and Sepals. — When there is only one whorl to the androecium, the stamens are generally alternate with the segments of a gamopetalous corolla — or with the petals of a dialypetalous one, when equal in number to the segments or petals {e.g., borages, Umbelliferas, &c.) In some cases the stamens are opposite to the petals, as in the primrose, vine, Plumbaginacese (sea-pink order), &c. In such a case we are justified in con- cluding, from our knowledge of the plan of the flower, that either one whorl of petals is suppressed, or, as in the case of Monocotyledons, only the calyx is present. Again, when, as in Silene, we find the number of stamens ten, while the petals are only five; the stamens, though seemingly of only one whorl, are looked upon as consisting of two. The other causes which lead to such apparent irregularity in the arrangement of the floral organ we shall in due course consider somewhat more in detail (Chap. V.) Adhesion. — They may be all distinct and free, or adhere to each other either by the filaments or anthers, or by both. In other cases they may be "inserted" on the sepals, or united to the petals, as in all cases where the simple perianth is gamosepalous, or where the corolla is gamopetalous {Ex., hyacinth, DapJme, in which they are inserted on the calyx, and Campanulacese, Labiatas, &c., in which they are attached to the corolla). The stamens may even be united to the carpels — e.g., in the case of the Aristolo- chiaceas and orchids, as we shall have occasion. to describe when speaking of the anther and filament. Let us now consider each of the parts of a stamen more in detail. Filament.2— This, when present, forms the stalk or support of the anther. It varies in form and dimension, and is usually colourless, though in some cases, both in form and bright colour, it simulates the petals. In some cases (grasses) it is capillary or hair-like, or thick, cylindrical, and dilated at the base, as in Orm- thogahcm Arabicuvi or O. Pyrenaicum. In the white water-lily, 1 Payer, 1. c, i86. 2 Capillimentum. or pcdicubis ; filavientuin—ixoxafiluni, a thread. iFILAMENT — ITS APPENDAGES AND UNION. Canna, &c., it is petaloid (fig. 201); in Dlanella cccridea (fig. 211), ribbon-like; and in Lopezia raceniosa (fig. 202) it is excavated, so as to have a groove or gutter down its entire length. In Thalictrum, Neriiitn Oleander (fig. 208), &c., it is clavate or club-shaped ; in Mahernia, &c., geniculate or kneed (fig. 211); in Crambe, bifur- cate ; in Anthericum, bearded or stupose, &c. But in general it is rather subulate or tapering in form (fig. 202). Appendages. — In a few cases the filament is enlarged at the base, and presents on each side a small ear-shaped appendage, which some morphologists look upon as representing the sheath of a leaf (as in the asphodel). In the borage and other plants, the filament appears to give rise, either at some distance from the base or at the base itself, to a little lamella-like appendage, the exact morphology of which is not very clearly made out. Union. — Each filament in an androecium may be either per- fectly free, or united, either by the whole or a part of its length, to the others, so as to give rise to one or more bundles — "brother- hoods," or adelphicE — of stamens in a single flower.^ r. If the filaments are so coalesced as to form one single bundle in the ^ The tube formed by the union of the filaments of monodelphous stems has been called androphores (male-bearer— ai/rjp, and ^o(tiu>, I bear) or phalanges (fingers). Endlicher styled each of them a synema ; but this term we have already used in a different sense. Fig. 201. — Stamen and style of Canna peduticulata, Lodd. e The anther ; Jl Its petaloid fila- ment ; / Style flat- tened into a petaloid lamina. Fig. 202. — Stamen of Lopezia raceino- sa, with an ovoid anther and the fila- ment grooved and subulate at its sum- mit. Fig. 203. — Reproductive organs of Fumitory {Fnmaria officinalis, L.) A, General view, showing the two bundles of stamens surround- ing the pistil ; B, The pistil isolat- ed ; ov Ovary ; si Style ; j-^ Stigma. A B 324 FILAMENT : ANTHERS. form of a tube (fig. 199), then the stamens are said to be Monodel- phous^ — Ex., Lysimachia vulgaris (loosestrife), lupines, flax, most Malvaceae, &c. 2. If the filaments are united so as to divide the stamens into two bundles, as in the fumitory, beans, &c., then they are Diadelphous^ (figs- I97. 204). {a) The bundles may be either composed of an equal number of stamens (as in the fumitory, fig. 203, where there are three in each bundle — or in the milkwort, where four is the number), or {b) they may be unequal in number, as in the haricots and some Leguminosae, where one of the bundles is made up of nine stamens and the other of one (fig. 197). 3. When there are three or a greater number of bundles, the stamens are said to be Polydelphous? Or they are more accurately termed Triadelph,ous, if, as Fig. 204.-Calyx and re- the St John's wort {Hypericum), they are productive organs of La- . •' ^ ■'^ " l ^ thyrus latif alius, L., ten three m number (fig. 198); Pentadelphous, ExSty of pistTl?"' = ^ if' as in Melaleuca, they are five; and so on. In the castor-oil plant {Ricinus) the " androphores " are numerous and unequal in the number of stamens in each. When the androphores are the same in number as the petals, then they are always opposite to them, as in Beaufortia, Mela- leuca, &c. Anthers.* — This is the only essential part of the stamen, con- taining and developing, as it does, the pollen, which is the fecun- dating principle of the seed. It is usually made up of two lobes or pouches, called Thecce,^ attached to each other either by their sides, or by the aid of an intermediate body called the connective.* Each of these thec£e opens at the proper season, and discharges the pollen which has developed in its interior. There are generally two lobes, in which case the anther is styled bilocular'' {i.e., with two loculi or pouches). Such an anther is shown on transverse section in fig. 205. The anther has just opened; the connective, through which the vascular bundle goes, is shown at fvj and right and left of this we see the two thecas a. At an earlier stage of the anther each of these thecas was divided into other two by a parti- tion, which gets absorbed in the course of growth, but the former existence of which is shown by the furrow on the wall where it 1 fioi/os, one ; a.Se\il>6s, brother. 2 Suo, two. ^ ttoXus, many. ^ Theca (Grew), Tcsticulus or Testis (Vaillant), Spermatocystidum (Hedwig), Capsula (Malpiglii) ; anthera, from afflrjpb! (Smith), belonging to the flower. 5 Loculi or coiiiothcca: of some botanists. 6 Connectcre, to join. 7 Sometimes terms of Greek origin are used instead, and the anthers are described as mono- di- tri- and tetra- thecal. ANTHER : SHAPE AND APPENDAGES. has opened at a. In a few instances there is only one theca (as in all true mallows, Epicradaceas, Polygalaceas, &c.), and conse- quently no connective. In those anthers there were originally two the- cae, but one has become abortive. On the other hand, some anthers are quadriloailar, or with four thecae — e.g.., some laurels, the flowering Likum snperbmn, two of rush {Bniomus timbel- "^^-^^ ^'^''^^ "^^^"^ latus), the joint fir {Ep- hedra altissimd), the genus Tetratheca, the cinnamon plant {Cinna- monum Zeylanicum, fig. 206), &c.^ In the anthers Fig. section 205. — Transverse of the anther of Fig. 206. — Stamen of the Cinnamon plant (Cinnatnonum Zeyla7i- icuin, Breyn. ), with quadrilocular anther, and at the base two imperfect stamens e' e' ; a' a' Valves by which the thecse dehisce. already opened to allow of the pollen escaping. a Lateral line where the thecae open ; /v Vascular bundles which penetrate the connective ; Jl Trans- verse section of the fila- ment, the top of which is inserted at the bottom of the longitudinal furrow be- of the mistletoe ( Viscuin ), '"'^^^ ''^^c*- Rafflesia, numerous thecK have been described. Lastly, in the genus Pachystemnon, one of the Euphorbiacese, the anther is trilo- cular, or possessed of three thecae. Shape. — The shape of the anther is very variable. It is generally more or less elongated, but sometimes ovoid or ellipsoid (fig. 202), globular, cordiform, linear, retiiform, sagittate, oblong (fig. 193), &c. In some Umbelliferse the anther is broader than long (didy- mous). The summit of the anther may terminate variously. For instance, it is acute in the borage {Borago officinalis) ; bifid or cleft either at its base or summit, as in many grasses ; bicorn (ter- minating in two horn-like points) in heath, the arbutus, &c. ; or quadricorn, as in the case of the Gaultheria, one of the heath order belonging to America. Appendages of the Anther. — These are derived from the con- nective, and are seen in the anthers of the stamens of many Com- positas in the form of terminal prolongations of the connective above the apex of the anther. In various of the violets we also see appendages, though of a different nature to that mentioned. They are figured in the accompanying illustration (fig. 207) in the shape of a long qtteue formed of a prolongation of the connective of two anthers. In the Oleander [Nerium Oleander) the anther is borne on a filament club-shaped at its upper end, along either side of which hang the two lobes in the form of horns, while the ^ According to Schleiden, there are more than a hundred families (grasses, sedges, lilies, Labiatas, Boraginaceae, Scrophulariaceag, Compositas, UmbelUf- erae, Ranunculacese, Leguminosae, Rosaceas) in which the anthers are quadri- locular before bursting. 326 ANTHERS : UNION OF THE LOBES : DEHISCENCE. connective is prolonged superiorly into a long cord bristling with hairs, and obtuse, and somewhat thicker at its extremity (fig. 208). In Borage the appendix is corniculate (fig. 209). Position of the Anther, &c. — Each anther is divided longitudinally by a furrow formed by the two converging sides of the thec^. The face of the anther is that side where the furrow is placed ; the back is the opposite part ; while the base is the inferior and the apex the superior point, or that exactly opposite to the base. When the face of the anther is turn- ed to the centre of the flower it is in- trorse^ as in wallflower, Iridaceae, many Ranunculaceae, Buttneriacese, &c. (fig. 210) ; when, as less com- monly happens, it is turned to the ex- terior, it is extrorse^ (some grasses). In many Lauraceae some of the an- thers are extrorse and others introrse in the same flowers ; while in passion- flowers, Oxalis, &c., the anthers are at first introrse, but become afterwards extrorse. Unio7t of the Lobes. — The lobes of the anther may be united in three ways : i. by simple union of their sides ; 2. by means of the summit of the filament on either side of which they are placed ; 3. by the intervention of the connective, which, in such cases, is found in greater or less quantity and of varied form. Dehiscence. — As the anthers develop and contain the pollen, they must in due season dehisce, or open, to allow of the escape of this substance, the production of which is the sole essential use of the stamen. This opening or dehiscence is accomplished in different plants in different ways. Four leading methods can be recognised, i. Where the anther opens by its whole length along the line of the furrow. This is the most common mode of de- hiscence, and is seen in the lily, tulip, &c. 2. The apicular method, in which the anther opens by a pore at the apex of each lobe, as seen in heaths, Vaccinium, Pyrola, Dianclla ccsrulea (fig. 211), all the genus kS'(?/««?^7;z (among others the potato), &c. In some cases there is only one pore common to two thecas ; and in the order Melastomaceas the pores open into a little tube, through which the pollen has to pass before being discharged. 3. In the laurels, barberry, &c., the anther opens by one or two little valves, 1 AnthercB antices (Robert Brown). 2 AnthercB fosticce (of the same botanist). A B Fig. 207. — Reproductive organs of Viola tricolor, L. , var. alpestris. A, General view ; e The five sta- mens, with very short filament, and the anther furnished with a terminal appendix, the two upper ones pre- senting a long basilar appendage, a, of the connective ; st Extremities of the pistil. B, Pistil detached ; ov Ovary ; si Stigma. DEHISCENCE AND UNION OF ANTHERS. like trap-doors, on the side, more or less to the inner face. This valvular dehiscence is shown in fig. 206, where there are four Fig. 209. — Entire stamen of Bo- ragoafficitialis,!.. (borage), viewed in profile. Jl Filament, much shorter and more slender than its appendage a; au Anther; b Line of dehisceoce. Fig. 208. — Stamen of Nerium Oleander, L. Jl Filament ; an Thecse of the anther longitu- dinally prolonged into horn-like prolongations at the base ; a Long terminal prolongation of the connective. Fig. 210. — Flower of ./?7<5zVi tinctorittm, L., in longitudinal section, and showing the introrse anthers, ov' Ovules d Disc. thecse and four valves. 4. The last and rarest mode of dehiscence is exhibited by the genus Pyridanthera, in which the pollen escapes by a transverse opening which allows the top of the anther to be lifted off, like an operculum or lid.^ Something simi- lar occurs in Achetnilla arvensis and Lernna, where the anther dehisces by a transverse opening. Union of the Anthers. — i. The anthers are usually free, but it 1 For some anomalous states of the anther and its dehiscence, see Robert Brown, Trans. Linn. Soc, xxiii. 214 (Collected Works); Gardner, Contri- butions to a Flora of Ceylon (under Duris Zeylanicus) ; Zuccarini, Ray Soc. Reports on Progress of Botany, 1845; Griffith, Trans. Linn. Soc, vol. xx, (Cryptocoryne ciliata) ; &c. 328 UNION OF THK ANTHERS. Fig. 211. — Full-grown stamen of Dia7iella cce- nilea, Sims, seen in two portions, tr The two ter- minal pores of the anther a7i ; Ji Filament bent, and forming a " knee " under the more thicken- ed portion Jl'. Fig. 212. — Reproduc- tive organs of the com- mon Balsamina hor- tensis, Desp. ; five sta- mens adherent among themselves by means of the anthers. may also happen that all the anthers in an androecium may be so soldered together as to form a tube. Such stamens are styled Syngenesious} or Syiiantherous?' We see this in the whole order Composita?, or, as it is sometimes called on this account, Synanthereae {e.g., the daisy, dandelion, sun- flower, chicory, hawkweed, &c.) We also see it in the case of the violets (fig. 207), and in a more mark- ed degree in the ordinary- balsam {Balsamina hor- te7tsis, fig. 212). 2. In a few cases not only are the anthers united together, but the filaments are also coalesced — e. g., in the melon, gourd, and Lobeli- aceas. Such stamens have been called Syuiphysand- rous. In Salix monandra there is popularly supposed to be only one stamen (hence the name); but in reality the two stamens char- acteristic of the willow (fig. 166) are there, but both are coalesced into one. The same explanation of the seemingly monandrous melons, gourds, and other Cucurbitaceae, holds true. For in- stance, in the bryony (fig. 213) there exist a calyx and corolla, each with five divisions, but only three stamens, remarkable for their peculiar sinuous and consolidated anthers. Of these three stamens two are shaped as in fig. "210, A, while the third is repre- sented at B. In reality, howev*, it is most probable that each of the two large stamens is formed of two, like that figured at B, coalesced, so that the flower has five unilocular stamens reduced by this coalescence to three.^ Clarke and Naudin, it ought, however, to be men- Jotar^-~to:rofi7Ci tioned, consider that the Cucurbitace^ ones. B, The small one : 7? Fiia- have really three stamens, of which two ment , an n er. Complete, and provided each with a bilocular anther ; while the third is only half a stamen, with a single theca. 3. Lastly, the stamens may not form a distinct verti- cil around the gynoecium, but may be so united together as to 1 irov, with ; ycVc<7ts, generation. * tvv, with ; anlhcra, anthers. 8 Duchartre, 1. c., 537, --an I COLOUR OF ANTHERS : GENERAL STRUCTURE OF STAMEN. 329 appear a single body, as in the birthworts (Aristolochiacese), all orchids, &c. Such stamens are called Gynandrous} and the body which results from such a union is known as the Gyno- stemiiim^ or column. It may occasionally happen that the an- ther may become one-celled by the confluence of two thecae into one, or di7nidiate by the suppression of one lobe. The Gomphrena, or globe-amaranth of America, is a specimen of the first, while the reniform unilocular anther of the mallow affords a type of the second-mentioned method. Colour of the Anther. — This varies from yellow, the usual colour, through all shades of red (peach) to purple (poppy, tulip), &c. ; but the colours change in course of growth, more especially after their dehiscence. Structure of the Stamen in general. — The anatomy of the filament is not the same as that of the anther. The filament com- monly consists of a central non-ramified fibro-vascular bundle, which stretches from its base to its apex. This is covered with an envelope of cellular tissue, which often contains starch-grains. The whole is covered by a true epidermis. When the connective is present, the fibro-vascular bundles do not penetrate it. This comiective is solely formed by cellular tissue, commonly distinct from that of the filament. When the connective is not prolonged to the termination of the two lobes, then it follows that the anther looks as if bifid, or in the form of the letter X, as is seen in grasses (fig. 214). Again, in some plants the connective spreads out horizontally, so as to form a little neck at either side of the apex of the filament, which separates the lobes of the anther con- Fig. 215. — Stamen of Mer- curialis annua, L. an, an, The two thecae of the anther, of which one is open at a, borne on a long transverse connective cn ; the vascular bundle can be seen through the transparent filament. ■yviT), and oi^jp. 33° STRUCTURE OF THE ANTHER. siderably from each other. A good example of this is seen in the common mercury (^Merctirialis anjiua) represented in fig. 215. Such an anther is termed disiractile. In the sages it is even more developed — in this genus {Salvia) two of the lobes being deformed and sterile, and two of the four stamens being atrophied. When speaking of the appendages of the anther, we noted how in some other cases the connective projects above the apex of the anthers, either in the form of a rounded lobe (as in the so-called " Papaw" of North America, Asimina triloba), or of a more or less acute point (as in Magnolia, tulip-tree {Liriodendroii), and various Zingiberaceas, &c.) In Asclepiadace^ it takes the form of a kind of horn. Structure of the Anther. — The wall of the anther is formed of two distinct layers : i. An exterior one, composed of true epidermis, called the Exothecium} often pierced with stomata. 2. An interior one, or Endothecitim^ made up of several super- incumbent layers of fibrous cells (fig. 216).^ This fibrous layer is formed out of cells which were originally closed and composed of two parts — viz. {a) a large vesicle ; and {b) a spiracle, formed of branching threads in the form of a thickening on the cell-walls. Sometimes these threads are rolled up in a helicoid or snail-shell-like manner ; at other times they are anasto- mosed into a veritable network. In the pro- gress of growth the membrane between the threads becomes absorbed and obliterated, and nothing remains but the network formed of these threads. The whole surrounds a cavity filled with pollen, the structure and Fig. 216. — Transverse development of which we will consider pre- section of the walls of the gently. This fibrous layer gradually de- anther of Lilium superb- . , , nm. £p Exothecium ; cf creascs m thickness as it approaches the L7tTm°es)!'''°"'""'^"''^' lii^e along which the anther dehisces, until at this point it is entirely obliterated. The use of this fibrous lining of the anther is not very clearly made 1 eloj, without ; lobe. 2 ivZav, within. 3 These names were originally applied by Purkinje (De Cellulis Antherarum Fibrosis, 1830), and are sufficiently descriptive of the two layers which are found in the walls of the adult anther. In the young state of the organ there is however, found a third delicate— almost gelatinous— layer lining the cavity, which disappears in progress of growth. Schleidep therefore distinguishes in the young anther, zx^ Exothecium, a Mesothccium (fieVos, middle)— whicli is tlie second coat in the adult state— and this transitory layer, ox Endothecium, as lie calls it. ATTACHMENT OF FILAMENT TO ANTHER. 33 1 out. The elastic and hygrometric character of these threads enables them to contract and lengthen, according to the state of the weather, and so assist in the discharge of the pollen. And no doubt in many cases this is the function they subserve. In some instances, indeed, such as lilies and grasses, the outer layer of this fibrous coat contracts more than the inner, and so not only opens the anther— along the line of suture — but absolutely turns it inside out. In those anthers which have a valvular dehiscence, it assists by the same means in raising the valves. On the other hand, numerous plants could be named in the anthers of which this fibrous layer does not exist at certain places, and is so situated as to render it doubtful whether it does not, in many cases at least, take a very passive part in the discharge of the pollen.^ Attachment of the Filament to the Anther.— There are three principal ways in which the filament is attached to or joins the anther — viz. : i. When it is innate or basifixed ; here the filament is attached at the very extremity of the base of the anther, as in the mallow, '&c. (fig. 202). 2. When it is adnate, mesofixed or united in the median groove along the whole length of the anther, as in the buttercup, &c. 3. When it is versatile^ or united by its apex to a point about the middle of the median groove, so that the anther oscillates as if on a pivot by the slightest motion or the smallest breath of wind. This is exceedingly well seen in grasses, Amaryllis belladona, the evening primrose, &c, (fig. 214). Finally, Richard distinguishes a fourth method (as seen in Westringia, the Pyrolas, &c.), in which the apex of the filament is attached to the apex of the anther. These apicijixed anthers are, however, only a variety of the versatile mode of attachment. Insertion of the Stamens. — The mode of insertion of the stamens affords most important characters for the* co-ordination of natural groups, and may be either relative or absolute — i. e., in the first case we concern ourselves with the manner in which the stamens are situated in regard to the pistil, and speak of them being inserted on, around, or below the ovary. In the second case the stamens are itiserted on the calyx, the corolla, the recep- tacle, &c. In reference to the relative insertion of the stamens, we distinguish four different modes, expressed by special techni- cal expressions. These are : i. Hypogynous"^ if they are inserted below the ovary — i.e., on the receptacle — and not united to any other organ. Ex., Buttercup, flax, poppy, Crucifers, &c. 2. Perigynous^ when they are partially adnate to any part of the . 1 For a full account of this see Chatin, Comptes rendus, Ixii. (1866) 172-176. * in-o, under ; and yur^, wife (by which female is understood). ' Trepi, around. 332 INSERTION OF THE STAMENS. calyx, SO as to appear to grow on it, but are quite free from the ovary. Ex., The cherry, hawthorn, and the order Rosacea^ generally, purslane, &c. (figs. 217, 220), 3. Epigynous^ when they adhere more or less to the ovary, so that their free tops seem to be seated upon it, and the ovary, of course, appears beneath the apparent insertion of the stamens, or is inferior. Ex., The ivy, cranberry, the carrot, and the Umbelliferae (hemlock order), &c. (figs. 218, 219). Fig. 217. — Longitudinal section of the flowering of Fennel (Foenicuhnn offici- the common Pear {Pynts cominwiis), with numerous nale, AH.), with epigynous perigynous stamens, though the ovary is inferior. stamens and inferior ovary. When the limbs of the petals do not cohere after they separate from the ovary, they are usually looked upon by descriptive botan- ists as distinct petals. 4. Epipetalous when the stamens partially adhere to the inner side of the corolla, so as to be "inserted" upon it. Ex., The dead-nettle. Campanula, and the whole division of dicotyledonous flowering-plants styled Corolliflorce (fig. 193). Though in general these modes of insertion prevail through whole natural groups, yet we occasionally find exceptions. Thus the pear (fig. 217), though belonging to a group in which the insertion of the stamen is essentially perigynous, has the ovary inferior; and not unfrequently we find transitions between the different forms of insertion. Nevertheless, when, as in the case of the pear, all the other characters of the flower agree with the great natural group in which the stamens are perigynous, it is placed in that division.^ The same terms are used to express the mode of insertion of the corolla as the stamens. Thus, in all gamopetalous corollas the stamens are inserted on, or rather it would be more correct to say coalesced inferiorly with, the inter- nal face of the corolla. Accordingly, it is the insertion of such a 1 en-i, upon. * Brongniart unites Jussieu's perigynous and epigynous stamens under one head, so that he only recognises the two categories of hypogynous and perigy- nous stamens. RELATION OF NUMBER OF PETALS TO STAMENS. staminiferous corolla, not the stamens themselves, relatively to the ovary, which is taken into account. Thus, we speak of the and the base of the ovary ; and when they seem to be inserted elsewhere they are only adherent to, or coalesced with, the parts on which they seem inserted. When the stamen is longer than the perianth, the apex of it overtops the floral envelopes, and accordingly it is styled exserted, as in the sensitive plant {Mimosa pudica, fig. 221) ; when the contrary is the case, as in the heath, it is called included; if the stamens all bend to the side, they are said to be declitiate. If there are two verticils to the androecium, then, in general, the most exterior one is superimposed on the corolla ; and if there is a difference in the size of the stamens in such an androecium, then it is the interior ones which are the smallest (figs. 225, 226, 227). Relation of the number of Stamens to the number of Petals. — We are thus led to remark that the number of the stamens does not always agree with the number of the petals. In some cases there are a great number of stamens. For instance, in the mallows (fig. 227) there are five whorls or verticils, each ver- ticil being composed of ten stamens ; while the corolla is com- staminiferous gamopetalous co- rolla of the Labiatas, &c., being hypogynous, that of the Ericace^ (heaths) being perigyiious, and, finally, that of the Rubiaceae, Compositae, &c., being epigynous. In reality, however, these terms, . though convenient, are inaccurate if they are taken literally. All stamens originate in the space between the base of the petals Fig. 219. — Longitudinal section of the flower of Fuchsia spleti- dens, Zucc. ov Inferior ovary ; s Calyx with long tube, at the orifice of which the petals (p) and the other stamens are insert- ed, both being epigynous. 334 STAMINODIA. posed of only a single verticil of five petals. Again, when there are two whorls of stamens, the number in each whorl is not always Fig. 221. — Sta- mens of the sensi- tive plant {Mimosa pudica). Fig. 222. — Diagram of the flower of Aiiemone nemorosa (one of the Ranun- culacese). the same. We have an example of this in the case of the flower- ing rush {Butomus Jimbellatus). The exterior verticil is composed of six stamens arranged in two ; while the interior verticil is corn- Fig. 223. — Diagram of the flower of the Whin (Ulex), one of the Leguminosse. Fig. 224. — Diagram of the flower of the Wallflower {Cheirianthus Chciri), one of the Cruciferae. posed of only three stamens. In gamopetalous flowers there is usually only one whorl of stamens. The heaths {Erica) are ex- ceptions, however, to this rule, there being two verticils in this genus. Staminodia.^ — On examining the figure of the stamen from the cinnamon plant (fig. 206), two organs will be seen near the base of it. These are imperfect, and accordingly sterile stamens. Again, in the flower-bud of Lopezia racemosa there are two op- posite stamens. One of these remains normal, while the other has 1 Parastemina of Link, while Dunal styles them Icpala. STAMINODIA. 335 deg-enerated into a spoon-shaped petal, notched at one end, and terminating at the otlier in an elastic claw. In this case the claw is the original filament of the stamen, the spoon-shaped termina- Fig. 226. — Diagram of the Fig. 225. — Diagram of the flower flower of an Almond {Amyg- of a Peach (Amygdalus Persica), dahis communis) (Rosaceae), one of the Rosaceae (stamens inde- in which the stamens are in- finite), definite in number. tion the anther ; while the notch indicates its division into two lobes (Duchartre). It is remarkable that in the young state (fig. 228) this false petal is interposed between two pairs of true petals, e Fig. 227. — Diagram of the flower Fig. 228. — Bud of Lope- of a Mallow (Malva). s Caly.x in zta racemosa, Cav., de- valvular prefloration ; c Corolla in prived of the calyx in twisted prefloration ; e Androecium ; order to show the stamin- cp Gynoscium. odia (mag. 6 times). covered by one {c c), and in its turn covered by others {c' c'). Such abortive transformed stamens are called stamitiodia, and in some cases all the stamens are so transformed into petal-like organs, as in " double flowers." These are occasionally found wild, and are more commonly produced by the unnatural conditions under which the plant is placed when cultivated. When any organ is transformed into stamens, the teratological change is termed stamiiwdy, while the change of stamens or other organs into petals is petalody. Botanists look upon " every appendage or process or 336 MORPHOLOGY OF STAMEN : POLLEN. organ which forms part of the same series of organs as the true stamens, or which originates between them and the pistil," as belonging to the androecium ; but it is not always an easy matter to determine, in particular cases, whether these " staminodial " organs belong to the stamens or to the petals. Morphology of the Stamen.— The stamens, like the petals and sepals, are only modified leaves, though further removed from the leaf type than either of the floral envelopes. Hence it is more difficult to trace the different parts of a leaf in a stamen; and accordingly there is considerable difference of opinion as to the exact morphology of the different parts, and how far they are homologous with certain parts of the typical leaf. On this sub- ject, however, there are two main views held. Of the one Schlei- den is the exponent, while Mohl's name is attached as the origin- ator of the second. According to Schleiden (i), the connective is the median nerve or midrib; (2) the lobes are the two sides of a leaf, each rolled round towards the midrib ; (3) the under surface of the leaf is therefore the outside, and the upper surface the interior lining of each theca, while the epidermis and nerves are not developed on the inside ; (4) the pollen is formed from the parenchyma of the leaf; (5) when the filament is present it repre- sents the petiole of a petiolate leaf, while, if it is wanting, then the primitive leaf was sessile. Mohl, on the other hand, taught that each part of the leaf doubles in thickness, so as to form the two thec£e of the anther, and that the pollen is formed from the parenchyma of the leaf.^ According to his view — which is not generally adopted — the edge of the leaf constitutes the suture which runs along the theca, and by which it opens to allow the pollen to escape.2 The theories of Mirbel, Agardh, Endlicher, Bischoff", or Wolff, we need not touch on. We thus see that leaves, bracts, sepals, petals, and stamens are only modifications of one and the same organ — viz., the leaf; in a word, they are appendicular organs. POLLEN. When the anther dehisces in any of the ways mentioned, a yellowish dust-like substance falls out. This is the pollen. 0" 1 Though in most cases the anther is formed by the blade of the leaf, yet as we often find, as a teratological appearance, petal-like filaments bearing pollen- sacs on their sides, it is clear that we must not attribute the formation of pollen to the blade of the leaf only, but must admit that it may be formed in the fila- ment as well (Masters, Veg. Teratology, 292). 2 On this question see Oliver, Trans. Linn. Soc, xxiii. (1862) 423; Masters, lib. cit., 292. POLLEN : SHAPE, ETC. 337 submitting this powder to microscopic examination, we find that it is composed of grains definite in shape, but different in form in different species and orders of plants. Most commonly these polleii-grains are single cells, globular or oval in form, yellow, and filled with a granular liquid, which is known as the fovilla. Shape. — In figure the pollen-grains differ much. In general they are roundish (fig. 139), but in chicory are many-sided or polyhedral — each of the numerous faces being circumscribed by salient eminences (fig. 230). In Basella rubra they are square ; Fig. 229. — An "echinated" or " spine- covered" pollen - grain of a species of Tree Mallow {Lavaiera triinestris, L.), mag. 200 times. Fig. 230. — Pollen- grain of Chicory (Cichoi-inm Ijity- bus) seen on two different sides (mag- nified 200 times). in Tradescaiitia, &c., they are cylindrical ; in musk {Miimihis moschatHs), spirally grooved or ribbed ; in mallows, Iponicea Fig. 231. — Pollen of the Tiger Lily {Lilium ti^rinum. Gawl.), with a "slit." A, Viewed in front ; B, Viewed at one extremity (mag. 200 times). Fig. 232. — A pollen-grain oi Pelargonium zonale, W., viewed in two different as- pects to show its form. A, Side view ; B, Its extremity (ma^. 200 times). hcderacea, &c., covered with little eminences, so that each grain looks like a miniature sea-urchin (figs. 139, 229, 232), — and so on. Sometimes these granulations or markings on the surface of Y 338 POLLEN : SHAPE AND SIZE. the pollen-grains are regular in their arrangement. In Ipomcea purpurea they form somewhat regular compartments ; in Cobcea scandens they are in large hexagonal spaces, not regular in shape, but surrounded each by a salient crenulated lamella. These mark- ings are formed by the external coat of the pollen-grain (which we shall have occasion to describe presently), but have nothing of the nature of a true cellular tissue in their character, as the late Hugo V. Mohl imagined. Most frequently these pollen-grains, which are marked by prominences, are also possessed of an oleaginous material, which renders the pollen glutinous ; but that all pollen- grains are divisible into two categories, as Guillemin ^ thought — spiny and glutinous, and the smooth and non-glutinous — is erro- neous. All pollen, when first emitted from the anther, has a slight mucosity, and the smooth as well as the hispid grains have the power of secreting a viscid substance. It has even been attempted by Guillemin, Brongniart, and Mohl,^ and still more lately by Bailey,^ to distinguish great natural orders, and even - species, by means of the form of the pollen-grains. The Com- positse, for instance, have three or more well-marked types, such as that which we have figured from the chicory (fig. 230), the minute, oval, spiny pollen of the Asters, Calendulas, Cacalias, &c. ; and a third form wholly destitute of Spines, as in the great knapweed {Centanrea scabiosd). The different species of the same genus are also distinguished by diff'erent-shaped pollen- grains. For instance, that of Anemone sulphurea is roundish, but that of A. inontana is elliptic, &c. The pollen of the orders Geraniaceas and Campanulacese is for the most part globular. This is not, however, regular ; for while some of the grains are quite smooth, others are covered with spines. On the whole, however, the characters derived from the pollen are, unless in a few very exceptional instances, too variable to be depended on for specific distinctions. Size. — The dimensions of the pollen-grains vary much. All of them are so small that if their form and other characters are to be made out with anything approaching to accuracy, recourse must be had to the microscope. Some, like those of Nyctago longiflora, are comparatively large ; while others, like those of Myosotis and Lithospenimm, are very small. Between these ex- tremes are to be found pollen-grains of every size. According to Schacht, the grains of the first-named species are ^nr of a millimetre, while those of Convolvuhcs Batatas are of a millimetre in diameter. On the other hand, those of Ficus elastica, according 1 M^m. de la Soc. d'Hist. Nat. de Paris, ii., 1825. 2 Uber den Bau und die Fornien der Pollen Korner (Verm. Schrift.); and Ann. desSc. Nat., 1835 (iii.), 148-180, 220-236, and 304-346. 8 Nature, Jan. 13, 1870, 297. — (Report, Manchester Lit. and Phil. Soc.) POLLEN ; STRUCTURE. 339 to the same eminent observer, are not over -^is of a millimetre. The species of the same genus will also vary much in the size of the pollen-grains. For instance, Gulliver has shown that those of Ranunculus arvensis are nearly twice the size of those of R. hirsutus. Again, the pollen-grains of Sile7ie acaulis are, according to the measurement of Mr Charles Bailey, already quoted, but half the size of those of S. alpina—tht latter having some beautiful markings in addition. The pollen-grains of this genus differ from the usual caryophyllaceous type in not having the pits or depressions common to the order, so that the grains become spherical rather than polyhedral. Structure. — Each pollen-grain is, in the vast preponderance of plants, made up of two superimposed coats, or of two vesicles, one within the other, and closely applied to each, the whole surround- ing the fovilla in the interior. The action of reagents proves the chemical composition of these coats to be cellulose, i. The exterior coat or exine} or extine? is comparatively thick, and resis- tant with little elasticity, so that it breaks easily when distended, and is often granular or fleshy in appearance. It is formed or secreted from the inner one, and all the markings belong to it. It can, though with difficulty, be separated from the pollen-grain, if this is macerated in slightly acidulated syrup. Mohl's idea that it is analogous to the cuticle is not borne out by recent obser- vations on its development. 2. The intiiie or inner coat is the proper cell-membrane. It is very thin, but of considerable strength for its thickness, and is without a trace of organisation. We have already referred to Mohl's idea that in some cases — among others Nyctago hortensis, Hemerocallis fulva, Statice latifolia, &c. — the exine partakes of the nature of a cellular tissue, an idea not entertained by the great body of Phytotomists, who are almost at one in the belief that neither coat of the pollen-grains shows the slightest appreciable structure. The same botanist an- nounced many years ago that in some genera of Coniferse (Yew, Juniper, Cypress, and Arbor-vitas), Gourd {Cucurbita Pepd), Tigri- diaPavonia, there are three coats, the two interior being very thin and diaphanous. Meyer and Schacht have shown that in some pollens, at least (CEnothera, Clarkia, &c.), the outer coat of the grain may be divided into two layers (fig. 233 B, a and cC), very distinct over the whole of the grain, but coalesced at each of the three emi- nences which characterise the grain ; though I am not aware that any other observer has confirmed Fritzche's assertion that in the \ These names were originally given to the coats of the pollen-grain by Julius Fritzche (M^m. de I'Acad. imp6r. des Sciences de St Petersbourg, 1837) ; but in the next year (1838), Richard, in ignorance of the prior nomenclature Fritzche, named them anew the Exiiymetiium and E7idhymenium. 2 This Fritzche calls the exintinc. 340 POLLEN : FOVILLA, AND MOVEMENTS IN IT. Fig. 233. — Pollen of Clarkia elegans, Dougl. A, Seen a dry object. B, Seen in water ; a a' The two layers of extine (mag. 200 times). pollen of certain Onograceas there are even four coats.^ On the other hand, in Zostera, and some other aquatic plants {Zanni- chellia, Naias, Cauli?iia, Riip- pia), the pollen of which is peculiarly formed (p. 346), there is no outer coat. Fovilla. — The interior of the pollen-grain is filled with a viscid liquid, rich in proto- plasm, which, under the mi- croscope, often appears slightly turbid, though in many cases transparent and often uncol- oured. Under still higher power — say 300 diameters — it is found that this fluid, to which Martyn gave the name of fovilla, is filled with minute particles, unequally-sized and variable in form, the largest of which are from 4000-5000 of an inch in length, and the smallest only one-fourth or one-sixth of that size. Movements in the Fovilla. — Count Gleichen, many years ago, described curious movements of these particles in the fovilla, which Brongniart^ and others considered spontaneous, comparing the fovilline particles to the spermatozoa of the animal generative fluid. It is now, however, universally believed that these move- ments are in no respect of this nature, but come under the same category as those observed in any fluid where exceedingly minute bodies — even inorganic — are contained, and which, out of compli- ment to the discoverer, the late Robert Brown, have been called the " Brownonian movements." In the cylindrical thread - like pollen-grains of Zostera, &c., already described, there is a cir- culation very similar to what we observe in the articulations ot Chara and the cells of various other plants (p. 20). It may be remarked, however, that unless these marine plants just named form an exception, all movement of the fovilla in the pollen-grain has ceased by the time the pollen leaves the anther. When the pollen- grain falls on the stigma, the inner coat, as we shall see presently, develops outward in the form of a tube. Into this tube Amici,* and others since then, have observed the fovilla " flowing down- wards in a broad stream and back on the opposite side." Sac- 1 The fourth he called intcxine. 2 Ann. des Sc. Nat., xii. 40, and xv. 381. 8 Tbid., ii. 68. Mohl, Veg. Cell, 128. COMPOSITION OF FOVILLA : PORES AND SLITS OF POLLEN. 34 1 cardo^ announces that he has detected in the fovilla small bodies exhibiting Brownonian movements, and making up its bulk. These he calls somafia. Their form is invariable in the same species of plant, and in plants of the same genus the form appears to be nearly identical. In the hollyhock they are disciform, in Portulaca grandijlora fusiform, &c. To see them, a magnifying power of from 800 to 1000 diameters is required. Treated with iodine, they take a blue colour, but only on the portion outside, the interior remaining clear. Chemical Composition of the Fovilla. — If further proof were neces- sary of the vegetable nature of the fovilline particles, it is supplied by the discovery of Fritzche that granules of starch and sometimes I of inuline, which are coloured blue and sometimes yellow by I iodine, accompany the minute drops of essential oil which swim in the fluid. It is these granules which perform the molecular Brown- onian movements about which there has been so much contro- vers)'. In addition, the fovilla also contains a certain proportion of sugar, which, under the action of sulphuric acid, turns to a rose colour, and various other azotised materials. Geraud found in the pollen of the snapdragon {Antirrhimwi inajus) potassa, and raphides of phosphate of lime among that of the Virginian spiderwort {Tradescantia virginicd). Fourcroy and Vauquelin found malic acid in the pollen of the date-tree, and Macaire- Prinseps malate of potash and other salts in that of the cedar.^ In addition to sugar, gum, albumen, cerin, resin, &c., Herapath^ found as much as 46 per cent of a peculiar inflammable azotised principle, insoluble in nearly every liquid, which Girardin* called Pollenine, in the pollen of Cerens speciosissimus, and nearly as much in two species of lily. Lastly, the outside of the pollen- grains of several genera — Phormium, Scorzonera, Nyctago — are surrounded with a thick oil, which gives a colour to the pollen. This oil may be a secretion of the mother cells (p. 344) of the anther, and is certainly contained in the walls of the anther. In the genera Gossypiujii, Molopa, and all the Onograceae, the oil is replaced by a glutinous substance (p. 338). Pores and Slits of the Pollen-Grain. — If the pollen-grain is brought into contact with water, owing to all the conditions for its exercise being present, endosmose immediately com- mences with great rapidity— the result being that the coats are ruptured, and the pollen-grain prevented from fulfilling the pur- pose which it is intended to subserve in the fecundation of the ovule, and the consequent production of the seed. Hence a 1 Nuovo Giornale Bot. Ital. {fcstc Pop. Sc. Rev., 1873, 307)- ''■ Bibliotheque Universelle, 1830, 45. 3 Pharmaceutical Journal, Feb. 1848. * Lefons de Chimie Eldmentaire, 3d ed., p. 839 {teste Lindley).J 342 POLLEN : PORES AND SLITS ON IT. wet season is unfavourable for the ripening of grain and otlier truits. In Holland it is always noticed that after a wet season there is a poor juniper crop. If, however, it is brought into con- tact with some thicker liquid than water — syrup or mucilage, for instance, or some substance of a similar consistency — then the endosmotic action takes place much more slowly. The grain swells, and any inequalities on the exterior get smoothed out ; the grain also changes its shape, somewhat getting rather more ellipsoidal ; and if absorption continues, the outer coat will burst, and the inner will protrude through it in the form of either one or more slender delicate tubes closed at the outer end. If the pollen- grain has fallen on the surface of the stigma, which is generally moist or viscid, this action takes place ; and, as we shall have occasion to describe in the course of a future chapter (ch. viii.), this pollen-tube with its fovilline contents, after penetrating through the stigma and style, enters the ovule or young seed, performing thereby the most essential process of fertilisation. The places where these tubular protrusions of intine take place are generally at the poles of t"he pollen-grain. But in many cases the tubes protrude through special portions of the pollen-grain, where the coats are thinner than over the rest of it. These spots are known as pores (or oscula), pits, or depressions, and, when more elongated, slits or folds — neither name, however, requiring to be received in its ordinary acceptation, as in no case are both the coats entirely interrupted at the pores or slits so called. In the pollen-grain of some plants (laurels, Aroideee, and Aristolochiacese) neither are present ; while in other plants the numbers and position of the pores and slits are rigidly determined. The slits are generally longitudinal, from pole to pole, in the median line of the pollen- grain {Plu7nbago Zeylanica, lily, fig. 231, &c.) In most cases only the intine is present ; but in some plants the exine is also present in the form of a thin layer at the bottom of the slit, even | though the rest of the pollen-grain is reticulated or corrugated ; but in every case the margins of the slits are bounded by the thickened fold of the exine in the form of a ridge-like eminence. The number of the slits varies. In most Monocotyledons there is only one (LiliaceEe (fig. 231), iris, palms, &c.) ; the number three is frequent among the Dicotyledons (roses, LeguminosEe, Solan- aceas, CruciferEe, &c.) ; more than three is rare, but from four to six are found on the common borage, and various other Borag- inaceee, Labiatas, Rubiaceae, Apocynaceas, &c. Pores are found on the pollen-grains of many plants. They are circular thinnings of the exine, through which the intine can be seen at the bottom, though Schacht asserts that in some cases, at least, there is not a mere thinning of the outer coat, but an absolute deficiency of it. The number of pores is also very variable. On DEVELOPMENT OF ANTHER AND POLLEN. 343 the pollen of Lhnodosutn, Furcroya, Amona, Oreodaphne, Persea, wheat and most other grasses, Cyperace^, &c., they have not been observed in greater numbers than one ; two are found on the paper- mulberry, Colchicum, and Broussonetia, but this number is rare. Three are seen on (Enothera biennis and other Onograceas, and on the pollen of the orders Proteaces, Urtica- 234.-P0I- ceae, Dipsacacese ; there are four on balsam, Trigo- j^^'^^s^rain of Fu- nia, Fumaria (fig. 234), &c. ; while on Nyctago hor- ria officinalis, tensis there are as many as 100. It is even said ^ftVe\°rli"t|ores that on the hollyhock {Althcea rosea) as many as on it (mag. 200 200 have been counted. The following table, com- piled from Mohl, Duchartre, and others, presents these curious facts in regard to the absence, presence, and number of the pores and slits of the pollen-grains in a synoptical form :— I. Pollen without either Pores or Slits.— Most Araceas, Musa, Strelitzia Reginas, Canna; Laurus, most Euphorbiaceae, Ranunculus trilo- bus, &c. II. Pollen with Slits, hut no Pores.— (a) One pore : most Monocotyledons ; and, among Dicotyledons, Salisburia, Magnolia, and Nymphasa, most markedly. (/3) Two slits : rare, Dioscoreacese, Tigridia, Cy- pripedium, Calycanthus, &c. (y) Three slits : most Dicotyledons, oak, Cereus, mistletoe, &c. (S) Foitr slits : rare, Sideritis scordioides, Houstonia coccinea. (e) Six slits : various Labiatae and Passiflorae. (C) Slits Diore numerous than six: many Rubiacece ; Pensea, Sesamum. III. Pollen with Pores, hut no Slits. — (a) 07te pore : Grasses, Cyperaceas, Anona, Cecropia. 0) Two pores : rare, Colchicum, Broussonetia. (y) Threa pores : Onograceae, Proteacese, Urticaceas, Dipsacaceag. (5) Four pores : Balsam, Phyteuma, Trigonia. (e) Pores more numerous thati four : (i) Situated o?i the equatorial line of the pollen-grain — alder, willow, ash, CoUomia ; (2) Nyctaginaceae, Convol- vulaceae, Caryophyllaceae, Cucurbitaceae, Malvaceas, Cobaea. IV. Pollen with hoth Pores and Slits. — (a) Three pores and three slits : most Dicotyledons, and notably the Compositae. (/S) Many pores and slits : most Boraginaceae and Polygalaceas. (y) Six to nine slits, and only three pores: (i) Six slits and three pores — Lythraceas, Melastomaceag, Combretaceas ; (2) Nine slits and three pores — Am- mania sanguinea. Development of tlie Anther and Pollen. — In the earliest period of its development — supposing it is examined in the bud — the anther is a simple sessile tubercle, composed of homo- geneous cellular tissue. The apex is somewhat elongated, and is medianly divided by a delicate furrow which makes its appearance in course of time ; then the filament begins to make its appear- ance, and a second furrow divides each lobe into four, so that in the earlier stages of the anther there are four thecee instead of two, as in most cases in the adult condition where the embryo 344 DEVELOPMENT OF ANTHER AND POLLEN, condition to a IS exceptional. Th^se external appearances point corresponding development going on within the anther. Making a transverse section of it, we • find that in the midst of the once homogeneous cellular tissue a change has taken place. In each of the divi- sions corresponding to what are after- wards the two lobes of the anther, two cavities appear, corresponding to the four lobes which the longitudi- nal furrows on the outside of the _ Fig. 235. — Transverse sec- tion (after Mirbel) of a theca of a Cucumber (Cucurbita). ep Exothecium ; b b Endothe- cium — between the two is the middle coat or mesothecium ; a Pollen-cells, in which are seen two, three, or in one four, grains of pollen, according as the line of section has exposed them (mag. about 250 times). Fig. 236. — Pollen-cells oi Laih- rcEd Clandestiiia, L. A, Utricle, in which a grain of pollen is escap- ing ; B, Utricle about to open ; B', Grain full-grown. young anther point to. At first very minute, and almost linear, they get filled by thick mucilaginous fluid, which insensibly organ- ises itself into a cellular tissue with thickened walls, which with the epidermis constitutes the whole mass of the anther. The most exterior of the cells are veiy small, and become, in the manner we have already described, the fibrous layer (p. 330, fig. 235, b b). The more interior ones are large, and full of colourless gelatinous protoplasm, and constitute the mother cells the. pollen (fig. 235, a). These mother cells after a time become divided, either by the formation of transverse partitions from the walls (Mirbel, Unger, Mohl), or by free cell-multiplication (Decaisne, Nagli, Hofmeister, Wimmel, Duchartre), into four triangular cells, which afterwards become the pollen-grains (fig. 236). At first the intine is the only coat which surrounds the grains ; but afterwards the exine appears, either by secretion from the intine, or by deposition, according to other -observers — a doctrine warmly espoused and defended by Schacht. Subsequently the line of division between the thecas gets, in the majority of instances, so far absorbed as to reduce COMPOUND POLLEN-GRAINS. 345 the number to four, though in some cases a greater number remains throughout the adult state of the anther by the non- absorption of the intervening cellular tissue (p. 325).^ Lastly, it may be mentioned that the transitory delicate lining of the thec^, which we mentioned in a former paragraph when speaking of the structure of the anther, may be intended for the nutrition of either the mother cells, or in some way minister to the development of the pollen,* or to the peculiar organisation of the still more external layer. On figs. 235, 236, some of the facts given in the foregoing description are more fully explained. Compound Pollen-Grains.— In the Coniferae (figs. 237, 239), and various species of Onograceae, the pollen-grains are not single cells, but are composed of three or four blended together by viscid and elastic material, so that in J£noihera biennis (evening primrose) Fig. 237. — Composite pollen of the Cedar. Clarkia, (fig. 233), Epicridacese, &c., each grain is triangular in shape.* In heaths (Ericaceae), Leschenaultia, &c., they are com- ^ The question of the development of the pollen has been the subject of numerous elaborate researches, the difficulty of the subject affording an excuse for the very contradictory statements made by different observers. We have only given an outline of the main results arrived at, touching as little as pos- sible on controverted points ; but for further information the student is referred, among others, to the following memoirs : Wimmel, Botan. Zeit., 1850, 225-235, 241-248, 265-270, 280-294, 313-320 ; Mirbel, Mdm. de I'Acad. des Sciences, xiii., 1836; Mohl, Vegetable Cell (Engl, trans.), 57, 127, Vermischte Schriften, 42, &c. ; Decaisne, Mdm. de I'Acad. Royale de Brux., xiii. (1840) ; Nagli, Zur Entvvickelungsgeschichte der Pollen, 1842; Hofmeister, Bot. Zeit., 1848, 425, 434, 649-658, 670-674, and Abhand. d. k. Sachs Ges., vii. ; Henfrey, Ann. of Nat. Hist., xviii. 364 ; Reichenbach, De Pollinis Orchidearum genesi (1852) ; Rosanoff, Jahr. f. Wiss. Bot., vi. 441 (Pollen of Mimosa) ; Notes in Sach's Lehrbuch, (1873) 472 ; and more especially to the important treatise of Warming, Untersuchungen iiber Pollen bildende Phyllome u. Kaulome (Hanstein's Bot. Abhandlungen, ii. Bd. 2 h. 1873). 2 Chatin, Comptes rendus, 1866 (Ixii.), 126-130. 3 In Coniferee it is remarkable that it is not the intine but a secondary struc- ture— viz., one or other of two unequally-sized cells produced in the median part of the pollen-grain— which elongates into the tube by which fecundation is effected. This curious fact was first observed by G^leznoff in 1849, but has of late been confirmed by Schacht. 346 COMPOUND POLLEN-GRAINS : SOLID POLLEN. posed of four grains united (fig-. 238) ; in Mimoseas (Leguminosae), eight; in several Acacias, sixteen; and so on. In the Zosteras, or eel-grasses, and allied orders of flowering-plants which grow in salt water, the pollen-grains are divested of the outer coat (p. 340), and consist of long slender threads, which, as they lie side by side in the unilocular anther, look not unlike a skein of silk. Solid Pollen. — As the pollen completes its growth, the walls ot the mother cells are usually obliterated ; but sometimes the walls of the enclosing cell remain persistent, and enclose pollen-grains of various consistence, as among the milkweeds (Asclepiadaceae) and various families of orchids. In contradistinction to the/«/- verulefit pollen found in all other orders of plants, the pollen of these orders is styled solid, or the combined grains are known collectively as pollinia, or "pollen-masses." The pollen-grains are united together either by a viscid substance, or more rarely by threads. In the evening primrose, the threads mixed with the pollen are only vestiges of obliterated mother cells. In most orchids the grains composing each pollinium are united in fours by an elastic network called the viassa sectilis, while in Epacris and Neottia these are simply coalesced by mutual pressure in the thecae. In this latter case the pollen is therefore still styled pul- verulent; while in the MalaxidcB, another tribe of orchids, the grains are so intimately united as to make a solid mass. In Cephalanthera and Limodosium the grains of pollen remain dis- tinct as in other plants. In some orchids {Orchis niaculata, for example) each of these pollinia is pear-shaped, narrowed to a thin stem-like part called the caudicle^ and terminated by a glandular disc or retinaculum,^ by which it attaches itself to the rostelhnn, or beak-like prolongation from the anther. In the AsclepiadacccE there are always two of these pollinia united by their retinacula, 1 Cauda, a tail. " Retinaculum, rein or band. Fig. 238. — Composite pollen of Typha (Bulrush). Fig. 239. — Composite pollen of the genus Pinus. VITALITY AND COLOUR OF THE POLLEN. 347 and depending on the thecci in the form of the sides of the letter V inverted. In this order a Icind of cellular membrane permeates the pollen-mass, forming a great number of cells, in each of which is found a grain of pollen alike in structure to those of orchids. The pollinia in each theca remains always separate in all true orchids {Orchis, Ophrys, and Gy?nnadenia), but they are united by their caudicle in the genera Anacamptis, Himantoglossum, Goodyera, Corallorhiza, &c. This caudicle is composed of numer- ous cells, which, in place of being transformed into pollen-grains, secrete a viscid substance which enables the two pollen-masses to unite. (Chap. IX.) Lastly, the shape of the pollen-masses is generally the same as the thecas of the anther, which have acted as moulds to them, and there may be two, four, or even sometimes eight to one anther. Vitality of the Polleft. — Pollen may be kept in the dry state for months, and even years, and sent from country to country to fertilise plants which produce only female flowers. For instance, the date - palm is dioecious, and accordingly, from the earliest periods it has been the custom for the Egyptians to bring branches with staminiferous flowers from the desert to fertilise the pistil- liferous flowers of the cultivated trees. In 1808, when the French were in Egypt, the inhabitants were thereby prevented obtaining the branches for the male flowers ; and the result was, as only female-flowered trees are cultivated, no dates were produced. The pollen will also be wafted long distances by the winds, as the " sulphur-showers " in the vicinity of fir-forests prove. In 1505 it is recorded by the poet Pontanus — and by even more credible wit- nesses— that a female, date-palm at Brindes, which had never pro- duced, was fertilised, and in consequence matured fruit, from the pollen wafted thirty miles from another tree of the same species at Otranto; and Henslow informs us that date-trees in St Helena have been fertilised by pollen obtained from trees on the con- tinent of Africa. Numerous similar cases are on record. Colour. — The colour of the pollen is generally yellowish, but it varies in this respect even in the same genus. .For instance, in the genus Lilium, all shades, from yellowish to brown, may be found. That of Ajuga Genevensis is yellow, but that A. pyra- midalis usually white. Again, the grains of Ortiithogallmn umbel- latum are large and yellow, while those of O. nutans are small and white. In Actcsa spicata the pollen is also whitish ; while that of certain species of Epilobium, and many Polemoniaceas, is bluish, and in Verbascum red. It is never green. The general teratology of the androecium will be considered with that of the rest of the floral whorls, when we shall have occasion (Chap. V.) to consider the metamorphosis and symmetry of the flower. 348 CHAPTER IV. THE GYNCECIUM, OR PISTILLINE^ WHORL. This constitutes the fourth, last, and in a perfect (hermaphrodite) flower the central whorl of the floral organs. The. pistil is made up of carpels,^ and may consist of a single carpel (when it is styled 2t. simple pistil) or of several in union, constituting a ftfwz- pound pistil. Again, the terms apocatpous^ a.n{[ syttcarpous* are applied to signify whether the carpels are separp.ted one from another, as in Caltha, Ranim- culus. Hellebore, &c. (fig. 240), or are in union (fig. 242). Some botanists style each separate carpel a pistil ; while others, more philosophi- cally, look upon the whole of the carpels, whether one or many, syncarpous or apocarp- ous, as merely constituting a pistil. Practically, it is im- material which view is taken. Fig. 24o.-(7^«;« urba7ium, L. (Herb-Ben- Let US now examine a pistil net). A, Head of the entire fruit (twice the consisting of a single Carpel ; nat. size). B, One of the little fruits or car- . , ° , . , ■ , - i pels isolated (4 times nat. size). m Other WOrds, a Simple piStll. It consists of five parts — viz., 1. the ovary, a cavity occupying the lower part, where it joins the receptacle, and which contains the ovules or young seeds ; 2. the style, a filiform prolongation of the summit of the ovar)^ ; 3. the stigma, a glandular body, terminating the style ; 4. the ovules or young seeds; 5. the place?tia, to which the ovules are attached. We have already noted the fact that the carpels may, like the other floral organs, be either separate or coalesced ; and this union may be only by the carpels or by a part of the carpels, 1^ So named by Roper. It is commonly spelt in English books gynwciiim (yviT), female ; oiko?, abode). ^ /copTTog, fruit. an-b, apart ; xapn-ds, fruit. •* . The ovules are minute oval bodies, each of the average size of a pin's head, contained in the cavity of the ovary attached to the placenta, and which, when fecundated by the pollen, become the seeds. Before, however, becoming the seeds, the ovules have to undergo many changes; so that the structure of the ovule and that of the seed, though theoretically the same, are in reality very consi- derably different. The number of ovules varies from one in a simple pistil (when it is called solitary) to a great number. They are styled, when few and easily counted, deji7iitej when in greater number, indefinite. Development and Structure. — Its first appearance on the placenta is in the form of a minute tubercle, composed through- out of homogeneous cellular tissue, without any division in parts, and originating from a single cell of the placenta. Little by little there forms round the base of this cellular body a kind of ring or collar, at first in the form of a cup, this .embracing the base only of the ovule, but by-and-by, developing by its free border, it ends by cover- ing the greater part of the pri- mitive tubercle. While this first envelope is growing, there is a second one forming at its Fig. le^.—Polygonmn orientnle, L. Ortho- haQP anH pnrlincr Kv rnvpr tropal ovule in two successive states of deve- pase, ana enamg Oy cover- lopment. a, Entire young ovule. B, Tlie ing it in a similar manner to ovule more advanced, divided longitudinally: , 1 • 1 .1 i- . 1 Primine ; sc Secundine : nc Nucleus; that which the first envelope /„ Funiculus ;> The vascular bundle, which adopts in covering- the primi- terminates its course at the chalaza, ch (mag- ' , , ' , . nified 80 times). tive tubercle. The result is, the ovule is composed of a central cellular body covered by two superimposed envelopes, the one interior, the other exterior, pierced each at its summit by a large opening, by which the top of the primitive tubercle often protrudes in the form of a conical body. The centre body is termed the nucletis; the ex- terior membrane the primi^te; and the interior one, which is immediately laid over the nucleus, the secuftdi?te. The opening which occupies the summit of the primine is the exostome^'^ while that of the secundine is the endostome? Such is the nomenclature of Mirbel,* and, as the most generally received one, we adopt it, 1 Latin ovtilum, diminutive of ovum, an egg. 2 efw, without ; (TTd^io, mouth. 3 Ivhov, within. 4 Mirbel, Ann. des Sc. Nat., xvii. 364 OVULE: RELATIONS OF POLES TO EACH OTHER. though it possesses the anomaly of calling the first-formed coat by a term which would signify that it is the second in date (secundine), and the primine the first, though in reality it is the last formed.-^ Lastly, the term micropyle ^ is applied to the single opening at the summit of the ovule formed by the united exostome and endostome (fig. 263). Chalaza, Hilum, Sec. — These mem.branes coalesce at the base of the ovule in a single body, which gets the name of chalazaj while the term hihim is given to the point at which the ovule is inserted on the placenta. The ovule may be either sessile, or, as in many crucifers, &c., placed on a stalk (the funiculus, or podosperm ^\ which is simply a prolongation of the placenta. The vascular bundle (figs. 262, 263, /z/) which enters the ovule does not pene- trate the nucleus in most ovules, but terminates abruptly in the chalaza. In the ovule of the castor-oil plant, Cycads, Conifers, &c., according to Gris and Favre, the vascular bundle does not terminate in the chalaza, but spreads throughout the nucleus almost half-way up its length. Relations of the Poles of the Ovules to each other.— The various coats of the ovules may maintain surh a relation to each other that the micropyle is at the one end and the chalaza at the other, or they may be so twisted as to present the two poles in entirely different positions. The ovules, according to the relations which the different parts, and more particularly the different poles, bear to each other, have received various distinctive names. The chief forms are as follows : (i.) The Orthotropal^ or ortho- tropous ovule. Here no change in the direction of the parts occurs in growth. The chalaza is the point of attachment to the placenta ; at the opposite end is the micropyle : and the ovule is therefore straight and symmetrical. Ex. Buckwheat and various species of walnuts (Juglandaceae), Myricacese, Urticace^, Cis- taceae, &c. (fig. 262). It is not a very common form. (2.) The Ca7npylotropal or campylotropous ovule.^ In this form the chalaza and the hilum do not change their position, and. the parts are superimposed .in the orthotropal form; but it 1 Thus Gaertner, and, following him, Robert Brown, have called the primine the testa, and the secundine (the tegmen of Brongniart) the internal membrane ; while the primine (the secundina exterior of Malpighi) is the itttcgumentum secundum externum, and the secundine the integumentum primum internum of Schleiden. 2 fiKcpos, small; and uu'Ar}, gateway or opening,— the foramen of Grew, the ei-munde of the Germans. 3 TTous, TToSos, foot ; cirepua, seed, — nalietstrang, or navel-string, of the Germans. 4 6p0os, straight ; and rpdn-os, form : also called atropous (o, rpeVu, not turned) or homotropous : in German, geradldufig. (ca/tTTvAos, curved ; in German, krumml&ufig. RELATIONS OF POLES OF OVULE TO EACH OTHER. 36$ grows unequally, the increase of one side of the ovule being more rapid than the other. The result of this is that it curves upon itself, so that the apex is brought close to the base (chalaza), Ex. In most Cruciferce, Caryophyllacea2 (chickweed family), Solanaceas (potato family), Chenopodiaceas, &c. The common mignonette affords a good example. (3.) The Anatropal^ or anatropous ovule. Here we find the ovule, during the progress of growth, inverted upon its funiculus or stalk, so that, though it still remains perfectly straight, the positions of the base and of the apex are entirely reversed, the micropyle being where the normal position of the chalaza is in the orthotropous ovule, and vice versd. Lastly, the funiculus adheres along the back of the ovule throughout its entire length, so as to form an elevated ridge, to which the name of Raphe'^ has been applied. Sometimes (as in the ovules of the Magnolia) the raphe is so coherent with the outer coat of the ovule as to be externally undistinguish- able. Ex. This is the most common of all the kinds of ovules, and is well seen in the Liliaceas, Ranunculaceae, Cucurbitaccce, &c. A good example is afforded by the common garden-plant, Eschscholtzia Cali- fornica (fig. 263), as well as by the apple, almond, &c. (4.) The Amphitropal or amphitropous ovule.^ This ovule may be looked upon as an anatropal ovule, in which the raphe only extends along the back of the ovule — only half-way from the chalaza to the ihicropyle — the result of which is, that it is attached to the placenta by the middle of one side. Between it and the anatropal form there is every gradation. Ex. Various Malvacese and Primulacese (mallow and primrose or- ders). Owing to the fact of such ovules standing with their axes at right angles to the funiculus, they are said to be transverse. In addition, some organographists distinguish catnptotropal'^ ovules, which are curved like a horse-shoe, and each portion beyond the curve is of equal length, as seen in Potamogeton ; and those called Lycotropal,^ of a similar shape, but in which (as Fig. . section of the anatropal ovule of Eschscholtzia Cali- /orttica, Cham. /rPrimine; sc Secundine; ex Exostome; ed Endostome ; nc Nucle- us ; se Embryonic sac ; /u Funiculus ;/v Vascular bun- dle ; rp Raphe ; ch Chalaza. 1 ava, from above ; rpeirw : in German, gegenl&ufig. " pa<^r), a line ; or vasiduct. 3 t, around ; rpeffw : also called heterotropal, hemitropal, or semiana- tropal. •» Ka^TTTOT, curved. 6 AuKoy, a hollow disc. 366 POSITION OF THE OVULES IN THE OVARY. in a horse-shoe) the two branches on each side of the point of curvature are not united as in the former case. Position of the Ovules in the Ovary. — The various positions and directions of the ovules in the cavity or cell of the ovary may be arranged as follows : (i.) Erect, when they rise from the bot- tom of the cell. Ex. Scabiosa or devil's-bit, buckwheat, &c. (fig. 262). In this case it will be attached to a "basal placenta," or a placenta at the bottom of the loculament (fig. 254). (2.) Ascending, when they rise obliquely upward — from the side, a little above the bottom of the ovary. Ex. Buttercup. (3.) Horizo7ital or transverse, when they project from the wall of the ovary in a transverse direction. Ex. Crassula. (4.) Pendulous, when they hang from the upper part of the ovary in such a manner as to hang downwards in an oblique direction, as in the dandelion, sea-pink, &c. (fig. 264). (5.) Suspetided, when they hang perpendicularly from the very summit of the cell of the ovary. Ex. Hippuris, Mycrophyllum, and other HaloragiacecC. When two ovules are placed side by side at the same level, they are collcJeralj if the one is above the other, they are supernnposed. In either case, they may be situated the same as to the axis of the ovary, or differently ; and the same rule is true when there are many ovules in a loculament. These terms, as well as those referred to in the Fig. 264.— Longi- preceding paragraph, also apply to the seed, tudinal section of Formation of the Tercine or Chorioji. — Up to the ovary of the ri i- c Sea-pink {Armeria this period the uucleus of the ovulc IS a mass 01 Showing '^the°'free ccUular tissuc. Gradually a cavity appears in the central placenta in interior of this uucleus, which increases at the ^threar^om whth expense of the walls— these walls constituting a the ovule is suspend- third membrane, which Mirbel has called the ed (mag. 12 times), (gj^^-i^g^ ^iwd Malpighi the chorion. This is some- times described as possessing an inner lining (the qiiartine). The sac in the interior of the nucleus is the embryonic sac (the ammotic sac of Malpighi).^ In the interior of the embiyonic sac is the germiftal vesicle (or primordial utricle, as it is sometimes called). It is found in the upper part of the sac, to which it is suspended by the siispensor^ and afterwards grows into the embr3-o or young plant. But this portion of the anatomy of the ovule will be best considered when we discuss the impregnation of the ovule (Chap. VIII.) Exceptional Structure of the Ovule. — We have seen, from 1 The sacculus colliquanicnti of the older writers ; the quintint of Mirbel ; the additional memhrane of Robert Brown. 2 Hypostasis of Dutrochet. EXCEPTIONAL STRUCTURE OF THE OVULE. the foregoing description, that the general structure of an ovule consists of a nucleus, most commonly conical, and covered by two superimposed membranes (primine and secundine) ; in the nucleus is a cavity (the embryo sac), in which develops the germinal vesicle attached to the top of the embiyo sac by the sus- pensor.and becomes, after impregnation by the pollen, the embryo, or young plant in the seed. There are, however, some exceptions where the structure of the ovule is still more simple. In the ovules of the whole walnut family (Juglandacese), for example, there is only one integument covering the nucleus. A similar structure is found in the ovule of various species of Veronica (particularly V. hedercefolia and V. Cymbalaria), all the Betulaceae (birch order), Asclepiadacese, Rubiacese, Labiatae, Lobeliacese, Gen- tianaceae, Boraginaceae, AmaryllidacecC, various of the Solanaceas, Polemoniacese, Piperaceae, all of the Coniferae (except the genus Podocarpus, which has two ovular integuments),^ and Caprifoli- aceae.^ Indeed the majority of gamopetalous Dicotyledons have only one ovular coat. In the whole orders Santalacese (particularly Saiitalu7n^), Loranthaceae (Vt'scum, Lorafithus), Thesium^ Halo- rageaceae (the common Hippuris or mare's-tail), and Balana- phoracese, there is a structure even less complicated ; the ovules of these orders have only the nucleus without any covering what- ever. The ovule of the coffee plant has only one envelope, forming, in this respect, an exception to the rest of the order Rubiaccce. When only one envelope is present, it is generally looked upon as the secundine.^ Variation in the Number of the Integuments and the Form of the Ovules. — The rule that the form of the ovules and the number of the integuments remain the same in the same group is not without exceptions. Thus, among the Ranunculaceae the genera Clejnatis, Adonis, Aqtiilegia, Aconitum, Pceonia, in addi- tion to several species of Delphi7ii7cm {I). Jissum, elatuin, con- solida, Ajacis, &c.), have ovules with two integuments ; while the genera Thalictrum, Aneinone, Hepatica, Rmiunculus, and, in the genus Delphinium, D. tricorne and Chilense, have only one integu- ment to their ovules. On the other hand, the order Arace^ has in the genus Calla anatropal ovules, orthotropal in Seuromatum, and intermediate forms in other genera.^ Naked Ovules. — Exceptions to the rule that ovules are con- 1 Fide Schacht. 2 J. D. Hooker, Journ. Linn. Soc, ii. 163. Griffith, Linn. Trans., xix. 185. ■* Decaisne, Ann. Sc. Nat., 2d ser., t. .\i. 95. ' Before leaving this subject, however, it is proper to remark that Griffith (Linn. Trans., xix.) denied that Viscum has an ovule uncovered with primine or secundine. « Schleiden, Beitraege, &c., 75-78; Duchartre, I. c, 595. 368 NAKED OVULES : MORPHOLOGY OF THE PISTIL. tained within the cavity of the ovary are casually presented by a few plants, — viz., the blue Cohosh of North America {Caulophyllum thalictr aides), the ovules of which, rupturing the ovary soon after flowering, become naked ; in the mignonette the ovules are also partially naked, the ovary being often at the summit, &c. In these plants, however, the ovules are fertilised in the ordinary way. In Cycadaceae and Conifera; there is, however, no ovary, each fertile flower consisting of an open carpellary leaf, in the place of a pistil, in the form of a scale. This scale bears two or more ovules on its upper surface, and the pollen is directly shed upon and fertilises these ovules without the intervention of a stigma and style, as in flowering plants proper. Hence these are called Gymnospermous or naked-seeded plants. In the firs, pines, &c., the above arrangement prevails ; but in the yew the fertile blos- som "consists of a solitary naked ovule, borne on the extremity of a short branch, and surrounded by a few bracts." In these plants there is, therefore, no carpel or pistil leaf at all. Morphology of the Pistil. — From what we have already said, it will be seen that a simple pistil or single carpel is a single leaf, and that a compound pistil answers to several leaves united into a single body, just as several petals in a gamopetalous corolla, or several sepals in a gamosepalous calyx, are coalesced into one. On this view the carpel is the blade of a leaf, bent so that the opposite margins meet and unite, forming in this way a close case (the ovary) : the under portion of the leaf will thus form the outside of the ovary, and the upper surface the interior lining of the same cavity. The ovules are borne on what corresponds to the united edges of the leaf, while the summit, " tapering and rolled together," forms the style. Lastly, the edges of the altered leaf, rolled out- ward at the top or along the inner edge of the style, form the stigma (p. 360). The line formed by the union of the margins of the leaf is called the ventral or inner side suture, and always looks towards the axis of the leaf ; while another line on the back of the ovary cor- responds to the midrib, and, always looking outwards, is called the dorsal suture. The placenta is a cellular growth from the edges of the carpellary leaves. The ovules, on this view of the morphology of the carpel, are equivalent to the buds borne on the edges of such leaves as Bryophyllum, Malaxis, &c. (p. 181).^ Numerous interesting observations confirm this view. In Malaxis, the buds produced in the margins of the leaves consist of a " flask-like cellular sac of a green colour, and within it and near its base a yellowish-green nucleus-like body. The cellular bag 1 Hence the ovule 5s called by the German supporters of this theory "seed- bud " (samenknospe). MORPHOLOGY OF THE OVULE. has a narrow opening at the apex, in some apparently bilabiate, in others slightly undulate," ^ — a structure resembling the young axillary buds of one of its near allies — namely, the orchid genus Microstylis. This structure in the leaf-buds of Malaxis, Professor Dickie most judiciously points out as indicating the homology of the ovule to that of a bud, the nucleus-like body corresponding to an axis ; the cellular open-mouthed sac he compares to an em- bracing leaf; the two coats of the ovule, when present, may be looked upon as homologues of two appendages {i.e., leaves) on two consecutive nodes. Finally, we may note that though the above view of the homo- logy of the ovule — originated by Schleiden^ — is very generally held, yet there are various other views adopted by several botanists whose opinions are entitled to respect. They may be briefly stated as follows : (a) That in most plants, and especially in Umbelliferae, Ranunculace^, Leguminosae, &c., the ovules are homologues of leaf-lobes (Brongniart, Godron, &c.) (i9) That they are only metamorphosed leaves (Cramer), (y) That they are comparable to the marginal glands of certain leaves. (S) That the ovule may be compared to a phyllary expansion, the podosperm corresponding to the petiole, the outer coat to the leaf itself, while the middle coat is an appendage to the outer, and comparable to that which surrounds the nectary at the base of the petals in Ranuncuhis graniineus, R. aconitif alius, &c. (Lesti- boudais). (e) That ovules are leaf-buds in a particular state, and their integuments composed of scales of rudimentary leaves (Lindley) — a view slightly different from the generally received one. (f) Lastly, it is held that the ovules are the marginal lobes of a carpellary leaf transformed and convolute round the nucleus, which, being destitute of vascular tissue, is a "parenchymatous excrescence," or trichome, to use the German term. The primine, characterised by vascular bundles, is, according to this view, com- monly the only membrane which persists in the mature seed. The secundine, except in rare cases (Euphorbiaceas), is only a dedupli- cation of the primine, and is mostly transitory.^ If the opinion which we have adopted regarding the mor- phology of the pistil needed to be supported by further argu- ment, we might point out the case of the " double cherry," where the pistil loses its character of a carpel, and reverts to the struc- ture of the leaf ; to the observations of Professor Dickie upon several monstrosities of Gentiana cajnpestris, in some of which the 1 Dickie, Journ. Linn. Soc. (Bot.), xiv. 2 (1873); and ref. to Irmisch, Beit- raege zur Biologie u. Morphologie der Orchideen, 1853, pi. iii. 2 Acta Nat. Cur., xix. i. Van Tieghen, Comptes rendus, Aug. 14, 1871 ; Ann. des Sc. Nat., Nov. 1872; and Le Monnier, Ann. des Sc. Nat., 1873. 2 A 37° MORPHOLOGY OF THE OVULE. ovary was transformed into a leaf, and the ovules into buds ;^ to the very similar observations of Henslow on the ovules of the migno- nette ; or to those of Schimper and Engelman ^ on various other plants. In willow flowers we sometimes find every gradation, from the true carpellary leaf back to stamens, until the retrograde development ends in true leaves. It must, however, be noted, in justice to those who take a different view of the morphology of the ovule, that the order of the development of bud-scales is different from that of the coats of the ovule, the inside scales in the bud being developed last — not the inside ones the first formed, as in the ovule ; still the preponderance of facts is in favour of the generally received view which we have adopted. ^ Trans. Bot. Soc. Edin., vol. iii. ^ De Anthylosi Prodromus, § 44, 76, t. 5, fig. 4, 5. For a complete descrip- tion regarding the theory of the carpel, &c., see Lindley, Elements, i. 369, 392 ; Chatin, Ann. des Sc. Nat. Bot., 56 sen, 1874, p. 5 et seq., with references in that memoir to the treatises of Brongniart, Mirbel, Decaisne, Duchartre, Planchon, Barndoud, Tulasne, Schacht, Rosanoff, Hofmeister, Robin, Chev- ruel, Duvau, St Hilaire, Baillon, and others, on the same subject (the structure and development of the ovule). V 371 CHAPTER V. DEVELOPMENT, PR^FLORATION, SYMMETRY, AND METAMORPHOSIS OF THE FLOWER. In this chapter we propose to consider briefly how the flower and its different parts are developed ; how folded up in the flower-bud (Prsfloration) ; a few particulars regardingthe symmetrical arrange- ment of the different parts ; and finally, Metamorphosis, or the changes from one part into another, which pi'ove that every part of the flower is only a modification of the leaf, or of the leaf-type. DEVELOPMENT OR ORGANOGENY. Nearly all we have said about the leaf is equally true of the development of the flower. Calyx. — This whorl appears first, and though in rare cases the separate sepals may unite, yet usually each sepal, in a dialysepal- ous calyx, is produced separately like a distinct leaf, and so re- mains ; while a gamosepalous calyx is produced in the form of a ring, which subsequently forms the tube of the calyx. In the early stage of the development of the whorl, all the parts are regular ; any irregularity occurs afterwards. Corolla and Androecium. — The petals develop in the same way as the stamens, only a little later. The stamens appear later than the petals, yet develop earlier, owing to the retardation of the growth of the latter. The anther, on the other hand, will often be formed before the filament, and while the petafs are yet merely embryonic. When once the corolla develops it grows rapidly, and encloses the organs lying within the whorl. The development of the petals differs from that of the calyx in the following respect — viz., that the base of each petal is frequently narrowed into a claw, which corresponds to the petiole of the leaf, and like it is formed after the blade ; while in the calyx this claw, if present, is formed before the blade. . Each of the whorls of the flower shows itself in the form of little 372 PRi«;FLORATION. prominences, disposed in a circle around the axis. If these emi- nences grow in size without uniting, we have then a dialysepal- ous or dialypetalous calyx or corolla. But if they coalesce, then a gamosepalous or gamopetalous calyx or corolla is the result. The lobes of the calyx or the corolla correspond, in general, to divisions on the prominences mentioned, out of which these whorls develop.^ PILffiFLORATION. All the different parts of the flower get packed in the flower- bud in various determinate ways, just as the leaves in the leaf-bud are packed after determinate methods (p. 162). A few words are therefore requisite regarding Praefloration, or Estivation, as it is very commonly styled, Linnaeus having applied this name to it, in contradistinction to vernation, applied to the leaves.^ We can study Praefloration from three points of view — viz. (a) Each verticil in particular, considered in reference to the parts which compose that verticil ; ((3) Each piece of the same verticil ; (y) Each verticil in reference to the position in which it lies to the other verticils. The study of praefloration, from any of these points of view, is often useful in the co-ordination of natural orders, as was long ago pointed out by Robert Brown. 1. General Prsefloration of the Floral Envelopes. — There are two general ways in which they are arranged in the bud : (i.) Su- perpositiofi, or one part being laid over the other in the verticil ; (2.) Juxtaposition, when the borders of the parts in each verticil touch each other. In Superposition.— Ih.^ parts are arranged in a spiral, like the leaves on the branches, the petals, &c., being only modified leaves, though so closely foreshortened as to seem to be in a verticil. This is spiral praefloration ; yet, according to the breadth of the parts and the extent of the superposition, it presents variousmodifications.and has received corresponding names. (i.) Iinbricative, where only the tops of the pieces composing the yerticil touch {Ex. Corolla of Camellia Japonica, fig. 265). (2.) Convolutive, when rolled round through almost their entire length {Ex. Calyx of Magnolia). In this case the outer pieces nearly entirely cover the inner ones, like convolute vernation of leaves (p. 163).^ 1 Martins, in Richard's Elements, 203 ; Alex. Dickson on Development of Flower of Pinguicula, Trans. Roy. Soc. Edin., 1870 ; Masters on Development of Androecium of Cochliostevia, Journ. Linn. Soc. Bot., 1872; M'Nab on Development of the Perigynium ot Scirfitts, ibid., 1873 (Ined.), &c. 2 y^siivus, summer ; prcs, before ; and Jlos, flower. 8 This is, however, a most improper term to apply. We agree with DrGray. PR/EFLORATION. 373 (3.) Quincuncial, when there are two pieces wholly interior, two wholly exterior, and one (the third) with one edge covered by No- 1 on one side, while it covers No. 5 with its other side. Ex. Ger- anuim, corolla of Rosaceae, &c. (fig. 267.) (4.) Vexillary, in the calyx and corolla of all true papilionaceous flowers, where the exterior petal or vexilliim (p. 31 1) is the largest. Fig. 265. — Opening bud of Camellia Ja- ponica, L. , var. Chandleri elegans, showing the perfect passage between sepals and pet- als, as well as imbricative sestivation. a a a Exterior leaflets, corresponding in appear- ance to sepals ; eC Leaflets beginning to assume the character of petals, larger in size and reddish on their margins ; a" A still more petal-looking leaflet; b b b Perfectly characterised petals, the last trace of the calyx-like appearance being gone. Fig. 266. — Diagram showing five differ- ent kinds of prsefloration. A, Imbricative ; B, Reduplicative ; C, Induplicative ; D, Vexillary; E, Cochlear. and at first embraces all the rest. As nearly the same thing occurs in the violet, it is probably caused by some slight dislocation that takes place during the early growth of the organs in the irregular blossom (Gray), (fig. 266, D). (5.) Twisted or Contorted. — " In this mode, the leaves of the circle are all, or at least apparently, inserted at the same height, and all occupy the same relative position ; one edge of each being directed obliquely inwards, is covered by the adjacent leaf on that side, while the other covers the corresponding margin of the con- tiguous leaf on the other side. This is owing to a torsion or twist- ing of each member on its axis early in its development ; so that the leaves of the floral verticil, instead of forming arcs of a circle, that it is practically inconvenient, and wrong in principle, to designate different degrees of the same mode by different names, and that it is to the vexillajj mode of aestivation that the term properly applies. Long custom among de- scriptive botanists compels us, however, to use some of the terms in the ordinary way. 374 PRyEFLORATION. or the sides of a polygon, having for its centre that of the blossom, severally assume an oblique direction, by which one edge is car- ried partly inward and the other outward." It is rare in the calyx, but common in the corolla. Ex. Most Malvaceae, St John's wort, &c. The term is often used interchangeably with " convolute." (6.) Codilear, in which one of the floral leaflets is large and rolled up like a snail's shell {Ex. Aconitum), only a modification of vexil- lary (fig. 266, E). The foregoing terms also apply to the disposition of the sepals and petals in the calyx and corolla (dialysepalous and dialypetalous), and even when the sepals and petals are coalesced into one piece (gamosepalous and gamopetalous). Prce/loration by Juxtaposition. — There is only one essential modification — viz., the valvate form, in which each piece of the verticil comes in contact, edge to edge, through their entire length, yet without overlapping. Here all the pieces are arranged in an exact circle, none being lower or exterior, the edges being as thick as the rest of the organ, by which mark valvate prsfloration may even be detected in an expanded flower. There are, however, several modifications of valvate prefloration, which may be classed as follows : (a) Induplicative (fig. 266, C), in which the edges of the petals or sepals are bent in, or as in the calyx of Clematis rolled round, so that the flower, w^hen cut across, does not present, in each piece, something like the arc of a circle. (|3) Reduplicative (fig. 266, B), in which the margins of the sepals project outwards in the form of salient projections. In the corolla of many of the Malvaceae, hollyhock, &c. (y) Open estivation. Lastly, in the mignonette, &c., the calyx and corolla are not closed at all over the parts of the flower in the bud, and hence this form of aestivation has been called " open." 2. Prsefloration of eacli piece of the Verticil in particular. — . Each part, when taken by itself, offers various positions, the nature of which it is well to know. For example, when the petals are irregularly plaited in every direction, as in poppies, they are styled (i.) corrugated. This points to a short calyx and a rapid growth of the corolla, for in very young buds there are no plaits on the petals. Some of the folds are inward, as in the corolla of the Gentians, and others outwards, as in that of the genus Campanula. Hence the streaks of colouring on the latter. In the bud of the Morning glory {Coftvolvulus), Stramonium, and many Solanaceti;, the pieces of each verticil are laid over one another in a convolute manner. Hence such verticils are said to be {2.) supcrvohitc. 3. Eelation of the pieces of the Verticil to those of the Verticil more interior. — If we examine a verticil relati\ e to those in its vicinity, we observe two modifications : (i.) The pieces of the neighbouring verticil offer the same position ; (2.) The PRiEFLORATION. 375 pieces of two neighbouring verticils have different positions. For example, in Faruassia and Elodea the prtefloration of the calyx and corolla is the same (quincuncially imbricated). In vines and AracecC the divisions of the calyx, like those of the corolla, equally are invalvate prsfloration. In Malvace^, Convolvulacese, &c., on the other hand, the calyx shows a valvate prjefloration, while the petals are imbricated. It sometimes happens that the calyx is in a spiral, and that this disposition continues equally with the petals, as in Magnolia, Ny7nphaa alba, and generally in all those plants in which the sepals differ little from each other. In these cases we see that the first pieces of the second verticil follow immediately that which terminates the first, and follow then without inter- ruption the spiral line commenced by the first verticil ; while sometimes there seems to be a gap between the innermost sepal and the outermost petal, showing that something is wanting or abortive. Not only is there this arrangement between the pieces which form the two external verticils of the flower (calyx and corolla), but in some orders between the petals and the sta- mens which form the third verticil of the flower. Thus — e.g., whilst in a small number of orders the stamens are opposite the petals {Ex. Rhamnacese), or in many others of those which are " diplostemonous " (p. 320), these are often concave or hood-shaped in form, and cover completely the stamens placed in front of them. Praefloration of Stamens and Pistils. — The stamen, like the other floral organs, first appears in the form of little tubercles, which in general appearance differ nothing from those which after- wards develop into the sepals and petals. By-and-by, however, the part which in the former organs develops into the limb becomes the anther, and what remains as parenchyma in the leaf becomes the mother cells, which develop the pollen-grains (p. 344). Often the staminal whorl develops before the petals and sepals, as in the Grasses and Cruciferze. In double flowers we see a transition be- tween petals and stamens. The development of the pistil and its relation to the other parts we have already touched upon in the chapter treating of the Gyncecium. The stamens and pistils have, equally with the other whorls, determinate positions in the bud. Thus, in all the family of Urticaceae — the nettle among others — the stamens are bent in the form of an arc, and curved toward the centre of the flower. An anomalous position may be remarked as existing in the carrot, parsley, and other plants belonging to the order Umbelliferae. We there see that przefloration offers varied and somewhat important characters. In order to examine these methods of praefloration — of which we have only given the barest outline, as the subject can be properly understood solely by referring to the plants themselves — the stu- 376 SYMMETRY OF THE FLOWER. dent should examine the buds just before they burst, as in a later condition of the flower the arrangements are totally effaced. We have seen that the fundamental law which reigns in the flower is that the parts of the four verticils alternate one with another (p. 283), though it is not often that this perfect symmetry is realised. The parts of the flower may consist of two, three, four, or five sets of organs alternating with one another. In Circcea liitetiana, for instance, each verticil consists of two parts, and these regularly alternate with each other. In Sisyrinchium, and other Iridaceae, the four alternate verticils are composed of three parts each. In Isnardia, and some other Onogracese, four pre- vails ; while in Sedum rubrum (fig. 267) five is the rule. Hence, to indicate the number of pieces which make up the different sym- metrical alternating whorls, and to express the particular kind of symmetry, the terms dimerotis,^ trimerous'^ (figs. 269, 270), tetra- inerous^ (fig. 26?,), peniamerous'^ (figs. 267, 271), according as two, three, four, or five pieces enter into the composition of each ver- ticil, indicated by the symbols, ^ ^ and ^ ^ Variations and Alterations in the Symmetry. — In a great number of plants the exact symmetry is "disguised, masked, or 1 8« twice ; m^p's. part. 2 Tpeis, three ; the symmetry is sometimes styled trigonal (rplis, three ; yiavXa, an angle). •* TCTptis, four ; sometimes the symmetry is called tetragonal. 4 jrei/re, five ; also called pentagonal. SYMMETRY OF THE FLOWER. Fig. 267. — Diagram of the flower of a species of Stonecrop {Sedum m- brum, L.) j Calyx ; c Corolla, both in quincuncial prsefloration ; e Andrce- cium ; gl Disk ; c/ Gynoecium. Fig. 268. — Diagram of the flower of Bitnias, DC, one of the Cruci- ferse, showing tetram- erous symmetry. VARIATIONS IN THE SYMMETRY OF THE FLOWER. 377 altered" by different causes, which we may indicate seriatim. . These are : — I. Multiplication.— In this case the number of parts entering Fig. 269.— Diagram of Fig. 270.— Diagram o{ the the flower of a Hyacinth flower of Muscari (Grape- (Hyacinthus orietitalis), hyacinth), one of the Aspho- one of the Liliacese. delaceae. into the composition of a verticil are increased beyond their normal number — this increased number of divisions forming two or more concentric verticils, alternating with each other. This is often seen in the androecium, as well as in the coroUine and the other whorls. In the case of the stamens, when they become very numerous, they are apt to take the spiral instead of the verticil- Fig. 271. — Diagram of the flower of Myosotis pal- nstris (Forget-me-not), one of the Boraginaceae. Fig. 272. — Diagram of the flower of an Iris, showing trim- erous symmetry. The three outer divisions of the perianth, with corolline appendages or hairs ; three inner alternating ; three .stamens, and the trilocular ovary; the spathe is seen below. late arrangement. This is shown in the figure of the gynophore of Magnolia grandijlora (fig. 146, p. 287), the points where sta- mens are situated being indicated by cicatrices on the gynophore (rt). In the water-lily {Nymphcea) all the whorls are much multi- 378 CAUSES OF VARIATIONS IN THE SYMMETRY, plied. The sepals, petals, and stamens occupy numerous verticils. In the great division of Monocotyledons the normal symmetry of the flower is trimerous— /. e., in threes, or multiples of threes (fig. 269) ; while in Dicotyledons it \s pentajnerous — i.e., fives, or mul- tiples of fives (fig. 267) : and accordingly, though there are many exceptions to the rule, yet it may generally be concluded, when we find the corolla has a different symmetry than the above, that it is due to multiplication ; or, when the parts are fewer, to the abortion of some members of the verticil. The multiplication of the members of a floral verticil does not necessarily interfere with the symmetry of the flower if the additional members are multiples of that which forms the basis of the flower, but it renders it diffi- cult to be detected : and when, as in the case of the stamens, there is a great increase, the regularity is obscure or disappears. 2. Chorosis or Deduplication ^ is the division of an organ into a pair or cluster. This may be accomplished in two ways, — (i.) by collateral chorosis ; (2.) by vertical or transverse chorosis. The first takes place when an organ is replaced by two or more situated on the same plane, the organs thus produced standing side by side. An example is afforded by tetradynanioiis stamens (p. 321) of the mustard and cress family (Cruciferse). In the case of vertical chorosis, the organs produced stand one before the other, as is seen in the " crown," or generally two-lobed appendage, on the inside of the blade of the petals of Silene (p. 313). Some stamens {Larrea, most plants of the Guaiacum order, and the Dodder) bear a similar but even more remarkable appendage. In both organs it may be looked upon as a " partial separation of an inner lamella from an outer," as the original theory of Dunal supposed was the case in the whole series of plants in which chorosis occurred. 3. Coalescence, or union of the parts. — This is so common that it is rare to find a whorl in which, to some extent at least, it does not occur. We have already fully considered it when discussing the gamosepalous calyx and the gamopetalous corolla, as well as the cases in which the stamens are united, either wholly or in part, to each other, or, in other words, become inonodelphous, diadel- phous, or polydelphous, &.c. (p. 324). The calyx of the common whin {Ulex) maybe cited as a familiar instance of the symmetry of the plant being obscured by coales- cence. At first sight the calyx of this plant appears to be com- posed of two portions almost entirely free, — an arrangement out of harmony with the law which prevails in these plants — viz., that the 1 Didoublement (diremptio, Lat.) of Dunal; literally, •" unlining, "— the original hypothesis being "that the organs in question u/ilinc, or tend to separate into two or more layers, each having the same structure." Chorosis is from x<"P"^'Si the act of separation or multiplication. CAUSES OF VARIATIONS IN THE SYMMETRY. 379 corolla is made up of five petals. However, on more closely examining the calyx, we find that one of the parts is terminated by two teeth and the other by three. We thus detect by means of these teeth that the calyx, like the corolla, is pentamerous, only that the five sepals are coalesced almost to the summit, on one side into two, and on the other into three— the five teeth pointing- out the disunited tips of the five sepals. 4. Arrest or defect in development. — There is a frequent cause of irregularity in the symmetry of flowers by the abortion or sup- pression 1 of parts of the same verticil, or of another verticil alter- nating with it, or of several verticils of the same flower. Take, for example, tobacco, Belladona (in the order Solanaceae), and we find five stamens alternating with five petals united in a gamo- petalous corolla. Again, take the mullein ( Verbascum Thapsus) ; one alone of the stamens which is placed between the two upper lobes of the corolla is much smaller than the others, owing to an arrest in development. Lastly, we may cite the flower of the snap- dragon {Antirrhinum) as an example of the same irregularity. In the flower of this plant there is no trace of the fifth stamen, which has entirely disappeared. In the greater number of the Labiatae (fig. 273) the calyx and corolla have a pentamerous symmetry, but the androecium has only four stamens ; but we find that the fifth is abortive, and the place which it should have occupied is occupied by a vacant space. In such cases of natural abortion, we find that in all cases of mon- strosity the wanting organ makes its appear- ance, thus pointing out what is the normal symmetry of the flower. Hence the value of the study of Teratology to the scientific bota- nist. In other genera of the same order, the sages (Salvia), for example, have only two t\I\^lr'~?'W7f^ium stamens; but we have already seen that in Scorocio>ua.{,wooAgsrma.n- ,1 ^, • , r , . der), one of the Labiatae. these cases there remam traces of two sta- mens, and the general law which prevails in the order enables us to account for a fifth abortive one. Examples of abortion and suppression we have already considered in the case of various Primulacese, — in brookweed — e.g., Samolus Vale7'a7idi (fig. 192, p. 313), where we find five scales {e') placed precisely where we ought to have found five normal stamens, which have been aborted, so that the androecium is in alternating verticils ; but by the abortion of one, the one which remains is opposite to the petals. Again, where we find, as in the primroses, all the verticils having a penta- 1 The term suppression is used when parts which belong to the plan of the flower do not appear in it ; and abortion in addition to partial obliteration, as, for instance, when a stamen is converted 10 a scale or filament. 38o CAUSES OF VARIATIONS IN THE SYMMETRY. merous symmetry, except the androecium, which has the five stamens opposite to the petals, we are inclined to see in this a case of vertical chorosis.-' Dr Gray also considers that anteposi- tion or superposition of parts which normally alternate in the flower is not to be considered a case of transverse chorosis, and that the cases of the vine and buckthorn families. Linden, purs- lane, &c., can be explained in another way. " The position of the stamens before the petals in these cases, as well as that of the numerous petals in double camellias, arranged throughout in five vertical ranks, is most readily explained by supposing a return to the regular | or five-ranked arrangement of leaves" (p. 184). Lastly, an example of suppression has already been seen in apetalous plants (like the Chenopodiacese), where the petals are entirely absent, and the stamens therefore opposite to the seg- ments of the calyx. 5. The degeneration of the parts nvhich form the floral verticils. — We have seen, and when considering the subject of metamor- phosis in the present chapter will consider the question more fully, that all the parts of the flower are only modifications of the leaf, and that frequently these parts return by regular gradations to the leaf, the pistils and stamens (as in double flowers) to petals, or even to true leaves, petals to bracts or leaves, and so on. 6. Adnation or Consolidation of the different floral verticils with one another. — This is seen in the familiar case we have already considered (p. 322), where one verticil or set of organs seems to grow out of another, as the corolla out of the calyx, or the stamens out of the corolla, or all of them out of the pistil, as ex- plained when discussing the terms applied to such a union — viz., hypogynous, perigynoiis, and epigynous {]). 331); or where, as in the orchids, the stamens cohere with the style, or become gynan- droics (p. 329). In the white water-lily, Nymphcea alba, a unique example is presented of the petals and the stamens being inserted on the walls of the ovary. 7. Irregularity by unequal development. — To all the foregoing causes of the disturbance of symmetry in the flower, we may add irregularity produced by the unequal development or unequal union of the different parts of the flower, though irregularity can also be produced by absorption or disappearance of some parts. A familiar example of irregularity produced by unequal develop- ment of certain petals is shown in the papilionaceous flower of the pea and bean order (Leguminoss), already described (p. 311). It is seldom, however, that any one of the foregoing inter- ferences with the symmetry of the flower occurs alone. Generally two or more occur in the same plant; so that it requires tne utmost care to detect the malformation, or to avoid being led astray by 1 Schimper and Braun, Flora, 1839, p. 314. PRIMITIVE REGULARITY OF THE FLOWER. 38 1 the appearances which present themselves. Several of the devia- tions may even occur in the same natural order. Primitive Regularity of the Plower.— Schleiden and Vogel showed that the papilionaceous flower, which is so markedly irregular, is in the bud quite regular ; and Barneoud has since pointed out that it is a general law among all plants, and that in the early stage of the flower not only do they show a perfect regularity, but even present certain organs which disappear in the adult flower.^ Relation of the Floral Whoris to the Axis. — We have con- sidered, when discussing phyllotaxis (p. 181), that the leaves de- scribe certain cycles around the stem, and that, after each revolu- tion, the next cycle commences exactly over the commencement of the former one, and so on. The material result of this is, that the homologous numbers are situated exactly over each other, and there must necessarily be as many vertical series as there are leaves in one cycle — e.g., 2, 3, 5, 8, 13, &c. These series cer- tainly appear more distinctly marked in some instances than in others, as Unger points out in a particular manner in the Echinocaciiis 79, fig. 51), in which the perpendicular ribs of the stem are produced " by the interfusion of the superimposed leaf." In the flower where the members of the different cycles are simply modified leaves, a similar arrangement prevails, though not so readily seen. However, their case is different in this respect from the leaves — in so far that "even when only two similarly numbered leaf-cycles follow each other, as well as when dissimi- larly numbered cycles are associated, there is never an uninter- rupted progression. It is only in this way that, notwithstanding the crowded position of the leaf-cycles, the leaf elements in the flower do not cover each other. The measure of progression in the succeeding leaf-cycle is increased exactly so much that the elements of it come to be situated between those of the previous cycle, the consequence of which is an alteration of the leaves, which, as may readily be conceived, is not without its influence in the agreeable impression which the flower always produces in us. Thus, then, there presents itself in the flower, together with the greatest simplicity of elements, the most beautiful harmony in their arrangement, so that the architectural aspect of the flower becomes really a model of perfection in this respect ; and, as the history of constructive art teaches us, it has always exercised a determining influence upon all the architectural works of man." This simplicity is not, however, universally prevalent. In some cases, especially when the floral whorls are made up of a great number of parts, more complicated relations present themselves, as can be seen in the cactus, white water-lily, the Calycanihiis 1 Comptes rendus, 1846, t. xxiii, 1062. 382 PRIMITIVE REGULARITY OF THE FLOWER. flower, &c. Even in the flower of the latter the unity of design can be readily recognised. In fig. 274, A, is represented (after A B . Fig. 274. — Longitudinal and transverse sections of the flower of Calycanthus JJoridus, DC. (Carolina Allspice tree). Unger) a vertical section of a flower and peduncle of Calycantlms floridus, and in fig. 274, B, a ground-plan of the same flower : /(fig. 274, A) indicates the origin of the true stem-leaves which have been removed ; p the coloured leaves of the envelope or perianth ; st the stamens ; stab the abortive staminal organs. In addition, there is represented at in the central substance of the peduncle, and g, the ovules situated upon its superior expansion. In fig. 274, B, are shown the relations and position of the different parts in the flower. After the two opposite leaves there follow from I to 28, the leaves of the floral envelope (sepals of the calyx) at first reduced in size, then larger, and then again becoming smaller ; after these from 29 to 41, the stamens (st) ; and lastly, from 42 to 55, the abortive staminal organs in the order pointed out.i In oi'der to study the relation of the floral whorls to the common axis, we should take the most external piece of the calyx as a point of departure, and then examine in what degree this piece corresponds to the axis, though placed semi-opposed to it. The same floral phyllotaxis, like the true phyllotaxis of the stem-leaves, is often followed out in all the genera of the same order. 1 Unger, Botanical Letters (trans, by Dr Paul), p. 72. METAMORPHOSIS OF FLOWERS. I METAMORPHOSIS OF FLOWERS. When speaking of the different floral verticils, we have re- peatedly pointed out that they are modifications of a single type, and that this type was ihe leaf; furthermore, that from the true leaf to bracts, from bracts to calyx, from calyx to corolla, and from corolla to stamens and pistils, there were in many cases regular gradations ; and lastly, that in certain monstrous (teratological) conditions of the plant, any one or all of the verticils are liable to return to the true leaf-type. To trace all the floral organs as originating from and constituting modifications of one type, con- stitutes one of the most interesting sections of botanical study, and has served to rescue the science from being turned into a puzzling maze of names alone. Probably the earliest botanist who turned his attention to these questions was Joachim Jung, or Jungius, who in 1678 published at Hamburg a work on the subject en- titled ' Isagoge phytoscopica.' The celebrated Linnaeus — the father of the modern science of botany — did not neglect this department. In his ' Prolepsis plantarum ' ^ he enunciated certain doctrines on the subject — rather crudely, it must be confessed. But it was not until 1759 that Caspar Friedrich Wolff, in ' Theoria generationis,* published anything like soundly philosophical views regarding the metamorphosis of the floral organs. His work abounds in errors, but it prepared the way for the ideas of a clearer-headed and more brilliantly philosophically-minded man than he — ^the celebrated German poet, dramatist, and naturalist, Johann Wolfgang Goethe, who, with the insight of genius, almost at once struck upon the real theory of the metamorphosis, as now held by almost every botanist.'-' Among the numerous writers who have advanced our knowledge of the subject of late years, De Candolle and Auguste de St Hilaire hold the first place ; and though, doubtless, much specious theory and hypothesis which have got spun around it could be dispensed with, yet, nevertheless, the study of the meta- morphoses of plants has thrown a flood of light on many obscure questions in systematic as well as in structural botany. With this prefatory sketch of the history of research on the sub- ject,^ let us call attention to a few of the leading points in this section of scientific botany. Having already touched upon all the main questions when describing the floral verticils, anything more than a brief outline is unnecessary. N 1 AmanitatesAcadetnicas, vol. vi. (1763) ; Philosophia Botanica, 301.— " Prin- a\>vxmflorum et/oliortnn idem est. Principium gemmarum et foliorum idem est. Gemma constat foliorum rudimentis. Perianthium sit ex connatis folio- rum rudimentis,"&c. 2 Versuch die Metamorphosen der Pflanzen zu erklaren, 1790. 384 TRANSITION FROM LEAVES TO SEPALS AND PETALS. Transition from Leaves to Sepals and Petals.— Examine the white-flowered garden peony {Pcp.otiia albijlora, Pall.), and there would seem to be the widest possible difference between the com- pound pinnatifid leaves of the stem and the ovoid white or rose- coloured petals of the corolla, perfectly simple in form, and entirely undivided on the margin, with the exception of a deep cleft at the apex of each. Nevertheless, a gradual transition from the one to the other exists. The inferior stem-leaves are of the normal type we have described ; still higher up they are smaller and less divided ; still nearer to the flower they become yet smaller, and. present three undivided segments; higher still, the leaves, almost touching the calyx, present a single form with the limb undivided, and with scarcely an appreciable petiole. Then higher up, and forming the first row of sepals, are leaves still netted- veined, but with a broad sheath not prominently marked by veins, which in other more interior rows become the main portion of the sepal, the blade being only represented by a long narrow point at its apex. This point in its turn disappears, and a cleft in which it was situated alone remains, as in the petals. Thus we can trace the gradual change from the very unpetal-looking compound leaves to the petals themselves. In Magnolia grandiflora, repre- sented in fig. 275, the calyx is composed of three sepals, which are so little different from the petals, more interiorly, that they are usually called corolliform. In Camellia Japonica (fig. 265) we also see a perfectly gradual passage from sepals to petals ; and the same appearance may be seen in many flowers, those, for instance, of Chimonatithus fragrans, Lindl.^ ^ In some notes which a very intelh'gent observer — Mr Alfred Grugeon, Lecturer on Botany in the Working Men's College, Great Ormond Street, Lon- don— has favoured me with, he discusses the question of how little of the foliar leaf or appendages is represented in the floral organs of Dicotyledonous plants. "The chain of reasoning," he writes, "that suggests this problem is this — that though compound and stipulary leaves are prevalent in many orders in the foliar condition, yet we invariably come to simplicity in the floral. Now, the first question that presents itself is, what is it that disappears? If we take a thoroughly compound order like the Leguminosae, we find the terminal leaf- let to be the first to alter or absent itself, being represented either by a seta or a tendril ; then another pair or two pairs become tendrils, or the leaf entirely disappears, and is represented by a phyllodium and stipules, as we find in many acacias, some species of Lathyrus and Lvpinus, In the papilionaceous division of this order we find a pentamerous arrangement of the flowers, but irregular in form. And it seems to me that the vexillum represents the ter- minal leaflets of a compound leaf, which in all cases seems to reappear and assert itself in the flower. The wings and keel, from this point of view, would represent two pairs of leaflets, or perhaps one pair only and the two stipules. Taking this in conjunction with the inequality of the sepals and their position, the large sepal being opposite to the large petal would seem to indicate that the calyx and corolla were two compound leaves ; and if we further carrj' out FORMATION OF STAMENS AND CARPELS. 385 Formation of Stamens and Carpels.— i. Stamens— We have already traced the homologues of the leaf in the stamen (p. 336). Fig. 275. — Entire flower Magiiolia grandiflora, L. e Mass of stamens ; p Mass of pistils. In the white water-lily {Nymphaa alba) the calyx is composed of four sepals, green exteriorly and white interiorly, a corolla of about eighteen petals, and numerous stamens in several rows around the pistil (fig. 276). The petals diminish in size from without inwards by regular gradations, until some of them are adherent to their tips on the internal aspects — a " little body, formed in general of two parts, adjacent and symmetrical," which it is easy to re- cognise as an anther (fig. 277, E). From this petal-like stamen there are regular gradations to the typical form of the stamen (fig. 277, E, G, H). In " double flowers," owing to changes in the constitution of the plant induced by cultivation, the stamens become converted into petals. The same monstrosity, however, occasion- ally occurs in wild plants, though usually in these cases all the the investigation, we must consider the carpel to be the terminal leaflet of the next leaf, and the stamens to represent the two leaflets and stipules, equivalent to those that carry the keel of the corolla, which here becomes split up into shreds, although cohering more or less towards the base. This cohesion occurs also in the two petals from the keel. This theory was first suggested to me by finding a variety of Trifolium repens, known as proli/era, where there was retrograde metamorphosis which pointed that way. To turn now to the neighbouring order Rosacese, I think the reverse condition prevails in the foliar organs. We will assume this to be an order where compound leaves are conspicuous, as where they are simple they are always stipular. The simple leaf shows that, whatever else had disappeared, the terminal leaflet still re- mains. In addition to this, the terminal leaflet in the truly compound, and the terminal lobes of the divided though still simple forms, are always the most luxuriant." . 2 B 386 FORMATION OF THE STAMENS, AND PISTIL, Stamens do not get converted into petals. Such flowers are seini- double. In most Monocotyledons, all the stamens except one are converted into petals (" pe- talised," as it is called). In a species of Caitna, this single stamen preserves only a part of the anther, carried upon the edge of a petaloid filament, which is as vividly coloured as the other parts of the flower, and the style itself is also in the form of a brightly- coloured blade. In full double buttercups the in- ner petals have a tendency to become green ; and a common monstrosity of the strawberry is for all the floral organs to revert to sepals or imperfect leaves of a green colour.'^ Some- times a leafy branch will spring from the centre of the flower, or one flower out of the centre of another, as very com- monly seen in roses. In this case the receptacle or axis of the flower assumes its ordinary veg- etative growth, and instead of being surmounted by a rosette of floral leaves, gives origin to ordinary green leaves* Dickson 2 has noticed the conversion of bracts into stamens in a species of fir {Abies excelsa), a metamor- phosis which Masters calls " sta- minody of the bracts." 2. Pistil. — In most plants the pistil is not very leaf-like; yet in Colutea, Stercularia, &c., it is foliaceous-looking. In double flowers the pistil also frequently takes the leaf-like form, as seen in double-flowered cherry, &c. When the flower is entirely re- placed by a tuft of green leaves, as mentioned in the preceding paragraph, the pistil is also transformed like the rest of the floral Fig. 276.- -Entire flower of Nyjitihaa alba, L. (White Water-Lily). Fig. 277. — Nym^kcsa alba, L., series of forms through which the petals (E, F, G), each of which bears an anther, passes to the btate of the normal stamen (H). 1 Duchartre, lib. cit., 443. ^ Trans. Bot. Soc. Edin., viii. 60. FORMATION OF THE STAMENS, AND PISTIL. organs. Such flowers are sometimes called chloranthotis (green- flowered). It is from such facts as these that botanists are led to the irresistible conclusion that the leaf is the type on which all the floral organs are formed, and that they only differ from the ordinary leaves of the stem in their special development. In an early stage of their growth they all look alike. These organs have thus a tendency to retrograde metamorphosis, or to return to their original type either directly or to one stage of it, such as stamens to petals, petals to sepals, and so on. It must not, how- ever, be supposed that the petal, though called a metamorphosed leaf, has ever actually been a green leaf, "and has subsequently assumed a more delicate texture and hue, or that stamens and pistils have previously existed in the state of foliage ; but only that what is fundamentally one and the same organ develops in the progressive evolution of the plant under each or any of these various forms. When the individual organ has developed, its destiny is fixed," ^ ^ Though the questions connected with the symmetry and metamorphoses of flowers constitute a most important section of botanical science, we have been forced, by the exigencies of space, to treat them very briefly. But even had we been able to do so at greater length, it is doubtful whether the student would have at this stage of his studies been benefited thereby. So much theory is mixed up with every question, that unless the subject is divested of this, and treated only in its barest outline, the tyro is apt to lose himself in the maze of mingled fact and fancy. The brevity of this chapter is the less to be regretted, because the subject is copiously treated, among others, in two books acces- sible to every student of the English language : Maxwell Masters's able work on Vegetable Teratology (Ray Society, 1869)5 and as regards American plants, in Asa Gray's Text-Book, » 388 CHAPTER VI. DISC AND NECTARIES, In addition to the regular floral organs described in the pre- ceding chapters of this section, there are in addition two accessory organs frequently present in the flower, which require notice before leaving the subject of floral anatomy. These are the Disc and Nectaries. DISC. This is a fleshy and glandular body found in certain flowers, but altogether independent of the four verticils described. Position. — This is variable : sometimes it is found under the ovary and placed on the receptacle ; at other times at the bottom of the calyx, or on the summit of the ovary, in which latter case it is adherent to the tube of the calyx. In many cases it is a pro- longation from the receptacle. Position in reference to the Pistils or Carpels. — i. It may be placed under the carpels in the receptacle, when it is hypogynous, as in Cruciferse, Labiatse, snapdragons. Rues, &c. 2. It may be applied to the internal wall of a gamosepalous calyx, as in cherry, peach, &c., when it is said to h&perigynous. 3. Or lastly, when the ovary is inferior, the disc is applied to the summit, and is epi- gynous, as in the Umbelliferee, Rubiaces, &c.^ Effect of Disc on Symmetry. — Though not invariably present, yet when it is it has an eff"ect on the symmetry of the plant, so that it may be looked upon as a fifth floral verticil. For instance, when absent, the carpels are, owing to the law of alternation, alter- nate with the stamens and opposite to the petals ; when it is present, these carpels are opposite to the stamens : so that in order 1 In the Umbelliferae it forms on the summit of the ovary a marked thicken- ing, almost hemispherical, which appears to surround the base of the style as with a globe, and has received the name of Stylopodium (otvAos, style ; T0S5, TToSby, foot). DISC AND NECTARIES. to establish the normal symmetry of the flower, it is necessary, as Richard has shown, to regard the disc as a verticil interposed between the stamen and carpels (fig. 278). Fig. 278. — Viiis vinifera, L. (the common Grape-Vine), a Fruiting branch, with b, the tendril ; c Flower-bud ; d Section of pistil showing the bilocular ovary with two up- right ovules ; e Flower showing the caducous petals united at the apex and separating at the base, with the disc surrounding the base of the ovary ; f Androecium and gynos- cium, with the small almost entire calyx, and the disc. The corolla has fallen. NECTARIES. Linnaeus first applied the name nectaries to the glands which secrete a sugary substance in various flowers, and which attract butterflies and bees to these flowers. Afterwards, however, he extended the name so as to apply to all accessory portions of the flowers — i.e., which did not belong to the calyx, corolla, stamen, or pistil, even when these organs or accessory parts did not secrete any honey-like substance. Hence considerable confusion has arisen as to the exact application of this term. If the term is to be kept up at all, it ought to be reserved for the mass of glands situated in the interior of the flower, and which 39° NECTARIES. serve to secrete a honey-like liquid or nectar, and not to be con- founded with the different kinds of discs, which are never secretory organs.^ This has been done by Kurr,^ and the idea has been carried still further by Caspary, in a special work he has written on the nectaries, who designates under this name, not only the glandular organs in the flowers, but even those in the petioles, stem, stipules, &c. 1 Payer— one of our best authorities on the flower — for instance, styles the disc as the collection of nectaries taken as a whole, just as the mass of stamens was styled the androecium. Many authors (following Robert Brown) comprise, under the head of nectaries, the abortive stamens (or " parastamina") which are often found in plants, either under the head of antherless filaments, scales, little tubercles, &c. In Persea Indica, these rudimentary stamens are even more numerous than the fertile stamens, and simulate their position, nature, and appearance. — Schacht, Lehrbuch, &c., t. ii. 305, figs. 210, 211. Tur- pin proposed to use the term Phycostema to designate these ' ' disguised " stamens. 2 Uber die Bedeutung der Nektarien (1833). 391 CHAPTER VII. THE INFLORESCENCE OR ANTHOTAXIS. The organs composing the flower and the leaves are morphologi- cally the same, and the flowers are accordingly placed, like leaves, either at the end of the stem and branches, or along the axis. If we examine the Gentianellaand the Pimpernel, we will find that the flowers are differently arranged on the stem, and are also different in their mode of development. The study of the mode, therefore, in which the flowers are attached to the peduncle, rachis, or axis of inflorescence, and the order in which they open (their evolution or ani/tesis), constitutes anthotaxis'^ or injlorescence. It is to the venerable Professor Roper of Rostock and MM. Bravais " that we are indebted for our first accurate knowledge of the various ways in which flowers are arranged ; and the various terms applied to the inflorescence are in most cases of their devising. In the fol- lowing pages we shall consider the subject, so far as our space will permit, from the stand-point of their original researches, and by the light which the recent studies of other botanists have thrown upon it. First, then, let us premise that a petal is morphologically a leaf — and a flower, accordingly, a collection of modified leaves, or a bud, but a bud which, unless in certain monstrous conditions (pro- lification) of the plant, terminates the axis on which it grows. Thus every axis is arrested by a flower, whether this axis is the main stem or one of its branches. If an axis is unbranched, then this is the most simple of all inflorescence — viz., a single axis with a terminal flower, as in Gentianella, Pimpernel, &c. If there is a flower in the axil of a normal leaf, then the stem is still simple, because there are only terminal leaf-buds and axillary solitary flowers. It differs, however, in this respect, that the elongation of the stem is capable of giving birth to many flowers, and in that the axillary flow- ers are primary, while the terminal ones are secondary in age. In the second case, the axis terminated by one flower is the peduncle. General: Division of Inflorescences.— We have already in- dicated that flowers are either axillary or terminal — that is, are 1 ai/flos, a flower ; and raft?, arrangement. 2 Ann. des. Sc. Nat., ser. 2, t. vii. 193-291 ; viii. 11. 392 DIVISION OF INFLORESCENCES. placed in the axil, or at the end of the axis. These are the two simplest ways of anthotaxis. In the first case, there is nothing to prevent the flowers being produced in indefinite numbers, the axis being always carried upward, and elongating by the terminal ieaf- bud ; while the flowers are produced in the axils of the leaf. Hence this is called the indefinite kind of inflorescence. In the second case, there is only one flower in the termination of the primary axis, which necessarily arrests the development of the axis in that direction ; but if secondary, tertiary, or other axes are produced, then these may produce flowers — each of these axes, however, being terminated by a single flower, which, as in the case of the primary axis, arrests the development of the axis in that direction. This, then, is known as the definite mode of inflorescence. We must therefore study anthotaxis from these two stand-points separately. First, however, let us further remark that in the indefinite in- florescence the outside or the lower flowers are produced first ; and hence this kind of inflorescence is also known as centripetal, or " centre-seeking," from the fact that — as in a daisy, which comes under this mode of anthotaxis — the outside flowers are produced first, made first, or form the .exterior towards the centre. In the definite inflorescences, on the other hand, it is the inside or higher flowers which are produced and fade first; hence this mode is known as the centrifugal, or " centre-flying," method of anthotaxis. The student may understand why in these inflorescences it is the outside or the lower flowers, or the inside or the higher ones, which are either produced or fade first or last, if we use Dr Maxwell Masters's familiar illustration : A daisy, or flower of that nature, we have already seen, consists of a number of flowers, all so crowded together on a foreshortened axis that they seem all together ; and accordingly, if the axis on which they are placed was elongated, then the outside flowers will be below, and the inside ones higher up — just as if we suppose a coil of measuring-tape rolled up to represent the rounded or flat-topped inflorescence. If, however, you pull up the end which is the centre of the coil, then you will have the analogue of the long inflorescence ; the outside coil, which was on a level with the inside ones in the former case, will now be below the inside ones by the elongation of that portion. A practical application of the nature of definite and indefinite inflor- escences may also be given from the same source. For instance, when the gardener has to prune fruit-trees or roses, or thin grapes, take cuttings, or even cut flowers for a bouquet, if he cuts off the top of the wallflower, no more flowers will be produced on that shoot, because the wallflower is an indefinite inflorescence, and the gardener, by cutting off the terminal leaf-bud, has prevented the axis elongating in that direction. But, on the other hand, if the central flowers on a rose-bush are cut, then there will be still DEFINITE AND INDEFINITE INFLORESCENCES. 393 more left to "cut and come again," because the inflorescence of the rose is definite, and each axis terminated by a flower. A'^ain in the indefinite inflorescence, the flowers are sometimes Fig. 279. — Juglaiis regia, W. (Walnut), a Fruiting branch ; b Amentum of male flowers ; c Male flowers ; d Female flowers ; e Longitudinal section of a female flower ; y Longitudinal, and g, transverse sections, of the fruit (the so-called " tryma," a modifi- cation of the " drupe "). produced in the axils of leaves, or sometimes in the axils of bracts. Accordingly, the flowers placed in the axils of leaves follow the same disposition of leaves — viz., are alternate, opposite, or verti- cillate ; or they may be pedunculated or sessile, or solitary, or in twos (geminate), threes (ternate), or fascicled (when there is a 394 INDEFINITE INFLORESCENCES. greater number than three), in the axil. The ways in which they are placed may therefore be described under the different kinds of inflorescence comprised under the head of definite or axillary, and distinguished by different names. Let us examine, then, first— in m erf INDEFINITE, INDETERMINATE, AXILLARY, OR CENTRIPETAL INFLORESCENCES. ' In this great division, the flowers of the inflorescence may be placed either on (i) primary, (2) secondary, or (3) tertiary axes or peduncles, or on the di- visions of the last. We will describe them un- der their subdivisions. (A) Flowers on the Primary Axis. — The inflorescences to be classed under this head lil ^^^''^^^^ ^^'^ spike and its sub- divisions, the catkin, spadix, spikelet, cone, capitjilum, and the coen- anthiu7n. I. Spike (spica). — Here we have a cylin- drical and elongated central rachis carrying sessile flowers. Ex. The Plantago, or rib- grass (fig. 277). There are certain modifica- tions of the spike de- pendent on the flowers being more or less ses- sile, and some of which often approach to the second class of indefinite inflorescences — viz., those on secondary axes. These are : (a) the ainetitnm or catkin, in which we have sessile unisexual flowers — male or female — of which the male is articulated at its base to the rachis, and falls off in one piece after the plant has flowered, and in which the perianth is a simple scale. Ex. Hazel, willow, walnut, poplar, alder, &c. ; hence called on this account Amentacese (figs. 279 b, 281).^ ip) The spadix, or spathe, in which the rachis is a cen- ^ The development of the flowers of the hazel is curious. In the early part of the year, all that is seen in the female flower is two pink styles surrounded by a few scales, but without a trace of ovary or of ovules. These latter are not produced till nearly midsummer, and do not arrive at their full development till the succeeding autumn. M. Baillon has lately succeeded in tracing the Fig. 280. — Spike of Planlago lanceolata, L. Fig. 281. — Two small cat- kins of the American Hazel i^Corylus Americana, Walt.) INDEFINITE INFLORESCENCES. 395 tral axis (generally fleshy) covered by flowers, unisexual and ordi- narily mcofup/efe — /. e., they have no proper floral envelopes, but are covered completely by a large enveloping bract. The flowers are, moreover, not only sessile, but are embedded into the fleshy sub- stance of the axis. This form of spike is only found in Mono- cotyledons, such as the cuckoo-pint, lords and ladies, and all Araceas and palms. Most frequently in the spadix the female flowers are placed on the lower part of it, and the male ones higher up, with no interval between them, as in Dracunculus vul- garis, Schott, &c. ; or, as in palms, each spadix may be unisexual, or dioecious, as in dates. The spadix may be either woody (palms) or fleshy {Artwi). In palms the spadix branches often to a great degree, and acquires immense proportions — sometimes bearing as many as 20,000 flowers (fig. 154, p. 292). (y) The spikelet of grasses is another variety of spike, and may be either simple or compound. In these plants the reproductive organs are made up of little inflorescences composed of several flowers at- tached along a common axis, the whole forming little spikes or spikelets (spicula, locusta). These spikelets, again, in their turn arrange themselves in various ways, most often in a raceme (as in Bromtis slerilis, the barren brome-grass), or as in the common Agrostis alba, which is usually called in descriptive books a pa7i- icle, though Duchartre asserts that this cannot be properly applied to any inflorescence. At other times (as in rye-grass) the inflores- Fig. 282.-Extremity of a leafing and flowering branch o{ Pimis Laricio, Poir., bearing male flowers. cence is so arranged that it becomes a true branched spike, and m cultivated wheat the spikelets are arranged in a distichous order, one bemg placed in each "tooth" of the sinuous rachis, which whole history of the development of these plants, which is remarkable not only for the great slowness with which it takes place, but also for the fact that the sty es take precedence in their development over the calyx and involucre, as well as over the ovary. 396 INDEFINITE INFLORESCENCES. is composed of scores of such teeth directly to right and left, (g) The cone is also a veritable spike, in which the scales or bracts which accompany the female flowers are greater than those in the last-named inflorescences, and often woody (the male flowers, fig. 282, are borne on other branches). They are also persistent in most cases (though not in most species of Picea), and are not arti- culated at the base. Ex. Firs, pines, and other Conifera, or " cone- bearers" (fig. 124). (e) The capitiilum, or "little head," is a spike in which the primary axis is enlarged at the suminit into a broad receptacle, on which are placed sessile flowers, united in a globose head. Ex. Sunflower, dandelion, daisy, and all other Compositae (fig. 148). These inflorescences are surrounded by an involucre (p. 289), and the calyx is reduced to the state of a few hairs, which surmount the seeds in the form of a pappus (p. 300). The capitu- lum, then, is only an axis excessively depressed at its summit, and the flowers therefore appear to be in rows alongside of each other, the outer ones corresponding to the ones on the lower portion of the axis in the other forms of indefinite inflorescence ; or the capi- tulum may be looked on as an umbel without peduncles. There are several kinds of capitula : (i.) the conical form, as in Eryn- gium (fig. 150, p. 289); and (2.) that seen in most other Compo- sitae.^ The receptacle bears a number of foveolcB, or little pits, into each of which a flower is inserted. The central portion of the flower of a capitulum of the ordinary type is styled its discj while the exterior portion or periphery is known as the radius. Lastly, we may mention that while in the petals of the greater number of flowers there is a median nerve which may be either free or anastomose with the neighbouring ones, in Compositae there is either no such nerve, or if there is, it presents a singular modifica- tion. "In the monopetalous quinquedentate corolla of these plants we see five nerves which correspond to the five sinuses at the apex of the petal. Each of these, when they arrive at the base of one of the intervals between the teeth, divides into two branches, which direct themselves along the borders of each of them in order to reach the summit. In due time they terminate there, and, uniting in a single trunk, descend along the middle line, thus simulating a median nerve, but directed from above below, and not from below upwards, as is the usual way." Canini, in order to distinguish the mode of nervation in the petal's composition just described, applied to them the name of Nevramphipetalce, or hairy " nerves around the petals." The capitulum may be compound, or, as in Peta- sites, there may be a raceme composed of capitula, just as other 1 This L. C. Richard has styled a cephalajithiutn (cephalanthe), or "head of the flowers;" Mirbel, a calathidium, — words, however, of but little value or necessity in descriptive botany, and seldom used (except by their inventors). The enlarged receptacle has been also styled the phoratithium or clinanthium. INDEFINITE INFLORESCENCES. 397 simple forms of inflorescence may, when compound, simulate in their mode of arrangement an entirely different inflorescence. (0 The Cananthium^ is the general name applied to the pe- culiar inflorescence of Dorstenia, Ambora, and the common fig {Ficiis). In Dorstenia (fig. 143) we see the receptacle very much Fig. 283. — Fruiting branch of the Fig {Ficus Caricd). a Fig cut longitudinally to show the collection of flowers inside the " ccenanthium ; " b One of the staminate flow- ers ; c One of the pistillate flowers ; d Ripe fig (syconus) cut open to show the collection of fruits ; e One of the fruits ; f Seed with embryo. enlarged, fleshy — somewhat quadrilateral, with the borders turned inwards and irregularly serrated — and the upper surface hollowed out in pits, in which are placed, intermingled, the male and female flowers. In Ambora'' (a tree of Madagascar and Mauritius) there is an expanded receptacle, but much more concave. Lastly, in the fig we see the utmost extent of the concave development of the receptacle. In this plant the fruit (sometimes called a syconus) is pear-shaped, and the whole central cavity is filled with male flowers in its upper portion ; while in the remainder, and greater ^ Nees V. Esenbeck, the Hypanthodium of Link. * Belonging to the order Monimiacea, 398 INDEFINITE INFLORESCENCES. part, are female ones — the receptacle having closed all around them, leaving only a small opening at the summit (fig. 280). Thus, while eating an unripe fig, we are in reality eating the fleshy receptacle and the whole inflorescence. Between the capitulum and the ccejianthhim, as shown in Dorstenia, there is only a slight difference ; and from Dorstenia up to Ficus the gradation is very gradual. (B) Flowers placed on the summit of Secondary Axes. Under this head we placed the raceme, co7ymb, umbel, and the so-called panicle. 2. The Raceme. — Here the main axis carries a secondary one all along it, as in the common gooseberry, the red currant {Ribes rubium), &c. It is such a characteristic form of the indefinite inflorescence that Guillard, in his treatise on the inflorescences,^ proposed to designate the whole of the great division to which it belongs by this name (fig. 284). Fig. 284. — The raceme. Fig. 285.— The corymb. Fig. 286. — The umbel. In the compound raceme each peduncle may ramify several times, and thus produce a compound raceme (fig. 287). Generally the bottom branches are the longest ; but sometimes the middle are so, giving it the appearance of the " thyrsus " of the Bacchantes. Hence this variety is often called a thyrsus — an indefinite and confusing term, as it is often applied to the inflorescences not only of the lilac (to which it properly applies), and to that of the horse- chestnut, which is conical, and even to designate inflorescences truly indefinite; while, on the other hand, De Candolle has trans- ferred the name to designate inflorescences in which " an indeter- minate rachis carries determinate floral groups." 3. Corymb. — If all the secondaiy axes of a raceme ascend to about the same height by the lower ones being more elongated than the upper, then the term corymb is applied to such an inflores- 1 Bull, de la Soc. Bot. de Fr., iv. (1857) pp. 29-39, 116-124, 378-381, 452-464, 932-939. INDEFINITE INFLORESCENCES. 399 cence. Ex. The hawthorn, &c. (fig. 285). In the compomid corymb the peduncles are branches; and the pedicels, as in the simple corymb though arising at different levels, terminate in flowers all Fig. 287 —Fruiting branch and flowers o{ Cinchona Calisaya, showing the compound raceme. more or less at the same level. A corymb is thus a shortened raceme; but in many Cruciferas, such as candytuft {Iberis), &c., the inflorescence is a corymb elongated to a raceme, and called a corytnbose raceme. The roses, pears, apples, and a family of Compositae {Anthemis, Arnica, Senecid), &c., are called Corym- bi ferae. 4. Umbel. — If the secondary axis or peduncles all arise from about the sanje place, and terminate on a level, then the term tembel is applied to the inflorescence (figs. 286, 288). It may, by the diminution of the rays (as in the cherry, primrose, &c.), be simple ; but if the umbels branch, and form timbellulesi then a compound umbel is produced, as in most of the Umbelliferas, the parsley, carrot, anise, &c. &c. (C) Flowers placed on the summit of Tertiary Axes or their Ramifications. 400 DEFINITE INFLORESCENCES. Under this head is usually classed the panicle, the thyrsus, the compojcnd corymb, and the compouiid tnnbel. 5. The panicle is a term very generally used in books ; but. as Payer truly observes, it cannot justly be applied to any char- acteristic mode of inflores- cence. It is usually applied to a more or less compound ra- ceme, as in grasses, but just as often to entirely different inflorescences, such as to a rachis, carrying numerous more or less unequal-branch- ed peduncles, and accordingly should be dropped. 6. The thyrsus we have already shown to be a term which comes under the same category, and should equally be relegated to the crowded domain of botanical termino- logy, either obsolete or which deserves to be. 7. The compound cory7nb and the compound umbel we have already, for convenience' n.. n ^ ir -1 f sake, described under the head rig. 200. — Carraway (Car?^w2C«r7«), one of the Umbelliferae. b One of the leaves ; c of the simple COrymb and Flower; d Fruit; e The two carpels of the „i„ +U„,,„u fruit suspended by the columella (the fruit is a Simple Umbel, thoUgh m re- " cremocarp ") ; / Tap-root ; g Flowering ality they COme Under the prc- branch showing the compound umbel and x i- • • umbellules. Sent dlVlSlOU. DEFINITE, DETERMINATE, TERMINAL, OR CENTRIFUGAL INFLORESCENCE. 8. Cyme (cyma). — In the definite mode of inflorescence, as I have already pointed out, the axis terminates by a flower, which necessarily terminates and arrests its development. When the leaves are opposite, we find, at the base of the terminal peduncle, two opposite leaves, in the axil of each of which is produced a new peduncle, equally terminated and accompanied by two leaves, in the axil of each of which arise two lateral peduncles, the result of which is, that the inflorescence is composed of a series of super- imposed bifurcations, in the centre of each of which there exists a terminal flower. Such an inflorescence is known as a cyme. If, DEFINITE INFLORESCENCES. 4OI ( on the contrary, the leaves, instead of being opposite, are in verti- ' eels of three, each of them sending out a flowering branch from ! its axil, the result is, that there is a series of successive trifurca- ] tions. The first of these modes is called the dichotomotis cyme j the second, the trichototnoiis cyme. An example is shown, among \ many other plants, in chickweed {Stellarici) and Ccrastium (fig. 289). In the figure the entire inflorescence of the plant is shown. ; Fig. 289. — Definite inflorescence of Cerastinm collinum. Led. i Primary a.\is ; t' Two secondary axes ; t" Four tertiary axes ; t'" Eight quaternary axes ; t"" Quinary axes (cyme). Here the primary axis / bears at its extremity, and is terminated by, a flower. All the inflorescence hinges upon this terminal flower. Lower down, however, there is an internode which bears two opposite bracts, from the axil of each of which springs a secondary axis, and these two axes comport themselves in exactly the same way as the primary one did — viz., they terminate by a flower ; and a little below, from the axils of two bracts, they emit two tertiary axes, or axes of the third generation. These four tertiary axes in their turn behave exactly in the same way, giving origin to quaternary axes,— and so on. We also see this mode of inflorescence in the elder-tree {Sambucus), Hydrangea, &c.; but 2 c 402 DEFINITE INFLORESCENCES, in some of these latter it is not always easy to detect the plan of the inflorescence, owing to the multiplicity and closeness of their bifurcations. (a) Dichotomous Cyme. — We have already mentioned this term. Cerastium collinum (fig. 289) furnishes a good example of this form, which has also been called biparous by MM. L. and A. Bravais, and by others alary {ala, a wing), or winged, from the idea that the flower situated between the two symmetrical ramifications is like the body of a bird between its two expanded wings. (jS) Trichotomous Cyme. — In like manner, when, in place of bifurcations, the cyme forms trifurcations, then either the above term or triparous is applied to it,— and so on. Such cases are, however, rare. (y) Monotomotis Cyme. — In some cases the dichotomy of the cyme continues regularly until it arrives at the last ramification, when one of the two lateral branches becomes abortive, as {e.g) in Cerastium tetrandrum. When, as in the case of Silene Gallica, this abortion of the branch on one side becomes constant, the cyme thus produced has been called a monotomous or uniparous cyme. (S) Scorpioidal Cyme. — From the monotomous, then, we are led to speak of that variety of it called the scorpioidal cyme, as seen in all the plants of the order Boraginaceze, such as Myosotis palus- tris (forget-me-not), in which the cyme is rolled round somewhat in the form of a crosier, or after the manner of a scorpion's tail — from which, indeed, it gets its name. In this form of cyme the flowers, arranged in a double row, only occupy the convex side of the curved or rolled axis, which is owing to the vigorous growth of the branches produced only in the axil of one dichotomous branch. Such a cyme has sometimes been called a cincinnus. (e) Helicoid Cyme?- — This form is much rarer than the former, and pertains to the Monocotyledons, Ornithogahim, Phormium, Hemerocallis, &c., and ought, according to Payer, to be defined as " an inflorescence in which all the flowers are of different genera- tion, opposite, and disposed in a helicoid manner." In other words, it is much the same as a scorpioidal cyme, but with this difference, that the flowers and bracts, in place of being situated on the same side of the rachis, are arranged in a spiral, helicoid, or snail-shell fashion round the false axis — hence its name. (f) Cotitracted Cyme. — Under this name De Candolle classed all cymes with very short peduncles. These comprise the fascicle (fasciculus) of Roper, where, as seen in the " Sweet- William," is a very compact cyme with "upright or appressed branches," though the term is applied by many botanists in an entirely different sense. The glomerule (glomerulus) is, again, a cyme so com- 1 e'Aif, a spiral ; and eifios, form : like a snail's shell. MIXED INFLORESCENCES. pressed as to resemble a capitulum, from which, indeed, it is only to be distinguished by its centrifugal evolution. Lastly, the cymide (cymulus) is a diminutive cyme, or " a branch or cluster of a compound cyme." Cymose inflorescence is often styled sympodial, and the cyme a sympodiian — a term also applied to axes branching in this manner. MIXED INFLORESCENCES. The student will already have seen that it is by no means easy to accurately define some of the inflorescences, and that in nature b c d Fig. 290.— Flowering branch of the Castor-oil plant {Ricinus cowviunis), with details of the male and female flowers, &c. The filament {a) is branched, each branch having a lobe of the anther ; b Female flower ; c and d Ovary entire, and in transverse section. they are even less distinctly divided from each other than in books. In truth, there are between many of them regular grada- 404 ANOMALOUS INFLORESCENCES. tions ; so that while the main types are sufficiently well marked, an ingenious name-maker would have abundance of room for the exercise of his somewhat unhappy talent in devising designations for various others beyond those we have mentioned. Nor has the opportunity been neglected, as the " philosophical " classification devised by various botanists — chiefly German — prove ; but these names are useless for the student's purpose, and have been desen'- edly neglected.^ There are, however, a series of inflorescences, to which De CandoUe applied the term " mixed," to which a few words must be devoted, as they comprise often the characters of both divisions of inflorescences — the definite and the indefinite. De Candolle ranged all these mixed forms under two great divisions — viz. (i.) Those in which an indeterminate rachis bears on its side determinate inflorescences. These he designates under the confusing name of thyrsus. (?.) Those in which a determinate axis bears indetermi- nate inflorescence. It is to these kinds that he gives the name of corymb, though the term is used by the best writers in a different sense. Payer mentions the following as ex- amples of mixed inflorescences: (i.) The horse-chestnut, in which there is a raceme with tmiparous scorpioidal cymes. (2.) Chiona7ithes Virginica, in which there is a raceme with biparous cymes. (3.) Sparmannia Africana, and, according to Payer, Bntomus umbel- latus (the flowering rush) also, in which there is an umbel of uniparous scorpioidal contracted cymes. (4.) In Datisca cannabiim there is a spike of contracted biparous cymes with sessile flowers. (5.) In Veronica centrifolia there is a uniparous scorpioidal cyme in the form of capitula. (6.) Lastly, we may mention the umbel composed of biparous cymes, the raceme of biparous cymes, &c., as examples of mixed inflorescences. ANOMALOUS INFLORESCENCES. Under this head Payer ^ has classed a number of inflorescences, such as when, in Tilia (fig. 147. P- 288) and Helwingia rusciflora, 1 See Sach's Lehrbuch, &c. (1873, p. 509, &c.) 2 Elements de Botanique, 113-124. Fig .291. — Euphorbia Canariensis (in longitudinal section), the male and female flowers grouped in a caly- ciform involucre. The flower figur- ed contains several male flowers and one female one, having three forked styles at the summit of the ovary. The flowers are naked, and the an- thers of the staminate ones two-lobed (dithecal). ANOMALOUS INFLORESCENCES. the peduncle adheres to the bract through some portion of its length ; the inflorescence of Rtisais aciileatum (p. 80, fig. 53) ; that oi Xylophylla obovata (p. 81, fig. 54), in which buds are produced on the cladodia, &c. It has been argued that the flower of Eic- phorbia (figs. 290, 291), sometimes called the Cyanthium, is not a flower, but an inflorescence.^ The latter view is, however, scarcely tenable. Many of these have been already described in an earlier portion of our studies ; and with the others, which but rarely occur, and regarding the interpretation of which much difference of opinion exists, the student's attention need not be occupied at an early stage of his botanical instruction. It is enough to refer to them. 1 For a discussion of the whole question see Dr Warming of Copenhagen's inaugural thesis — " Er Koppen hos Vortmaelken (Euphorbia, L.) en Blomst elleren Blomsterstand? En organogenetisk morfologiskUndersogelse" (1871). 4o6 CHAPTER VIII. FERTILISATION OF THE OVULE : ORTHOGAMY. We have seen (Chap. III. p. 326)that the anthers open and discharge the pollen. This pollen is conveyed to the stigma either by falling directly upon it or by other agencies, which we shall duly consider in the next chapter. When the pollen-grains come in contact with the stigma, which is frequently moist, 'the grains do not burst, but the inner coat (endothecium) slowly projects through the outer one (exothecium) at particular points, such as the pores or slits in the outer, in the form of a long transparent tube, filled with the fovilla, which tube pierces the surface of the stigma (which is uncovered by epidermis), and penetrates through the loose " conducting tissue," which in the adult plant fills up the central canal of the style, until the tube reaches the mouth or micropyle of the ovule, when a mysterious operation is performed, necessary to the fertil- isation of the ovules. After this fertilisation, the embryo or young plant grows in the ovule, and other changes take place which convert the ovules into seeds capable of reproducing the species. The process of impregnation or fertilisation may therefore be divided into three stages — viz. (i.) the preparatoiy or precursory phenomena ; (2.) the essential process ; and (3.) the consecutive changes. Let us consider this important function from these three points of view. PREPARATORY PHENOMENA. These commence with the opening of the flower, and in Com- positas and Campanulaceas even before the flower has expanded. It is necessary that the pollen must have access to the stigma; and for this end there are various contrivances. In hermaphrodite flowers the stigma is often lower than the anthers of the stamens. In the fumitory family the stamens are placed in a close-fitting little sac formed by the spoon-shaped ends of the two inner petals, thus bringing the anthers close to the stigma. In the barberr)-, the anthers, when irritated by an insect finding its way into the FERTILISATION : PREPARATORY PHENOMENA. 407 flowers, spring up with force, and scatter the pollen on the stigma. The rapid growth of the stamen at the period of the opening of the flower is also favourable to fertilisation. In Kahnia and other plants, the stamens, when ready to discharge their pollen, gradu- ally approach the stigma until they close over it. Very frequently, too, at the time the anthers are shedding their pollen, the surface of the stigma or stigmata e.xude a viscous liquid, which retains the pollen-grains after they have once come in contact with it. Lastly, we may mention that in many plants the pollen is con- veyed by insects, the wind, and other agencies, from one flower to another ; and that though in this chapter we shall describe the process of fertilisation as if the pollen of a hermaphrodite flower always fertilised the stigma of the same flower, yet it is known that this is by no means a general rule, as the remarkable dis- coveries of late years have abundantly proved. Whether, however, the pollen falls directly on the stigma, or is conveyed to it by other agency, the physiological phenomena are the same, and may be described preparatory to entering on a study of the various secondary ways in which the pollen is conveyed to those plants in which this heteroga7no7is^ fertilisation prevails, in contradistinction to those in which orthogamy'^ is the rule. Among gymnospermous plants (pines, firs, and cycads), no ovary existing, the pollen falls directly on the naked and exposed ovules. In all other plants the ovules can only be fertilised through the stigma and style in the manner mentioned. The period of impregnation is also usually distinguished by the de- velopment of a higher degree of heat in the flower than is usual. [Sect. IV. Heat.] To insure fertilisation, there is, among other provisions, a large number of anthers and stigmas, and a superfluous quantity of pollen, in many plants. Morren found that in a single flower of the great-flowered cactus {C. grandiflorus) there are about 500 anthers, 24 stigmas, and 30,000 ovules. Each anther may contain about 500 grains of pollen ; so that in a single flower there may be as many as 250,000 pollen-grains. From the stigma to the ovules in this plant the distance is g-bout 11 50 times the diameter of the pollen-grain. It has been calculated by Mr Stephen Wilson that wheat-plants produce about fifty pounds of pollen per acre. In all other grasses, Coniferte, &c., there is also more pollen than is necessary to fertilise the ovules, supposing that each grain took effect. In a single flower of Maxillaria, Fritz Muller calculated the number of pollen-grains to be 34,000,000. erepos, crooked ; yajxew, I marry. - opSos, straight ; ya^iew. 4o8 FERTILISATION : ESSENTIAL PROCESS., ESSENTIAL PROCESS. The loose papillae, hairs, or viscous substance on the surface of the stigma and style, serve to retain the pollen-grains after they have once reached the top of the stigma. On the stigma of the lily there is a notable amount of this viscous matter exuded. These grains absorb the moisture from the stigma, and then commence to grow or germinate — in other words, to protrude their pollen-tubes, which eventually reach the ovules. This is accomplished by the inner coat protruding through the thicker but more brittle outer coat. This takes place through the pores or slits ; but if there are none (p. 343) on the pollen-grains, then the pollen-tube (or tubes) breaks through the outer coat at indeter- minate places. Most frequently there is only one pollen-tube protruded ; but it occasionally happens that there are two or more. In the pollen of Onogracese, as many as twenty or thirty are sometimes protruded :i and in Morrenia odorata, so many are emitted as to give the head of the stigma the appearance of a mass of tow.^ As a rule, also, no pollen-tubes appear at any place not in direct contact with the stigma. The inner coat, once it has protruded through the outer coat of the pollen - grain, lengthens into an attenuated tube, closed at the lower end, and filled with the fovilla or contents of the grain. It now penetrates be- tween the loose cells of the stigma and the connecting tissue of the style, and appears at the placenta, or some other part of the lining of the ovary, when its end looks in appearance like a cell. The tube now enters the ovule at the micropyle, and therefore per- forms the fertilising process in the manner to be presently de- scribed. In gymnospermous plants the pollen-tube grows from the surface of the naked ovule ; otherwise the process is exactly the same. Usually each ovule has a single pollen-tube entering it ; but in the beech, often in the Coniferee, the crocus, ^7iothera muri- cata, and the violet, the tube sometimes divides itself, so that one tube can fertilise several ovules. Length of time taken to fertilise Ovules. — The time which the pollen-tube takes to penetrate the stigma and style varies in differ- 1 Amici, Ann. des Sc. Nat., Nov. 1830. 2 Lindley, Bot. Register, 1838. Fig. 292. — Longitudi- nal section of a fragment of the stigma oi Matthi- ola annua. Sweet (the " ten weeks' stocic "), showing some pollen- grains, which have emitted their tube tp. Several of these tubes have entered into the cavities of- the stigmatic IJapillse, ; t Proper tissue of the stigma (af- ter Tulasne) (mag. 163). LENGTH OF TIME TAKEN TO FERTILISE OVULES. 409 ent species. In Gladiolus segeium, the style of which is four centi- metres in length, the tube, according to Schacht, arrives in three days at the ovule.^ In the Colchicum, Hofmeister found that the tube penetrated to the ovule in about from ten to twelve hours, though the distance to be traversed is about Qooo times the dia- meter of the pollen-grain. In Tigridia conckifera, Professor P. Martin Duncan calculated that the pollen -tube penetrated the style at the rate of one inch in four hours, and that under favour- able circumstances it might be even less. In grasses, the time required is very short. In Zostera it is about 12 hours ; in Naias major, about 24 ; in Orchis niorio, 48 ; and in the greater number of Liliace£B, Amaryllidace^, Iridacese, and Araceae, it is much longer (Hofmeister). It is very dubious whether endosmosis setting in, owing to the moisture of the stigma, is the sole cause of the protrusion of this hernia-like tube. More probably the elongation of the tube is a true growth — like the elongation of a cell — and that it is nourished by the substance of the style, which it absorbs in its course to the ovule. This view is fortified by the fact that the tube elongates in some plants while the grains are still inside the anther — as, for example, in Limodoritm abortivum, cypress, Strelitzia regincB, and S. angusta. In Gymnospermas, however, there is a liquid secreted by the integuments of the ovule, which seems to determine the issue of the pollen-tube from that part coming in contact with it. We may also mention that (as shown in fig. 292) the pollen-tubes, tp, descend between the large salient cells which form the stig- matic papillae, or even (according to Tulasne) penetrate into the cavity of these papillae, and finally arrive at the fundamental tissue of the stigma. When (as in Clarkia elegans) the canal of the style opens in the centre of the stigma, the pollen-tubes enter without difficulty ; but if, as is generally the case, the tissue forming the centre of the style is firm superiorly, the pollen-tubes, in penetrating the stigma, generally insinuate themselves into the vacant spaces between the cells. In some cases the pollen-tubes, in passing through the conducting tissue of the style, branch. ^ Rate of Growtli of Pollen-Tubes. — In some cases the pollen- tube protrudes almost immediately after the pollen has come in contact with the stigma. In other cases, it will not protrude for from ten to thirty hours, or even more, after the grain has fallen 1 Monatsbericht, &c., 26th May, 1856 Duchartre). " By Decaisne and Gasparini it has been asserted that the emission of a pollen-tube is not always necessary to fertilisation ; and so careful a botanist as Professor Dickie of Aberdeen (Ann. of Nat. Hist., vol. xvii.) has shown that in many plants the pollen-tubes found at the micropyle at the time of impregnation really originated there, and were not derived from the pollen. How these exceptional cases are to be accounted for on the general theory of impregnation, is difficult to understand. GROWTH OF POLLEN - TUBES : EMBRYO-SAC. on the stigmatic surface. In most cases the pollen-tube fades away with the stigma after it has arrived at the ovule and presum- ably performed its functions. In many plants, however, a long interval elapses between the time of the pollen coming in contact with the stigma and the fecundation of the ovules — for example, in the walnut and alder. In the former of these two trees the pollen falls on the stigma in February or March, and in the latter in June or July, but their fruit is not ripened until autumn. In most Coniferse the ovule is not fecundated for a year or more after the pollen has been shed on it, the pollen-tubes seeming to remain inactive, but still living, during that period, in the conducting tissue of the style. Some of the Coniferas, such as the junipers, take three years to ripen their seeds. In Colchicum autumnale the pollen falls on the stigma in the autumn, but it was not until the following April that Hofmeister could see any sign of the fertilisation of the ovule. In any case, after the pollen-tube has penetrated the style and the stigma, the pollen-grain dries up, as does the stigma, the whole of the fovil- line contents being then transferred to the pollen-tube, the lower part of which is in a growing state until it performs its function in fertilising the ovule. The Embryo-Sac. — Before the pollen- tube has reached the ovule, or, even more commonly, before the pollen comes into contact with the stigma, the centre of the nucleus of the ovule, which has hitherto been a continuous mass of cell- ular tissue, gets hollowed out into a cavity, which gradually increases in size at the expense of its walls, until a con- siderable space is left in the nucleus near its apex. The walls of this cavity form the tercine} or third coat of the nucleus, and the cavity itself is known as the embryo-sac, or, to use the term applied to it by Malpighi, the sac of the amnios. Most probably it results from the " special growth of a particular cell, which expands into a bladder or closed sac, at length commonly occupying a nucleus — sometimes remaining enclosed m its tissues towards its summit or orifice — sometimes displacing the upper part of the nucleus entirely, or even projecting through 1 The "additional membrane" of the late Robert Brown. Fig. 293. — Longitudinal sec- tion of an ovule of the Garlick (Allium odoratis) at the moment when fertilisation has begun to act. The promine has been sup- pressed, sc Secundine ; nc Re- mains of the nucleus; se Embryo- sac ; Extremity of a pollen- tube which has performed the act of fertilisation; ve Germinal ves- icle fertilised and already subdi- vided into two cells ; vf Germi- nal vesicle not fertilised ; va " Antipodal vesicles" (after Hof- meister). considerable part of the ORIGIN OF THE EMBRYO. 411 the micropyle." It may be remarked, the embryonic sac does not always present itself in the form of a more or less swollen-out cavity — sometimes it is a slender tube stretching from the summit of the tercine above to the chalaza below. It is in this sac that the embryo, or young plant, in the seed forms. Origin of the Embryo. — History of opinio^i on the subject. — From the very earliest period since it was believed that there was some connection between the stamens and pistil of a sexual nature, it was also understood that the embryo was the product of the ovule, and was in some way fertilised or incited to growth by coming in contact with the pollen. The Greeks and Romans had some vague ideas regarding the two sexes in plants, observing that in order to produce fruit the pollen had to be taken from one date-tree, on which one kind of flower grew, to another, producing a different sort — the date being dioecious. Pliny knew that plants had different sexes, though he indicated no organs in which these sexes resided. In 1685, Grew admitted the existence of two sexes in plants, though Millington, Cassalpinus, Malpighi, and others, have disputed the honour of this discovery with him ; and in 1694, Camerarius published his views on the subject in a clear and explicit manner. From this time we may date anything like accu- rate ideas regarding the sexual differences in plants — the specula- tions of the medieval botanists being almost more vague than those of the Roman poets, Ovid and Virgil. In 17 18, Sebastian Vaillant ^ published his opinion that the application of the pollen to the stigma was absolutely necessary, combating, however, at the same time, the view of Morland^ that the pollen-grains traverse the style to the ovary and penetrate the ovules, substituting for it an infinitely more incorrect theory — viz., that it was only the vapour or volatile essence (" vapeur ou I'esprit volatil "), which, disengag- ing itself from the pollen-grain, fecundates the ovules. Passing over the singular, and singularly erroneous, views of Tournefort (which, however, found supporters in Siegesbeck, Heister, Schelver, who wrote as late as 1829, and did not believe in the sexuality of plants), we come to the celebrated Linnasus, who in 1735 pub- lished his 'Fundamenta Botanica,' who, in basing his classification of plants on the sexual organs, called anew the attention of botanists to their importance, and so gave a stimulus to the pro- gress of research on the subject. Though Bernard de Jussieu in 1 Discours sur la structure des fleurs, leurs differences at I'usage de leurs parties: Leyden, 1718. Sermo de stmctura florum ; Paris, 1718. In Alston's Dissertation on the Sexes of Plants (Edin. Physical and Literary Essays, i. 228) is a history of embryogeny up to 1770. 2 Philosophical Transactions, 1703 (xxii.), p. 1474 ; Acta eruditorum, 1703. P- 275- 412 FUNCTION OF THE POLLEN -TUBE. 1739, arid Needham again in 1745, had observed the expulsion of the fovilla when the pollen-grains came in contact with moisture, it was not until 1822 that J. B. Amici,^ of Modena, detected in Portulaca oleracea a pollen-grain emit the pollen-tube and enter the stigma and style; though in 1781 Gleichen, and Franz Bauer and Richard in 181 1, had both seen, but did not divine its use in the economy of fertilisation. In 1826, Brongniart'^ clearly estab- lished the truth of Amici's observation, and the economy of the pollen-tube; though it is only of late years — thanks to the re- searches of many observers, and notably, Amici, Brown, Schleiden, Fritzche, Mohl,^ Hofmeister,* Tulasne, Deecke, Schacht, Henfrey,^ Radlkofer,*' and others — that we have derived perfect knowledge regarding the passage of the pollen-tube through the style, and its uses in the fertilisation of the ovule, though on this little point our information would still bear improvement. Function of Pollen-Ttibe. — At one time it was believed that the pollen-grain absolutely entered the ovule by the micropyle and be- came the embryo — an ingenious idea that was speedily abandoned. Then came the views of Horkel and Schleiden ^ — late professor of botany in the University of Jena — who held that the end of the pol- len-tube entered the nucleus of the ovule and became the embryo. From the year 1837 up to a very recent date, this view was held by many botanists, among others by Schacht, Wydler,^ Gelenzoff,' and Deecke,^" but has now been completely disproved by the numerous observations of Mirbel, Brongniart,^^ Tulasne, Amici,^^ Herbert Giraud.^s Mohl, Karl Miiller,i* Hofmeister, Schacht,!^ &c. Finally, the surviving eminent author of this theory, Dr Schleiden, and his most eminent supporter, Schacht, having themselves abandoned it, it would be a clear waste of time and space to give a rhume the arguments either ^r Einige Betrachtungen iiber dimorphe Bliithen ; Bot. Zeit., 1863, p. 309. 6 Die Geschlechter-Vertheilung bei den Pflanzen, 1867. 7 Et Bidrag til Kundskab om dimorfe og dichogame Blomster ; Vidensk. Meddel. fra den Naturhistoriske Forening i Kjobenhavn, 1869, p. 68. 8 Natural History Review, 1862 ; see also, Parish on Dimorphism of Cym- bidium tigrinum, Journ. Linn. Soc. Bot., x. 505. DIMORPHISM AND TRIMORPHISM. 1 and A. W. Bennett, have contributed to the literature of the subject. Mr Darwin's observations v^ere made chiefly on Primulas. Having covered up a pot of long-styled and another of short-styled primulas, the most part of them flowered, but did not produce seeds. Hence he considered that the agency of insects was necessary for their fecundation; but as he never saw an insect visit the plant during the day, he considered that probably night- moths might visit them for the sake of their honey. He tried to imitate the action of insects in searching for the honey of the flowers, and, as we have seen, the results were of great interest. If we introduce into the corolla of a short-styled cowslip the proboscis of a bee, the pollen of the anthers, situated at the entrance of the tube, adheres around the base of the proboscis; and it will necessarily happen that when the insect visits subsequently a long-styled cowslip, the pollen so taken up will be scattered on the -stigTria of that plant But in that new visit to the long- styled cowslip, the proboscis, in descending to the bottom of the corolla, will find the pollen of the anthers which lie at the bottom of the tube, and that pollen will attach itself to the summit of the proboscis; and if the insect should visit a third flower which is short-styled, the tip of the proboscis will touch the stigma situated at the base of the corolla, and there deposit the pollen. Furthermore, it is necessary to admit as probable that in the second visit mentioned above — to the long-styled flower — the insect, in retracting its proboscis, would leave upon the stigma a part of the pollen taken from the anthers situated below ; and thus the flower would become self -fecundated. On the other hand, it is almost certain that the insect, in stretching its proboscis into the short-styled corolla, will have brushed against the anthers inserted at the top of the tube, and thus caused a certain quantity, more or less, of the pollen to be shed on the stigma of its own flower. Finally, the corolla of the cowslip contains, in abundance, minute insects belonging to the genus Thrips, of the order Hemiptera, which run about the flower in every part, transporting the pollen of the anthers to the stigma. Thus, again, the plant will, be, by another agency, self-fecundated. Hence, in the fecun- dation of dimorphic species, there are four operations possible, — viz., 1st, fecundation of the long -styled flower by itself; 2d, of the short-styled flower by itself; 3d, of the short-styled flower by the long-styled ; and, 4th, of the long-styled by the short-styled flower. Darwin has further remarked, that while these dimorphic and trimorphic plants cannot fecundate themselves, this may be partially done by the agency of currents of air, if the pollen is I 432 USE OF DIMORPHISM AND TRIMORPHISM : DICHOGAMY. dry ; for if the corolla is without colour, no honey is secreted. If, on the contrary, the corolla is brilliant, honey is secreted, and insects most effectually discharge the office of carrying the pollen from one flower to another. Among American plants, dimorphism can be seen in the com- mon Hotistonia and the Partridge-berry of the northern woods, while trimorphism is seen in Nescea verticillata (a species of Loose- strife), &c. The use of Dimorphism and Trimorphism. — To prevent the pollen from the anthers of a flower acting on the stigma of the same flower, and thus, by too close inbreeding, causing the plant to lose its vigour. The gain in this case has been obtained at the expense of all the plants of the same form being rendered more or less sterile with the same form, both in first cross and in their offspring. Hooibrenk and Koernicke^ have even attempted to carry this into practical agriculture in Belgium and Germany, by drawing a rope across the full-flowering ears of a field of corn, and thus causing the plants to be fertilised by the pollen of differ- ent individuals, by the rope slightly brushing the ears of grain. It appears fo have been useful in some cases in increasing the yield of certain crops. DICHOGAMY.^ We have already remarked that though, for the sake of con- venience, when speaking for the first time of the fertilisation of the ovule by the pollen, we considered the typical method by which this was accomplished was simply — in the greater body of plants which had both sexes on one flower (hermaphrodites) — by the pollen of the anther falling on the stigma of its own pistil, ready, simultaneously with the anther, to accomplish ^ Gartenflora, 1866, s. 29. 2 Sprengel first used this term (dichogamia) in the sense now used in contra- distinction with what he called ' ' Homogamy " (homogamia) — i.e., ' ' when both parts of a generation are formed in a hermaphrodite flower exactly at the same period." This seems identical with what Hildebrand proposed the term "non- dichogamy" for — an inconvenient expression, for which Alfred Bennett has proposed to substitute "Synacmy. " "Protandry" and "Protogyny" — ex- pressions first used by Hildebrand, and corresponding to Sprengel's ' ' Dicho- gamia androgyna" and "Dichogamia gynandria" — Mr Bennet has proposed ('Nature,' 1870, p. 482) to express under the general term of "Heteracmy." Both these words are good ; but still Sprengel's term Homogamy, which is faultless in expression, has a prior claim over Bennett's Sytiacmy. In this text- book I have used Sprengel's term Homogaviy in the same sense as he did (having, indeed, resolved to do so before I was aware of Sprengel's prior use of it) ; while all other modes of fertihsation — dichogamy, dimorphism, trimorphism, &c. — I have comprehended under the term Heterogamy. DICHOGAMY. 433 fertilisation; we furthermore showed certain mechanical con- trivances by which this was accomplished. In monoecious and dioecious plants this fertilisation could, of course, not be so accom- plished unless accidentally; and to accomplish this the agency of insects was necessary. However, as the student has proceeded with the study of fecundation, he will have found that the time- honoured idea we have mentioned admitted of many exceptions, and that, indeed, the most elaborate contrivances exist to abso- lutely prevent the pollen of each flower from acting on the stigma of that flower. In orchids and other plants we will see how this is accom- plished by many curious mechanical contrivances. Thus, we have already seen that hybridity is of the most common occur- rence: and in our last paragraph we find the same end gained by dimorphic and trimorphic flowers, in which the pollen of each flower, and consequently of the flowers of the same form, has been rendered more or less impotent on their own stigmas ; so that its action is easily and wholly obliterated by pollen habitually brought from other individuals and forms of the same species.^ Finally, nature, as if lavish of her powers to accomplish the same end by the most diverse means, has made another provision for the same purpose — one long known to botanists, though until recently its import and bearings were not sufficiently appreciated, or forgotten. As early as 1793, Karl Konrad Sprengel — then Rector at Spandau — in his remarkable work, ' Das Entdeckte Geheimniss der Natur in Bau und in der Befruchtung der Blumen' (The Secrets of Nature in the Structure and Fecundation of Flowers), described certain plants in which the anthers and the stigma are never ripe at the same time, so that these plants can never fertilise themselves. These he called Dichogajnous plants. Those in which the stamens were ready to discharge their pollen before the stigma was ready to receive it {e.g., Foxglove, Epi- lobium angtistifolmin, Ranunculus repens, Silene inflata, Geranium pratense, Campanula rotundifolia, &c.) are called protrandrous; and those in which the stigma is ready to perform its functions before the anther is ready to discharge the pollen, protogynotis (e. g., Potentilla anserina, Erythrcea Centaurea, Plantago, &c.) These dichogamous plants are found in many orders — such as Malvaceae, Geraniaceas, Umbelliferas, Scrophulariaceae, Campanulacese, Lo- beliaceae, Gramineas, all of the Compositce (protrandrous, according to Hildebrand), Scitaminacese - {Calathea grandiflora, Lindl.), &c. A few familiar examples will suffice to explain it. 1 Origin of Species, p. 325. « CErsted, Videnslc. Medd. fra den Nat. Hist. For. Kjob., 1869, p. 73. For list of protrandrous and protogynous plants, see A. W. Bennett in Seemann's 2 E 434 DICHOGAMY. In Leguminosce and Labiatac, all the species, with scarcely an exception, range themselves into the protrandrous, protogynous, or homogamous series, while in Rosacece and some others they are distributed over all three ; and in some instances even closely- allied species of the same genus differ in this respect — as, for instance, Potentilla and Ranunculus. In those natural orders in which the flowers are furnished with two sets of stamens of differ- ent lengths, it is most usual for the longer ones to discharge their pollen at an earlier period than the shorter ones ; and they have probably different functions to perform. Such plants are therefore both dimorphic and dichogamous. This is commonly the case with CrucifercE, Caryophyllacece, Geraniacea, and Onogracece, but not, apparently, with Labiates or Scrophularice. The same phe- nomenon is found in those orders where the numerous stamens are arranged in different whorls, as Ranunculacea and Rosacece} In Lobelia fulgens (another of these dichogamous plants) there is an elaborate and beautiful apparatus, by which all the numer- ous pollen-grains are swept out of the conjoined anthers of each flower before the stigma of that individual flower is ready to receive them. Now, Mr Darwin noticed that, in his garden at least, this Lobelia was never visited by insects ; while another species grow- ing close by, which was visited by bees, seeded freely. However, if the pollen from one flower was placed on the stigma of another, it raised abundance of seedlings from it. In many other cases the anther bursts before the stigma is ready for fertilisation, or the stigma is ready before the pollen of that flower is ready. In a word, these plants have, to all intents and purposes, separate sexes physiologically, though anatomically they are hermaphrodite. The same may be said of the dimorphic and trimorphic plants. All this would be strange and inexplicable except on the view of an occasional cross with a distinct individual being beneficial or indispensable to the life of the plant. In fact, in the berberry, a hermaphrodite plant, specially endowed, as we will see (Sect. IV.), with an apparatus for scattering the pollen over the stigma, so large is the capacity for intercrossing, that it is well known that if closely-allied forms or varieties are planted near each other, it is hardly possible to raise pure seedlings (Darwin). Darwin found that if several varieties of the cabbage, radish, onion, and of some other plants, be allowed to seed near each other, a large majority will turn out mongrels. Yet the pistil of each cabbage-flower is sur- rounded not only by its own six stamens, but by those of the many other flowers on the same plant ; and the pollen of each flower Journal of Botany, Oct. 1870 and Nov. 1871 ; also his Paper in Pop. Sc. Rev. October 1873 ; and " How Flowers are Fertilised," Manchester Sc. Lectures, Nov. 5, 1873. 1 A. W. Bennett in 'Nature,' 1870, p. 482. DICHOGAMY. 435 readily gets on its own stigma without insect agency— for in one of his experiments it was found that a plant carefully protected yielded its full number of pods. How, then, does it happen, he asks, that such a vast number (scarcely 78 out of 233 seedling cabbages grown by him were true to their kind) are mongrelised ? " I suspect that it must arise from the pollen of a distinct variety having a prepotent effect over a flower's own pollen, and that this is part of the general law of good being derived from the inter- crossing of distinct individuals of the same species. When dis- tinct species are crossed, the case is the reverse ; for a plant's own pollen is almost always prepotent over foreign pollen" — as we have already seen when discussing hybrids. Campamda, Scrophularia, &c., are all protrandrous ; but one of the most beautiful examples of protrandry is exhibited by Clero- dendron Thomsonce, Balf., a plant from the Old Calabar River in West Africa, but now very common in our conservatories. " Four stamens, with very long filaments and an equally long slender style, are rolled up together in the corolla bud. When this ex- pands, the stamens straighten out nearly in the line of the tube of the corolla, and their anthers open ; the style has bent so far for- ward as to point downwards ; and the stigma is not yet ready for pollen, its own branches being united. So a butterfly in the act of drawing nectar from this flower will get the under side of its body dusted with pollen, but will not come near the reflexed or still immature style. But in a flower a day older the stamens are found to be coiled up (the opposite way from what they were in the bud), and turned down out of the way, bringing the anthers nearly where the stigma was the day before, while the style has come up to where the stamens were the day before ; and its stigma, with branches outspread, is now ready for pollen— is just in position and condition for being dusted with the pollen which the butterfly has received from the anthers of an earlier blossom." Let us now examine the " grass of Parnassus " {Parnassia palustris), a common plant of northern bogs and swampy heaths, and an excellent specimen of a protrandrous plant. Though known for long, it is only recently that its reproductive organs have been correctly described. Its affinities are doubtful, some botanists putting it among the Hypericacea, others among the Droseracecsj a third party consider that its nearest allies are the Saxifragacea ; while a fourth section have solved the question by consti- tuting it an order by itself— viz., the Parnassiacea:} The flower is 1 Cosson and St Pierre (Flore des environs de Paris, ist ed.) consider it as the type of a special section of DroseraceEB ; but they unite Droseracese and Pyrolacese into one order, called Roridulacece—so named from the genus Roridula, which by its characters forms a connecting link between the two 436 DICHOGAMY. remarkable for its glandular petaloid scales, which have been sup- posed to be " modified polyadelphous stamens, united together at the base," and even as metamorphosed carpels ^ — both opinions being dubiously correct. The physiology of the phenomena of fecundation is, however, the most remarkable thing about it, and has been described by Vaucher, and more recently and more cor- rectly by Mr A. W. Bennett.^ The former author remarks, that when " the flower is fully open, the filaments, at first very short, suddenly lengthen and place the anthers on the top of the ovary ; so that all the glandular globules, and especially the scale which bears them, and which is covered with little drops of honey, can dissolve the pollen with which they are sprinkled. This operation accomplished, the anther falls and disconnects itself, and the fila- ment resumes its original place." Each of the anthers successively executes the same movement; but Bennett does not confirm Vaucher when he says that those which succeed each other are alternate and not contiguous — for the former author has frequently seen contiguous stamens to follow each other. " The anthers are extrorse and somewhat lateral — the pollen consequently cannot fall on the stigma, but falls on the nectaries, which are, as it were, smeared with it, and only the emanation from which can, I think, fertilise the stigmata. . . . The stigmata are entirely invisible while the anthers are discharging their pollen, and they only begin to display themselves, and expose their papillose tongues, at the moment when the emission is accomplished."^ The lengthening of the filaments to at least three or four times their original length is accomplished in an incredibly short space of time, and the adhesion to the ovary is so strong that they cannot be removed without breaking them ; but once the pollen is discharged, they retire to a horizontal position between the petals, and the anther falls. Previous to the discharge of the pollen the anther contracts. Altogether, this is one of the most singular of all the arrangements in flowers to prevent cross-fertil- isation. Not only is the back of the anther turned to the very apex of the pistil at the time of the ripening of the pollen, so as to close the approach to the ovary, but the stigmata (4-5 in number) are not developed until the anthers have discharged their pollen. tribes Droserece and Pyroleae. This ajrangement lias not been adopted by otlier botanists ; and in the 2d ed. of their Flore the authors have dropped it, with the protest, however, that they still consider it good. 1 Buchanan in Botanische Zeitung, xx. 307. 2 Journ. Linn. Bot. Soc, xi. 25. See also Gris in Comptes rendus, Nov. 2, 1868. 3 Hist. Physiologique des Plantes d' Europe, 324 (/a'c Bennett, 1. c); and Arthur Gris, "Sur le mouvement des Etamines dans le Paniassia palustris" (Mem. de la Soc. Nat. de Cherbourg, t. xvi., deux. ser. t. vi.), 1871-72. FERTILISATION BY MEANS OF INSECTS. 437 The function of the nectaries is thus shown to be, not, as Vaucher supposed, for " the absorption of the pollen," in order to return it to its own stigmata, but to enable insects "to carry it away to other flowers in which the stigmata are already expanded." Fertilisation by means of Insects.— From the frequent refer- ence made to this agency while discussing the foregoing subjects, the student will have had little difficulty in arriving at the conclu- sion that the primary agents in effecting fertilisation in dimorphic, trimorphic, and dichogamic plants are insects. Linnasus was ac- quainted with dichogamous plants, but he supposed they were fertilised by the wind wafting the pollen to them. Kolreuter was the first to clearly state that insects served this purpose ; but Sprengel, in his famous work already quoted, first clearly worked out the idea that insects assisted in fertilisation. Yet it is only within the last few years that the exact details of this curious subject have, to any extent, been elaborated. The odour and bril- liant colours of flowers, or the instinct to seek for nectar, attracts beetles, butterflies, bees, moths, thripsidas, ichneumons, various diptera, &c., to these flowers, and all are busy in assisting in this great work. To use the language of a famous American bot- anist, " Where ' free lunches ' are provided, some advantage is generally expected from the treat." A knowledge of Transatlantic customs may be required to appreciate the humour of the illustra- tion ; but the results of insects thus feeding in flowers, and paying for their food by assisting in fertilisation, will be readily under- stood if the facts which follow are considered. In a word, to reach these supplies of nectar the insects are obliged to disturb the pollen-grains, which, being often viscid, attach themselves to the legs and heads of the insects, which thus unconsciously carry them off to impregnate the next " heteromorphic " flower they visit. Only those flowers which secrete a sweet juice are visited by in- sects, and chiefly those which are bright-coloured, or have bright- coloured spots— what Sprengel calls maculcB indicantes, as they indicate that a plant produces honey. Sprengel also declared — and I am not aware that eighty years' observation has disproved his assertion — that many insects are limited to one species of flower; while others that are not so confined visit many indiscriminately, but will, during a whole day, remain with the species on which they fixed in the morning, and will not visit another provided there be enough of the first species to provide them with work. Therefore, before dismissing this subject, let us briefly review the whole sub- ject from this stand-point.^ Among dichogamic plants protrandry is more common than protogyny. The important families of the 1 See the work of Hildebrand, already quoted, for an admirable pricis of this question ; or a summary by M. Micheli, trans, by Mr Dallas in Ann. Nat; Hist., ix. 234, 4th ser. 438 FERTILISATION BY MEANS OF INSECTS. Labiatce, ScrophulariacccE, Compositie, and Campanulaceae, belong to this category. Accordingly, tlie details of organisation are adapted especially for fertilisation by insects. For example, in all the Com- positse examined by Hildebrand,^ the five stamens have the anthers soldered in a cylinder, which envelops the pistil; they open and allow the pollen to escape before the style has become elongated. The style bears, below the stigma, a certain number of rigid hairs, which retain the pollen-grains, and carry them forward with them in their ascending movement at the moment of the elongation of the style. The pollen thus carried up out of the cylinder of the anthers is collected by insects, and transported to flowers the stigma of which is already expanded. The same apparatus — though in a more variable form, as far as concerns the appendages destined to retain the pollen on the style — prevails in the Campanulacea:, LobeliacecB, &c. " In the whole of the group of scrophulariaceous Labiatse the axis of the flower is horizontal, and the stamens are approximated beneath the upper lip of the corolla. The insects, in passing, separate and jostle them, cause the pollen to fall from them, and then transport it to a more advanced flower. In certain genera the stamens stand alone in the way of the insects, which always seek the bottom of the flower, where the nectaries are. Later on they curve outwards, the style in its turn becomes elon- gated, and advances to take their place, and its recurved extremity caresses the body of the insect laden with pollen."^ In some of the Urticacese, the common nettle among others, several species of Trophis, Batis, &c., the filaments are bent down upon the disc until the pollen is ripe, when the slightest touch of a marauding insect causes them to spring, and scatter on every side a cloud of pollen. In the Irzs " there is a stamen to each of the three stigmas, and close beside it. Behind each stamen, and partly overhanging it, is a petal-like body peculiar to the Iris : these three bodies, appearing like supernumerary petals, are divi- sions of the style, in a peculiar form notched at the end ; and in the notch is the stigma, in the form of a thin plate. We notice that the stigma is higher than the anther ; but that is only a part of the difficulty. The anther and the stigma face each other. The anther faces outwards, and discharges its pollen through two 1 ' ' Uber die Geschlechtsverhaltnisse bei den Compositen," Acta. Leop. Carol. Nat. Cur., vol. xxv. (1869) ; also in a separate form, p. 104. Hildebrand is, however, in error when he says that all the Compositas are fertilised by the aid of insects, for it has been shown by Delpino that the sections Af/tbrosiaceca and Xafithice are fertihsed by the aid of the wind ; and so important does he consider this, that he has given the name Artemesiacece (wormwood being one of the species) to all these ancmophilous Cotnposiice (Studi sopra un lignaggio anemophile delle Composte, &c., Florence, 1871). 2 " Ulteriori osservazioni sulla dicogamia nel regno vegetale," Atte della Soc. Ital. di Sci. Nat., vols. xi. and xii. {teste Micheli, 1. c.) FERTILISATION BY MEANS OF INSECTS. 439 long slits on the outer side only. The thin plate or shelf is stigma only on its upper or inner face, which is roughened and moistened in the usual way for receiving the pollen; the face turned towards the anther cannot receive the pollen at all." i There are hundreds of similar cases in which the pollen is placed close to the stigma, but can never, or at least only seldom or accidentally, reach it of itself. Insects alone can accomplish their fertilisation, as seen in the case of /m quoted above. "A little nectar is produced in the bottom of the tube of the blossom. The only access to it is a narrow channel, leading down to the united bases of the six petals of the flower. Now the three inner of these are upright, with their lips curved inwards, shutting off all access in that quarter. But the three outer and larger divisions recurve, and afford a convenient landing-place directly before the stamen and the overarching stigma. Here the bee alights. To reach and suck out the nectar with his proboscis, will bring the head at least as low as the base of the anther. On raising his head to depart, he sweeps with it the whole length of the anther, and dusts it with the pollen now shedding. A little higher the shelf of the stigma is hit, but only the outer face of it, which is smooth, and does not take the pollen at all. Flying to the next blossom, the first thing which the pollen-powdered head of the bee strikes is the stigma, but this time on the upper face of the shelf, or real surface of the stigma, which takes some of the pollen brought into contact with it, and so is fertilised. Sinking lower, the head next brushes the anther downwards in entering for the nectar, then upwards in departing, and receives a fresh charge of pollen to be deposited upon the shelf of the stigma of the next blossom visited, — and so on," In Arethusa, Aristolochia, Kalmia, &c., fertilisation requires equally the aid of insects. In the first genus no insects have yet been seen about the plant ; but its structure shows that it must require their agency in fertilisation. In Aristolochia^ (fig, 171) (birthwort), however, the process has been repeatedly observed. The long, contracted throat of the corolla is lined with hairs, and at the bottom expands into a chamber, where there is a broad sessile stigma, surrounded with the stamens, which are placed a little below it, and with their anthers turned away from the stigma, so that none of the pollen can fall on it. If an insect enters, the hairs prevent it making its exit ; but as the flower advances, the hairs somewhat relax, and permit of the escape of the winged mes- senger laden with the pollen, which it has got covered with in its 1 Gray, How Plants Behave (1872), p. 22. ^ Insect fertilisation in Aristolochia was first accurately described by Spren- gel. He considered that Tipula pennicornis was the insect which always effected this, at least in A. Clematis. A. Sipko (the pipe-vine, or Dutch- man's pipe) of the United States also shows it well, 440 FERTILISATION BY MEANS OF INSECTS. Struggles at the bottom of the corolla to escape, and carry it to another plant, the stigma of which is ready to receive it. In Kalmia, another American genus, some species of which are common in our shrubberies, under the name of "American laurel," the anthers are contained in little pouches on the inside of the corolla, so that the ten stamens are bent all around the stigma in the form of springs. When a bee visits the flower to seek for honey, its proboscis lowers the stamen, which springs up with force, discharging, by the pores of the anther, pollen-grains, either on to the stigma or on to the insect, which flies to another flower with them, repeating the same process, and so aiding again , and again in cross-fertilisation. Such is the account given by Professor Beal of Michigan, who states that if the flowers are covered with gauze, and insects thus prevented visiting them, no seeds set. It is thus probable that this, like many other plants, re- quires cross-fertilisation before impregnation can be effected. What proves still more remarkably that self-fertilisation is of extremely rare occurrence in the vegetable kingdom is, that in certain families in which stamens and pistils get ripe simultane- ously, and of necessity are spontaneously fecundated, the inter- vention of insects is equally required. For instance, in the order LeguminoscB'^ the stamens and pistils are united in the form of a sort of keel, so close together that it is impossible but that some of the pollen-grains at least will have fallen on the ripe stigma. Yet the fact is, that without the intervention of insects, carrying off the pollen from another plant, rarely is a single seed produced. The intrusion of the insect causes the staminal column to free itself from the place where it lies in the keel, and so cover the winged visitor with a cloud of pollen. Darwin showed that bees, in visiting the flowers of the scarlet kidney-bean, always alight on the left wing, and in so doing depress it. This immedi- ately acts on the keel, which forces the pistil to protrude. On the pistil is situated a little tuft or brush of hairs, which, by the re- peated movements of the keel, brushes the pollen from the anthers on to the stigmatic surface.* Hildebrand has shown ^ that in the 1 " On the Fertilisation of a few Common Papilionaceous Flowers ; " T, H. Farrer in ' Nature,' 1872, p. 478-498. 2 Gardeners' Chronicle, Nov. 18, 1858. 3 " Bestaubungsvorrichtungen bei den Fumariaceen," Pringsheim's Jahr- buch, Bd. vii. s. 423-471. On the same subject, with reference to the effect of insects in cross - fertilisation, see H. Muller, of Lippstadt, in Verhand. des naturhistoriche Ver. der preussischen Rheinlande u. Westphalens, 1869, Cor- respondenzblatt, s. 43 ct seq.; and also to some extent Dr Buchanan White, in Journ. of Botany, Jan. 1873, p. 11-13. In a recent work (The Naturalist in Nicaragua, 1874), Mr Belt mentions that the scarlet-runners in his garden at Santo Domingo bloomed abundantly; but as none of the humble-bees of the country frequented the flowers, they never produced a single pod. The FERTILISATION BY MEANS OF INSECTS. 441 Fumariaccce, with the exception of Hypecoum, though the stamens and pistils are seemingly securely placed between two petals, out of reach of all ulterior influences, insects, to reach the store of nectar which is placed at the base of these organs, must pass be- tween the petals, and so carry off pollen to fertilise another plant while searching for their food in a similar manner. Hence the showy " bleedingjheart " {Dielytra spectabilis), which comes from Japan and China, rarely sets fruit in our gardens ; while the wild species of Corydalis and fumitory do, if ftot covered with gauze. In some of the orders allied to the Fumariacese a similar arrange- ment prevails. For example, in Camta (Cannacese) the arrange- ments depend, according to Delpino, on the viscidity of the pollen and the bursting loose of the style ; the pollen is first depo- sited on an expansion of the style, whence it is taken away by the insect, to be deposited on the stigma of the flower visited. The humble-bees, Darwin shows, are nearly indispensable to the fertil- isation of Viola tricolor (heart's-ease), for other insects do not visit it. Bees are also necessary for the fertilisation of some kinds of clover. For instance, twenty heads of Dutch clover (Trifolitim repens) yielded 2290 seeds ; but twenty other heads, protected from bees, yielded, according to Darwin's observation, none. Again, he shows that while 100 heads of red clover {T. pratense) produced 2700 seeds, the same number of heads protected from the visits of insects were all sterile. Hence it may be logically inferred that, as no other insect visits the clover and heart's-ease, if the humble-bee was becoming scarce or extinct in England, the two plants named would either become very rare or perhaps altogether extinct.^ It has been affirmed, by some objectors to Darwin's theory of the fertilisation of flowers by insects, that in Salvia the bees do not enter the corolla, but cut a hole on the outside in order to obtain the honey. This is not true, as bees have been seen repeatedly to enter the flower ; and when they do cut a hole in the manner described, it is only when they are too large to get into the tube. Mr C. V. Riley of St Louis has only recently shown flowers of the lofty climber, or " liana," Marcgravia nepentholdes, are disposed in a circle, hanging downwards like an inverted candelabrum. From the centre of the circle of flowers is suspended a number of pitcher-like nectaries, which, when the flowers expand in February and March, are filled with a sweetish fluid. This liquid attracts insects, and the insects numerous insec- , tivorous birds. The flowers are so disposed, with the stamens hanging down- \ wards, that the birds, to get at the pitchers, must brush against them, and thus, convey the pollen from one plant to another. Many other interesting instances are given in the same book. 1 See Darwin's discussion of this in Origin, &c., p. 83, 84, and p. 103-108. Field-mice destroy the nests and combs of the humble-bee ; they are in their turn destroyed by cats,— and hence the existence of the species of clover named may be said to be dependent on the number of cats in a district ! 442 STRUCTURE OF THE FLOWERS OF ORCHIDS. that the American Yuccas are protrandrous, and that therefore the glutinous pollen must be conveyed to the stigma by some other agency. This agency is a little moth — Pronuba Yticcasella — which is the only insect which assists in this operation ; and accor- dingly, in the Northern States and elsewhere, the Yuccas, though cultivated for their flowers, cannot seed, on account of the absence of the insect. The female insect only has the basal joint of the maxillary palpus w^onderfully modified into a long prehensile- spined tentacle. With this tentacle she collects the pollen and thrusts it into the stigmatic tube, and after having thus fertilised the flower, she consigns a few eggs to the young fruit, the seeds of which her larvae feed upon.-^ In Duvernoia adhatodoides, an acanthaceous plant of the Cape of Good Hope, Mrs Barber has shown that fertilisation is accomplished by a large hymenopterous insect of the genus Xylocopa, which insect fertilises no other plant.2 Fertilisation of Orchids. — A^iatomy of the Flower. — We have already (p. 318) referred to the structure of the flowers of the orchids, and sufficiently remarkable they are in their anatomy ; not less so is their physiology. Before, however, describing the func- tion, it may be well to describe the general anatomy of the flowers, which we have left as most appropriate to this place. The flowers of this order are often most bizarre in form, simulating the ap- pearance of various animals. To use the language of Mr Bate- man : " Flies are seen in Ophrys muscifera, bees in O. apt/era, drones in O. fucifera, spiders in O. aranifera. The columns of many of the Catasetums and other genera make excellent grass- hoppers. Mosquitoes are borne by Trichoceros ante7inifer, or Flor de Mosquito of the Peruvians ; dragon-flies by Renanthera arach- nites j moths by Phalcenopsis atnabalis. Insect-like antenna are also conspicuous in the flowers of Restrepia antetmi/era. The butterfly - plant of Trinidad is now the well-known Oncidium Papilio. Swans are found in the species of Cycnoches ; doves in Peristeria elata; pelicans in Cypripedium irapceanum, which, from the great resemblance of its flowers to the bird of that name, is styled by the natives Flor de pelicano. The skins of the tiger and the leopard are rivalled by the petals of such plants as Stanhopea tigrina, Bolbophylhim leopardinum, &c. The Jlos lyttcea of Her- nandez {Stanhopea Martiand) is so called from its lynx-like eyes and teeth ; Dendrobium taurinum has much of the bull about its face ; and various Cataseta — C. sejniapterum especially — grin like the ugliest monkey. Aceras aiithropophora, the man-orchis, is a well-known plant. Even extinct animals do not always escape : a 1 Paper read to Am. Assoc. for Adv. Science, Aug. 24, 1872. Reported in ' Nature,' 1872, p. 444. 2 Joum. Linn. See. Bot., xi. (1871) 469-472. MORPHOLOGY OF FLOWERS OF ORCHIDS. 443 r 4 geologist would instantly recognise the head of a Difwtherhim in the flowers of Masdevallia infracta. P leurothallis ophiocephala has a strong resemblance to a serpent's head, and Pholidota imbricata an equally strong resemblance to a rattlesnake's tail. Lizards occur in P leurothallis saurocephala and Epidendrum lacertinnm, and frogs in Epide7idriim raniferuni:' The anatomy of the flower of an orchid is fully displayed in fig. 298, where will be found the dissection of one of the most common species which appear in early spring or summer. The perianth, as already mentioned (p. 318), is made up of six segments in two rows, these segments being generally coloured. The lowest (owing to the twisting of the ovary) differs in form from the other segments, is often spurred, and known as the labellum. It is frequently tripartite — i. e., divided in three portions, distinguishable from each other. The lowest portion, when this is well marked, is known as the hypo- chilurn, the middle mesochilum, and the upper the epichiluin. The stamens and pistils are united into a single column, the gynos- teinuim (p. 329). The stamens are three in number ^ — the outer two, and sometimes the central one, being abortive. The anthers are placed in a cavity at the apex of the column called the clinandrhim. The pollen is rarely powdery, more frequently, as in the species figured (fig. 298, C and E), adhering mpollinia (p. 346). The stigma is an open space in front of the column, or gymnostemium. A small thickened process intervenes between the anther and the stigma, covering the latter over as with a roof, and acting as a floor to the former, and is called the Rostelluin j in most orchids it secretes a viscid fluid. Finally, there is a spur-like nectary. The flower is thus so formed that, without extraneous aid, the pol- linia could not escape from the anthers. But an insect (a moth, bee, &c.), while sucking the nectar from the flower, would detach the anther and expose the pollinia, which would attach themselves by their discs to its proboscis, and so enable these pollinia to be carried to another flower in the manner to be presently described. Morphology of the Flowers of Orchids. — The exact morphology of the flowers of orchids is not yet settled, different authors taking different views in regard to the parts which are coalesced. Mr Darwin looks upon an orchid flower as consisting of five simple parts — namely, " three sepals and two petals " (not adopting the usual view of the monocotyledonous perianth) ; " and of two com- pounded parts— namely, the column and the labellum. The column is formed of three pistils, and generally of four stamens, all com- pletely confluent. The labellum is formed of one pistil, and two petaloid stamens of the outer whorl, likewise completely con- 1 Dr Masters has given (Veg. Terat., p. 383-387) a whole series of intermediate forms between the common orchid with one stamen only up to forms in which six are developed. 444 FERTILISATION OK ORCHIDS. lluent. , . . This view of the nature of the labellum explains its large size, its frequently tripartite form, and especially its man- ner of coherence to the column, unlike that of the other petals." The six stamens or anthers, which ought to be represented in every orchid, are explained in this manner: "The three outer belonging to the outer whorl are always present, with the upper one generally fertile, and the two lower ones invariably petaloid and forming part of the labellum. The three stamens of the inner whorl are less plainly developed, especially the lower one, which, when it can be detected, serves only to strengthen the column, and in some rare cases, according to Brown, forms a separate projection or filament. The upper two anthers of this inner whorl are fertile in Cypripedmm, and in other cases are represented either by membranous expansions or by minute auricles without spiral vessels. These auricles, however, are sometimes quite absent, as in some cases of Ophrys. . . , We can" (taking this view of the homology of the orchids) " understand the exist- ence of the conspicuous central column ; the large size, generally tripartite form, and peculiar manner of attachment of the label- lum ; the origin of the clinandrum ; the relative position of the single fertile anther in most orchids, and of two fertile stamens in Cypripedium ; the position of the rostellum, as well as of all other organs ; and, lastly, the frequent occurrence of a bilobed stigma, and the occasional occurrence of two distinct stigmas."^ In fig. 297 is shown a diagram of the flower of an orchid on the views of the illustrious naturalist quoted. With scarcely an exception, all of them require the aid of insects to fertilise them. To accom- plish this, the most beautiful and elaborate contrivances exist in their varied flowers (about 6000 of them). The bee-master was for long acquainted with the fact that the club-shaped pollen- masses were carried by bees, from seeing them attached to the heads of these and other insects, but, it need scarcely be said, with- out understanding the import of it. To him it was only the " club sickness " (fig. 299). Within the last ten or twelve years an immense mass of facts has been accumulated on this subject, chiefly through the labours of Charles Darwin, and the school which his wonder- ful researches have stimulated into action. Almost every separate species has a different method of accomplishing its fertilisation through insect agency, but our space will only admit of giving two or three instances as specimens of the whole, referring the reader to the original sources, or to the plants themselves, for further information. The first method which we shall mention was communicated by Dr Criiger to Mr Darwin. In a species of Coryanthes, a tropical orchid, he " found that the labellum is hol- lowed into a great bucket, into which drops of almost pure water 1 Fertilisation of Orchids, p. 294, 295, 301, 302. FERTILISATION OF ORCHIDS. 445 continually fall from two secreting horns which stand above it, and when the bucket is half full the water overflows by a spout on one Upper or Posterior Petal. Upper Petal. ^cv // Lower Lower Sepal. Labellum. Fig. 297.— Section of the flower of an Orchid. S S, Stigmas ; S r Stigma modified into the rostellum ; A i, Fertile anther of the outer whorl ; A 2, A 3, Anthers of the same whorl combined with the lower petal, forming the labellum ; « i, a 2, Rudimentary- anthers of the inner whorl (fertile in Cypripediu7ii), generally forming the clinandrium ; a 3, Third anther of the same whorl, when present, forming the front of the column. The fifteen little circles show the spiral vessels, which in every case can be traced down to the six large ovarian groups. They alternate in five whorls (as represented). In order to guide the eye, the three central groups running to the three pistils are connected by a triangle (after Darwin 1). side. The bare part of the labellum stands on the bucket, and is itself hollowed out into a sort of chamber with two lateral en- trances ; within this chamber are curious fleshy ridges. The most . ingenious man, if he had not witnessed what takes place, could never have imagined what purpose all these parts serve. But Criiger saw crowds of large humble-bees visiting the gigantic flowers of this orchid, not in order to suck nectar, but to gnaw off the ridges within the chamber above the bucket. In doing this they frequently pushed each other into the bucket, and their wings being thus wetted they could not fly away, but were compelled to crawl through the passage formed by the spout or overflow. Dr Criiger saw a ' continual procession ' of bees thus crawling out of their involuntary bath. The passage is narrow, and is roofed over by the column ; so that a bee, in forcing its way out, first rubs its 1 Orchids, p. 291, 292. See also Robert Brown in Trans. Linn. Soc, xvi. 696 ; Link, Bemerkungen tiber der Bau der Orchideen (Bot. Zeit., 1849, 745); Brongniart, Ann. des Sc. Nat., t. xxiv., &c. 446 FERTILISATION OF ORCHIDS. back against'the viscid stigma, then against the viscid glands of the pollen-masses. The pollen-masses are thus glued to the back Fig. 298. — Anatomy of the flower of Orchis mascjtla, L. a Anther ; r Rostellum ; j Stigma ; / Labellum ; 71 Nectary ; Pollinium or pollen-mass ; c Caudicle of poUinium. A, Side view of flower, with all the segments of the perianth cut off, except the labellum, of which the near half is cut away, as well as the upper portion of the near side of the nectary ; ov Twisted ovary. B, Front view of flower, with segments of the perianth removed, except the labellum. C, One pollinium or pollen-mass, showing the packets of pollen-grains, the caudicle, and the viscid disc. D, Front view of the discs and caudicles of both pollinia within the rostellum, with its lip depressed. E, Section through one side of the rostellum, with the included disc and caudicle of one pollinium. F, Packets of pollen-grains tied together by elastic threads, here extended.! 1 From a copy of a drawing by Franz Bauer in Darwin's Fertilisation of Orchids, p. 18. FERTILISATION OF ORCHIDS. 447 of the bees which first happen to crawl out through the passage of a lately-expanded flower, and are thus carried away. . . . When the bee, thus provided, flies to another flower, or to the same flower a second time, and is pushed by its comrades into the bucket, and then crawls out by the passage, the pollen-masses necessarily come first in contact with the viscid stigma and adhere to it, and the flower is fertilised. Now at last we see the full use of every part of the flower, of the water-secreting horns, of the bucket half full of water, which prevents the bees from flying away, and forces them to crawl out through the spout and rub against the properly- placed viscid pollen-masses and the viscid stigma." ^ Could anything be more extraordinary? And yet a hundred other such instances could be given. Not less interesting, though probably at first sight not so startling, is the arrangement in the common Orchis masaila of our damp pastures, which, with the aid of the figures given by Mr Darwin (fig. 298), and the descrip- tion of the structure at p. 442 of this text-book, we may explain, as the plants can easily be obtained. Should an insect alight on the labellum — a good landing-place — and push its head into the chamber (fig. 298, A, or front view B), at the back of which lies the stigma {s), in order to reach with its proboscis the end of the nectary — or, which does equally well to show the action, push a sharply-pointed common pencil into the nectary — the result is that, " owing to the pouch-formed rostellum projecting into the gangway of the nectary, it is scarcely possible that any object can be pushed into it without the rostellum being touched. The exterior membrane of the rostellum then ruptures in the pro- per lines, and the lip or pouch is most easily depressed. When this is effected, one or both of the viscid balls will almost infallibly touch the intruding body. So viscid are these balls, that whatever they touch they firmly stick to. Moreover, the viscid matter has the peculiar chemical quality of setting like a cement, hard and dry, in a few minutes' time. As the anther-cells are open in front, when the insect withdraws its head, or when the pencil is with- drawn, one pollinium, or both, will be withdrawn firmly cemented to the object, projecting up like horns. The firmness of the attach- ment of the cement is very necessary, as we shall immediately see; for if the pollinia were to fall sideways or backwards, they could never fertilise the flower. From the position in which the two pollinia lie in the cells, they diverge a little when attached to any object. Now, let us suppose our insect to fly to another flower, or insert the pencil with the attached pollinium into the same or into another nectary (fig. 298, A), it will be evident that the firmly attached pollinium will be simply pushed against or into its old position— namely, into the anther-cell. How, then, can the flower 1 Origin of Species, 6th ed., p. 154, 155. 448 FERTILISATION OF ORCHIDS. be fertilised ? This is effected by a beautiful contrivance. Though the viscid surface remains immovably fixed, the apparently insig- nificant and minute disc of membrane to which the caulicle ad- heres is endowed with a remarkable power of contraction, which causes the pollinium to sweep through about 90 degrees, always in one direction — viz., towards the apex of the proboscis or pencil — in the course, on an average, of thirty seconds. Now, after this movement and interval of time (which would allow the insect to fly to another flower), it will be seen, by turning to the diagram (fig. 298, A), that if the pencil be inserted into the nectary, the thick end of the pollinium will exactly strike thestigmatic surface. Here comes into play another pretty adaptation, long ago noticed by Robert Brown.^ The stigma is very viscid, but not so viscid as, when touched, to pull the whole pollinium off the insect's head, yet sufficiently to break off the elastic threads (fig. 298, F), by which the packets of pollen-grains are tied together, and leave some of these on the stigma. Hence a pollinium attached to an insect, or to the pencil, can be applied to many stigmas, and will fertilise all. I have seen the pollinia of Orchis pyramidalis ad- hering to the proboscis of a moth, with the stump-like caudicle alone left, all the packets of pollen having been Itft glued to the stigmas of the flowers successively visited " (fig. 299). The balls of viscid matter within the pouch - formed rostellum are surrounded with fluid, which is important, as the viscid matter sets hard when exposed to the air for a short time. Various other similar smaller contrivances, as noticed by Darwin, might be mentioned. For instance, the pouch, after being depressed, springs up to its former position : and this . „ , , , . ^ is of the greatest service; Fig. 200. — Head and proboscis of Acontia . -r^i • j- j ^ ^ i i Inciuosa (a moth), with seven pairs of the pol- for, if thlS did nOt take place, linia Orchis pyramidalh attached to the ^nd an insect, after depressing proboscis (after Darwin). .,° the hp, failed to remove either viscid ball, or if it removed one alone, in the first case both, and in the second case one, of the viscid balls would be left exposed to the air ; consequently they would quickly lose all adhesiveness, and the pollinia would be rendered absolutely useless." " In Catasetum, another orchid closely allied to Coryanthes, the 1 Trans. Linn. Soc, xvi. 731 (Miscell. Bot. Works, i. S34)- 2 On the Various Contrivances by which British and Foreign Orchids are Fertilised by Insects, and on the Good Effects of Intercrossing (1862), p. 14-19. FERTILISATION OF ORCHIDS. 449 Structure of the flower is widely different, though serving the same purpose, and is equally curious. According to Mr Darwin's de- scription, bees visit these flowers, like those of Coryanthes, in order to gnaw the labellum. In doing this they inevitably touch a long tapering sensitive projection, the "antenna" of the rostellum. This antenna, when touched, transmits a sensation of vibration to a certain membrane around the whole exterior surface of the ros- tellum, which is instantly ruptured ; this sets free a spring, by which the pollen -mass is shot forth like an arrow in the right direction, and adheres by its viscid extremity to the back of the bee. The pollen-mass of the male plant (for in this orchid the sexes are separate) is thus carried to the flower of the female plant, when it is brought into contact with the stigma, which is viscid enough to break certain elastic threads, and, retaining the pollen, fertilisation is effected.^ In the Lady's slipper {Cypripediuin), of which we have one rare native species (C Calceolus, L.), but many exotic ones are in our conservatories, the plan of fertilisation is so very different from that of any of the Orchis family, that, even at the risk of infringing on the space allotted to other departments of vegetable physiology, we must describe it in the words of Dr Gray, not having seen the action ourselves. In Cypripedium spectabilc of the Northern United States, unlike other orchids, there are two stamens ; the pollen is powdery, or between powdery and pulpy, and not very different from that of ordinary flowers. " As it lies on the open anther in a broad patch, it somehow gets a film-like and thin coat of sticky varnish. The stigma is large, flat, and somewhat trowel-shaped, the face turned forwards and downwards ; it is supported on a short style, to which the anthers have grown fast, one on each side. This apparatus is placed just within the upper part of the sac or slipper (rather like an Indian moccasin than a slipper), which gives its name to the flower. There are three openings in the slipper : a large round one in front, and the edges of this are turned in, after the fashion of one sort of mouse-trap ; two smaller ones far back, one on either side, directly under each other. Flies and the like enter by the large front opening, and find a little nectar apparently bedewing the long hairs that grow from the bottom of the slipper, especially well back under the overhanging stigma. The mouse-trap arrangement renders it difficult for the fly to get out by the way it came in. As it pushes on under the stigma, it sees light on either side beyond, and in escaping by one or other of these small openings, it cannot fail to get a dab of pollen upon its head, as it brushes against the film with which the surface is varnished. Flying to the next blossom, and entering as before. ^ Origin of Species, 6th eel., p. 155. 2 F 450 FERTILISATION OF THE ASCLEPIADACE^. as the insect makes its way onward it can hardly fail to rub the pollen-covered top of its head against the large stigma which forms the roof of the passage. The stigma of every other orchid is smooth and glutinous. This is merely moist and finely rough- ened. The roughness arises from very minute projections, all pointing forwards ; so that the surface may be likened to that of a woolcard or of a rasp on a very fine scale. So, as the insect passes under, the film of pollen is carded or rasped off its head by the stigma, and left upon it ; and when the fly passes out it takes a fresh load of pollen on its head with which to fertilise the next flower." ^ Fertilisation of the AsclepiadacecB. — The flowers oi Asclepias are also fertilised by insects, though their flowers are hardly so com- plicated as those of orchids, and the poUinia are in pairs hanging by curved stalks from a dark-coloured disc. At the moment of fertilisation, the anthers of the Asclepiadaceae, which are in a manner applied against the stigma, open, and the cellular envelope in which the pollen-grains are enclosed ruptures on the side near- est the stigma, and allows of the protrusion of a great number of pollen-tubes, which are identical in their nature with those emitted by the pulverescent pollen-grains.^ The flowers of some orchids resemble butterflies and moths (p. 442) — e.g., Oncidium, Papilio, and Phalcenopsis, &c. — and it is just possible that these forms may serve to attract insects, though, as already noticed, the bee orchis {Ophrys apifera) is, curiously enough, the only one which is capable of self-fertilisation. On the whole, looking at the manifold contrivances in orchids to en- able insects to get entangled with the pollen-masses, a noble author is well justified in saying that — mutatis mutandis — the ancient warning of " spring-guns and ;«(7//z-traps set here " might well be written over the flower of every species of that great order. The student who can witness all these wondrous forms, and their not less wonderful physiology, without seeing in plant-life a deeper significance than even his ordinary studies of organography would lead him to, may be very sure that he has mistaken his vocation, and had better turn to pursuits where scientific curiosity and rev- erential wonder in no way add to the amenity of his daily life.^ 1 How Plants Behave, p. 31, 32. 2 Robert Brown on the Asclepiadess, in Miscellaneous Works, ii. 193-247. For further information, seethe works of Darwin and Gray already quoted ; a paper by Mr Darwin in Ann. Nat. Hist., 1872 ; Journ. Linn. Soc. Bot., vi. 77, 151, vii. 69, viii. 169 ; and Gardeners' Chronicle, 9th June i860; another by Dr Rutherford in Trans. Bot. Soc, 1865 ; Mansel-Weale in Journ. Linn. Soc, xiii. 42-45, 1871 ; Ibid., 45-47; Ibid., 47-48; Ibid., 48-51; Trimen in Journ. Linn. Soc. Bot., ix. (1865) 144; Ogle, Pop. Sc. Rev., April 1870; and, more THE WIND AS A FERTILISING AGENT. Considering how important a part insects play in fertilising nearly all plants, even the homogamic ones (for though in these plants the stamens and pistils are present in one flower, it would be a mistake to say that, because they are capable of self-impreg- nation, this is accomplished in every case, for insects often com- plete what rain or unfavourable weather may have prevented), might it not be worth trying the value of the suggestion made more than seventy years ago by Willdenow, after the first publica- tion of his friend Sprengel's observations, that when gardeners wish to make cherry or other fruit trees bear early in the season, when they often get little or no fruit at all, they should place a beehive with bees in the hothouse, and at the same time take care to let those busy insects get at as many flowers as possible ? ^ The Wind as a Fertilising Agent. — We have seen that nature trusts not alone to insects to accomplish this cross-fertilisation, but employs also inorganic agents. In Coniferse, Amentacese with pendulous anthers, some Chenopodiaceae with enormously superabundant pollen, passion-flowers, &c., with versatile anthers pendent from the extremity of a long filament, the wind assists in carrying the pollen from flower to flower ; and as in these plants the pollen, instead of being viscid, is dry, this is easily accom- plished. Perhaps the fact that in hazels and willows the pollen is distributed before the appearance of the leaves, or, as in the case of evergreens and in pines, is produced more abundantly, and meets with little obstruction from the smooth and circular leaves, may be also looked upon as further evidences of design to assist the winds in their office. Again, in many instances, where the wind performs the office of wafting the pollen from flower to flower, there is no corolla to hide the pistil ; while the stigmas are downy or plumose, the better to intercept and retain the floating grains. At the same time, the interference of insects is checked by the absence of honey and of perfume.^ In fact, in all the plants which Delpino has called Anemophilous, the wind wafts the pollen for fertilisation— a method of fertilisation which perhaps particularly for the fertilisation of Cypripedium, a separate work by H. Miiller, entitled Uber die Anwendung der Darvvin'schen Theorie auf Blumen und blumen besuchende Insecten, 1870. The same author has discussed insect fertilisation very fully in Die Befruchtung de Blumen durch Insekten, und die gegenseitigen Anpassungen beider, 1873 ; Hart in Nature, Aug. 4, 1870; Scott in Trans. Bot. Soc, vii. 543, Journ. Linn. Soc, viii. 91 ; Bentham "On the Stigmatic Apparatus of Goodenovieas," Journ. Linn. Soc. Bot., x. 293, &c. 1 For the connection of insect fertilisation with the geographical distribution of plants, see Phyto-geography. The whole question of the agency of insects has been discussed by Hermann Miiller in his recent work, already quoted, which contains a risumi of the now rather voluminous literature of the subject in German, Italian, Swedish, and English. 2 Elliot in Trans. Bot. Soc, vi. 4. 452 FERTILISATION OF GRASSES. Mr Darwin has rather underestimated. It is especially well seen in grasses. Fertilisation of Grasses?- — The earlier observers — Morren, Naudin, and Bidard — believed that self-fertilisation was the rule among grasses. The more recent observations of Delpino and Hildebrand have, however, shown, that with the exception of those grasses the flowers of which never open, the agent of ferti- lisation is the wind, insects rarely visiting the flowers of these plants, and therefore playing but a minor part in the conveyance of the pollen from one to another. To facilitate this, the pollen- grains of grasses are in general rounded, smooth, and not attached to each other ; so that as soon as the anthers open, they are dis- charged and dispersed through the air. In addition, the filaments of the stamens are, in most cases, long; so that the least breath of wind shakes out the pollen. The stigma is usually of a feathery character, presenting a large surface to the action of pollen, and provided, as Hildebrand points out, with a large number of hol- lows and projections, in and on which it may lodge. Still, though these contrivances render cross - fertilisation almost inevitable, self-fertilisation is not, as in orchids, absolutely prevented. The flowers of grasses only remain open for a short, for an extremely short time ; and this, in different species, occurs at different periods of the day. Thus, for example, Avena ptibesceiis — a species of wild oat — flowers only in the morning ; ^gilops cylin- drica and Oryza sativa towards noon ; while Phalaris canariensis (canary-grass), the ordinary cultivated species of oat {Avena), and some other grasses, flower towards evening. The mode of fertilis- ation of these plants has therefore hitherto been overlooked. The state of the weather, by keeping the flower closed if the season is wet,^ as among plants belonging to other orders, also determines the mode of fertilisation. With respect to the facts which have 1 For a full account see Hildebrand, ' ' Beobachtungen iiber die Bestaubungs verhaltnisse bei derGramineen," Monats. d. preuss. Akadem. d. Wiss. zu Berlin, Okt. 1872, p. 737-764; or abstract by Mr A. W. Bennett in the 'Gardeners' Chronicle,' March 15 and 22, 1873; also Delpino, "Sulla dicogamia vege- tale e specialmente suquella del Cereali," Bolletini del Comizio agrario par- mense, March and April, 1871 ; Ascherson, in Bot. Zeit., 1871, No. ohetseq.; Spruce, Journ. Roy. Hort. Soc, Dec. 21, 1869; Wilson, Trans. Bot. Soc. Edin., vol. xi., May 1873, and Feb. 12, 1874 (Gardeners' Chron., March 21 and 28, 1874) ; A.xell, Om anordningarna for de fanerogama vaxternas be- fruktning, p. 52 et seq. ^ Observations made during the summers of 1872 and 1873 (also confirmed by Mr Wilson) show that oat flowers open almost as freely in wet or cloudy days as when exposed to a clear sky and bright sunshine, though individual plants may remain shut (while the neighbouring ones are open) during gloomy or rainy weather. Mr Wilson has observed that the upper flowers of the oat panicle are often in blossom before the lower are out of the sheath. FERTILISATION OF GRASSES. 453 been absolutely determined, grasses may be classed under the following heads : — (i.) Diacmis Grasses. — These are necessarily cross- fertilised, but are few in number. Ex. Calainigrastos dioica, Guada dioica, Buchlde daciyloides (the American buffalo grass), &c. (2.) Moncecious Grasses. — These are more common, and must always be, in the strict sense of the term, cross-fertilised. The maize {Zea mays) affords a good example of protrandrous monoe- cism, " the upper male flowers in the spike having often lost their pollen before the stigmas are protruded from the lower male flowers." On the other hand, Croix lacryma (Job's tears) affords an instance of protogynous monoecism. (3.) Polygamous Grasses. — Here, though self - fertilisation is probable, cross-fertilisation may take place, as in the genera Panic7im, Arrhetiathertim, Andropogon, &c. (4.) Protogynous Grasses. — In these grasses the stigma is ex- tended from the closed palese long before the opening of the flowers or dehiscence of the anthers ; and in only a very few cases is the stigma receptive beyond a brief period. Examples are afforded by AntJwxanthum odoratum (the vernal grass), Ala- pecurus pratensis (meadow foxtail), Nardus stricta (mat grass), &c. (5.) Grasses with Synchronous Development of Pistil and Anthers. — (Homogamous or synacmic.) {a) Even in these plants, in which self-fertilisation is not only possible but probable, cross - fertilisation is often favoured in preference to self-fertilisation — as, among others, in the common rye {Secale cereale), rice {Oryza sativa), and in wheat {Triticum vulgare), and other species of that genus. It is quite erroneous, as Delpino has shown, that wheat is necessarily self-fertilised. In a wheat-field not more than perhaps one in 400 of the flowers are open at one and the same time. The opening of the flower of wheat is a very interesting phenomenon, and happens with great rapidity. "While the flowers are still closed, a motion of the glumes is observable ; these separate suddenly, in a moment ; at the same time the anthers protrude laterally from the opening, open, and about one-third of the pollen falls inside the flower upon its own stigma, while the remaining two-thirds is dispersed into the air ; the anthers are emptied in a moment, and the whole process does not last more than half a minute. The stigmas remain receptive for a considerably longer period, and can then receive the pollen of other flowers." In rye the same acute observer shows that "the filaments elongate gradually ; the anthers are extended between the apices of the paleae, which are still nearly closed, and finally become free to their base, and are then tilted up laterally, thus projecting a 454 FERTILISATION OF GRASSES. portion of the pollen through a longitudinal slit which commences at the apex. At this period the flower is still almost entirely closed and the stigma unreceptive; so that this portion of the pollen which is first shaken out goes to the fertilisation of other flowers which are already open. Only after the tilting up of the anthers the two paleje separate for several hours, the stigmas bend forward and become receptive, the slits in the anthers at the same time lengthen, and the rest of the pollen is then shaken out by the least breath of wind. A portion of this may fall on the pistil in the same flower, but by far the greater part, owing to the relative positions of the parts, is conveyed to other flowers. In Secale montanum the process is precisely similar." {b) In others — such as Briza maxima (quaking grass) and B. media (darnel grass), Cynosurus cristatus (crested dog's-tail grass), Hordeum jubatum, Lolium temulentum, &c., the fact of the stigma and the anthers being mature at the same time, either protruded or in close flowers, and the filaments either stiff or bent round towards the anthers, renders cross-fertilisation and self-fertilisa- tion possible to almost, if not quite, the same degree. ic) Finally, in others — such as Avena sativa, Bromtis secalintis, &c. — though self-fertilisation is favoured, it does not occur exclu- sively. The conditions of pollenisation or fertilisation must be observed in each species separately, since closely allied species of the sartie genus show startingly different phenomena in this respect, and even exhibit different behaviour, according to the different conditions of climate. The common Poa annua, a winter- flowering plant, is, for instance, self-fertilised ; and in India the different varieties of rice remain constant, even though grown in an adjacent field, so that it would seem as if no crossing took place in this instance.^ 1 The observations of Mr A. Stephen Wilson, made in Scotland, do not thoroughly confirm those of Delpino and Hildebrand. In all except one variety of barley {Hordeum distichon, the golden or Italian barley) the flower opened during the act of fertilisation. This variety alone fertilises in an un- opened flower, though the cause of this is still unknown. He considers that it is not rigorously proved that cross-fertilisation takes place in the cereal grains whieh he examined, and believes that though insects are certainly not the agents by which cereals are fertilised, yet that the wind is not an agency in this function in the same sense as it is in dicecious plants— "The essential agency is probably the sudden extension of the filaments, causing a few grains of pollen to be emptied out of the anthers before they are entirely ejected from the flower-cup." In some recent observations by the same experimenter, he remarks : " It seems to be the case that wheat, barley, and oats, whether they fully or but partially open their flowers, are fertilised before the anthers are visible outside. The coming of their anthers outside, or discharging a rem- nant of pollen in that position, is an accidental circumstance of no essential importance ; while with rye an exterior discharge is always essential, but fre- FERTILISATION OF GRASSES. 455 In the plantain or rib grass {Plaiitago major, lanceolata, &c.)— belonging, however, not to the order GraminacecC, but to the order Plantao-inaccce — fertilisation must also be accomplished by means of the wind, as the flowers of these plants are, equally with those of grasses, unvisited by insects, and are protogynous. Delpino — Professor of Natural History at the first school of Vallombrosa, but at present one of the scientific staff of the Italian circumnavigating expedition on board the Garibaldi — who has so identified himself with this subject of dichogamy, has suggested a convenient nomenclature to express the different methods in which this dichogamous fertilisation is accomplished. On this principle he divides plants into the following groups : — (i.) The lower orders of plants, in which the mobile antheridia accomplish fertilisation without any intermediate agent, he calls Zoogamous, while the term (2.) Diamesogamous is applied to those which require such agency. This last section he divides into three subdivisions : (a) Hydrophileas, (/S) Anemophileas, (y) Zoidiophilese. The plants under the first heading (Hydrophilese) are fecundated by the aid of the water in which they grow acting as the intermedi- ate agency. Such are the Floridese, the Naiadaceae (notably Posi- donia caulini, a kind of water-grass), Ceratophyllum, Vallisneria, &c. The second group {Anemophilece) comprises Coniferae, Amen- taceze, Negundo, palms, Urticaceae, Euphorbiaceae, many apetalous quently a failure. The flowers are seldom open above half an hour ; and seldom are there more than three or four florets open at one time on a spike. 'It is generally believed,' says Mr Alfred W. Bennett (How Flowers are Fertilised, a Lecture, 1873, p. 11) — 'though on this point further experiments are still wanting — that our cereal crops, especially wheat, rye, and barley, are fertilised exclusively by the agency of the wind. The flowers are small and uncoloured, without calyx or corolla ; the anthers are hung lightly on the end of long slender filaments ; the pollen is very fine and powdery ; and insects are hardly ever seen to visit them. Favourable weather (fine and sunny, with light breezes, and yet not so strong a wind as to disperse the pollen to too great a distance, so that it will not perform the purpose for which it was designed) at the time when the plants are in flower — i. e., in the early part of June — is therefore of very great importance for the insuring of heavy crops. ' But we have seen that the rule which applies to wheat, barley, and oats, does not apply to rye. We have seen, also, that the wind is entirely unnecessary to the fertilisation of wheat, barley, and oats. The Belgian farmers who trailed ropes over their flowering wheat, to insure complete fertilisation, were doing that which the very appearance of the anthers told them in whispers, not yet heard, had already been accomplished. The pollen of these plants, which the winds disperse, is not that which fertilises, but that which is not required for fer- tilisation. It is manifest that in the Itahan barley, the largest-fruited of all the varieties, and which never opens its pales, nor disperses any pollen in flowering, cross-fertilisation has never taken place in all the lapse of its existence ; while in the case of the other barleys, wheats, and oats, even the florets which do fully open, are self-fertilised before space is afforded for the admission of neighbouring pollen." 45*5 FERTILISATION OF WINTER-FLOWERING PLANTS. genera, Thalicirum (one of the Ranunculaceas), Polygonacea;, and nearly all grasses. Fertilisation is accomplished by the wind carrying the pollen from one plant to another ; while the third division (Zoidiophilcce) are those in which fertilisation is accom- plished by the aid of animals — insects chiefly — though the hum- ming-birds may also aid in this work. Fertilisation of Winter-Flowering Plants.— If insects are thus instrumental in effecting the fertilisation of plants, it may reasonably enough be asked, how can plants, which, like the gorse (Ulex Eu- ropaeus) or the butcher's broom {Rnscjts aculeatus), flower almost in mid-winter, or in early spring ; or others, like the dead-nettles {Lamiicm album and pur- pureuni), Veronica Bauxbaumii, dais)^ dandelion, groundsel, common spurge {^Euphorbia peplus), and others, which flower almost regardless of season or temperature, be fertilised ? In the " dead season," when these plants are flowering, the number of insects which can assist in fertilisation is small indeed. Thanks doilfi, Cmnte.^'pSiis and'^stf- to the interesting observations of Mr A. mens from open flower, the lat- w. Bennett,^ we are able to answer this ter discharging pollen (after ,. , . tt i i Bennett). question to some extent. He shows that in some of these plants at least, fertilisa- tion, " or at all events the discharge of the pollen by the anthers, takes place in the bud before the flower is opened, thus insuring self -fertilisation under the most favourable circumstances, with complete protection from the weather, assisted, no doubt, by that rise of temperature which is known to take place in cer- tain plants at the time of flowering." The truth of this is shown by the dissection of a flower of Lamium album (white dead- nettle), gathered in the last week of December (fig. 302), which "shows the stamens completely cur\'ed down and brought into contact with the bifid stigma — the pollen being at that time freely discharged from the anthers;" in Veronica Bauxbaumii, V. agrestis, V. polita, Vinca major, gorse, dandelion, groundsel, daisy, shepherd's purse (in which the four stamens appear to dis- charge their pollen into the bud, the two shorter ones not till a later period), Lamium purpureum (purple dead-nettle), Cardi- mine hirsuta, and Stellaria media, in which plant (the chick- weed) the flowers open only under the stimulus of bright sun- shine. ■ 1 Nature, i. (1869) ir. We are indebted to Messrs Macmillan for the accompanying figures, originally prepared to illustrate Mr Bennett's paper. FERTILISATION OF WINTER-FLOWERING PLANTS. 457 On the contrary, in a few summer-flowering plants tempted by the mild winter weather to put forth a few sickly flowers, there Fig. 30T. — Chivto>iantInisfragrans(N.O.CalycaiithacecE). i, Early stage of flower, calyx and corolla removed ; 2, Later stage, stamens surrounding the pistil and discharg- ing their pollen outwardly (after Bennett). was no pollen discharged before the opening of the flower, and no seed was observed to be formed. In Lainmin Galeobdolon — or yel- low archangel — notwithstanding its near relationship to the dead- nettle, the anthers did not discharge their pollen until after the opening of the flower (fig. 300). In some plants of warmer climates, which nevertheless flower in our gardens in winter, the pollen is not discharged until the opening of the flower. ^ This is well illustrated in Chimo7ianthus fragrans, the "allspice tree," a native of Japan, which has a most perfect contrivance to prevent self-fertilisation (fig. 301). In a manner somewhat the same as Bennett has described in the "grass of Parnassus" {Parnassiapalus- trts, p. 435),i " the stamens, at first nearly horizontal, afterwards lengthen out, and rising up perpendicularly, completely cover up ^ Joum. Linn. Soc. Bot., 1868-69, P- 24' 45S FERTILISATION OF WINTER-FLOWERING PLANTS. the pistil, and then discharge their pollen outwardly, so that none can possibly fall on the stigma." Accordingly, fruit is never pro- duced in this country, though doubtless in its native climate it is cross-fertilised by insects. In dioecious winter-flowering plants this method of self-fertilisation in the bud cannot possibly take place. It is, however, accomplished — as in the case of the hazel — by the staminiferous catkins not only being in great number, but by the fact that each flower produces more stamens than the pistilliferous catkins, which are comparatively few in number. By this means the stigma runs every chance, amid the cloud of pollen discharged by the slightest breath of wind, of getting fertilised. In the Euphorbias a single female flower is enclosed in a common envelope of involucral glands, along with a large number of male flowers — the flower being thus, though structurally uni- sexual, physiologically bisexual. In both the common winter- flowering species {E. peplus and E. helioscopia), the pistil makes its appearance above the involucral glands considerably earlier than the bulk of the stamens (fig. 303). "A single one, howeverj Fig. 303. — Euphorbia Jielioscopia, L. i, Head of flowers opened, pistil and single stamen appearing above the involucral glands ; 2, The same somewhat later, with the stigmas turned upwards (after Bennett). of these latter organs, was observed to protrude beyond the glands simultaneously, or nearly so, with the pistil, and to discharge its pollen freely on the stigmas, thus illustrating a kind of $^7^^zj2- fer- tilisation. The remaining stamens do not discharge their pollen till a considerably later period, after the capsule belonging to the same set has attained a considerable size. In E. helioscopia the capsules are always included within the cup-shaped bracts, and the stigmas are turned up at the extremity, so as to receive the pollen freely from their own stamens." In the spring and summer flowering species, on the contrary, there is an arrangement for cross-fertilisation. It thus appears, from these interesting obser- vations of Mr Bennett, which we have considered worthy of some space, even in the limited range of a text-book, that winter- flowering plants are self-fertilised in the bud ; but that species FERTILISATION OF WATER-PLANTS. 459 which are properly summer - flowering, and only straggle into blossom in winter, have no such provision, but are either fertil- ised in the ordinary way or by means of insects. CLEISTOGENOUS FLOWERS. I This term has been given to inconspicuous self-fertilised flowers, very different from the large and conspicuously - coloured ones found on the same plant in various species of Impatiens (/. noli- , 7?ie-tangere, I.fjilva, 3Sid I. parviflord). The two kinds of flowers are probably different in structure from the beginning, and the development of the two is entirely different. Self-fertilisation takes place in these " cleistogenous " flowers at a very early period, fruitful capsules appearing almost invariably to result from them ; while in a vast majority of cases the conspicuous flov^ers are barren. If they are not barren, then the capsules contain the same average number of seeds as do those produced from the "cleistogenous" flowers. How these conspicuous flowers are fertilised is not known. As their structure appears to render self-fertilisation absolutely impossible, it is probable that this is ' accomplished by the wind or by insects, though there seems little to attract insects, and none have as yet been seen to visit these flowers. As Mr A. W. Bennett has remarked, it would, however, be strange if so handsome and complex a flower has been con- structed without any benefit thereby resulting to the species.^ 1 FERTILISATION OF WATER-PLANTS. A well-known dioecious plant is Vallistieria spiralis, L., which, in many European canals, ditches, and lakes, grows in such abundance as seriously to impede navigation. It is one of Delpino's hydrophileoiis plants (p. 455). The male flowers are "very small, and united, in a little spadix, shortly pedunculated, which is embraced by a spathe of two valves." The female flowers are, on the contrary, much larger, and at the end of a long peduncle, which is capable of elongating still further to enable the flower to reach and float on the surface of the water, , ! 1 For a full account of the structure and physiology of these cleistogenous | flowers in one of the British species (/. fulva), the student is referred to an ex- haustive paper by Mr Bennett in the Journ. of Linn. Soc. Bot., xiii. (1872) ' 147, t. 3 : and for general details, to Mohl in Bot. Zeit., 1863 ; Gray's Genera i Florae Am. bor-orien talis ; and Seemann's Journal of Botany, i. 147 ("Dimor- phism in the Genitalia of Flowers ") ; Weddel in Jussieu's Monographic des Malpighiacdes {teste Bennett), &c. 46o FERTILISATION OF WATER-PLANTS: PARTHENOGENESIS. Shortly before the period of fecundation the male flowers detach themselves, and reaching the surface of the water, there perfect the development of their pollen, and float about until they reach the female ones. Fertilisation accomplished, the spiral peduncle of the female flower again contracts, and draws the fecundated plant to the bottom, where it matures its fruit and seeds. Lagaro- siphon 7miscoides, an African plant, is fertilised in a very similar manner. Submerged water-plants, though developing their flowers and fruit beneath the water, invariably rise to the surface to per- form the act of fecundation. In Aldrovandra vesiculosa and the "•N^X-tx-soXCii^r {Stratiotes aloides\ for instance, the vesicular leaves, full of air-cavities, perform this buoying-up function. In Ranun- cuhis aquatilis and Alis7na 7iatans the perianth becomes vesicular at the season of reproduction. In Trapa natatts it is the petiole which becomes vesicular (p. 159); and in Utricularia, special buoys in the shape of little ascidia or bladders perform this good office (p. 158). In Zostera, or sea-grass (p. 346), the herbaceous spathe which encloses the flowers gets filled with air ; while in Nymphcea, and other water-lilies, the peduncle which bears the flowers lengthens in proportion to the depth of water, in order to bring the flowers to the surface to fecundate. PARTHENOGENESIS. Th. von Siebold described certain insects belonging to the genus Aphis, which he affirmed could produce fertile eggs for several generations, without there being in each case direct generation, and to this phenomenon he applied the name Par- thenoge7iesis ^ — a term which some botanists have retained to describe the production of seed without the fecundation of the ovule, which they affirm occurs in certain plants, notwithstand- ing the mass of facts which seem to prove incontestably the sexuality of plants. As early as last centuiy, Spallanzani was led to believe that hemp, spinach, &c., could produce seeds without fecundation by the male plant ; and since then various observers, among others Fresenius, Franz Bauer, Marti, Serafiiio, Volta, Girou de Buzareingnes, Ramisch, Bernhardi, Tenori, and more lately Liebmann, Gasparrini, Lecoq, Klotzch, Thuret, and Naudin, have hazarded their opinion of this existing in some unisex- ual plants. However, none of the plants which they described as showing this phenomenon — hemp, spinach — would bear strict investigation,^ until, in 1829, Allan Cunningham sent to the Kew Gardens, from Australia, a euphorbiaceous plant — Coelebogymc 1 7rap0eVo5, virgin ; and yeVeo-is, generation. 2 John Smith, Linn. Trans., xviii. 510. PARTHENOGENESIS. 46 1 ilicifolia — which for long was thought to show true Parthenogene- sis. It produced female flowers which matured true seed, from which were raised other plants sent to the various botanic gardens of Europe, and these in their turn produced female flowers, no male plants being in Europe — nor could the slightest trace of sta- mens be detected.^ Braun, Radlkofer, Schenk, and Kegel, how- ever, from their studies of the plant, began to doubt the existence of true Parthenogenesis in Ccelebogy7ie, until, in 1857, Baillon announced that he had found in the plant in the Paris garden a stamen at the base of the pistil, which assertion was formally de- nied by Decaisne, who affirmed that Baillon had mistaken for a stamen a glanduliferous bract. Finally, in i860, Karsten settled the dispute by affirming that after studying the plant for two years in the Berlin Botanic Garden, he had come to the conclusion that the fifth flower on the plant was hermaphrodite ; that there had existed on that plant two hermaphrodite flowers during the course of the summer, from the beginning of May to the end of August,^ each containing a single stamen placed at the peripheral part of the flower, and containing a spherical pollen. Thus, in the present state of our knowledge, there is little or no ground for believing that any plant exists which can produce true seed susceptible of germi- nation without fecundation — unless, indeed, the fig be taken as an example, Gasparrini having asserted that figs developed in sum- mer never contain male flowers, but nevertheless produce seeds which contain an embryo.^ Might they not be fertilised by means of insects or otherwise ? Yet this careful observer considered that he had taken proper precautions against this method of fertilisation. It may also be noted, that still more recently — viz., in 1863 — the late Dr Thomas Anderson stated* that he observed in the Botanic Gardens of Calcutta a plant of Aberia cafra with pistillate flowers, in none of which could he, after two years' observation, discover a single stamen. Nevertheless the tree fruited, and the seeds pro- duced vigorous plants. Still, as this tree might be visited by insects laden with the pollen, if not of this species, yet of others closely allied, the mere facts quoted, especially in the present state of our knowledge of hybridisation, are not sufficient to cause us to throw aside the vast accumulation of proofs in favour of the sexuality of plants, or even to affirm — sub judice lis est.^ ^ As shown by Achille Richard, Desfontaines, and even by Marti and Volta. 2 Ann. des Sciences Nat., i860, xiii. 254-287. Ibid., sesdr., v. 206, 365; also Radlkofer on Parthenogenesis, Ann, Nat. Hist., 1857; Regel, ibid., 3d ser., iii. 100; &c. * Journ. Linn. Soc, vii. 67. 5 For further information, see Bemhardi, in Otto and Dietrich's Allgemeine Garten Zeitung, 1839; Ann. des Sc. Nat., ser. ae, xii., s^r. 40, i. ; Annals of Nat. Hist., vii. ; and Liebmann Proc. Linn. Soc, 1850. 462 SUMMARY OF MODES OF FERTILISATION. SUMMARY, The following table exhibits a classification of plants according to their method of fertilisation : — I. HoMOGAMOUS Plants = Synacmic (Bennett) plants, in which the stamens and pistils are ripe about the same time. Homogam- ous plants may be — 1. Hermaphrodite, when the stamens and pistils are on one flower and ripe at the same time, when the fertilisation is ortho- gainic (p. 281). 2. Monoecious,! when the stamens and pistils are on separate flowers, but one plant (p. 281). 3. Dioecious, when the stamens and pistils are on separate flowers on separate plants (p. 282). 4. Polygamous, when the plant has mixed flowers (p. 282), II. Heterogamous Plants^ = Heteracmic (Bennett, /ar/m), comprising all methods not homogamous. It may comprise — 1. Dichogamous Plants, in which the stigma is not ripe at the same time as the anther is. These, again, may be — (a) Protandrous = Dichogamia androgyna (Sprengel), in which the anthers are ripe before the stigma (p. 433). (S) Protogynous=Y)\z\\o%zx?^\?L gynandra (Sprengel), in which the stigma is ripe before the anther (p. 433). These two methods Mr Bennett has comprised under the term Heteracmic. A Dicho- gamous plant may be monoecious, dioecious, or polygamous. A hermaphrodite plant is frequently so also. 2. Dimorphic Plants, when two of the stamens are long and • two short (p. 428). 3. Trimorphic Plants, when the stamens are of three different lengths (p. 428). 4. Cleistogenous Plants, in which the inconspicuous flowers are self-fertilised in an early stage, and are markedly different from the conspicuously-coloured ones found on the same plant (p. 459). Finally, there may be added to all these — 5. Parthenogenetic Plants, in which it is said that seeds can be produced without the application of the pollen (p. 460). As a rule, monoecious and dioecious flowers are not homogamous, but it is not impossible for them to be so. More usually, however, they are heteracmic. ^ Unfortunately, the term is applied by Maxwell Masters (Veg. Terat., p. 190) in a different sense — viz., to any cases in which the reproductive organs . have a different arrangement from the habitual one. SUMMARY OF MODES OF FERTILISATION. In whatever way impregnated — orthogamically or heterogami- cally — the end is simply the production of the fruit and its con- tained seeds. To this end is the life of the plant directed. It is the alpha and omega of purely vegetable existence. All the other functions and organs only tend to the production of the seed, and the reproduction and continuation of the individual and the species. Our next studies must therefore be directed to the consideration of the product of the fertilised ovules, — treating previously, how- ever, of the ve'ssel in which they are contained — viz., the ripe ovary or base of the pistil, which now takes the name of the Fruit. 464 CHAPTER X. THE FRUIT. As " all roads lead to Rome : " so no matter how the ovules are fertilised — whether orthogamically or heterogamically — the result is the same, — viz., the pistil swells and increases in size, and be- comes the fruit J while the ovules in like manner grow and be- come the seed. To the latter organs the next chapter will be devoted. In the present one, we propose considering the mature pistil or fruit, its general character, structure, and different forms. GENERAL REMARKS. An exception to the general rule that the fruit is not matured until after the fertilisation of the ovules, is afforded by the Corinth grape (from which currants are made) and the St Michael orange : hence these fruits are almost seedless ; or in other words, the seeds are in the form of ovules, if the oranges are taken before the latter are mature. The fruit, then, in the language of the botanist, is simply the matured pistil, or the seed-vessel and the seed — though, for the sake of convenience, we will consider the seed-vessel as the fruit, and so describe it under that head. In botanical language, a fruit need not be edible so long as it is the matured pis- til. In some cases it is hard- ly recognisable in the popu- lar eye as such. An exception to the almost universal rule that the fruit matures itself in the air, is afforded by the ground-nut {Arachis hypoged) and Trifolhim sub- terrajtenm, both of which, after fertilisation, bury themselves in the Fig. 304. — btraw- berrj'. showing the lit- tle fruits on the swol- len peduncle, and the persistent calyx. Fig. 305. — Straw- berry, cut longitudin- ally. FRUIT : GENERAL REMARKS. ground ; and if anything intervenes to prevent this, tlie fruit does not mature, but withers away and dies. Like the pistil, of which it is simply an enlarged edition, the fruit may consist of one carpel or of several, or of several carpels all coalesced, or of several carpels separated one from another ; in other words, it may be syncarpous or apocarpous. The number of carpels entering into the composition of the fruit may be de- tected by the number of stigmas on the top : if there is only one, then only one carpel enters into the composition of the fruit ; if more than two, three or a greater number make it up. There are various forms of fruit, popularly so called, which pro- perly have no correct claim to that distinction, or which do not come within the definition of the fruit which we have given. In the rose, for instance, the fruits are the seed-like bodies (achenes) concealed within the "hip " ^ (figs. 157, 158, p. 302). In the apple and pear the carpels are entirely within the edible portion of the fruit, which is a much swollen calyx and peduncle combined — the remains of the calyx being on the top of the fruit so called. In a strawberry, the fruits are the little seed- like bodies lying on the top of a swollen juicy peduncle, which is the real edible portion. Each of these carpels is surmounted by a style, even when the strawberry is ripe. Among other forms of true fruits are the cherry and peach, in which the middle portion of the seed-vessel (pericarp) is pulpy and fleshy, while the third or innermost is hard and woody — this "stone" enclosing the true seed within it. In the raspberry and bramble (fig. 306) we see a collection of little stone fruits all arranged on a raised receptacle ; while in the gooseberry and grape we see another form in which the pericarp is fleshy, and the seeds are embedded in a pulpy mass. We mention these examples to show the varieties which the fruits assume. These and numerous other forms will be again spoken of when we describe the various kinds of fruits in a systematic manner. Fig. 306. — Ripe Bram- ble (Rubits fnccticosns, L.), showing stone fruits on a common receptacle, and the persistent calyx (s). Each carpel is sur- mounted with the re- mains of the style. PARTS OF THE FLOWER ADHERENT TO THE FRUIT. The seed-vessel, which constitutes the bulk of the fruit, is called pericarp;^ and being only the matured pistil, ought to have he same structure as that organ. In general it has, but still there is usually some change which compels us to describe it 1 The so-called cynarrhodum or cynarrhodon. ^ n.p., around ; Kap^o,, fruit. 2 G 466 PARTS OF THE FLOWER ADHERENT TO THE FRUIT, separately. In Gyinnosperms (Conifers, Cycads) there is no peri- carp, while in all Angiosperms there is. After the ovules have been fertilised, the life of the plant becomes concentrated in them and in the fruit generally, and the style and stigmas soon fade and die. In some plants they remain attached to the fruit in a shrivelled condition ; while in other cases they not only remain fleshy, but even take a new development, and become a marked addition to certain fruits^ — e.g., Geitm jcrbafium, anemones, and Clematis (fig. 308), in which each fruit or carpel is terminated Fig. 307. — Thorn-apple [Datura Stramo7iiic7>{). a Plant showing leaves, flower, and fruit ; b Transverse section of the fruit, and c, longitudinal section of the same, both showing the frill-like remains of the persistent calyx. by a long feathery appendage, which is simply a special develop- ment of the persistent style (p. 359). The calyx is the most general of all the floral verticils, but it does not often take any marked development, though, as in the strawberry (figs. 304, 305), Geum, or in the thorn-apple, where it partially persists, like a ruff or frill, under the fruit (fig. 307, and fig. 244, p. 353). In the apple, the greater part of the fleshy or edible portion must be looked upon as due to an increase of the tube of the calyx, which, in this case, has become fleshy (fig. 309). In the mulberry {Morus), the calyx gets united with each of the little fruits forming a part of it ; while in the bramble (fig. 306), the calyx remains perfectly distinct from the fruit, which is there- fore only like that of the mulberry in general appearance. In Gatiltheria the calyx becomes to all appearance a part of the fruit (p. 301) ; the real fruit is, however, a dry pod within. In Blittnn (the " strawbeny blite ") — a member of the order Cheno- b a c PARTS OF THE FLOWER ADHERENT TO THE FRUIT. 467 podiaccce the fleshy calyces of a head of flowers, " each surround a small seed-like fruit, and together form a false multiple fruit, Fig. 308. — Clematis erecta, L. Group of fruits with the terminal appendix, consisting of a development of the persistent style (nat. size). resembling a strawberry ; " while the indtivhmi of the winter cherry (p. 302), though seemingly a pericarp, is simply a fleshy _ Fig. 310. — Longitudinal section of Fig. 309.— Longitudinal section of an Apple, the T\%, {Fiats carica], showing the showing the persistent calyx, more or less dried fruits enclosed by the fleshy concep- up (i), its peduncle {pd). and one of the seeds tacle, which is only an enlargement of or 'pips m position {^). the peduncle calyx. Finally, in Mirabilis the calyx remains around the fruit in the form of a dry envelope. 468 PARTS EXTERIOR TO THE FRUIT SIMULATING THE FRUIT. Parts exterior to the fruit simulating the fruit. — In the fig, the peduncle swells up and surrounds the seed - like fruits inside, leaving only a hole exteriorly (fig. 310, and fig. 283, p. 297). In the Anacardiaceae — for example, Anacardium occidentale and Semecarpns Anacardium — the " fruits," which are valued for their pleasant acidulous flavour, are only the swollen peduncles. In Hovetiia dulcis, one of the finest of Japanese fruits, the edible portion is also the swollen peduncle. In the wig-tree {Rhus cotim(s) — so called from its hairy pedun- cles— some of the peduncles are simple and bear fruit, while others branch much and are ster- ile (fig. 142, p. 284). In the pine- apple (Anassa sativa, Lindl.) the edible fruit is of a very complex character. It is a "reunion of a great number of fruits properly so called, or pericarps, in which the seeds are abortive — conjoin- ed with the bracts of the flowers which are found interspersed in the flower to the number of one median and two lateral ones for each — and which thus become succulent" (fig. 311). These preliminaries are neces- sary to a right understanding of the structure of a typical fruit, in which the pericarp, or matur- ed wall of the ovary which en- closes the seed, is composed of three layers. Previously, how- ever, to describing this, it may be well to consider what changes P'ig.311.— Pine -apple {Aiiassa sativa, the fruit has undergone from ''"'"'^'■^ the time we last studied it as the pistil — in a word, the processes undergone in ripening. RIPENING OF THE FRUIT.^ The ovary, during the process of maturation, which ends in its being transformed into the fruit, becomes in general sappier 1 Duchairtre, Elements de botanique, p. 647 ; Lindley, Elements, vol. ii. ; Couverchel, Ann. de Chimie et de Physique, xlvi. 147 ; Fremy, Comptes ren- dus, vol. xix., 1784; Ann. de Chim. et de Phys., sdr. 3, xxiv. ; Journ. de Chim. Med., 1845, p. 132. RIPENING OF THE FRUIT, 469 and more swollen out, and the materials in the cells become considerably enlarged. In some cases, like that of the pod of the pea, the pericarp remains more or less crustaceous in texture, or becomes thin, dry, and membranous, like the Bladder senna pod (fig. 321). In such cases the pericarp is furnished with sto- mata, has chlorophyll in its cells, and in other respects acts like an ordinary leaf. In other cases we have seen the pericarp thicken (as in the gooseberry, date, &c.), or become hard and dry like a nut. In the case of the cherry, plum, peach, &c., the outer layers of the pericarp remain soft and pulpy, while the inner one (endocarp) hardens, and forms the putamen or "stone," character- istic of "stone-fruits." During maturation the fruits not only modify their texture, but also undergo certain other changes, which we may sum up in a few words. Changes in the Tissues. — As far as the changes of the tissues are concerned, the chief modification is the multiplication of the cells of the mesocarp, or other portion, which become thickened, so as to form the pulp ; while the fibro-vascular bundles become attenuated, modified, and finally almost undistinguishable as such in the midst of the pulp. On the other hand, a contrary course of development takes place in certain cells of the pulp, which become quite hard, as is familiarly seen in the gritty particles scattered through the fleshy portions of many varieties of pears. An analo- gous development of hard matter results in the stone of certain fruits. Changes in Substance. — The change in the substance consists chiefly in the contents of the cells undergoing certain chemical changes, the general result of which is, that the amount of sugar contained in them becomes greater, while the acids, starch, and tannin proportionally diminish. The fruit, while still green, it may be remarked, decomposes COg and emits O, like the leaves ; but when it ripens, this chemical action on the atmosphere alters. In other words, COg is given out, accompanied by a sensible rise of the temperature, while O is absorbed. Fruits are taste- less or slightly bitter at an early age, when, both in structure, chemical composition, and action on the atmosphere, they are almost identical with leaves. They are afterwards sour, from the production within their cells of acids, the chief of which are tartaric acid (as in grapes), citric (lemons, oranges, cranberry), malic (in apples, gooseberries, &c.) At this period they exhale little oxy- gen; it is even said that they inhale a little of this gas. Subse- quently a slow oxidation takes place : tannin first, and afterwards vegetable acids disappear ; while sugar becomes notably increased as the ripening goes on ; and the fibrous and cellular tissues also diminish as the sugar increases, the latter substance being partly 47° CHANGES IN GREEN FRUIT WHEN COOKED. produced at the expense of the former. This is proved by the fol- lowing table, from analyses by Bdrard, of the amount of lignine found in one hundred parts of the fruit during the green and ripe states : — Green. Ripe. Apricots, . . . . .3.61 1.86 Currants (including the seeds), . . 8.45 8.01 Duke Cherries, .... 2.44 1.12 Green-Gage Plums, . . . 1.26 i.n Melting Peaches, .... 3.01 1.21 Jargonelle Pears, . . . .3.08 2.19 Yet Buignet is in doubt whether this table of B^rard supports this view, and is of belief that the sugar is not derived from the starch, which he declares is not found in the green fruit, except in bananas, but from an astringent substance, " which forms a colourless combination with iodine." Be this as it may (and we are by no means sure of the soundness of M. Buignet's view), it is still open to doubt whether the lignine of the green fruit in reality decreases as it ripens, or whether the dilatation of the cellular tissue, and the consequent augmentation of the aqueous products, render it proportionally less without being absolutely so (Bdrard). But it was found by Couverchel that the gummy, mucilaginous, and gelatinous matters are capable of being changed into sugar. Thus, if apple-jelly is treated with a vegetable acid and dissolved in water, a sugar analogous to grape- sugar is obtained. Variations. — There are, however, some remarkable disparities in this respect. Thus, in apricots and pears, malic acid keeps diminishing while their fruits ripen ; while in currants, cherries, plums, and peaches, that acid augments during the same period. In currants, cherries, plums, and pears, gum keeps diminishing ; while in apricots and peaches it augments, and so on. Changes in Green Fruits when Cooked. — When green fruits are cooked, a change somewhat similar to what we have men- tioned takes place in the fruit by the chemical elements, particu- larly the acids and mucilaginous products, reacting one on another, and by the aid of heat being converted into sugar. Along with sugar is also produced vegetable jelly or amyloid (of which bassorin, salep, and pectine are apparently modifica- tions), which in its characters is intermediate between starch, dex- trine, and cellulose, and " has nearly the properties of starch when this has been altered by hot water," When dry it is horny or cartilaginous ; but when moist it swells up, becomes gelatinous, and is capable of being perfectly diffused in cold water. In the tubers of orchids, and in the almond, bean, and other esculent PRODUCTION OF SUGAR : CLETTING TO ROTTING. 47 1 i seeds, it abounds. In some fruits, oils (volatile or thick) accu- mulate during the process of ripening. The sugar produced is sometimes liquid, or in other cases partly concrete, as in the grape, fig, and peach. Production of Sugar during Ripening.— To sum up, we may therefore say, in general terms, that the increase of sugar keeps pace with the ripening of the fruit. The following table, also compiled by Bdrard,^ shows this more graphically than the mere statement of the fact would do : — Green. Ripe. Apricots (a trace when young, afterwards), 6.64 16.48 Red Currants, .... 0.52 6.24 Duke Cherries, .... I. 12 18.12 Green-Gage Plums, 17.71 24.81 Melting Peaches, .... 0.63 II. 61 Jargonelle Pears, . . . . 6-45 11.52 The observations of Frehling upon grapes brings out the same fact. On the 29th August they yielded to analysis 5.4 per cent of sugar, and 3.1 of acids; on the nth September there was present 10.3 per cent of sugar, and 1.6 of acids ; while on the 7th October, when the grapes were ripe, they contained 12.6 of sugar, with 1.20 only of acid, the density of the juice being at these three periods respectively, 46°, 59°, and 66° of the areometer. According to Fremy, pears and apples contain, before being ripe, pectose, which in the course of ripening, by the action of the citric and malic acids, is changed into pectine. When the fruit passes maturity, this pectine passes completely into the state of metapectine. On the other hand, unripe fruits contain at the same time with pectine a ferment, " pectose," susceptible of act- ing on the pectine. It is under the action of this ferment that this last-named substance turns into pectannic acid, and at a later period into pectinic acid. The acids in their turn act on the starch, so as to transform it into sugar. When succulent fruits are ripe, the sugar in its turn is oxidised, and then a series of changes occur which finally culminate in the rottiiig of the fruits. Changes from Bletting to Rotting.— The first change after the sugar in the ripe fruit has commenced to oxidate is called " blet- ting." 2 It is, in fact, the intermediate stage between maturity and decay. The fruit, just before bletting sets in, is full of the mate- rials we have already mentioned, and the plant is in a weak con- dition ; for all we have said regarding the exhaustion of the plant 1 Mdm. sur la Maturation des P'ruits, Ann. de Chim. et de Physique, s^r. 2. XVI. 152, 225 ; teste Lindley, 1. c., 256. 2 A convenient word Anglicised by Lindley from the French blessd—VL word signifymg that pecuHar bruised appearance we see in some fruits. 472 BLETTING : ROTTING. by flowering is true of fruiting in even a iiigher degree. Tlie water, too, has climinislied after the fruit is ripe, on account of the fruit absorbing less and less as it approaches maturity ; and by the action of endosmose and e.xosmose the cell-contents are now of a tolerably uniform consistency throughout. De Candolle's descrip- tion of this process is so clear that I will quote it in full: "After the period which is generally called that of ripeness, most fleshy fruits undergo a new kind of alteration — their flesh either rots or blets. These two states of decomposition cannot, according to Bdrard, take place except by the action of the oxygen of the air, although he admits that a very small quantity is sufficient to cause it. He succeeded in preserving for several months, with little alteration, the fleshy fruits which were the subject of the foregoing experiments (apricots, currants, cherries, green-gages, peaches, pears), by placing them in hydrogen or nitrogen gases. All fruits at this extreme period of their duration, whether they decay or whether they blet, form COg with their own carbon and the oxygen of the air, and moreover disengage from their proper sub- stance a certain quantity of COg. Bletting is, in particular, a special alteration. This condition is not well characterised in any other fruits than those of Ebenaceae (Ebony order, to which belong the Diospyros or 'persimmon' of the Southern United States) and the Pomaceas (or apple order). Both these natural orders agree in having the calyx adherent to the ovary, and in their fruits being austerely sour before ripening. It would even seem, from the fruits of the persimmon, the sorb, and the medlar, that the more austere a fruit is, the more it is capable of bletting reg- ularly. It has been found that a Jargonelle f)ear in passing to this state, loses a great deal of water (83.88 reduced to 62.73), ^ good deal of sugar (11.52 reduced to 8.77), and a little lignine (2.19 reduced to 1.85), but acquires rather more malic acid and animal matter. Lignine, in particular, seems in this kind of alteration to undergo a change analogous to that of wood in decay." The practical deduction from all this is, that if certain of the fruits named be kept in close vessels free of oxygen, they will preserve for a much longer period than they would otherwise do. Acidity may be corrected by exposure to light and air (as seen in cider-apples, which are sour until crushed and exposed to the air), and excessive sweetness or insipidity by diminution of light. In selecting wild fruits for cultivation, sour varieties should be selected, as it is the propensity of cultivation to develop sugar ; and to render fruits at all well flavoured, a certain amount of acid requires to be present in the fruit. Rotting is simply putrefaction — and putrefaction, M. Pasteur shows, commences by fermentation, this fermentation being in most cases produced by the germs of other plants. He comes to RIPENING : STRUCTURE OF THE PERICARP. 473 the conclusion that " there are two orders of life, one of which requires pure oxygen for its sustenance, while the other is killed by- it. Apples, pears, cherries, gooseberries, currants, and the like, continue to' live after being taken from the tree. As shown by Bellamy and Lechartier, they absorb and exhale CO2, and ripen. Being prevented from absorbing oxygen, these- fruits begin to assimilate oxygen from their own tissues, an alcoholic fermenta- tion commences, and the fruit becomes soft and pulpy." Such, at least, are the views of this eminent French chemist.^ The Period required for the Ripening of the Fruit varies from a few days (as in the case of grasses, Setaria viridis, fescue- grass, Briza media, Avena p-atense, Aira ccespitosa, &c., re- quiring from 13 to 17 days; while Holais lanatus, Elymus are- naruis (bent), and Holcus odoratiis, require from 40 to 57 days) to a year or more (as in the case of Coniferae). Most of our fruits require from 3 to 6 months, while the mistletoe takes 9 months to mature. STRUCTURE OF THE PERICARP, The pericarp is formed by the walls of the ovary, and most fre- quently determines the form of the fruit. Though greatly varying in size and thickness, the pericarp is present in all fruit, except those of gymnosperms, already mentioned. It varies in size, from a line to 2 or 3 feet, and is of all consistencies — fleshy, woody, horny, &c. When the fruit is composed of one carpel only, then, as a rule, the pericarp is very thin and closely adherent to the seed, so as to seem absent, or to cause the fruit to look like a seed. It was these kind of fruits, such as are found in Cyperaceae (sedges) and Compositae (fig. 1 56, p. 300), that the older botanists used to style, most erroneously, " naked seeds." Naked seeds, properly so called, are only found in Coniferae and Cycads. The base of a fruit is the point where it is united to the pedun- cle ; while its apex or " organic summit" is the point where the style or stigma often remains persistent. If these are present they point out the summit of the fruit. In Helleboraceas, Cruciferse, poppies, &c., we see the style or stigma thus remaining. Hence, in those fruits where the style grows from the side, as in Labiatae, Boraginaces, Rosaceae, the organic and apparent summits are not the same. The structure of the pericarp, owing to the fact that it is a modified pistil, must be very much the same as that of a leaf, the pistil being only a metamorphosed leaf (p. 368). Ac- ^ Pasteur, Comptes rendus, 1872; Trans. Quart. Journ. Mic. Sc., new- series, xiii. 351 ; and for a summary of the same views, see Wyville Thomson, Trans. Bot. Soc. Edin., 1872. 474 STRUCTURE OF THE PERICARP. cordingly, like a leaf, we find the pericarp composed of three layers. 1. The oictside layer or epicarp, corresponding to the upper epidermis. 2. Iftside layer or endocarp, corresponding to the inferior epi- dermis of the leaf; and 3. Middle or parenchymatous layer, which corresponds to the middle parenchyma or mesophyle of the leaf. (1.) Epicarp.' — This is a simple membrane, sometimes thin, at other times rather thick. It is easily torn off, as in the peach, cherry, or prune. In an inferior ovaried fruit, where it is adherent to the calyx, the epicarp is formed at once by the calyx and by the epidermis of the ovary fused into one membrane — e. g., gooseberry, pomegran- ate, &c. (2.) Endocarp.— This is the membrane which lines the cavity of each carpel when ripened into a fruit. It re- presents the epidermis or up- per surface of the carpellary membranous. Sometimes, as Fig. 312. — Longitudinal section of a Peach, (or the fruit of Amygdabis Persicci, L.) ^pc Epicarp ; me Mesocarp ; end Endocarp or stone, in the cavity of which is (g) the seed ; fn Funiculus or cord by which the seed is attached {}A nat. size). leaf. It is generally very thin and in the pea, it takes the consistence of parchment ; or it may become fused more or less with the nearest portion of the mesocarp, and become thickened ; or even acquire a woody consistence, and become the stone or ptctamen, as in a peach, cherry, or prune (figs. 312, 313). (3.) Mesocarp. — This comprises all the vascular or parenchy- matous parts contained between the two membranes of the peri- carp. It is extremely well developed in fleshy fruits,^ constituting the edible portion or pulp, as in the peach, melon, &c. However, it is sometimes excessively thin, as in dry fruits, shell of the pea, wallflower, &c. But whether thick or thin it is always present, and the structure of the pericarp is the same. There thus enter into the structure of the pericarp two mem- branes (the epicarp and endocarp) and a vasculocellar structure (the mesocarp). Pulpy fruits are no doubt, in the vast majority of cases, formed by the mesocarp. But this, we have seen, is not always so. In some cases (p. 49) the pulpy portion is formed by the calyx, either conjoined with the ovary or alone, as in the mul- 1 Hence Richard calls it the Saicocarp. LOCULAMENTS AND DISSEPIMENTS. 475 berry, roses, apple, and pine-apple. In other cases, in the juniper and yew, the scales become fleshy, and cover the seed in a more or less complete manner. This does not, however, constitute a true pericarp, which is the walls of the ovary, and is wanting in these g>-mnospermous plants. Lastly, the succulent portion of the strawberry, fig, &c., was supplied by the peduncle. In the almond (fig. 313) we find a downy epicarp {a) ; a meso- ^"ig. 313. — Fruit of Almond »y^^fa/?«j connnimis, L.) A, Entire fruit. B, Longi- tudinal section : a Epicarp ; Mesocarp ; b Stone or putameti (endocarp) ; g Seed ; f}i Funiculus. carp thin but firm, and almost coriaceous ; and all the remainder of the total thickness is made up of a thick stone or putamen {b\ which is spongy in its middle portion. The mesocarp detaches itself from the stony endocarp at the period of maturity. The difference between the fruits of the peach and the almond, ana- tomically, is this, that in the one (peach) the mesocarp is fleshy, while in the other (almond) it is not. Yet this is but an unimport- ant difference ; for in the variety of the almond called the Peach- almond {Amygdalus communis, L., var. persicoides), the stone is covered by a pulpy flesh which is edible (Duchartre). Loculaments or Cells and Dissepiments. — What we have already said on this subject in reference to the ovary (p. 352), to a great extent holds true in regard to the fruit. If the fruit is si7n- ple — /. e., of one carpel — it will consist of a single loculament, or be what, in descriptive language, is called unilocular.^ However, as in the case of the ovary, the fruit may consist of several locula- ments. Thus, that of the tobacco is bilocularj that of the flax A B 476 LOCULAMENTS. guadrtlocular ; and so on— the tern->. multilocjilarh^xw^ applied if there are more than four. Subdivision of Loculaments— \\. may, however, happen, that an ovary may be unilocular, while the fruit may have two or more loculaments, by the form of partitions during the sub- sequent growth of the ovary. Take, for instance, the horned poppy (fig. 314). The ovary of this plant is unilo- cular, showing two parietal placentas, distinct and separate as usual. How- ever, on making a section (fig. 314, B) on the long straight fruit (fig. 314, A), the result of an unusual increase in length of the ovary, we see that there has been produced between the two placentas a large spongy body, which unites them, and by the union divides the once unilocular ovary into a bilo- cular fruit. Duchartre points out the same peculiarity in several species of Personia (a genus of Proteaceee). In like manner, while in the plants com- prised in the tribe Hedysej-ecs, of the sub-order Papilionaceee, of the order Leguminosae, the ovary is unilocular, but by the bending in of the pericarp during the ripening process, the fruit is multilocular, each loculament con- taining one seed. Numerous similar instances might be quoted ; but, as the two last examples, we may point out that in Tribulus terrestris the ovary is composed of five loculaments, each of which in the fruit is subdivided into three or four little cavities, each con- taining a seed ; and that in the flax an ovary containing five loculaments has ten in the fruit, owing to the growth of false dissepiments in each, locula- ment. Obliteration of Loculaments. — On the other hand, the number of loculaments in a fruit is not the same as in the ovary, from quite an opposite cause — viz., that frequently the dissepiments disappear, and a multilocular ovary may become unilocular, or with Fig. 314. — Glauciwn httenvt. Scop. A, Entire fruit (nat. size). B, Transverse section of the same (mag. s times). , LOCULAMENTS : DEHISCENCE OF THE FRUIT. 477 a'smaller number of loculi than what the ovary possessed. In pinks and roses we often see this. It also affects the number of seeds contained in the fruit. Thus, in the olive order there are in the ovary two loculi, each containing two ovules ; while there is in the fruit only one loculament containing one seed. In the oak, in like manner, the ovary is 3-celled, with two ovules in each cell ; but the fruit is unilocular — the solitary loculament containing a solitary seed, owing to the non-development of two loculaments and five ovules. Exactly the same thing is seen in the hazel. In the cocoa-nut, again, a trilocular ovary becomes a unilocular fruit ; while the bilocular ovary of the beech and elm produces in both cases a single seed of unilocular fruit — one of the ovules being abortive, while the other enlarges, breaks down the dissepiment, and so in time obliterates the empty loculament. The dissepi- ments, as in the case of the ovary (p. 352), may be either true or false. The same terms are applied to the placentas in the fruit as in the ovary (p. 563). If the pericarp is simple, then the placenta occupies each of the borders of the carpellary leaf, where they unite in a line or suture, as in the case of the pod of the pea, fruit of hellebore, &c. ; hence such a placenta is called siihiral, and so on. The position of the placenta is often extremely useful in char- acterising natural orders. DEHISCENCE OF THE FRUIT. The fruit, when ripe, must allow the seed to escape in order to enter the ground and germinate. In most stone-fruits, berries, &c., the fruit does not open, the seed simply falling out after the pericarp has rotted ; while in the others the fruit opens in various ways when it is ripe. The opening of the fruit, to allow of the escape of the seed, is known as its Dehiscence. Fruits may therefore, in reference to this point, be divided into two great divisions, — the Dehiscent and the Indehiscetit — those which open and those which do not. Dry fruits which have a single locula- ment and a single grain are generally indehiscent, — such as, for ex- ample, the fruit of the wheat (the wheat grain), barley, rye, and all the other grasses ; the sedges, the Compositae, &c. : while the same is true of the fleshy and succulent fruits — such as apples, pears, oranges, peaches, &c. To put it in other words — in capsules and berries the seeds are disseminated ; in stone-fruits the stones contain the seeds ; in achenes, or fruits where the thin pericarp is closely adherent to the seed (as in the wheat grain), the fruit is disseminated as a whole ; while in a fourth case, the fruit breaks up into little pieces, each piece or coccus containing a seed, as in the Indian cress, Borage, Platystevion, &c. There are. 478 DEHISCENCE OF THE FRUIT. however, exceptions even to the rase of achenes being disseminated whole — for example, in Oxalis (sorrel), when, on dehiscence of the capsule, the elastic " testa " or " spermoderm " becomes ruptured, violently expelling the body of the seed with its covering (the "tegmen"). In the pomegranate, the fruits are swallowed by birds, and after digestion of the pulpy testa, the body of the seed, with the hard tegmen, is evacuated and disseminated. Or again, in such a drupe as an apple, where the induration of the endocarp is slight, we have the fruit behaving as a berry, dissemination tak- ing place by means of seeds.^ When dehiscence takes place, the fruit breaks up into several pieces, regularly round its axis, or columella, when this is present, generally by valves, which constitute the walls of the pericarp. If the fruit is simple, or of one piece, it presents on the outside certain sutural lines, which mark the point where the free "borders of each carpellary leaf unite. These lines are called ventral suttires, and each valve possesses one ; while on the back of the valve there is another line — the dorsal suture — which corresponds to the midrib of the carpellary leaf. In a pea-pod, for example, the two sutures are equally well seen — one on the back and another on the front. When many carpels are soldered together by the greater part of their lateral aspects, in order to form a composite fruit, then the ventral sutures are found united in the middle of the fruit, and we see externally only the dorsal ones. Hence most frequently the pericarp has double the number of sutures it has carpels, the valves by which it opens being equal to the number of carpels. Thus the pericarp of the tobacco-plant is composed of two carpels, and opens by two valves, or is bival- viclar. In the tulip it is trivalvular, or composed of three carpels, and opens by three valves ; that of the Epilobhnn is quadrivalvu- larj that of flax quinquevalvular, &c. In a unilocular fruit, made up of several carpels coalesced, the fruit dehisces by as many valves as there are carpels entering into its composition. Thus the fruit of the violet is unilocular, though made up of three car- pels, and accordingly it dehisces by three valves.^ Taking up, therefore, dehiscent fruits, we may recognise several methods of dehiscence, which we will now briefly describe. 1. Porous Dehiscence, in which the seeds are liberated through holes or pores, which open when the fruit is ripe, near the upper end of the fruit. Ex. Poppy (fig. 315). This, though a method of liberating the seeds, is altogether different from valvular dehiscence, which, we have seen, is connected with the loculaments, and accordingly directly with the seeds ; while this is simply rup- 1 Alex. Dickson, Nature, August 31, 1871, p. 348. 2 Richard, Nouveaux Elements, 272. DEHISCENCE OF THE FRUIT, 479 turing, by which, as also in mignonette, snapdragon, and Cam- panuiacece, a hole or holes are produced by the spontaneous ab- sorption of a portion of the pericarp. 2. Valvular Dehiscence, in which the pericarp opens by valves. There are various ways in which this is done — viz.: (a) Loculicidal, in which the valves open each along the line of its dorsal suture, and allow the seeds to escape. Ex. Iris, Fig. 315.— Fruit of the cul- Fig. 316. — Tulipa Ges- tivated Poppy {Palaver ori- neri, L. Fruit, /r, opening entale), with seeds («, b, nat. by loculicidal dehiscence, size and magnified) illustrat- allowing the seeds (^) to be ing porous dehiscence. seen. Hibiscus, evening primrose, and indeed most Monocotyledons, including the greater part of the Liliaceas, Juncaceas, Amarylli- daceae, many Dicotyledons, such as Polemonacese, &c. (fig. 316). ()3) Septicidal, in which the fruit opens at the line of junction of the carpels. Ex. Azaleas, Rhododendrons, St John's wort {Hy- pericuin), Menziesia, Colchicum, Verbascutn, Calceolaria, Scroph- zilaria, Sec. In some plants, such as chickweed. Lychnis, Cerastium, tobacco, pinks, and primroses, the pericarp only opens for a little way at the apex to allow the escape of the seeds. This variety of dehis- cence has been called apiciilar. In the sea-pink {Anneria), how- ever, we" see such a gradation from the apicular to the septicidal as to justify us in considering this apicular dehiscence only a form of the one under consideration. It has sometimes been called the denticidal, or tooth-like dehiscence, from the teeth-like tips of the valves which surround the opening. (y) Septifragal. — In this form of dehiscence the valves fall away. 48o DEHISCENCE OF THE FRUIT. leaving the dissepiments behind adliering to the axis. Ex. Fruits of the mahogany, and other Cedrelaceas, Hydrolea, Convolvulus, &c. It is much rarer than the other two methods of valvular dehiscence. 3. Circumcissal Dehiscence. — In the rib-grass {Plantago), pimpernel {Anagallis), Hibiscus, Lecythis, or monkey-pot, &c., the .seeds escape by the summit of the pericarp contracting in such a manner that it rises up in the form of a cap. Hence this is called transverse or circumcissal, and is remarkable, in so far that it has no connection with the line of union of the carpellary leaves (fig. 317). In the American genus Jeffersonia, the pericarp is only Fig. 317.— The Pimpernel (Anagallis arvensis, L.) A, Its entire fruit, /r, before dehiscence, and embraced by the persistent calyx, ^; a Transverse, along which the pericarp dehisces. B, The same fruit, opening or divided into two hemispheres, a and b, of which the first («) is raised up, allowing the seeds {g) to be seen (mag. twice nat. size). constricted half round, so that the summit is simply raised like the lid of a box, not lifted off, as is the usual way. The late Pro- fessor Hinks of Toronto considered that circumcissal dehiscence was due to the " force of cohesion of the parts of the circle, the absence of any of the causes favourable to dehiscence along the midrib of the carpellary leaf, and the operation of some force pres- sing either from without or from within on one particular line encircling the fruit." ^ Dehiscence of Unilocular Fruits. — Unilocular fruits, made up, nevertheless, of several carpels, may dehisce in the valvular man- ner exactly as if they were plurilocular. In some cases the septi- cidal dehiscence prevails, when the separate carpels of the unilo- cular pericarp open along the line where they meet or are attached to each other. In another form the loculicidal dehiscence is the rule, and the pericarp opens along the line of the dorsal suture of each valve, or carpellary leaf. In the pea, &c., the unicarpellary unilocular fruit, or pod, dehisces along the line of the ventral suture ; such a mode of dehiscence in a simple fruit, such as the pea, being called sutural. Elastic Dehiscence.' — Some fruits in opening scatter t.he seeds with great force, thus affording one of the numerous methods by 1 Annals of Nat. Hist., xvii. DEHISCENCE : CLASSIFICATION OF FRUITS. which seeds are dispersed abroad to find a congenial soil at a dis- tance from the parent plant, and thus better enable it to survive the " struggle for exist- ence." In the ordinary Balsamina hortensis and Lathraa Clandestma we see this elastic dehiscence. But the best known, and not the least remarkable instance of it, is afforded by the squirting cucum- ber {Ecbalium Elaterium), which yields the elaterium q( the 7naieria 7nedica. De- taching itself from its pe- duncle, the fruit suddenly contracts its walls, and forces out the seeds along with the liquid contents in the manner represented on fig. 318, and which peculi- arity has given it its popu- lar name. In the sandbox-tree, the " Savilla" of the Hispano- Americans of the Isthmus of Panama, where it is found {Htcra crepitans, L.), the fruit is composed of from twelve to eighteen carpels, partly coal- esced, and with woody walls. These cocci {as carpels incompletely united among themselves by their sides are called) separate when the fruit is ripe, and open, each into two valves, with such force and noise that it has been likened to an explosion (Duchartre). Accordingl}^ in collections, the fruits of this plant, in order to pre- vent their opening, are generally firmly tied round with string, or even with iron wire. Fig. 318. — Ecbalutin Elaterium, Rich. Flower- ing and fruiting branch (ci); b Fruit discharging its seeds. CLASSIFICATION OF FRUITS. The fruit being the mature pistil, will be as varied as the pistil itself; and accordingly, numerous names have been devised for these varied forms, by which the study of the fruit has hardly been simplified, but rather rendered such a chaotic mass of technical names, that Carpology has been dignified with the name of a science, — a science with all science left out — a field wherein the name-maker and the form-splitter have revelled, to the loss of 2 H 482 CLASSIFICATION OF FRUITS. Others who view botany from worthier stand-points. Linnaeus only used eight terms, which Gartner^ reduced to seven — adding, however, three secondary forms. Willdenow raised the number to seventeen, but defined them vaguely and inaccurately. Link, again, strove to reduce the number, and considered that eleven would have met the necessities of descriptive botany in his day. Richard proposed a somewhat more philosophical classification, though coining fresh names unknown to previous writers. Mir- bel and Desvaux equally strove at distinguishing themselves in the same field, but with limited success — unless, indeed, running up the number of separate forms, as in Desvaux's case, to forty- three, be looked upon as such. The same may be said of the classifications of Lestiboudois, De Candolle, and Durnortier.^ In- deed, the writers who have laboured in the fruitless field of fruit- classification are almost as numerous as the forms for which they have invented names. Again was the voluntary task essayed by Lindley in 1848, with a success sufficiently great to allow his classification to be retained by most writers up to this date. It was, however, cumbersome, and burdened with many unnecessary names. He divided fruits first into the class Apocarpi, which comprises the Utricuhis, Achejie, Drupe, Follicle, Legttme, and Lomentum; (2.) Aggregati, includ- ing the Etcerio, Syncarphnn, and Cynarrhodum j (3.) Syncarpi, including the Caryopsis, Carcerulus, Samara, Ainphisarca, Pyxi- diuin, Regma, Conceptacuhmi, Siliqua, Silicula, Cerathim, Capsu- la, Hesperidium, N7iaila7iiiim, Tryma, Cremocarp, Glans, Cypsela, Diplotegia, Pepo, Babesia, Bacca, and Pomumj (4.) Anthocarpi, or collective fruits, which embraced the Dicleshiin, Sphalerocarp- ium, Sy comes, Strobilus, and Sorosis. It was an improvement on some of its immediate predecessors ; but, on the other hand, un- necessary terms were introduced, and a number which (like the Tryma, Diplolegia, Amphisarca, &c.) it is utterly impossible to clearly define. Since Lindley's day, carpological classification has been tinkered at by a number of botanists more or less quali- fied for the task. Schacht and Sachs, among others, have pro- posed classifications ; and that of the former eminent botanist has Ijeen emended with considerable advantage by Professor Alex. Dickson of Glasgow.^ Most working botanists will, however, agree with Dr Maxwell Masters,* that much undeserved labour and refinement of nomenclature has been spent in trying to make a philosophical classification, and in devising terms which the exigencies of descriptive botany might require, but rarely or ever do. The truth is, that it is impossible to find a classification of \ De Fructibus et seminibus plantarum, 1788. Mem. de I'Acad. Roy. des Sc. de Bruxelles, vii. and ix. Nature, August 1871. * Ibid., Nov. 2, 1871. CLASSIFICATION OF FRUITS. 483 fruits which is founded on strictly scientific principles — the forms merging into each other ; and to multiply terms to the extent which has been done, is simply to render the acquisition of the knowledge of the few forms which the student requires to be acquainted with intensely repulsive and difficult. In reality, if we examine the writings of the best living descriptive botanists (not themselves the authors of fruit-classifications) — Hooker, Bentham, De Candolle, Oliver, Baker, and others — we will find that they use very few carpological terms, modifying those in use by various adjectives, and so serving — what is the end of all organographical nomenclature — the purposes of systematic description, without resorting to the use of terms difficult to define, and at best vaguely applied. Accordingly, in the following classification, in which we have mainly followed Dr Masters, all the less easily defined forms are omitted, and the list reduced as much as possible, without at all destroying its usefulness. It is far from faultless ; but we con- sider that its convenience and simplicity will atone for its " philo- sophical " imperfections. MONOTHALMIC^ FRUITS. A. Ripe pericarp uniform. Fruits indehiscent. — I. Nuts, or Achaenocarps — viz., Achene, Caryopsis, Carcernle, Glans, Samara, Nut. Fruits dehiscent. — II. Pods, or Regmacarps — viz., Follicle, Legume, Siliqua, Capsule, Pyxis. B. Ripe pericarp, easily distinguishable into two or more layers. Seeds within a hardened endocarp. — III. Stone-fruits, or Pyre- nocarps — viz., Drupe, Pome. Seeds embedded in pulp. — IV. Berries, or Sarcocarps— viz., Bacca, Hesperidium, Pepo. P0LYTHALMIC2 FRUITS. Fruits of several pistils on a common axis. — V. Cones, &c. — viz., Strobilus, Sorosis, Scyonus. I. (i.) Achene.^ — This is a dry, indehiscent, one-seeded, seed-like fruit, composed of a wingless solitary carpel, in which the pericarp 1 (xoros, one ; and floAofio?, bed : fruits formed from one pistil. iroXvs, several ; and floAo/ios : fruits formed from several pistils. ^ Achenium of authors ; Akena (Necker), Stepha7iouni (Desvaux), Cypsela of Mirbel and Lindley, to wbom I am chiefly indebted for the synonyms of the fruits given. It is derived from the Greek i, privative ; and xi'''«'»'. to open, —that is to say, a fruit which does not open. It should, therefore, not be written " Akene," as it is commonly by many writers. The forms within [ ] are those which, though commonly used, need not be kept up. 484 CLASSIFICATION OF FRUITS, does not adhere to the seed. Ex. Rose, dandelion (and all other Composita;), buttercup, buckwheat, anemone. The seed-like bodies placed on the top of the succulent receptacle of the strawberry are also fruits of this nature. [The term Utricle (utriculus), used by Gartner, differs only from achene by the fact that the pericarp surrounds the seed loosely, like a bladder, as in the Chenopodiacese (or goose-foot order), &c. It is now being dropped by the best descriptive writers.] (2.) Caryopsis.* — In this fruit the pericarp adheres to the seed. The fruits of the genus Sporbolus, indeed, differ only from achenes in this solitary respect. Ex. All grasses, including wheat, " grains," and other cereals. (3.) Carcerule.2 — It may be defined as " a many-celled fruit, in which the cells are dry, indehiscent, few-seeded, cohering by a common style round a common axis." Examples are afforded by the borage, lime or linden, Indian cress, mallow, &c., the fruits of which ultimately separate, but do not open. (4.) Glans.^ — The pericarp is hard or tough, but free from the seed. Ex. Acorn of oaks, chestnut, hazel (fig. 1 53). (5.) Samara.^ — This is a two or more celled fruit, from a supe- rior ovary. Seeds few, indehiscent, dry, and expanded into wing-like extensions at either side. Ex. Elm, ash, maple. [Cremocarp ^ is the kind of fruit we see in the hemlock order (Umbelliferce), in Ara- lia, Galium (bed-straw), &c., and is applied to a fruit, from an inferior ovary, in which the lobes separate from below, and for a time Fig 319 — Fruit of ^ang from the extremity of the common Galium Aparine la. One forked axis, or " Carpophore." De Candolle tudta^'rsho^thei^^^^^^ calls the halves of the cremocarp, ;«mV«r^.. ture of the seed. The fruit They are indchisccnt (figs. 288, 319)-] jfh^aSt^s'of'th'e so! (6.) Nut proper is a hard one-celled and called "cremocarp" are not one-seeded indehiscent fruit, like an achene. Originally, it has one or more loculi, but they all disappear during the progress of growth. II. (7.) Follicle is a fruit composed of one carpel, of which the 1 Cerio (Mirbel). 2 Carcerulus ; Dieresilis (Mirbel), Cesnobio (Mirbel), Syiiochorion (Mirbel) Sterigmum (Desv.), Microbasis (Desv.), Polcxostylus (Mirbel), Sarcobasis (DC), Baccaularius (Desv.) 3 Anglicised gland ; but the Latin term ought to be used, to avoid conftision with the secreting organs of that name (p. 65) : Calybis (Mirbel), Nucula (Desv.) 4 Pieridmm (Mirbel), Pterodium (Desv.) 5 Cremocarpium (Mirbel), Polakenium or Pentakeniuvi (Richard), Carpa- delium (Desv.) CLASSIFICATION OF FRUITS. 485 pericarp is usually thin, and opens by the ventral or inner side, and which thus forms a single valve, of which the two borders carry each a series of seeds. In fig. 320 A, is shown the fruit of the A B Fig. 320. — Pteonia officinalis, L. A, The three follicles produced in one flower (J^ nat. size). B, One of these fruits cut transversely to show the suture (a) by which it opens, with the seeds in position (nat. size.) peony, or " hundred-leaved rose," made up of three follicles ; and in fig. 320 B, a transverse section of one of the three fruits just before dehiscence. Other examples are afforded by all the members of the order Ranunculaceas which belong to the tribe Pceonia, all the Fig. 321.— Follicles (fl a a), and leaves {b b b), of Senna {Cassia acuiifolia). Hellebores, Aqiiilegia, Caltha, Magnolia, Asclepiadaceae, Apocy- naceae. 486 CLASSIFICATION OF FRUITS. (8.) Legume.^ — One-celled, one or many seeded, but differs from the follicle in dehiscing by two sutures (the dorsal and the Fig. 322. — Tamarind (Tamarindiis Iiidica). Flowering branch (rt), and fruit (i). The pulp, which constitutes the internal layer of the pod and surrounds the seeds, is sweetly acidulous. ventral) into two pieces. Ex. All the order Leguminosas, such as beans, peas, clover, &c. (fig. 322). In Astragalus, two spurious loculaments are formed by means of a false dissepiment from either the dorsal or ventral suture ; and 1 Legumen (Linnasus) ; Goiisse of the French botanists. For figures of dif- ferent forms, the student is referred to Ralph's Icones Carpologicee, Part I. CLASSIFICATION OF FRUITS. 487 in Cassia, a number of transverse diaphragms are formed by pro- jections of the placenta. In Cassia Fisttila, Cathartocarpiis, &c., the legume is indehiscent ; but in such a case the line of dehis- cence is indicated by the sutures. When the two sutures separate from the valves they form a kind of frame called the replum, as in Carmichcelia, Lindl. It is also seen in the fruits of Cruciferas, where it is formed by the placenta. [Lomentum is a form of legume which opens transversely, breaking up into one or more one-seeded joints, which usually remain closed (as in Desmodiuin), though in Mimosa they split up into two valves. Usually these pieces, into which the lomentum breaks, are formed by the spaces between the seeds contracting. Sometimes spurious dissepiments form, so as to divide the fruit into many articulations or divisions (fig. 323).] Fig. 323.— Plant which chiefly yields the snm-a.rah\c {Mimosa Arabica) ; flowering branch (a), and fruit (i). The leaves are bipinnate. (9.) Siliqua is the term applied to a slender two-valved capsule with two parietal placenta, from which the valves separate in de- hiscence. Ex. All the order Crucifer?e, or turnip order (fig. 324). The term Silicula is commonly used to describe ,the shorter form 488 CLASSIFICATION OF FRUITS. of Siliqua, which is seen in (for example) the shepherd's-purse {Capsella Bursa-pastons), Thlapsi, Lepidwn, &c. ; but the term is unnecessary, and might be abolished with great advantage, (lo.) Capsule, a fruit opening by pores, teeth, or valves — indeed and dehiscing : v v The Fig. 325. — Different forms of the cap- two valves; The par- sules of the same species of poppy tition (replum) to which ver somniferuiii), from which a large the seeds are attached portion of the opium of commerce is (nat. size). made, a Seeds nat. size ; b Magnified. the term is applied to almost any pod or dehiscent fruit of a compound pistil. Ex, Tulip (fig. 316), poppy (fig. 325), iris (fig. CLASSIFICATION OF FRUITS. 489 Fig. ■yA.—Bahamodendron Myrrha (tree producing Myrrh), i, Fruiting branch of the natural size ; 2, Capsule, unilocular and monospermous (by abortion) ; 3, Transverse section of the capsule and seed ; 4, Seed, exendospermous, consisting of an embryo with foliaceous cotyledons ; 5, Male flower (magnified); 6, Section (magnified) of the male flower (the ovary is present in an abortive condition) ; 7, Pollen-grain (magnified) ; 8, Female flower (the stamens are present in an abortive condition) ; 9, Section of ovary with two carpels and two bi-ovular loculaments. 49° CLASSIFICATION OF FRUITS. 25 0> Lychnis, Viola, Rhododendroti, Campanula, rape, &c., as well as in Balsainodendron, the details of the anatomy of which plant are given in fig. 326. [Regma is a term sometimes used to describe a fruit " in which the seeds escape by ruptures along the inner angles of the lobes, into which the fruit separates." Ex. Geranium, Eu- phorbia, &c.] [Conceptaclum and Tryma are two other terms which might safely be disused. The first has been applied to the fruit of the Asclepias, Echites, &c. ; and the latter to that of the walnut (fig. 279), and sometimes to the Euphorbia also, though it is almost impossible to define it. We have seen, however, that follicle is a fruit wide enough in its definition to embrace the first, and Regma, if necessary, to be used for the latter. The walnut is really a drupe. Dichisma, also proposed to be applied to the fruit of Platy- stemon, comes under the same category.] (11.) Pyxis ^ is a well-marked form, in which the fruit de- hisces by a transverse incision, so that when the fruit is ripe, "the seeds and their placen- ta appear as if seated in a cup covered with alid" (fig. 317). Lind- ley looks upon this fruit as one-celled by the obliteration of the dissepiments of several carpels, from the fact that the bundles of ves- sels pass from the style through the pericarp down into the recep- tacle. III. (12.) Drupe is applied to a fruit made up of one or more carpels, the endocarp of which is cartilaginous or bony, constitut- ing the "stone" or putamen in the last case, and free from the receptacle. Ex. The cherry, plum, and "stone-fruits" generally (figs. 312, 313, 327). [In Cocos, Grewia, &c., the term false drupe has been applied to the fruit.] 1 Pyxidium (Ehr,, Rich., Mirbel), the Capsula circumcissa of Linnasus. CLASSIFICATION OF FRUITS. 491 (13.) Pome.^— This is a fruit composed of one or more carpels which are cartilaginous or bony, and enclosed within and adherent to a fleshy hollow receptacle which, with the swollen lower portion of the calyx, constitutes the edible part of the fruit. Ex. The apple, Ct?/6;;i6m/^r, haw of the hawthorn, &c. (fig. 309.) , , r • [The term Sphacerocarpucm is sometimes applied to the fruit of Hippophde (the sea-buckthorn, yew, &c.)] IV. (14.) Bacca, or berry proper.^ This is a fruit with one or more loculaments, gene- rally many-seeded, inde- hiscent, pulpy. The at- tachment of the seeds to the placenta is lost at maturity, and they are scattered in the sub- stance of the pulp. Ex. Gooseberry, and all the genus Ribes (fig. 252), Vaccinum, the fruit of the vine (fig. 278). The term is applied rather vaguely, however. Thus, the fruit of the white water-lily (fig. 328) is called a berry, though the pericarp is membran- ous, and is surrounded by an enlargement of the receptacle, which be- comes fleshy, and bears marks of its origin in the cicatrices which are on -the outside of the peri- carp, marking the places Fig. 328.— A>;«//2«rt alba, L. a Flowering plant where the parts of the entire, showing flowers, expanded leaves, and others in n , 1 involute vernation ; b Fruit with scars on the outside, rloral envelopes were at- formed by the expansion of the receptacle over the tached before thev fell '"^"^ pericarp, showing places of attachment of the , . , , ' perianth, which has fallen ; c Transverse section of the 1 he bacca is also shown fruit (p. 357); d Seed cut longitudinally ; e Seed show- (fig. 329) in the fruit of '"S ^'"'"^o ; Seed natural size and magnified. the papaw, which may be classed under this head, as well as the somewhat peculiar fruit of the duckweed (fig. 330). [The term Uva, proposed to be applied to the fruit of the vine. Solatium, &c., in which the outer pericarp is very thin, is quite unnecessary.] >■ Melonidium (Richard), Pyridium (Mirbel), Pyrenarium (Desvau.x), &c, 2 Acrosarcum (Desv.) 492 CLASSIFICATION OF FRUITS. (i 5 ) Hesperidium i is the term applied to the fruit of the orange, and the genus Citrus generally, in which the pericarp (the rind) Fig. 329. — The Papaw (Carica Papaya), the type of the order Papayaceae. i, Whole plant ; 2, Young plant ; 3, Flowering branch magnified ; 4, Flower-buds ; 5, Baccate fruit, cut open to show seeds loose in the pulp. The fruit, when ripe, is edible; but the juice of it, when unripe, acts as a vermifuge. In some countries the leaves are used as soap. is leathery, owing to the thickening of the mesocarp ; while the endocarp, which is membranous, forms several loculaments filled with pulp, in the midst of which are the seeds, and separable one from another without tearing (fig. 330). (16.) Pepo.2 — When speaking of the peculiar ovary of the melons, gourds, cucumbers, &c. (p. 357), we described this form of berry, when we adopted the theory of Lindley in reference to its produc- tion. It is " one-celled, many-seeded, inferior, indehiscent, fleshy ; 1 " Hesperus, and his daughters three, That sing about the golden tree." —Milton's "Comus." 2 Of Linnseus— Peponida (Richards). CLASSIFICATION OF FRUITS. 493 also occasionally divided by folds of the nlacenta into spurious cells, which has Sen rise to the belief that in Pe^o mac rr.«r^.. there is a central cell, which is not only untrue, but impossible. rBalausta.-De Candolle designatesthe fruit of the pomegranate under this name. Tt is manv-celled, many-seeded, inferior, p. o._Longitudinai sec- !ndehiscent; the seeds with a pulpy coat, tion oyhe^nut (^^^^^^^^^ and distinctly attached to their placentae. ^.^^^). r-prirart) called by Ruellius the Mah- has'; coriaceous mesocarp. The term Amphisa^ca ap- plCdTo ?he fruit of Adansoma, Passiflom. CrescenUa, &c.. m which Fig. 33i.-Flowering branch («), fruit {Hesperidium) bc, of an Orange ^CUri^vul- ^arS, vit. Bigaradia); d Flower complete ; e Pistil ;/ Transverse section of ovary. the ovary is superior, and the outer part of the pericarp firm, leathery, or hard, may be also dropped.] Hitherto we have only been speaking of Monothaltnic fruits, 494 CLASSIFICATION OF FRUITS. or the products of a single ovary. There are, however, others which must also receive a place in any carpological arrangement, and which bear the same re- lation to the monothalmic fruits as the inflorescence does to the flower. Such fruits may therefore be de- scribed under the head of the Infructescence (St Pierre), and are multiple or Polythalviic fruits. The following may be enumerated : — (17.) Strobilus, or Cone.^ — This is applied to the fruits of firs, pines, &c., in which the naked seeds are not en- closed in a pericarp, but are placed behind woody scales, which often adhere in a firm mass (figs. 124, 125). In the Fig. j-i'z.-Htmmhts /«/«/7«-the common ^op (fig. 532) the fruits are in Hop. The upper is the male plant and flower ; a kind of foliaceOUS COne, the the lower is the female flower. , .... scales covermg them bemg charged with resin, that gives the active properties to the hops. [The term Glabulus has been applied to the "berry" of the juniper, cone of the cypress, &c., but it does not differ from the cone proper, except in being round and having the heads of the scales much enlarged.] (18.) Sorosis is the term applied to the fruit of the mulberry, pine-apple (fig. 311), bread-fruit (fig. 333), &c., in which the bracts are united with the floral envelopes into a fleshy mass, situated on an elongated receptacle, and thus converting a spike or raceme into a fleshy fruit. (19.) Syconus. — This we have already described in discussing the structure of the inflorescence of the same nature in the fig. Dorstenia, &c. (p. 285, 397, 467; figs. 143, 310, 397). [The Cynarrhodum of the rose and Calycaiithus, we have already shown, is not a true fruit (p. 302), the true fruits being achenes ; and the same is true of the .5Iterio ^ of carpological writers — the little seed-like fruits on the top of the receptacle while it is swollen and fleshy, as in the case of the strawberry (p. 464), or dry, as in the case of the Rammculus, being achenes.] The fruit having shed its seeds either by dehiscence or by rot- 1 "Arcesthide (Desvaux), Cachyrs (Fuchs), &c. 2 Pqlysecus (Desvaux), Amalthea (Desvaux), Erythrostomum (Desvaux.) CLASSIFICATION OF FRUITS. 495 ting, these seeds get scattered abroad in the various ways it is the province of Phyto-geography to take cognisance of— by birds, by Fig. 333. — Ariocarpns hicisa — the Bread-fruit tree. Scale, i inch to 40 feet. Leaf and fruit, i inch to a foot and a half. the winds, by wild animals, by rivers, currents, icebergs (to a very small extent), and by man himself in his commerce, wars, and migrations — are deposited within fitting media for growth, and spring up into the future plant. It is therefore necessary, at this stage of our studies, to consider the structure and functions of the Seed. 496 CHAPTER XI. THE SEED. The seed, we have seen, is the fertilised ripened ovule ; and though its structure and general nature are in some respects the same as that of the ovule, yet owing to its higher development, and the changes produced in its maturation, it differs in many respects, both in its external appearance and internal anatomy, from the ovule. Let us therefore inquire into the structure of this important part ot vegetation — the link, as it were, betv/een the old plant, whose life is either for a time or altogether o{Aufi^^mm expiring, and the new one, the germ of which lies maj7es, L., much embedded within it. In appearance the seed is magnified. generally more or less roundish or flattened, though occasionally some very anomalously-shaped forms are seen. The ovoid-globose form is the most common, but it is sometimes angu- lar, cylindrical, linear, helicoid (or rolled up like a snail), or like a snake curled up {jOphiocarpon paradoxum), &c., and marked ex- ternally with varied sculpture (fig. 334).^^ It is, when not sessile, attached to the seed's end by a stalk, which, as in the case of the ovule, bears the name of ftmiculus? and through the stalk it is supplied with nutriment until it has attained its maturity. The scar which remains behind when the seed detaches itself at matur- ^ ity from the funiculus is termed the hilum^ or " external umbili- cus ; " this mark may be either small or punctiform, or elongated, as in horse-chestnut, &c.* It is frequently black in colour. The 1 These markings are sometimes of considerable use in furnishing characters for species. For an elaborate account of the sculpture of seeds see Joh. Lange, " Bemasrkninger om froenes form og skulptur hos beslasgtede arter i forskellige slsegter," in the Botanisk Tidsskrift (of the Botanical Society of Copenhagen), Bd. iv. (1871). 2 Podosperm of Richard ; the cordon ombilical of some French writers. 3 Or hilus. 4 Such an elongated hilum, occupying often a third of the surface of the seed, has been styled a nauca by Gartner ; while the brownish punctiform or point • like hilum of grasses has been called a spiliis by Richard. Again, Turpin has called the centre of the hilum, through which the nourishing vessels pass into the SEED : POSITION AND GENERAL CHARACTERS. 497 place of this hilum on the seed is generally considered the base, and the point diametrically opposite the summit of the seed. The micropyle is now closed, but the place where it existed on the ovule can be seen in most seeds. The chalaza and raphe, when present, are in most cases apparent in the seed as well as in the ovule, and the same names are applied to the seed and its relation as we have already been familiar with in the ovule. The terms anatropal, campylotropal, ortJwtropal, &c., are also equally used to characterise the relative positions of the micropyle (or correspond- ing position), and the place where the funiculus joins the seed, as in the ovule. The face of a seed is that side which is most nearly parallel with the axis of a compound fruit, or the ventral section or sutural line of a simple fruit ; while the back is the opposite side. The edge of the seed is the point of junction of the face and back. " These points are best seen in a compressed seed {e.g., lentil) — i.e., flat- tened lengthways ; when it is flattened vertically, it is said to be depressed {e.g., nux-vomica). This distinction is of some import- ance. M. L. C. Richard — perhaps the best authority on the seed^ — attaches some importance to the relative direction of the seed to the axis of the pericarp when the seeds are in determinate num- bers,— these points affording good characters for the co-ordination of plants. Thus all the Compositse have their seeds erect — /. e., fixed by their extremities to the bottom of the pericarp or of one of its loculaments, when it is multilocular. On the contrary, it is inverse when it is attached in the same manner to the summit of a loculament of the pericarp, as in the Dipsacacese. In these two cases the placenta occupies the base or the summit of the locula- ment. If, the placenta being axillary or parietal, the seed directs its apex (or the part diametrically opposite to its point of attach- ment) towards the upper part of the loculament, it is called ascend- ifig (apple, pear, &c.) On the contrary, it is styled suspended when its summit is towards the base of the loculament (Jasminaceas, some Apocynaceae, &c.) The name peritropotis is given to the seed when its rational axis (z. e., the line which would pass from its base to its summit) is transverse in relation to the walls of the pericarp. When the seed is attached by a funiculus, if that is long and thin, it may exercise a great influence on the true direc- tion of the seed. Thus, for example, in Thesium, Statice, and in a certain number of RutacecB, the seed is inverse, and hangs from seed, the omphalodium. These superfluous names, luckily adopted by few any descriptive botanists or teachers, are specimens of the absurd extent to which the multiplication of terms has been carried in all departments of organ- ography, but more particularly in that relating to the fruit and seed. 1 Observations on the Structure of Fruits and Seeds, translated by John Lind- ley (1809). 2 I 498 STRUCTURE OF THE SEED, the summit of an erect funiculus attached to the bottom, or near to the bottom, of the loculamem. The position of the seed in the pericarp has no reference to the direction in which the fruit hangs (pendulous, erect, &c.) ; and indeed the two may be quite in opposition — /. ^.,the seed may- be pendulous while the fruit is A • B erect. Fig. 335. — Seed of Tobacco {Nicoiieina Tabacnjii, L.) A, Entire ; fu Part of funi- culus. B, Longitudinal section : y>i Ex- ^•^.nTT,"-^.ITT^r- ^-r^ ^..t^ tremity of funiculus ; tg Hard thickened STRUCTURE OF THE SEED, tegmen ; al Endosperm ; ei7i Embryo (mag. Integuments.— The seed, like the ovule, consists of a nucleus or kernel enclosed with two coats or integuments — viz., the Spermodenn and the Tegmen — in general readily separating from one another. 1. The Spermodenn^ or outer coat, is formed by the blending of the primine and secundine, which in most seeds are soldered together, but in some cases (the seed of the castor-oil plant, for example) they are perfectly distinct. In this case the secundine is termed by De Candolle the mesosperm,''' sarcoderm? or sarco- sperm, and, according to him, serves in the seed the same purpose as the mesocarp in the fruit. Such seeds are usually thickly swollen with juices, and have accordingly been called setnifia baccata. In anatomical structure the spermoderm presents great diversity in the number and nature of the layers of cells which compose it, and may be with or without bundles of vessels inter- mixed. In colour it differs much, as it also does in the form and nature of its inequalities and physical composition. It may be coriaceous, crustaceous, spongy, bony, fleshy, woody, or simply membranous, smooth or rough, polished with appendages (figs. 334. 335)- 2. The Tegmen,^ or inner coat, is much thinner than the outer one just described, though in some exceptional cases it is thick- ened (fig. 33S). It may even be entirely wanting. The thickness of the integuments varies much in different gen- era. Thus, in the glands of the oak, the seeds of the beech, wal- 1 Of De Candolle, from (xnepixa, seed ; and Sep/ia, covering : also called by Richard the perisperm (nepi, around ; and amepixa), and afterwards the epispcrm (cTTi, upon ; and (nrepua) or Usfa, DC. (Latin for a shell) ; lorique {lorica) of Mir- IdcI ; tunica exterjia of Willdenow. 2 fieo-o?, middle ; and (nripna. s o-apf, flesh ; and Sep^io. 4 Of Mirbel ; Endopleura (endoplevre) of DC. (eVfioi', within ; and TrAevpa, side); the tunica interior of Gartner ; tunica interna of Willdenow : also called iiilofere by Mirbel. STRUCTURE OF THE SEED. 499 nut, hazel, almond, cherry, prune, and other Amygdalaceas, these are dry and membranous, and the inner coat immediately sur- rounds the embryo. But in the fruits of the Opuntia Fiais-Indica (Indian fig), the numerous seeds with the fleshy integuments con- stitute the sugary and acidulous portion of the fruit, as is also the case in the passion-flowers and pomegranate. In these last-named plants the pericarp is even hard and woody. In the yew, ginko, peonia, magnolia, and cycas, the integuments are formed of seve- ral layers of cells, and the internal layer forms a firm nut, so that the fruits of such plants might be mistaken for true drupes — so much the more that the endosperm is surrounded by a tolerably consistent yellow envelope.^ M. Bdchamp has announced the discovery, in the fleshy integu- ment of the ginko {Salisburia adiantifolia, one of the yew order), of a series of acids, chief among which are formic, caproic, besides proprionic and valeric or phocenic acids. In the flax, and some other plants, the integuments of the seed develop a mucilage. On the whole, according to Schleiden, the integuments of the ovule experience so many changes during the process of ripening, that their original number cannot be often made 6ut in the seed. " They are sometimes all consolidated so as to form but one ; or they are broken up into many layers, having no relation to the original numbers of integuments. In Menyanthes (the bog-bean), which has but one integument of the ovule, the seed appears to have two, because of the separation and lignification of the epider- mis of that integument ; and in Canna there are five layers of tissue resembling integuments, though the ovule has not even a complete integument. In the case of spurge-worts, rock-roses (Cistacese), and daphnads, a peculiar process takes place— namely, upon the seed becoming ripe the external integument is gradually absorbed, until nothing but a thin membrane is left, usually de- scribed as an epidermis testcz; or, as in spurge-worts (Euphorbi- aceze), it has been described as an aril (p. 501) ;^ and, on the other kahd, the actual modified epidermis testae has also been described as an aril — for instance, in the oxalids." In some plants {e.g., convolvulus) the integuments are thrown off separately during germination. Appendages of the InteguDients. — Exterior and secondary to the seed are various parts which may be described as appendages to the integuments; these are wings, hairs, &c., and the peculiar appendages known as the arillus, caruncle, and strophiole. Hairs. — These are found on various seeds, but the most inter- 1 Charles Martins in Richard, lib. cit., 286. 2 See Baillon, Etude gdndrale du groupe des Euphorbiac^es, for discussion of this and similar points. 500 APPENDAGES TO THE INTEGUMENTS. esting ones are those of the cotton {Gossypiuni), one of the Mallow order (Malvaceae), which constitutes the textile material known as " cotton." Each thread of cotton consists of a single cylindrical cell, often of consider- able length, which, when dried, twists upon itself in a sort of spiral manner, very charac- teristic of this material (p. 40, fig. 336). The internal wall of the pericarp of Bom- baceae also develops the superficial cells into long woody or cottony hairs, which form a material analogous in aspect to cotton, but which cannot be utilised in the same man- ner. According to M. Duchartre, it is the columella in the genera Eriodendron, Bom- bax, and Sahnalia, which is charged with the production of these hairs, while it covers the interior of the valves themselves in Och- roma Lagopus, Sw. In various species of Epilobium and As- clepiadaceas, the seeds are furnished with a tuft of hairs called a coma, or aigrette, at- tached to one end, in the case of the Ascle- piadaceae at the summit, but in that of the Epilobium at the end near the chalaza ; while tened and twisting on '''^ ^^e case of Several Bromeliaceae the entire itself; c As it appears Seed IS surrounded by a sort of wing hairs. This coma has, however, the student must remember, no analogy whatever with the tuft Fig. 336. — Hairs of Cot- ton {Gossypium herbage- itin), with the character- istic twist which they take in drying, a Tubular hair beginning to flatten on, the median line; b The same hair more flat- bands with rounded mar- gins (mag. 400 diameters). when completely dry. The figures represent the hairs as rather too round- theyafI'merdy"flat'teMd (P^PPUs) found On the achenes of the Com- positae — since, the one being found on the entire fruit, and those mentioned above on the seed alone, there can be no connection one with the other. Dr Asa Gray has called attention to the fact that the integument of " numerous small seeds is furnished with a coating of small hairs containing spiral threads, and usually appressed, and con» fined to the surface by a fibre of mucilage. When the seed is moistened the mucilage softens, and these hairs spread in every direction. They are often ruptured, and the extremely attenuated elastic threads they contain uncoil and are protruded in the greatest abundance, and to a very considerable length. This minute mechanism subserves an important purpose in fixing these small seeds to the moist soil upon which they lodge when dispersed by the wind. Under the microscope, these threads may be ob- served on the seeds of most Polemoniaceous plants,^ and on the achenes of Labiate ^ and Composite plants — as, for example, in many species of Senecio or groundsel." E.g., Collomia linearis. E-g-, Salvia, WINGS : ARILLUS : ARILLODE. This may be something- of the same nature as the layer of spiral vessels which have been described as existing below the epidermis of Casuarina, Sivietenia febrifuga, &c. In most BignoniacejB, and in many other plants, the cellular tissue of the integuments of the seed is reticulated. Wings. — These expansions of the spermoderm are seen in the catalpha, trumpet-creeper (7i?£-<7;;;« radicans), &c. ; but the " winged seed " of the firs and pines is in reality only "a part of the surface of the scale or carpel to which it is attached, and which separates with it." The Arilhis. — This is an exterior covering with which some seeds are provided, usually incomplete and of a fleshy texture, entirely exterior to the other integuments, and arising from the expansion of the apex of the funiculus, or, if this is not manifestly present, from the placenta itself. It forms, in fact,, an accessory integument to those seeds in which it is formed. M. J. E. Plan- chon ^ has distinguished a false arillus or arillode (arillodium), re- serving the first name for the true arillus arising from an expan- sion of the funiculus, and the latter for those which arise from the t)order of the exostome — the one growing from the funiculus to the micropyle (that is, from below upwards), the other from the micropyle to the funiculus (or in an exactly opposite direction — viz., from above downward). It is not, however, always easy to distinguish the two, unless the development of the seed is fol- lowed ; for neither arillus nor arillode is found in the ovule, but forms during the development of the seed. However, owing to their mode of development, the arillus — according to Brown's ob- servations— when present, always covers up the micropyle, while the arillode leaves it uncovered. This test forms an easy method of distinguishing the two when a more analytical method is not practicable. As examples of the arilhis, we may cite the seeds of the passion- flower when it forms a loose fleshy sack with a large opening at the extremity. In the order Dilleniacece we find every extent of development of the arillus— from Pachynema and Heniistemma, in which it forms a simple cup, surrounding the lower part of the seed, to Tetracera, where it almost entirely covers it. In the seeds of the white water-lily (Nyjuphcea) it forms a thin, semi-trans- parent, cellular bag, open at one end ; in Turnera it appears as a 1 M^moire sur les ddveloppements et les caractferes des vrais et faux arilles, &c., Montpellier, 1844; Comptes rendus, Dec. 1844; Ann. des Sc. Nat., 36 s^r., 1845, iii. 275-312. Pages 33-53 of vol. ii. of Lindley's Introd. to Botany contain almost a full translation of this able essay. The characteristic sneer with which the illustrious author of the ' Grundziige der Botanik ' greets M. Planchon's labours, only shows how incapable he is of rightly valuing the labours of his contemporaries or adversaries— a fact of importance to keep in mind when reading his works. 502 CARUNCLE : NUCLEUS OF THE SEED. mere lateral scale (Gray) ; while in Bixia, Cytinus Hypocistis, and various genera of Sapindaceae, it forms a more or less extensive appendage to the seeds. The false arillus, on the other hand, is seen in the spindle-tree genus [Euonymus) ; and the similar pulpy envelope of the seeds of Podophyllum and Celastrtcs, and other genera, is probably of the same nature. It is also seen on the seeds of Polygala} and various other plants ; but the one on w^hich it is most familiarly known is on the common nutmeg {Myristica fragrans), where it forms an irregular network of a fleshy character, orange-red in colour, and highly scented, known in commerce under the name of mace (fig. 337). Caruncle (Caruncula). — This is very analogous to the false arillode. It consists of the thickened edge of the exostome, in the form of a fleshy, lenticular, or hemispherical excrescence, at the side of the hilum. Examples are seen in Ricinus, Euphorbia, and many other Euphorbiaceae. Strophiole. — Under the name of Stro- phiolae,^ Gartner described certain cellular excrescences on the integument of various seeds {e.g., Chelidonitiin niajus, Dicentra, Sanguinaria Canadensis, or blood-root of America, &c.), formed independently of the funiculus or exostome, and, for the most Fig. 337.— Seed of Nut- part, placed on the raphe, where they form meg (Myristica fragrans), . . , -j r with the arillode which con- a conspicuous crest along one side ot the stitutes the spice called seed.^ Nucleus.* — The nucleus or kernel of the seed comprises all those parts covered by the integuments, and may consist of the endosper7n and embryo, or of the embryo alone. The kernel is attached to the integuments by the chalaza, though in the ripe seed this connection is usually destroyed. The embrj'o must always be present in every perfectly fertilised seed, and, as in the case of Phaseobcs, it may form the only part of the kernel. At other times there is, in addition, a distinct body called the endo- sperm present (as in the castor-oil seed, Oxalis, snapdragon, to- 1 The distinction between the different organs of the aril nature is so little defined that by some authors this is called a caruncle, while Schleiden declares it is only a " rather loose epidermis to the seed. " 2 Sometimes called crista or crests, from their appearance. 3 The term embryotega has been given by Gartner to a small callosity near the hilum of some seeds {e.g. , the bean), which at the period of germination is pushed up like a lid to allow of the emission of the radicle. •1 Amande of the French, and Samenkern of the German botanists. NUCLEUS OF THE SEED : ENDOSPERM. bacco, &c.) The embryo grows into a new individual ; but the endosperm, if present, is consumed in supplying nourishment to the embryo in process of growth. Endosperm or Albutnen.—This part of the kernel is thus not essential to the life of the seed, not being present in those of all species of plants. The embryo, we have seen (p. 414), is formed in the embryonic vesicle, which shows itself in the upper part of the embryo sac, and in most cases the endosperm originates from a tissue formed within the embryo-sac. Robert Brown has, however, shown that in Nymphsa and other Nymphaeaceas, Zingiberaceae, Pipera- ceas, Cabombacese, Saururus (Saururacese), a cel- lular tissue develops exterior to the embryo-sac, so as to form two endosperms, the one surround- ing the other in a concentric form. In some cases the cellular tissue, forming the bulk of the di^f sectiM^o°"see"d kernel, is absorbed by the embryo in develop- of Snapdragon {An- .... , . , tirrhtnujii jnajus, ing, and m this case there is no endosperm pre- l.), greatly magni- sent in the adult seed, the embryo forming the fied erepos, different ; and rpomj. STRUCTURE OF THE EMBRYO. from an orthotropal or anatropal ovule, the embryo (the radicle) is opposed to the chalaza ; in a seed derived from a campylotropal ovule, the radicle approaches lat- terly towards the chalaza, without, however, being opposite to it, as in the other case. These relative directions of the embryo are valuable as furnishing characters for the co-ordination of natural groups.^ Conneciion between the Endos- perm a7id the Embryo— HxceT^t in the Coniferse, there is no organic connection, or even adherence, between the embryo and the en- dosperm. In this order, however, the radicle appears to be contin- uous with the endosperm, the ad- herence between the two being due to the remains of the suspen- sion of several embryos, which were produced in the same ovule, but of which one alone attained its complete development (p. 414). Let us examine more in detail the different parts of the embryo of a young plant shut up in the seed. (i.) Radicle?' — This is one of the extremities of the embryo, and owing to its mode of origin, is always directed towards or near cotyledons expanding and showing the ^ ^, • I Tr iU plumule. C, The same still more ad- tO the micropyle. If the embryo is X,s.xv<^^^ in germination, showing the cau- Straight, or only shares in the gene- I'^e "ow developed into the first inter- , c ^\ J iT- I.V. node, and the gemmule expanded mto ral curvature Oi the seed, then the a pair of leaves borne on it (after Gray). radicle is directed to the opposite extremity — viz., to the chalaza. It is usually the first portion pro- 1 It would, however, be a more scientific, and an infinitely less embarrassing nomenclature, if all the terms applied to the position of the ovule were also used with reference to the seed. This may come to pass when it is thoroughly understood that to manufacture a new barbarous compound of indilferent Latin, or still more dubious Greek, is not to discover a 7iew fact. However, so long as they are used, it is necessary for the student to know them ; though the men least capable of advancing science, are, to use Schleiden's words, most anxious for the poor short-lived notoriety gained by coining a new word, and, I may add, of the less excusable one of using them. * Radicula, Rostellum, Rhizoma. Fig. 339. — Illustrations of Dicotyle- donous Germination. A, The embryo (i. e., the entire kernel) of the bean. B, The same in early germination, the thick STRUCTURE OF THE EMBRYO. truded through the integuments of the seed. It is the axis or rudi- mentary stem : from its lower portion the rootlets proceed ; from its upper the gemmule ; the cotyledons are also attached to the upper end. Its nature and mode of development in Monocotyledons and Dicoty- ledons we have already discussed while describ- _ ing the root (p. 128), and will hereafter have Fig. 3^.— Longitu- occasion to say something more while describ- dinal section of the ing the proccss of germination. In some cases seed of Rubin tine- .1 i- 1 / .1 i- 1 \ • i torum, L. (Madder), the radiclc (or rather the cauhcle) is very large, «y Endosperm; ct while the cotylcdons remain small; such em- Cotyledons; t Cauli- , t.-uiu iij zj i cie ; r Radicle, or bryos Richard has called macropodotis} (mag"Jtimesr''^™'^ (2.) P IwHule .—i:\{\s is that part of the embryo in a line with the radicle, which, in fact, it is only a continuation of superiorly. It gives birth to the stem, and commences at the point of insertion of the cotyledons, which are attached to it. It may be divided into two parts — (a) the caulicle, terminated by (/3) the gemmule. (a) The Caulicle"^ is not easily made out in all embryos before germination ; but as soon as this process sets in, it lengthens and becomes quite distinct (fig. 339). The point between the inser- tion of the cotyledons into it, and the crown of leaves (gemmule) with which it is terminated, Fig. 341. _ Trans- Constitutes the first internode. As the name verse section of the expresses, it is really the " little stem." ^^'^E'r^. O) The Gemmule' (fig. 339). or terminal bud ing through a seed, of the plumule, is, like all terminal buds, com- In the embryo of this i /- . ■ . r . , is the radicle r, direct- posed of an ajils contmuous With the axis 01 the ly the length of the plumule, and of rudimentary leaves. In Dicoty- median Ime of one of ' ' . . , i , i the two cotyledons ledonous plants it IS usually placed between the Idlnto^So^'o've^ which cotylcdons, which by their approach cover and arecondupHcate. The conceal it. In Monocotyledons it is placed in ^wTthltt tZl a little or pit. as the base of one side of ments, and the par- the cotylcdon, which pit represents the sheath ates'them(!o/i).TTh[s of the cotyledonary leaf. The gemmule gives ieed") origin to a shoot -which commences the aerial stem of the plant, and upon which grow the rudimentary leaves, which in due course take the form, position, and characters which belong to the leaves of the particular species to which the embryo may belong.* 1 /aaxpos, large ; wovs, woSds, foot. 2 Cauliculus, scapus ; the tigelle (tigellus) of the French botanists. ^ French ; Latin getnmula, the diminutive of gemma, and means literally the " budlet." ■ ■■■ , * One of the most successful investigators of the physiology of the seed — M. STRUCTURE OF THE EMBRYO. (3.) Coiyledons?—Thtse are the lateral appendages of the embryo, and may be either one or two in number. Take, for instance, a bean, and the two lobes into which it divides show the two cotyle- dons; while a grain of wheat is solid, and cannot be divided — in other words, it has only one cotyledon. This elementai7 arrange- ment of the seed-leaves in the young plant is important, in so far as it is accompanied by other differences in other parts of the plant which allow us to form the two great divisions of the vegetable kingdom, called respectively Dicotyledons and M 0710 cotyledons — plants the seeds of which have two cotyledons or only one (p. 73). This character does not, however, invariably hold true. In Coni- ferae (pines, firs, &c.) there are apparently from one to ten, and even fifteen (there being much variation even in the same plant) coty- ledons, arranged in a verticil. Hence the accuracy of the classifi- cation named, founded on the number of cotyledons, has been called in question ; and another division, founded on this supposed peculiarity in Coniferas, has been founded by some systematists, and called Polycotyledons, or plants with many cotyledons. M. Duchartre has, however, shown ^ that in this order of plants there are in reality originally only two cotyledons, which are repeatedly divided, so as to form, in appearance, many cotyledons, and that therefore the old classification is in reality quite correct. Some LeguminosK and Cruciferas also occasionally show examples of plants with three cotyledons, or, as in the case of the cruciferous genus Schisopetalum, four cotyledons ; but M. Duchartre, in the Memoir quoted, shows that, as in Coniferse, there are in these plants only two cotyledons, subsequently, in the progress of devel- opment, divided into a greater number.^ Three cotyledons have also been seen in embryo plants of Correa, Cratcegus, Dianthtis sinensis, Daticus Carota, Cerasns Lau7'0-cerasus, bean, a Solanuin, Apinm Petroselimcvi, marigold {Calendula), beech (Fagus), vari- ous Loranthacese {Nuytsia, Psittacanthus), &c., and in Cola acu- minata, the cotyledons in some seeds vary from two to five.* Arthur Gris — used the seeds of the castor-oil plant, as best fitted to follow out the anatomy and germination of seeds in general on. See also Chatin, Ann. des Sc. Nat. Bot., 5e s^r., xix. 5. 1 KOTvAi)«i)i'. Mirbel admitted two parts of the embryo— viz., the cotyledons and the blastema, a term under which he included the radicle and plumule. 2 Comptes rendus, 1848, t. xxvii. p. 226; Ann. des Sc. Nat., s^r. 3 (1848), X. 207-237. 3 Perhaps, instead of saying that Schizopetalum has four cotyledons, it would be more accurate to describe the two cotyledons as lobed. The coty- ledon of the linden has five such lobes. Between these lobed cotyledons, and those which, as in Coniferse, are divided almost to their base, there is an almost insensible gradation. In the rue, sycamore {Acer peudoplatanus), &c., seedlings with lobed cotyledons are often seen. 4 Masters's Teratology, p. 370-371, and the papers of De Candolle, Jaeger-,- STRUCTURE OF THE EMBRYO. In consistence, the cotyledons may be fleshy ; thick, as in the case of acorns, chestnuts, &c. ; or thinner and more membranous. The fleshy cotyledons are found in exendospermous seeds, and the thinner or membranous in endospermous ones — the difference being due to the fact that, when the endosperm is not present, the cotyledons, from the nutriment stored up in them, furnish food for the young plant ; while in the thin membranous cotyledons, in which their foliary nature is shown by the presence of nerves not easily seen (if at all) in the fleshy ones, the young plant is nourished by the stored-up endosperm.^ As specimens of the fleshy cotyledons, the bean or acorn may be cited; while Ricinus, Euonymtis, Rubia tinctorum (fig. 340), &c., afford good examples of the thin, delicate, flattened cotyledons, which, from their more perfect resemblance to leaves, have been called foliace- ous. In such a case it is the endosperm which makes up the bulk of the seed. (i.) In Dicotyledons, the cotyledons are in general opposed like ordinary leaves, and when two are present, are both of equal size. (2.) Sometimes, however, in some Malpighiacese, we find one in- creased in size at the expense of the other (as in Sorocea, Hircea, and Trapa natafis, where the large fleshy cotyledon constitutes the edible portion of the seed). When the embryo is coiled or folded, it is always the inner one which is smaller than the other. In some of the Cycadaceae they are also somewhat unequal. (3.) In Dicotyledons, one may be even wanting altogether. In Lentibu- lariacese, Abronia, Cyclamen (in which genus the radicle is much enlarged), and Corydalis solida (Bischoff) generally this is the case ; so that these are in reality monocotyledonous — so far as this character goes, though in reality dicotyledonous — as all other portions of their structure show them to be. (4.) Finally, in various parasitic flowering-plants — such as the dodder, M0710- tropa, Rafflesia, Hydnora, orchids, &c. — the list of exceptions finds its extreme, — these plants having no cotyledons at all.^ In Ehrenberg, Reinsch, and A. de Jussieu, cited there. Mr Meehan will even have it, "all seeds are primarily monocotyledonous, and that division is a subsequent act, depending on circumstances which do not exist at the first commencement of the seed -growth" (American Nat., 1871 ; and Nature, 1871, p. 153 ; Proc. Phil. Acad. Sc., April and May 1871). 1 Van Tieghen, Note sur le divers modes de nervation de I'ovule et de la graine, Comptes rendus, Ixxiii. (August 1871) ; Ann, des Sc. Nat., 56 s^r., xvi. 228; Le Monnier, Ann. des Sc. Nat., 50 ser., xvi. 233. 2 It is erroneous to describe, as is sometimes done, Lathrcea Clandcstina (Orobanchaceae) as deprived of cotyledons. Lecythis, which Richard de- scribes as wanting cotyledons, cannot also properly come within this category. The great division oi A cotyledons is not, however, founded on such exceptions ; but on ferns, hchens, mosses, fungi, sea- weeds, &c., which do not grow from seeds proper, and none of which have anything like cotyledons. EMBRYO : COTYLEDONS. the dodder the embryo is of considerable size ; but in most such parasites— ^.o-., the mistletoe— the embryo is very minute, and reduced to a state of great simplicity, and seems to remain, until germination, in a very rudimentary state (Gray). (5.) In some dicotyledonous plants— horse-chestnut (where they are well developed), Tropaolum, Careya herbacea^ Castanea, buck-eye (American species of /Esculns), various Cactaceae — Echinocactus, Echinopsis, and Phyllocacius, — they are small and solidified in one mass ; but in Opuntia, Cereiis, &c., the cotyledons are separated and tolerably well developed — two Dicotyledons are more or less consolidated or coherent by their contiguous faces (conferrumi- nate)." In the case of the chestnut it is, however, generally more or less easy to trace the line of connection between the cotyledons ; but in the other examples of conferruminate cotyledons which we have given, this is by no means so easy, if possible — the cotyledons being solidified into one mass instead of having their contiguous faces in contact, as in the first example. In form the cotyledons^ are very varied, — being rounded, elofigated, linear, winged, obtuse; and though in general sessile and entire, maybe lobed (p. 511), petiolate (Geranium moUe), auriailate (ash). We also find, as de- scribed in some of the foregoing examples, that most of the forms of the praefoliation of ordinary leaves are seen in the seed-leaves or cotyledons. They may be conduplicate'^ (cabbage, mustard, crambe, &c.), recliftate (p. 163), convolute (pomegranate), circinate {Bioiias and Erucaria), equitant or semi-equitant (p. 163). As to the relatio7i of the cotyledons (in the dicotyledonous embryo) to one another — (i.) the two faces are usually applied to each other before germination, the back of the cotyledon being 1 Griffith in Linnean Trans., xx. 270. 2 Pseudo-monocotyledonous (Gartner) ; macrocephalous (Richard). s M. Germain de St Pierre is inclined to believe that in Cyclamen the single cotyledon, so called, is in reality developed by the gemmule, so that it vi^ould supply another instance of Dicotyledons being not monocotyledonous, as usually believed, but acotyledonous. He also asserts that Bunium Biilbocas- tanum, and other tuberous Umbelliferas— notably Biasolettia tiiberosa—ger- minate with one cotyledon. Probably, as the development of plants is more attended to, such exceptions will be found to be more common than is at pre- sent believed. * Certain signs have been used to express the different methods in which the cotyledons are folded, these variations being used as characters to divide the order Cruciferse into tribes. For instance, conduplicate is distinguished by O > —i.e., bent longitudinally, so as to form a groove, in which the radicle is placed, characteristic of the Orthoplacese ; accumbent by O = ; incumbent by O II ; circinate by o || ||, characteristic of the tribe Spirolobeje. In the division Diphcolobeas, the cotyledons are folded twice upon themselves, as seen in Setie- biera, Subularia, and Heliophila, such an arrangement being expressed by the sign O 11 II II. 2 K 514 EMBRYO : COTYLEDONS. considered the convex portion turned outward. (2.) In some rare cases (as in some Ranunculaccaj, and the genera Motiimia and Boldea among the Monimiaceaj), the two cotyledons are turned out from one another. (3.) In some seeds of the order Combre- tacCcG, in the pomegranate, the cotyledons are spirally rolled on their axis. (4.) Sometimes " the embryo, having a more or less elongated shape, rolls upon itself in forming a spiral, the turns of which are placed on the same plane " as in certain Cruciferae, par- ticularly in the genus Bunias (Richard). The epidermis of the cotyledons differs in structure, accord- ing to the function which it is required to fulfil, (i.) If the cotyledons are hypogeous — e., remain concealed in the ground (p. 527) — their surface absorbs the endosperm when this exists, and increases in size in a ratio proportionate to the rapidity of absorption {e.g., in palms, grasses, &c.) In such cotyledons the epidermis is delicate ; and numerous vascular bundles in the midst of a parenchyma, gorged with juices, favour this function of absorption. (2.) If, on the contrary, the cotyledons are epigeous (p. 527) — or rise above the ground to furnish the first " seed- leaves " — they are, like ordinary leaves, furnished with stomata to a greater or less extent {e.g., beet) on both surfaces, or at least on Fig. 342. — A male plant oi Stangeria paradoxa, one of the Cycadaceae. The flowers are dioecious ; in the male plant they are reduced to very small ovoid anthers, opening by a longitudinal slit, borne in great numbers on the inferior face of the scales of large terminal cone-like catkins. one of their surfaces {e.g., beech and birch). However, if the cotyledons increase by the absorption of endosperm, then the face NAKED SEEDS. in contact with the endosperm is not provided with stomata (Coniferas). Hitherto the seeds which we have been describing are enclosed within a pericarp ; and hence the plants having their seeds so ar- ranged within seed-vessels are called Angiospernm} In ConiferjE (figs. 124, 125, p. 187) and Cycadacese (figs. 342-345). however, the pistil is formed of a single carpellar>- leaf, which is entirely open and exposed, and thus leaves the ovules naked. Such ovules pro- ducing naked seeds, not contained in a pericarp, are characteristic of tharsection of flowering-plants which, on that account, are called Gymnosperma? In Ephedras (joint-firs) ^ and junipers, the seed is Fig. 343. — Scale of Ceraio- Fig. 344. — Cone of Fig. 345. — Cone of Za- zania robiisia, one of the Cyca- Dioon edule, one of the inia hitcgrifolia, one of dacea:, bearing naked seeds at Cycadaceae (i-yth nat. the Cycadacese (K nat. its base. size.) size). surrounded by a fleshy arillus, and accordingly looks like a berry. The juniper "berry" (fig. 346) contains three seeds, whilst that of the Ephedra and yew only contains one. In Podoca7'pus it is the extremity of the branch which swells out and becomes fleshy, as in the fruit of Anacardium ; it is then the funiculus. The wings of the I ayyecov, a vessel ; tTTTepixa, seed. 2 yufivbs, naked ; and (mepixa. ■* Mr J. Miers considers that Ephedra is improperly placed among Gymno- sperms, and maintains that it has neither naked ovules nor naked seeds, and is more allied to the Urticacew than to the Cycadacem or Conifera (Contrib. to Botany, vol. ii., 1869). NAKED SEEDS. NAKED SEEDS. seeds of firs (Abietina2) are prolongations of a part of the scale which accompanies the seed (fig. 125, p. 187). This opinion regarding the gymnospermy of the Coniferae was first promul- gated by Robert Brown in 1825,^ and since then has been adopted by the greater number of botan- ists, among whom Lind- ley, Brongniart, Endlicher, Richard, Schleiden, Cas- pary, Schacht, Alphonse de Candolle, Sperk, Sachs, Duchartre, Hooker, and Bentham, are in the first rank. An opposite opinion has, however, been pro- mulgated by Mirbel, and supported by Agardh, Spach, Payer, Parlatore, Baillon, Strasburger, and a few others of less note (or of no note at all). According to them, it is the seed-integument, not the, carpellary envelope, which is wanting. From this point of view, the ovary of Coniferae is made up of two carpels without floral envelopes, containing an orthotropal ovule placed upright on a basilar placenta. The cup of yew, &c., which has been considered an arillus, is, in this opinion, a production anterior to fecundation, just as the floral organs called discs are the result of the expansion of a consecu- tive axis.^ Such naked seeds must necessarily be impregnated in ^ Targioni-Tozzetti, however, as early as 1810, enunciated very similar views as Caruel pointed out in 1865 (Strasburger, Coniferen, s. 174). 2 In respect to this question the student may consult, as regards Coniferas, the following papers and separate works (regarding origin of embr}'o and fe- cundation): R. Brown in Brit. Assoc. Rep., 1834, and Collected Works (Ray Soc.) ; Hartig, Forstl. culturpfl. (1840), t. xxv. ; Geleznoff in Ann. des. Sc. Nat., sdr. 3, xiv. (1850) 207; Hofmeister in Development of the Higher Cryptogamia (trans, by Currey in Ray. Soc. Publicns.) ; Schacht, Lehrbuch, Bd. ii. p. 401, and Der Baum, ed. 2 (i860), p. 273 ; Mohl in Verm. Schrift, s. 45 (on fruit-bearing scales) ; Caspary, De Abietin. fl. fern. (1861), and in Ann. des Sc. Nat., sir. 4, xiv. 200 (regarding the ovule, naked or within an Fig. 346. — Juniper {Junipenis communis) fruit- bearing fronds, with details of the flower and fruit. NAKED SEEDS. the state of ovules without the intervention of style or stigma, or any stigmatic apparatus (p. 414)- With the exception of the orders named, we know of no other instances of true naked seeds. In Qphiopogon spicatns, Leontice thalictr aides, Peliosanthes Teia, Sec, Robert Brown has, however, pointed out something in reality very similar. In these plants the ovules rupture the ovary at an early period of growth, and thus are, when ripe, really naked seeds ; and in Reseda'^ the seeds are almost uncovered after the ovary begins to swell. The seeds of some plants will occasionally pro- trude, owing to the bursting of the fruit {e.g., grapes), and ripen in that situation. By Linnseus and the older descriptive botanists, the term "naked seeds" was applied to the small seed-like fruits of Labiatas, grasses, sedges, &c. ; but the term was manifestly incor- rect, as. such "naked seeds" are all covered with pericarps. Accordingly, the expression is now never applied except to express the true naked seed's of Conifers, &c., just described. ovary) ; R. Brown "On the Structure of the Unimpregnated Ovule,"in Appen- dix to King's Voyage (1825), or in Collected Works (RaySoc); D. Don in Trans. Linn. Soc, xviii. 163 (1838); Eichler in Flora Brasiliensis, fas. 34, p. 441 ; E. Favre in Ann. des Sc. Nat. , sdr. 5, iii. 379 ; Sperk, Die Lehre v. der Gymnospermie im Pilanzenreiche (1869) ; and various papers by Hartig, Hofmeister, Caspary, Schacht, already quoted, as well as others by Lindley Endlicher, Mohl, A. Braun, Eichler, and others in various works, in advocacy of the gymnospermy of the ConiferEE : while the following papers advocate the doctrine of a closed monospermous ovary, as existing in this and allied orders (Gnetacese, &c.), — Rich., Mem. Conif. et Cycad., 1826; Mirbel and Spach (1. c); J. G. Agardh, Theor. Bot. (1858), p. 317-323 ; Heinzel, Nov. Act. Nat. Cur. (1844), xxi. I, 203 ; Baillon, Rec. d'observation, i. (i860) ; Alex. Dickson in Edin. New Phil. Journ., July-Oct. 1861, p. 183, and Trans. Bot. Soc. 1861 ; Parlatore in Comptes rendus, 9th July i860 and Feb. 1861, Studii organ, dell. Conif. (1864), and De Candolle's Prodromus Par., xvi. (1868); J. D. Hooker on Welwitschia, Trans. Linn. Soc, 1862; and W. M'Nab on the Develop- ment of Flowers of Welwitschia in Trans. Linn. Soc, xxviii, 507 (Dec. 1872) ; A. S. CErsted in Naturh. Forenings Vidensk. Meddel. Kjob., 1869 ; Hofmeister inVergl. Unters., 1851, and Jahrb. f. wiss. bot., i. s. 167; Strasburger, DieBe- fruch. der Coniferen, 1869 : (on the pollen) Schacht in Jahrb. f. wiss. bot., ii. s. 142; Strasburger in Janaische Zeitschr. Bd. vi. ; Pfitzer, Niederrh. Ges. f. Nat. u. Heilk., 7th Aug. 1871 ; Reinke in Gottinger Nachrichten, 1871, p. 350 ; and Sachs in Lehrbuch, 436 ct seq. The following references relate more especi- ally to the Cycadaceas : — (regarding the development in general) Karsten, ' ' Or- ganogr. Betracht der Zamia muricata," in Abhandl. Akad. Berl., 1856, p. 193-219; Regel. Bull Soc. Nat. Mosc, 1857, vol. i. : (in regard to germination) Miquel in Linnasa, Bd. xxi. p. 503 : (regarding inflorescence and the nature of the scales in the strobilus) Mohl in Verm. Schrift, s. 45 etseq. ; Gottsche in Bot. Zeit., 1845, p. 307; Kraus in Jahrb. f. wiss. bot., iv. s. 329; Geyler, ibid., vi. s. 68 ; Thomas, ibid., iv. 43 : (regarding the ovule and embryo) Miquel in Ann. desSc Nat., sir. 3, iii. (1845) 195; Arthur Gris in Bull. Soc. Bot. Fr. (1866), xiii. 10; Dippel, Bot. Zeit., 1862 and 1863 ; Rossmann, Bau des Holzes (1863) ; Abstract of Eichler's views by Wright, Trans. Bot. Soc. Edin., xi. 535; &c. 1 Such seeds are called scminude. 5l8 GENERAL CHARACTER OF THE EMBRYO. Let US now, in concluding- this account of the structure of the seed, sum up the characters of the embryo in the two great divisions of plants. Dicotyledofious Embryo. — Its essential character consists in the fact tliat, as a rule, it has two cotyledons, and a naked radicle which elongates to form the root. In form it is extremely variable — being often ovoid, or almost globular, even flat, or finally cylin- drical or very slender, an elongated ovoid being the most common form (fig. 341). The radicle is under the form of a minute conical elevation, which does not represent anything but a small part of the embryo, which is almost entirely made up of the cotyledonary bodies. More rarely, as in the genus Pekea, it is the portion most developed, and in such a case the cotyledons are very small. The form of the cotyledons varies much, and their thickness is greater or less, in proportion as the endosperm is found in greater or less quantity ; and above all, when it is altogether wanting, the gem- mule is always placed on the summit of the caulicle, which is, however, often not very naked. This gemmule is covered by the cotyledons, placed face to face ; more rarely the two cotyledons are united together so as to form a more or less undivided body, as in the case of the horse-chestnut. Mo7iocotyledonous Embryo. — Here the embryo is very simple, consisting of a single cotyledon, and most frequently does not show a marked distinction into radicle, cotyledon, and plumule; but, as in Iris and Triglochin (palustre), is only a " homogeneous, undivided, cylindrical, or club-shaped body." In grasses, especi- ally in cereal grains, the plumule is more manifest and complex, showing as it does the rudiments of several concentric leaves, or a well-marked bud even, before germination.^ In other plants, however, such as the iris, onion, &c., there is nothing like a dis- tinction of parts until germination commences. The form of the embryo is very varied (ovoid, depressed, cylindrical, &c.), but in most cases it is ovoid or oblong, or more or less obtuse at its two extremities. The single cotyledon, and the radicle sheathed by a coleorhiza (p. 529, fig. 348 c), or lips of the passage through which they protrude from the radicular extremity, are the two chief 1 In wheat and some other grasses the caulicle has at its base in front, a great lateral projection (fig. 351 g, the Scutelbim of Gartner) ; but this is apparently another of the exceptions we have spoken of — viz., a second rudimentary coty- ledon, and not the primordial radicle, asL. C. Richard thought, — or, according to Adrian de Jussieu, a special modification of the caulicle, to which the former botanist applied the name of hypoblasUis. Lindley broached a theory, which in its main features has been adopted by A. de Jussieu (Ann. des. Sc. Nat., 2d ser., XX. 350), that the embryo of a Monocotyledon — a palm is the speci- men he takes — is "analogous to that of a Dicotyledon of which one of the cotyledons is abstracted, and the other rolled round the plumule and consoli- dated at its edges." GENERAL CHARACTER OF THE EMBRYO. characters distinguishing it. The embryo is contained in a little vaginal cavity at the base of the cotyledon, usually opening by a small longitudinal slit. The form of the cotyledon varies much. It is, however, generally cylindrical, even in embryos accompanied by an endosperm.^ In Cryptocoryiie spiralis'^ there is an exception to the monocoty- ledonous character of the division to which it belongs ; but all such exceptions are only peculiar modifications of structure, and do not invalidate the general rule, or warrant us in altering the names applied to the great division of plants founded on the pre- vailing character.^ As regards development in Orchids, Monotro- pacepe, Pyrolacese, Orobanchaceas, Rafflesiacese, Balanophoracese, and Hydfiora, the embryo is very simple, consisting of a spherical body made up of a few cells. In Monocotyledons in general it is more complicated, it being possible to distinguish the plumule and the cotyledon which surrounds it, and at the radicular ex- tremity a tissue in which the radicles are developed (figs. 347- 352). In Dicotyledons the embryo attains the highest develop- ment before germination — the two cotyledons, plumule and radicle, being in nearly all cases well marked (fig. 339), though there may be cases where there is, as in Cyclamen and Trapa, only one de- veloped cotyledon, or even none (p. 512).* 1 Achille Richard, lib. cit., p. 295. 2 Griffith, Linn. Trans., xx. 271. ^ For instance, Cassini proposed to style Dicotyledons Jsodynamozis or Iso- brious, and Monocotyledons Anisodynamous o\ Anisobrious, because in the first the force of development is equal on both sides, and because in the other the force of development is greater on one sort than the other, resulting in the single cotyledon. The student has already seen that there are plenty of excep- tions to this rule, so that in point of accuracy of nomenclature the one series of names is as faulty as the other. Again, Lestiboudois calls Dicotyledons Exoptiles, and Monocotyledons Endoptiles, because in the first the plumule is naked, while in the latter it is enclosed within the cotyledon. Perhaps more correct were the terms Endo- and Exo-rhizal, proposed by Richard for the two divisions ; for in reality the fact of the radicles being sheathed as they pass out of the radicular extremity of the seeds, is the only invariable distinc- tion which separates Monocotyledons from Dicotyledons. Dumortier's terms of Endo- and Exo-phyllous were of parallel value, being founded on the distinction afforded by the fact that in the first division (Monocotyledons) the leaves are evolved within a sheath (Cokophyllum or Coleoptilum), while those of the second (Dicotyledons) are always naked. Of making names there is no end — a fact which might be to the advantage of botanical science if the end of the accu- mulation of facts was simply that names might be applied to them ; but as the object of names is only to facilitate the remembrance and recording of facts in something like a system, the value of one name over another is not of parti- cular moment, except in so far as it may be more convenient than the other. This does not apply to the names quoted. ^ In Monocotyledons, Hofmeister has laid down the law, that in vertical seeds, whether erect or pendulous, the medial plane of the cotyledons coincides with that of the seed, while in horizontal seeds the plane of the cotyledon is at S20 GROWTH OF THE SEED. The further distinctions as regards developments we will reserve until we have occasion to speak of the process of germination ' (P- 527)- In the mean time, let us speak of the conditions of the 1 seed necessary to that process being performed ; and first, regard- j ing the GROWTH OF THE SEED. A seed attains its maximum size at an early stage of its growth. After this the tissues within the spermoderm solidify as the seed ripens, without, however, any further increase in size. There is even a decrease in the dimension of the seed as it ripens, by the ' contraction of the exterior, in this respect somewhat resembling the pericarp of some fruits. That the outside dimensions of the seed should be the parts which first arrive at maturity, it is neces- sary that the parts in the interior should have room to increase and solidify. After the secondary parts have thus attained their maxi- mum size, the embryo and the endosperm, which are the primary parts of the seed, become the chief centres of growth. The shape ' of the seed is greatly determined by the relative rapidity of the growth of parts. Ripetiing of Seeds. — Seeds are in their early state green — and 1 even the embryo is so also ; ^ but when they ripen, the exterior gets paler, whitish, white, or yellowish brown, owing to changes in the contents of the cells of the spermoderm. Some seeds are diver- sified, and often brilliantly variegatedly coloured, as we have a familiar example in the different varieties of kidney-beans. The bright glistening appearance of immature seeds is owing to the I presence of water in the spermoderm, and it decreases as the amount of water diminishes by drying, though some seeds are bright even when mature, owing to a peculiar condition of the epi- I dermal cells, or perhaps to the presence of some oily or waxy sub- stance. The decrease of the dimensions of the seed as it ripens is owing to the loss of water, on account of less and less sap arriving in the seed as it gets ripe, the result of which is the atrophy of the funic- ulus. The amount of water in dry seeds is about 4 per cent on right angles to it ; but in the date-palm, where the slit of the cotyledon is a . vertical one situated near the base of the cotyledon, Professor A. Dickson has pointed out that there is presented an exception to the invariability of that rule (Nature, 1870, p. 38). The most recent research on the development of the j embryo in Monocotyledons and Dicotyledons is one published as these sheets ' are passing through the press — viz., by Johannes Hanstein (Botanische Ab- hand., Heft i.), which I have only seen in an abstract (by Dr M'Nab) in ^ Month. Journ. of Mic. Sc., 1873, p. 51. ^ ^ | 1 Some embryos, even in the ripe seed — e.g., mistletoe, Pistachia, some Cnici- \ ferae, &c. — remain quite green. ' , ] GROWTH OF THE SEED. an average, but it varies in amount from 8.50 per cent in seeds of wild plants of Barbarca prcccox, down to 0.50 in those of Erysi- mum officinale. Ripe seed is usually denser than the unripe seed, to the extent that it will sink in water ; hence the common test for it. The less density of unripe seed is owing- to the imperfect or entire want of development of the embryo ; hence it floats. This test is not, how- ever, infallible ; for some perfectly ripe and sound seeds will float also. The density of seeds varies, according to the observations of Schiibler and Renz, from 0.210 up to 1.450; while those of others, like some Leguminosce, Polygonaceas,Amarantace8e, grasses, &c., sink before being ripe (Duchartre). It is always of import- ance for the cultivator to know what value is to be attached to seeds. If, for example, he finds that only two-thirds of his seed will germinate, then he must sow a corresponding quantity over a given extent of ground. To test the germinating pow^er, the fol- lowing procedure, recommended by the eminent French agricul- turist Matthieu de Dombasle,^ may be useful : — " Cover the bottom of a saucer or plate with two pieces of rather thick cloth which have been wetted, and place the one over the other. Spread on this a certain number of seed, taken at random from the package to be tested, each seed being separated by a small space from its neighbour. Then cover them with a third piece of cloth like the first two, and wet it. Now place the plate in some moderately warm place, such as on a chimney-piece, or in the vicinity of a stove. As the cloths begin to dry, wet them again, but allow no surplus water to accumulate about the seeds ; and accordingly, after the cloths have absorbed all they can, pour off the surplus by raising gently the plate from the horizontal. The progress of germination can be watched day by day, by simply raising up the topmost piece of cloth. Those seeds which have lost the power of germinating will generally in a short time get covered with moulds." 1 Moniteur du Soir, 7th March 1867 (quoted in Cave's Cours Eldmentaire de Botanique, p. 102). 522 CHAPTER XII. GERMINATION. Before investigating the nature of the process of germination, or " sprouting," it may be well to discuss a few points regarding the vitality of seeds— a subject which is of the greatest importance, not only in physiological but in geographical botany. Duration of Vitality.— If seeds are kept dry, the embryo re- mains dormant ; but the time during which the embryo will retain its vitality varies much with the seeds of different species. For instance, it is said that the seeds of willow will not grow after having been once dry, and that if even kept fresh they lose their germinating power in two weeks. The seeds of coffee and other RubiacecB, Angelica, and other Umbelliferas, do not germinate freely after having been kept for any length of time. The seeds of wheat usually lose the power of growth after being kept seven years, though it has been found quite capable of being used as food even after being kept more than two centuries. The stories about " mummy wheat " sprouting after remaining in Egyptian tombs for thousands of years are, to say the least of them, very dubious, no well-authenticated instance of such being extant ; while among other articles sold by the Arabs to credulous travel- lers, as coming out of the same tombs as this ancient wheat, have been dahlia bulbs and maize — the deposition of which in the re- ceptacles from which they were said to be extracted necessitating the belief that 3000 years ago the subjects of the Pharaohs were engaged in commerce with America! Dietrich^ experimented with the seeds of wheat, rye, and a species oi Bromus 185 years old, but failed to induce them to germinate, the place of the em- bryo being occupied by a slimy putrefying fluid. If, however, excluded from the air, damp, &c., seeds have been known to keep for somewhat lengthened periods. For instance, those of leguminous plants have been known to sprout after being kept dry for 60 years. In 1810, fruit was obtained in the Jardin des Plantes from a species of Phaseolus or Dolichos taken from 1 Hoffman's Jahresbericht, &c., 1862-63, s. 77 (^rfe Johnson). germination: duration of vitality of seeds. 523 the herbarium of Tournefort, who flourished about 1694. The seeds of the sensitive plant have germinated after being kept 60 years ; while Gerardin records that haricot-beans, after being kept for more than 100 years in herbaria, sprouted. Rye has been said to have sprouted after 140 years (Home). Alphonse de Can- dolle found, from experiments in the Geneva Botanic Garden, that large seeds keep longer than small ones, and that the germinating power of seeds was in an inverse ratio to the rapidity of germina- tion.i The seeds of woody species seemed to preserve their vitality longest, and biennials shortest ; while those of perennials were longer-lived than those of annuals. Seeds of the ordinary Rubus Idceus, or raspberry, found in a British tumulus near Maiden Castle, Devonshire, in 1834, along with coins of the Emperor Hadrian (and therefore, if co7itevipora7ieoiis, sixteen or seventeen hundred years ago), germinated under the care of Professor Lind- ley, and produced vigorous fruiting plants. M. Charles Desmoulin also generated seeds of Medicago lupulina, Centaurea Cyanus, Heliotropimn EuropcBum, &c., found in Roman tombs dating most probably to the second or third century of our era. Numerous instances are recorded of seeds which have been supposed to be buried in the soil under old houses springing up ; but most of these cases must be viewed with a certain degree of scepticism, the openings for error or deception being too many. As one specimen, I quote the following instance, communicated in 1866 to the Botanical Society of France, and said to be authentic : Under the foundations of a very ancient building demolished recently in the " He de la Seine " where the city was founded, Dr Boisduval took a quantity of blackish earth, in the midst of which an attentive examination revealed the presence of seeds. These seeds, grown with great care under a bell-glass, or "cloche," gave origin to plants of Jtmcus bufonhis, L., a plant of moist places and grounds inundated during the winter — /. e., growing ordinarily in conditions similar to that presented by the ground on which was built the ancient city of Lutetia ! Gilbert White long ago noted that, when beech-trees were cleared off from the "Hanger" at Selborne, the ground got covered with strawberry plants, which might have probably lain in the ground for many years, but could not vegetate till the sun and air were admitted ; and that places, where in his day, and for a century before, beech-trees had grown, were known to the people by the name of strawberry " slides " or trenches, though no strawberries had grown there in the memory 1 Sur la dur^e de la facultd de Germiner, &c.; Ann. des Sc. Nat., 1846 (t. yi.), p. 373-382; Ann. Nat. Hist., ist ser., xx. 38; Lefebure, Sur la Germi- nation des Plantes, 1804 ; Gerardin, Sur la propri^td des Graines de conserver longtemps leur vertu germinative, 1809; British Assoc. Rep., 1850, p. 62; &c. 524 DURATION OF THE VITALITY OF SEEDS. of man.i In some experiments made in 1817 by Sir Thomas Dick Lauder, he found that four species of plants {Hieracium pilosella, Myosotis scorpioides, Lamium ptirpurcum, and Spergula arvensis) germinated in soil taken from beneath a covering of sand, -.vhich had lain over a portion of Morayshire for at least sixty years.* Numerous such cases could be quoted. For instance, maize from the tombs of the Incas of Peru — and therefore probably at least 300 years old — has been known to germinate. Seeds of ragwort taken from the centre of a solid mass of peat-earth, at a depth of 16 feet, in a bog in the Isle of Man, have germinated. Some hazel- nuts, discovered at a considerable depth in a morass in the county of Durham, grew when sown, &c.^ Kemp * records an instance of having germinated seeds of Polygonum Cotivolvuhis, Rumex Acetosella, and an A triplex, taken from the depth of 25 feet in a sand-pit near Melrose, and in regard to which he had satisfied himself that there had been no deception or error. He considered that they might have been more than 2000 years old. Mr Grugeon has communicated to me a similar instance of vitality in buried seeds of a Ru7}iex, It therefore appears that if seeds are buried at a depth in the soil where they may be removed from the influence of light, heat, oxygen, and other conditions of germination, they may preserve their vitality for a considerable period ; but there are so many probabilities of mistake or collusion to be eliminated, that any extraordinary cases of vitality reported require to be carefully examined before any- thing like implicit credence is given to them. On the whole, it may be said that the rule is, that the fresher seeds are, the more cer- tainty there is of their germinating, and that the percentage which spring is in a tolerably direct ratio to their age.^ Londet and Haberlandt made experiments with cereals which proved this decisively. The following table gives the results of the latter observer : — 1 Nat. Hist, of Selborne (Blyth's ed.), p. 300. 2 Macgillivray, Edin. Journ. of Nat. Hist, and Phys. Sc., 1836, p. 35. These and various similar facts are given at lengtli in an anonymous little work published at Edinburgh in 1835, entitled the ' Physiology of Plants ; or, the Phenomena and Laws of Vegetation,' which contains some original mat- ter worthy of attention. 4 Ann. of Nat. Hist., ist ser., xiii. 89. " The vitality of seeds will be discussed at greater length in Phyto-Geo- GRAPHY. RESULTS OF THE USE OF £oNG-KEPT SEEDS. 525 Name of grain. Percentage of seeds that germinated in 1S61, from the years 1S51. 1854- 1855- 1857- 1858. 1859. i860. Wlieat, 0 8 4 73 60 84 96 Rye 0 0 0 0 0 48 100 Barley 0 24 0 48 33 92 89 Oats 0 56 48 72 32 80 96 Maize, .... 76 56 77 100 97 Eesults of the Use of long-kept Seeds. — Old seeds yield weak plants, and this peculiarity is taken advantage of by horticulturists in producing new varieties. It is said that while one-year-old seeds of the ten-week stock yielded single flowers, those which had been kept four years produced, for the most part, double flowers, which are a monstrosity, the result of feebleness in the constitution of the plant (p. 385). From observations made at the instance of the Prussian Horticultural Society by Schmidt, Spren- gel, D'Arenstorff, Treviranus, and Voss, it has been found, as a general result, that in the case of melons and cucumbers, the longest-kept seeds, though less certain to germinate, yet yielded the greatest amount of fruit ; while new seed produced vigorous plants, which ran too much to leaf.^ M. Voss reared, from 24 seeds of a Spanish melon thirty years old, eight plants which gave good fruit. Cucumber-seeds 17 years old gave the same result ; while some seeds of Althcea r^?j known that the movements are propagated through the 1 Comptes rendus (1870), t. l.\x. ^ Masters, Nature, 1870, p. 343. IRRITABILITY OF VENUS' FLY-TRAP. 573 fibro-vascular bundles alone. Meyen/ Briicke.s and Sachs,^ have all studied the anatomical structure of these plants with a view to determine this matter. At the base of the common petiole, and as well at the secondary ones, are swellings which are concerned in causing the raising of the leaves when the irritation communicated along the fibro-vascular bundles, by a peculiar arrangement of these bundles around the periphery of the swellings, as described by the authors named, reaches them. This movement is probably accomplished, according to Sachs, by a movement of the liquid contents of the cells composing these swellings.^ It may also be noted that it is a common subject of observation, that if the lower surface of these swellings, at the base of the common petioles, is touched, instantly the leaf is depressed ; but no such effect follows if the tipper portion is subject to irritation. The opposite is the case if the swelling at the base of the leaflets is the subject of experiment. Again, it has been found that if the leaflets at the extremity of a secondary petiole are touched, the folding of the leaves consequent on the irritation is continued from above down- wards ; but if a pair at or near the base is touched, the contrary ensues — viz., the irritation is conveyed from base to apex. Dionsea. — Near Wilmington, in the State of North Carolina, U.S., is found a very curious plant, often called "Venus' fly-trap {DioncBa 7}tuscipula). Every leaf (fig. 359) of this plant bears at its sumit an appendage which is probably the true blade, while what seems the leaf is only an expanded winged petiole.^ A midrib divides this appendage into two equal parts, on the upper surface of which are three or four hairs, and along their margins are also rows of long, closely-set hairs. On an insect alighting on the leaf, the 1 Pflanz-Physiologie, iii. s. 532 et scq. 2 Miiller's Archiv. fiir. Anat. u. Phys., &c., 1848, ss. 434-455. ^ Bot. Zeit., 1857, col. 793-802, 809-815, pi. xii. and xiii. ; and Handbuche der Experimental-Physiologie der Pflanzen, s. 481. See also Dutrochet, Re- cherches Anat. et Physiol, sur la structure intime des Animaux et V^g^taux, 1844. 4 Pettigrew considers that the cells of these swellings constitute, as it were, two springs, which act in opposite directions, "so that if from any cause the one be paralysed, the other pushes the leaf in the direction of least resistance." These " springs " are set in motion, he thinks, by the rush of fluid creating a turgid state of the one set of cells and an empty state of the other. Moisture, being necessary to the life of the plant, cannot act as an irritant. "The only explanation that can be given is, that the plant lives, and that it sucks in mois- ture by the one set of cells, and ejects moisture by the other." — Lectures on the Circulation, 1 c, p. 99. 5 Though in its mechanism it acts much more like a rat-trap. B Meyen, on the contrary, looks upon the inferior portion as the true leaf, and the terminal contractile portion only as a sort of appendage ; while Dassen has hazarded the opinion that the two lobes of this latter part are only the remains of distinct rudimentary leaflets. 574 IRRITABILITY OF VENUS' FLY-TRAP. two sides close along the line of the midrib, the marginal bristles dovetailing into one another like the teeth of a rat-trap, so that the F'S- 359' — Leaves ot Dioneea i7ttiscipula, L., closed and open (almost the natural size). insect is crushed to death, and the harder it struggles to escape the firmer it is clasped. The leaf then remains closed until the insect is dead, when it opens for another capture, though in time it acts sluggishly, and by-and-by becomes insensible. The leaf performs this movement equally well in daylight or dark, and the younger leaves possess a much higher irritability than the old ones. What is the purpose of this we are yet in ignorance. The old ideas of Ellis and Curtis, though generally discredited until re- cently, that the plant feeds on the insect remains, are not quite so undeniable as might be supposed. Recently some remarkable observations go far to prove that the face of the blade is thickly scattered with glands which secrete a saliva-like liquid. In the course of a week or two this liquid acts as a sort of gastric juice, and dissolves all the soft parts of the insect. Little pieces of raw beef were acted on in the same way ; so that really here we have a carnivorous plant ! When it is mentioned that these obsen^a- tions were made by, among others, Asa Gray and Charles Darwin (though those of the latter botanist are as yet unpublished), the reader will consider that he has a strong guarantee that the facts stated are correct. The observations of Knight, made many years ago, were to the same purpose — viz., that those leaves supplied with bits of raw beef were more flourishing than those not so sup- plied. Finally, we have Dr Burdon-Sanderson announcing^ that the closing of the leaf oiDioncsa in the manner described, is accom- panied with electrical phenomena analogous in their nature to 1 At the meeting of the British Association at Bradford, Sept. 20, 1873. IRRITABILITY OF THE LEAVES OF THE " SUN-DEWS." 575 those which occur when nervous or muscular actions are induced in animals. Drosera.— The leaves of the " sun-dews " of our bogs {Drosera rotundifolia, D. viedia, and D. lofigifolia), which are covered with glandular hairs (p. 6i), have been proved to be also sensitive, though in a much smaller degree than those of the plants de- scribed in the foregoing paragraphs. These glandular hairs, each secreting a drop of glutinous fluid, attract insects to their destruction. Each hair has a spiral within it, and when a fly alights on the limb of the leaf on which they are placed, all the parts of the limb, as well as the hairs, move towards that part, the result of which is, that the insect is smothered by means of the viscid fluid which they secrete — a remark made by Roth nearly a century ago. Mr A. W. Bennett, who has recently made careful ob- servations on this subject, observed that it was not until the insect was dead that the hairs bent over the dead fly — a fact not easily accounted for by the supposition of the presence of a "contractile tissue " at the base of the glands. To quote the ipsissima verba of the description which he gives us of his experiments on D. rotundifolia : " The contact of the insect appeared to excite a stronger flow of the secretion, which soon enveloped the body ot the animal in a dense and almost transparent slime, firmly gluing down the wings and rendering escape hopeless. It still, however, continued its struggles, a motion of the legs being clearly per- ceptible after the lapse of three hours. During all this time the insect was sinking lower and lower down among the glands to- wards the surface of the leaf, but only a trifling change had taken place in the position of the glands themselves, which had slightly converged so as to imprison it more completely. But after the struggles of the prisoner had practically ceased, a remarkable change took place in the leaf. Almost the whole of the glands on its surface and its margin, even those removed from the body of the insect by a distance of at least double its own length, began to bend over and point the knobs at their extremities towards it, though it was not observed that this was accompanied by any increased flow of the secretion from them. The experiment was made in the evening, and by the next morning almost every gland of the leaf was pointing towards the object in the centre, forming a dense mass over it. The sides of the leaf had also slightly curved forwards, so as to render the leaf itself more concave." Though this irritability has been denied, the researches of numerous observers, particularly of the botanist just quoted (many of whose observations I am also enabled fully to confirm), and of Nitschke, have quite proved this, at least in reference to D. rotundifolia, in which it is shown that all portions of the leaves are irritable, but that this power chiefly resides in the hairs. 576 IRRITABILITY OF THE LEAVES OF THE " SUN-DEWS." and that the leaf is h-ritable in proportion to the activity of these glandular hairs. After the hairs have covered over the insect like the fingers of the hand, they do not straighten for some days, when a fresh drop is exuded for a fresh prey. This secretion is acrid and bitter to the taste, and is sufficiently acrid to cause irritation if applied to the skin.^ In a recent note presented to the French Academy of Science,^ M. Ziegler has made some curious observa- tions on this subject. He found "that all albuminoid animal substances, if held for a moment between the fingers, acquired the property of making the hairs of Drosera contract ; though, if such substances had been in contact with a living animal, no such action was visible on the hairs. The cause of this is obscure. After a time the hairs get insensible to insects, or to organic bodies modified by living contact." The properties of these plants were reversed, and, strange to say, their hairs were found to con- tract under the influence of organic matter which had been pre- viously in contact with packets (of double or triple envelopes) containing sulphate of quinine. Organic matter, influenced in this purely physical way by sulphate of quinine, has no contractile action on the hairs of Drosera in their normal state. The plants whose physical properties had been reversed by the influence of albumen (animal albumen was used), could be restored to their normal condition by placing them for twenty-four hours, with the platinum capsules containing them, on a packet of sulphate of quinine. The method may be adopted whenever, from any cause, the leaves have become insensible to insects. In every case the contraction of the hairs is slow ; it commences visibly, and is not complete till after several hours. In all our experiments, and those of Mr Bennet, the contact of a minute chip of wood, or other dead matter, had no effect on the movements of the hairs or leaf. In some cases the insect is merely fastened to the leaf, and in time dies of starvation ; but in other species with stronger hairs, the insect is really secured by the bending inward of the hairs, so as to bring it within reach of the glutinous drops, though the move- ment is so slow as not to be visible except in the result. In D. longifolia, it has been affirmed, the limb of the leaf not only shows an inclination, as in D. rotundifolia, to curve, but actually " in- curves itself so as to fold round its victim." Linnaeus long ago observed that the flowers of D. rotundifolia in Sweden opened at nine o'clock and shut at noon ; but whether this has any connec- tion with the peculiar irritability of the leaves is very dubious. 1 It has been used in the treatment of dropsy, intermittent fever, and ophthal- mia, but without effect. The superstition of many countries invested it with a virtue of supplying suppleness to the limbs if applied to them. 2 May 6, 1872 (Comptes rendus, t. lx.\iv. 1227-29). OTHER PLANTS WITH IRRITABLE LEAVES. 577 The whole subject will bear reinvestigcation.^ It has even been affirmed that, as in Dioncea, the frond has the power of digesting the flies ! ^ Lastly, Treat has confirmed most of the above obser- vations on Drosera filiformis, but with the additional observation, that when living flies are pinned at a distance of half an inch from the apex of the leaf, the leaf actually bends towards the insect until the glands reach it and suck its juices !^ Other Plants with Irritable Leaves. — In addition to the plants named, there are others which show sensibility of the same kind, though not in the same degree. Among these may be enumerated various other species of Mimosa (above all, M. sensi- tiva, and, in a less marked degree, M. viva, M. casta, M. speciosa, M. asperata, &c.) Among other Leguminoss showing sensi- bility, are Acacia jnlibrissin of Turkey, Smithia sensitiva of India, yEschytiotnene sensitiva of the West Indies and Brazil, Indica and yE. pianila^ both of India, Desmanthus stolonifer of Sene- gal, &c. Outside of the order Leguminosae, the most remarkable sensitive plant is Biophytum sensitivicni, DC. {Oxalis sensitiva, L.) — a small plant of India, which in its native countiy has a sensibility almost equal to that of the Mimosa, though in our hot- houses it is much less sensitive — Averrhoa Ciirambola of Bengal, &c. The frond of Onoclea setisibilis, a fern, will, if touched, bend downwards. If the ordinaiy butterwort {Pinguictda vulgaris^ is rudely torn up, the flower-stalk immediately begins to curve back- ^ I have, in accordance with universal custom, both here and in former pages, designated the peculiar glandular appendages of Drosera as " hairs." Trecul and Gronland, I am aware, have, however, denied that they are true hairs — though this is simply a question of difference of definition as to what a hair is — but integral portions of the substance of the leaf penetrated by a fibro-vascu- lar bundle with spiral vessels (in other words, by a vein). Be this as it may — and all physiologists are not at one on the subject — the student will find these hair-like structures (or " trichome," as the Germans call them) in Drosera in- vestigated with great care by Meyen, Uber die Secretions-organe der Pflan- zen, s. 51, tab. vi., fig. 15; and Pflanzen physiologic, ii. s. 478; Gron- land, Ann. des Sc. Nat., ser. 4, t. iii. ; Trecul, ibid., iv. 3 ; Nitscke, Bot. Zeit., No. 22 ; Ibid., No. 33 {i860) ; Caspary, ibid., No. 26 ; Martinet, Ann. des Sc. Nat., ser. 5, xiv. (1872) 195-198; Hanstein, Bot. Zeit., 1868; Rauter, Zur Entwickelungsgeschichte einiger Trichomgebilde (1871) ; and most recently of all, by Warming in Videnskab. Meddel. fra den naturhisk. Forening i Kjobenhavn, No. 10-12, 1872, p. 159-202, where the "trichomes" or hair- like structures of the petals oi Menyanthcstrifoliata, Gtmnera scabra, Datura Stravionium, Drosera rotundifoUa, Agrimonia Eupatoria, the pappus of the CompositcB, &c., are described, and their development traced. 2 Millington, American Naturalist, vol. ii. (1868). See also a discussion of this question by Warming in Tidsskrift f. popul. Fremstill. af Naturvidens- kaben ; 4 Raekke, Bd. i. p. 417 ; and Otto Norstedt's paper, Kunna bladen hos Drosera-2.nen ata Kott? (Botaniska Notiser, 1873, p. 97-102). 3 American Naturalist, Dec. 1873; Nature, Feb. 26, 1874. 2 O 578 IRRITABILITY OF STAMENS AND STIGMAS, wards ; and when the plant is deposited in the collecting case the leaves are soon reflexed, and by iheir revolution conceal the root. Irritability in the Stamens and Stigmas of Plants.— The stamens of the common berberry and various other plants are so excitable, that when the filament is brushed by an insect, or by any other point near the base, it will approach the pistil with a sudden jerk, so that the pollen is dislodged from the cells of the anthers (by means of a sort of "trap-door" on either side), and sprinkled on the stigmatic surface of the pistil. Jourdain ^ has found that the irritability of the stamens is suspended by chloro- form, just as similar irritable movements in the leaves of other plants are. In an Australian Stylidhim the stamens and style form a united column, which is bent over to one side of the corolla; but if slightly irritated, it will immediately spring over to the opposite side of the flower. If the throat of Schizanthus pinnaUis be slightly pressed, the stamens spring forward and discharge their pollen. In Apocynum androscemifolhim (dog's-bane) the anthers converge towards the nectaries, consisting of five glandular and somewhat oval bodies, which are sufficiently separated below to admit air to the anthers. As soon as a fly introduces its proboscis between the anthers from the top, they close so suddenly as to detain the fly a prisoner for life, for the insect generally perishes.^ Similar irritability is displayed by the stigmas of Martytiia and the style of Goldfussia anisophylla. Many other similar instances could be quoted,^ but the above will suffice to illustrate this inter- esting subject. Why they should exhibit this irritability is un- known, no anatomical peculiarities which would account for it having as yet been observed. Professor J. B. Schnetzler has attempted to explain it on other grounds than irritability. In some remarks on the stamens of the common berberry and other species of Berberis,^ he was led to the belief that the term "irritability" or "contractility" of the vege- table tissue explains nothing of its real cause. Previous investi- gations by the same observer into the movements of the leaves of Mimosa and Dioncea, and of the stamens of Parietaria, had in- duced him to attribute some part of its production to the protean matter or protoplasm which constitutes a portion of the living cells 1 Comptes rendus, April 25, 1870. 2 The Physiology of Plants (Anonym.), Edin., 1835, p. 270. 3 E.g., in Helianthemum vtilgarc (where the motions of the pistils are even more remarkable than those of the stamens), Parnassia palustris, Sparmania Africana, Cereus grandifloms, MimulusgluHnosits,Bignonia(sX\gms.), Maranta bicolor (stigma), Saxifraga tri dactylites, Riita graveolcns, various Cactaceas, passion-flower, Cistns, nettle, pellitory, &c. ■» Communicated to the " Soci^t^ VaudQise des Sciences Naturelles;" The Academy, 1869, p. 48. MOVEMENTS OF CLIMBING PLANTS. 579 (p. 20). The experiments which he made on the stamens of the berberry confirm in this respect those which he had previously made on the leaves of the sensitive plants. For instance, the ourali poison, which does not destroy the contractility of animal sarcode, and leaves untouched those same properties in proto- plasm generally, has also no influence on the movements of Mimosa, nor on those of the berberry. On the other hand, nico- tine, alcohol, and the mineral acids, destroy the life of sarcode and protoplasm, and the irritability of the leaves of Mimosa and of the stamens of berberry. This explanation is only one contribution to an explanation — not one in itself. The so-called irritability of the stamens of Kalmia, an American plant, is a mechanical act (p. 407, 440). The elastic, bursting pods of the Touch-me-not {Iin- patiens noli-tangere) come under the same category — /. e., the movement is mechanical, not vital. MOVEMENTS OF CLIMBING PLANTS. Perhaps the most remarkable contribution to the history of " vegetable irritability," or, if you will, "instinct," which has been made of late years, are the remarkable observations of Charles Darwin on climbing plants.^ As these observations open up a wonderfully fruitful field for inquiry, we will devote some space to a notice of a few of the more remarkable of them. A student igno- rant of these researches is ignorant of some of the most important observations which have ever been made in his science. Climb- ing plants may be divided into (i.) those which spirally twine round a support ; (2.) those which ascend by the movement of the petiole or tips of their leaves ; (3.) those which ascend by true tendrils ; (4.) those which are furnished with hooks ; and (5.) those which are furnished with rootlets. The last two are not distinguished by any special movements, and the interest accordingly centres in the first three. Spirally Twining Plants. — Both Darwin and Beal note cases in which vines will twine round a support, and after running above the support, still continue their spiral movements, "swing- ing around, following the course of the sun." In one case the movement lasted as long as the plant continued to grow, but each separate internode, as it grew older, ceased to move. In the case of the hop, and most other twining plants, about three internodes at a time partake of this motion. This particular vine performed a revolution in from one to two hours, moving most rapidly in the warmest part of the warmest day. 1 On the Movements and Habits of Climbing Plants, t866. See also Journ. Linn. Soc. , 1865. 58o LEAF-CLIMBERS. Hoya carnosa, one of the Asclepiadaceae, revolves opposite to the sun in five or six hours, making a circle of over 5 feet in diameter. The tip traces 32 inches per hour. It is an interest- ing spectacle to watch the long shoot sweeping, night and day, this grand circle, in search of some object round which to twine. To prove that Mohl was wrong when he ascribed the revolutions to the twisting of the stem, it may be noted that some stems are not regularly twisted, and others twist in an opposite direction to the revolving plant. If a stick, shortly after having been wound around, be withdrawn, the climber will for a short time continue its spiral form, but soon it will straighten itself out, and again commence its revolutions in search of a fresh support. Experi- ments prove that stems do not in general twine, owing to a dull irritability of the stem, as Mohl imagined. If the support of a twiner be too short for it, it will fall to the ground, and then the tip will commence to climb afresh. Sometimes the flexible shoots of several climbers will form a cable, and thus support each other. Rarely do plants of the same order twine in opposite directions, and no two species of the same genus go in contrary directions, though most plants twine in a direction opposed to the sun. Climbers of temperate zones do not often climb round thick trees ; while those of the tropics do, in order to reach light in the dense tropical jungle. In Testudinaria elephantipes, according to Mohl, it is only the branches, not the stem, which revolve ; and in the aspa- ragus, on the other hand, it is the leading shoot, not the branches, which revolves and twines. The twining of some is regulated by the season — twining, as they do, in the summer, and not in the autumn ; and the climate also alters their habits in this respect, plants which grow erect within their native country twining in this. They will also show an antipathy, if the term may be used, to certain trees, and refuse to climb around these if even they be close at hand. For instance, M. Paul Ldvy noticed that the lianas of Central America will not attach themselves to particular trees, even when brought into juxtaposition with them ; and these trees thus slighted are just those which are most unsuited for the pur- poses of twining plants — viz., smooth-stemmed, umbrella-topped species. This antipathy of the climbing plants to these trees is also, to a less extent, shown by moss, ferns, orchids, Bromeliaceas, and other epiphytal plants.^ Leaf-Climbers. — The stems of several species of Clematis, Lopho- speriiijim, Maitrandia (all flowering garden-plants), are twiners like the hop, &c. " But in addition to this mode of holding fast, the petioles are sensitive to the touch, slowly bend in the form of hooks, and if successful in catching a stick, they clasp it firmly, and soon become greatly enlarged and strengthened by an extra 1 Cited by Masters in Gardeners' Chronicle, 1870, p. 383. TENDRIL-BEARING PLANTS. growth of woody fibre. If they come in contact with no object, they retain this position for a considerable time, and then, bend- ing upwards, they reassume their original upturned position, which is retained ever afterwards." Some petioles are so sensitive that they will catch firmly at anything they feel the weight of — withered blades of grass, soft young leaves of a maple, or flower- ing peduncles of the quaking-grass {Brizd). In Tt-opceolum trico- loriim, van grandifloruin, a remarkable fact has been noticed — viz., that the petioles of young leaves, if they catch no object after standing in their position for some days, will move gradually to- wards the stem, oscillating a little from side to side as if in search of the needful support. The flower-peduncles of Maurandia scm- perflorens (order Scrophiilariacece) are sensitive like tendrils, and exhibit revolving powers which seem of no service to the plant, as it loses the power when the flower is old enough to open. In Solamim jasminoides, as in no other leaf-climber yet noticed, a full-grown leaf is capable of clasping a stick; but the movement is extremely slow, requiring several weaks. The effect of this is to much increase the thickness of the petiole. Plants belonging to eight orders are known to have clasping petioles, and plants to four families climb by the tips of their leaves. With rare excep- tions, the petioles are sensitive only when young ; they are sensi- tive on all sides, but in different degrees in different plants. If rubbed with a piece of wood, these leaf-climbers will generally respond to the irritation by curving in the course of two or three days. This shows that climbing in these plants is the result of a movement under sensitiveness of touch, no matter how slow that may be. Tendril-Bearing Plants.— Plants belonging to ten orders are tendril-bearers. Between leaf and tendril climbing there are all gradations. For instance, look at the tendril of the pea, which is only the developed end of the midrib. In Nepenthes, the prolonga- tion of the leaf, at the end of which the pitcher is placed, twines ; in Gloriosa, the end of the leaf is developed into a hook ; while in CobcEa, the grapples and hooks by which it climbs so vigorously are only the upper portions of a compound leaf changed into ten- drils— and the same is true of the tendrils of the pea, &c. Species of Bignonia and a few others afford connecting-links between climbers, leaf-climbers, tendril-bearers, and root-climbers. " Some little time after the stem of Bignonia Tweedyana has twined round an upright stick, and is securely fastened to it by the clasping petioles and tendrils, it emits at the base of its leaves aerial roots, which curve partly round and adhere to the stick ; so that this one species oi Bignonia combines four different methods of climb- ing generally characteristic of distinct plants— namely, twining, leaf-climbing, tendril-climbing, and root-climbing." The move- 582 TENDRIL-BEARING PLANTS. ments of Bignonia vcmista are very complicated. Not only the tendrils, but the petioles bearing them, revolve— these last, how- ever, being in no way sensitive ; and all the parts revolve at a different rate, and quite independent of each other. In a few days after the tendrils have clasped the stem, their extremities often become developed into irregular disc-like balls, which have the singular power of adhering firmly to the wood. The undivided tendril of Bignonia speciosa ends in an almost straight, sharp, un- coloured point, and the whole exhibits a trait which, if seen in an animal, would be called instinct, for it continually searches in its movements over the surface of the wood for any little dark hole in which it may insert itself. Mr Darwin tells us that the same tendril would frequently withdraw from one hole and insert its point into a second one. " Improbable as this view may be," Mr Darwin remarks, " I am led to suspect that this habit in the ten- dril of inserting its tip into dark holes and crevices may have been inherited by the plant after having lost the power of forming adhesive discs." The tendrils of a plant oi Bignonia capreolata sought the dark- ness and avoided the light unerringly. When a tend'.il does not succeed in clasping something, it bends downward to its own stem, which it seizes ; and if it seizes nothing, it soon withers and drops off. In Corydalis claviculata we have an instance of a regu- lar transition from a leaf-climber to a tendril-bearer, its tendrils still bearing leaflets, though very much reduced in size. In Echinocystis lobata, and other plants, the tendril will — though only touching a support placed some distance from the plant — in a few hours curl twice or thrice around the stick by a sort of vermicular motion — "just as a strong man, suspended by the ends of his fingers to a horizontal pole, works his fingers on- wards until he can grasp the pole with the palm of his hand." Though the tendrils of plants belonging to Vitacea;, Sapindacece, PassiJloracecE, &c., may be modified peduncles, their homological nature makes no difference in their actions. In Ampelopsis, or Virginia creeper, discs are developed at the end of the tendrils (p. 125). " In revolving tendrils, the most wonderful thing is the way in which they avoid winding themselves round the stem they belong to. The active tendrils are, of course, near the top of the stem or branch. The growing summit beyond the tendril, now seeking a support, is often turned over to one side, so that the tendril, revolving horizontally, has a clear sweep above it ; but as the stem lengthens and rises, the tendril might strike against it, and be wound up and around it. It never does. If we watch these slender passion-flowers, which show the revolving so w-ell on a sultry day, we may see with wonder that when a tendril, sweeping ROOT-CLIMBERS. horizontally, comes round so that its base nears the parent stem rising above it, it stops short, rises stiffly tipright, moves on in this position until it passes by the stem, then rapidly comes down again to the horizontal position, and moves on so until it again approaches and avoids the impending obstacle."^ Spiral Contractions.— It is seen that the tendrils of several kinds of plants, if they catch nothing, contract, after an interval varying from a day or two to several weeks, into a close spire, and " a few into a helix." The tendrils are thus made highly elastic, so that a plant with this coiled tendril can " safely ride out the gale, like a ship with two anchors down, and with a long range of cable ahead to serve as a spring as she surges to the storm." A tendril which is uncaught contracts spirally always in the same direction from tip to base ; while, if the contrary is the case, it invariably becomes twisted in one part in one direction, and in another part in another direction, the oppositely twined spires being separated by short straight portions. Many extremely interesting observa- tions of a like nature have been made. Some tendrils are excess- ively sensitive, the slightest touch causing them to become hooked. After a touch, the tendril of Passiflora gracilis moved in twenty- tive seconds. Many of the tendril-bearing plants come from the American continent, and possibly a connection might be traced between this and the abundance of arboreal animals (?). Eoot-Climbers. — These we have referred to when describing the root. The rootlets of Ficus repens emit minute drops of clear fluid, slightly viscid, to assist its upward progress — and so on. Now, what does all this tend to? No doubt plants become climbers jn order to reach the air and light, and in climbers this is effected with very little expenditure of organised substance, compared with trees which have huge solid trunks to enable them to do the same. Darwin thinks, in accordance with the well-known views which are associated with his name, that because these climbing plants graduate into one another, they have become climbers by gradual change, and that leaf-climbers were primordially twiners, and tendril - bearers were primordially leaf- climbers. He believes that the capacity of acquiring the revolving power, on which most climbers depend, is inherent, though undeveloped, in almost every plant in the vegetable kingdom.^ Whether this is so or not the student must determine for himself. Theory apart, the facts are strange enough to excite wonder and inquiry. They look almost instinctive ; yet in the present state of our knowledge we must, almost with a yearning after something more, call them merely displays of " vegetable irritability." 1 Gray, How Plants Behave, p. 18 (1872). See Beale in American Naturalist, p. 405-419. 584 WHAT IS VEGETABLE IRRITABILITY? What, then, is this Vegetable Irritability ? — We have al- ready alluded (p. 578) to Schnclzler's attempted explanation, but what does it amount to ? We may explain how the motions are accomplished ; but when we come to consider how one mass of tissue in one particular plant has this power, and the same tissue, differing in no appreciable degree in appearance, in another part of the same or a different species or individual, wants it, we arrive at a problem which it is beyond our present knowledge to solve. The probability is, that most of these movements consist either in shortening the cells on the concave side, or elongating them on the convex side. Gray has pointed out — what is perfectly to the point — that stems curved towards the light, curve still more when the convex side is cut away, thus showing that the cause of the curvature is due to the contrac- tion of the cells on the concave side. In Impatiens (p. 579) the phenomenon of the elastically bursting body confirms this view. Here the valves of the capsule curve inwards very strongly when liberated in dehiscence : and that this is owing to the short- ening of the cells of the inner layer, and not to the enlargement or turgescence of those of the thick outer layer, is readily shown by gently paring away the whole outer portion before dehiscence ; for the inner layer, when liberated, still incurves and rolls itself up as strongly as before. The short valves at the summit of the pod of Echinocystis slowly cun^e outward in dehiscence : here the cells of the outer layer of the valve are longer and narrower than those of the inner, and the latter are stretched and torn in open- ing ; so that here the contraction of the cells on the side which becomes concave is undoubtedly the cause of the movement. And since muscular movements are effected by the contraction of the cells, which, placed end to end, compose a muscular fibril, we may suspect that vital movements generally, both in vegetables and animals, are so far analogous that they are brought about in the same general way — viz., by the shortening of the cells. We have seen that the opening and closing of the stomata is effected by a change in the form of the cells forming them ; and probably this is effected by the vital force. However, how light or other causes affect the cells to secure this shortening or elongation, we knovv not. The student ought, however, to bear in mind, that in plants we have never yet discovered anything either analogous to, or homo- logous with, the nervous, system as found in the higher animals, though various botanists have not hesitated to look upon these movements as due to something of the kind. There is. however, no denying that as we approach the confines of the animal and vegetable kingdoms, the developments of life are exceedingly similar; so much so, indeed, that Ernst Haeckel has proposed — WHAT IS VEGETABLE IRRITABILITY? perhaps on insufficient grounds— to group these organisms, which combine the characters of both kingdoms, into a separate one— his Reg/turn protisticum. In the protozoa there is no trace of a nervous system, yet it is a familiar fact to every zoologist that they contract and perform vital movements with the greatest readiness; and even in some higher animals, where no nervous system has as yet been detected, very complex vital movements are performed — apparently quite as much due to "animal irritability" as those described in the preceding paragraphs are to "vegetable irrita- bility." Finally, in the words of Asa Gray, whose pertinent re- marks on this subject it would be unjust not to quote in full : "When we consider that the excitability of sensitive plants is often transmitted, as if by a sort of sympathy, from one part to another; that it is soon exhausted by repeated excitation, . . . to be renewed only after a period of repose ; that all plants require a season of repose ; that they consume their products and evolve heat under special circumstances, and with the same results as in the animal kingdom ; that, as if by a kind of instinct, the various organs of the vegetable assume the position or the directions most favourable to the proper exercise of their functions and the supply of their wants, to this end surmounting intervening obstacles ; when we consider in this connection the still more striking cases of spontaneous motion that the lower Algse exhibit, and that all these motions are arrested by narcotics, or other poisons — the narcotic and acrid poisons even producing effects upon vegetables respectively analogous to their different effects upon the animal economy, — we cannot avoid attributing to plants a vitality and a power of ' making movements tending to a determinate end,' not differing in nature, perhaps, from those of the lower animals. Probably life is essentially the same in the two kingdoms, and to vegetable life faculties are superadded in the lower animals, some of which are here and there not indistinctly foreshadowed in plants." ^ 1 Op. cit., p. 350. 586 CHAPTER IV. ODOURS, COLOURS, LUMINOSITY, TEMPERATURE, AND NOSOLOGY OF PLANTS. The various delightful or disagreeable odours of plants generally reside in the flowers, though in some the leaves or other portions are the seat of these ; but in both cases the odour is due to the presence of essential oils, or other glandular product, in the epider- mis of the odoriferous organ. Some flowers only smell powerfully at night, and not during the day. These Linnseus called flores tristes, or melancholy flowers. They belong to various orders and tribes, as discordant as possible, but agreeing in the peculiarity named, and in the fact that in all of them the odour is very delicious, and in the fact that they all bear pale-yellowish or brownish-tinted flowers. Examples of such plants are Mesembryanihe7num noctijiorum, Pelargonium triste, Hesperis tristis, Cheiraftthus tristis, Crassula odoratissijjia, &c. Some others, which exhale a most powerful lemon-like scent, are great favourites with the Chinese, but bear no resemblance to each other, or have anything in common except in the hue of their blossoms. Again, various plants belonging to very different orders have a camphorous odour. The sweet smell of hay is found not only in the grass called Anthoxanthe7num odoratum, but in woodruff {Asperula odoratd), melilot [Melilota officinalis), and all the varieties of Orchis inilitaris — plants all differing widely from each other in botanical characters. Their odour, moreover, has one peculiarity, in that it only begins to be per- ceptible when the plants yielding it begin to dry. It proceeds from their whole herbage, and would seem to escape from the ori- fices of its containing cells, only when the surrounding vessels, by growing less turgid, withdraw their presence from such orifices. When the scent of new hay is vehement, it becomes then like the flavour of bitter almond, and in some people gives rise to " hay fever." Perhaps it may be cited as analogous to this identical odour being yielded from otherwise dissimilar plants, that the taste of capillaire syrup, given by an infusion of orange-flowers, is ODOURS OF PLANTS. found in the foliage of Gaultheria procumbens and in meadow-sweet {JSpirea ubnaria) — two very dissimilar plants, belonging respec- tively to the orders of Ericaceae and Rosaceas.^ We are told by Mr Bateman that in the order Orchidacca: alone may be found the odours of honey, musk, citron, allspice, cinnamon, noyau, angelica, aniseed, pomatum, violets, wallflowers, fresh hay, and cocoa-nut milk ; and similar instances from other orders might be cited. Some plants have a very disagreeable instead of a pleasant smell. For instance, Poederia foetida, an African plant, excites fever and headache in those inhaling its odour ; a smell as of decayed animal matter is given off by the carrion-plant {Stapelid) ; while the odour of the "skunk-cabbages" {Symlocarpus, Pothos) of America, is sufficiently expressed by their popular name. Some plants only give out their odour during the opening of the flower ; others only give it out at night ; while in another class it is only yielded at particular periods. In Epidetidrium aispidatum, Lindl., an exotic orchid, M. Riviere found a curious periodicity. It exhaled a pleasant odour at five o'clock in the morning, and remained inodorous until the following night. On the other hand, E. cochleatuiii, Lindl., var. fragrans, gives forth a fragrance like that of the hyacinth between 6 A.M. and 6 p.m. ; the perfume of Catileya bulbosa, Lindl., is only exhaled between 6 a.m. and 9 a.m. ; while that of Ayigrcemm disti- clmm, Lindl., is exhaled between 1 1 a.m. and 6 p.m. Finally, to finish the enumeration of the peculiarities of the odour of these orchids, it may be mentioned, on the authority of M. Duchartre, that the flower of Rodriguezia crispa commences to give out its scent at 6 a.m., and continues to do so to 11 p.m. In most cases, flowers lose their odour during the heat of mid-day ; while the night- flower, Cereus grandifiorus, emits its powerful fragrance at inter- vals of a quarter of an hour during the brief period of the expan- sion of the flower. In reference to odours given forth at particular times, M. Rivifere observed that in an araceous plant of the genus Cono- phalhcs, from Cochin China, the female flowers exhaled an odour just at the moment when the male flowers, situated a little higher up on the same common axis, opened their stamens to shed the pollen, after which the odour disappeared. A similar observation was made by Warming regarding the Philodendron he examined (p. 598), and Morren found that a Maxillaria ceased to give forth its aromatic odour after the pollen was applied to the stigma. There seems to be some analogy between the smell and the colour of flowers. For instance, Chrysanthetmwi hidicuin, with orange-coloured flowers, agrees faintly in scent, as it does in 1 See Sir J. E. Smith's Introduction, &c., p. 44 (ed. 1836), and Grew's Anat. of Plants, p. 279-292, for a further expansion of the facts which we have noted. 588 ODOURS OF PLANTS. colour, with the common wallflower {Cheiranthus Cheiri). It has been found that white flowers have the greatest average of pleasant-smelling ones ; orange and brown flowers are often disagreeably scented ; while the order which has the most odoriferous flowers is not, as commonly supposed, the Rosacece, but the NymphceacecB, to which the water-lilies belong. An analogy might also be traced between taste and smell, in so far that the two are strongly connected, and with many people almost undisseverable— so much so, that unless the flower is smelt there is no taste perceived ; nor can the difference of taste be appre- ciated without the eye and nose being called in to assist the gustatory nerve. The roots of some plants {e.g., Arum macnlatwii') have, when fresh, a most acrid taste and irritant quality, though, when dry, they become farinaceous and inert. The tise of taste and odour is not very apparent. Plants might have been less odoriferous or sapid without at all disarranging their functions ; but no doubt these qualities are not there except to serve some wise purpose, or to serve to the gratification of man's senses. Possibly they may be connected with the fertilisation of plants by means of insects. Classification of Odours. — Various attempts have been made from time to time — among others, by Linnaeus — to classify odours. The latest of these attempts is by M. F^e.^ The following is a synopsis of this classification : — I. Odorotis bodies: (a) Superodorants ; 0) Subodorants. 2. Nido?'ous bodies : (a) Supernidorants ; (|3) Subnidorants. A. Odorous bodies : (a) Superodorants are substances which have an agreeable perfume, which is often owing to volatile oils, which are distilled for the sake of their scent. He divides these odours into camphorous (odour of camphor), citronous (odour of citron and orange), myrtilloid (odour of myrtle), anisoid (odour of aniseed), rhodoid (odour of the "hundred-leaved rose"), and anthemisoid (odour of camomile). When the odours are owing to the presence of resins, they are divided as follows : Balsamoid (balms, vanilla). Certain odours of an analogous nature are owing to principles not yet determined. These are as follows : Nar- dosmoid (Tussilago, Nardosmia fragrans), Ambrosoid (Cheno- podium ambrosioides), Moschoid (Erodium moschatum, Scandix odorata, &c.), Narcissoid (Narcissus poeticus, N. Jonquilla, Lilium candidum, Polianthes tuberosa, &c.), (Viola odorata, wallflower, Matthiola, mignonette, &c.) Stcbodorants are those in which there is a mild, agreeable odour. The following are the classes : Meliosmoid"^ (Galium verum, 1 Mdm. de la Soc. Roy. Bot. Beige, cited in St Pierre, 1. c, p. 960. 2 Honey odour. COLOURS OF PLANTS. flowers of lime), yasminotd (odour oi iasmint), Amygdaloid (odour of bitter almonds, Sambucus herbacea, &c.), Cyamoid (flower of acacia, Robinia Pseudacacia, Lathyrus odorata, «S:c.), Maloid (odour of apple), and Tannoid (odour of tanned leather). B. Nidorous bodies are those in which the odour is strong, and often disagreeable, and are divided into super and sub-nidorants, according to the intensity of the odour. Fde divides them into the following classes : r. Odours due to volatile oils holding resin in solution, and isolable by distillation — Terebinthoid (Coniferae, Terebinthaceze, &c.) 2. Odours due to volatile oils — Peganoid (odour of rue, Ruta graveolcns), Dictainnns, Tagetes patida. 3. Odours due to the presence of sulphurous oil — A I lioid {odour of garlic), asafoetida, acacia-roots, &c. 4. Odours due to different principles — Fetid (various species of Sterculia, Datura, Nicotiana, and other Solanaceae), Mecanoid (odour of opium and poppies), Cicutoid (Conium maculatum, &c.), Hircoid (odour of the goat, Hypericum hircinum, Loroglossum hircinum), Ciminoid (Corian- drum sativum, Coris Monspeliensis), Pteridosmoid (fern odours) ; and lastly, there are the following odours : cadaverous, marine, spermatic, sterctcliiie, tiriiious, and vulvary. The different kinds of odours have brought certain descriptive terms into use to designate them. These are (in Latin) alliaceus, ambrosiacus, aromaticus, fcetidns (or teter), graveolens, hircimis, muriatictis, pungeiis, spermaticus, stiaveolens, virosus, &c., most of which are explained above, or are self-descriptive. COLOURS OF PLANTS. With the exception of the parts composing the flower, the epi- dermis is in general coloured green, owing to the presence of chlorophyll. Occasionally, however, it is variegated, especially in the leaf, which is frequently differently coloured on the under and upper surfaces. For instance, the leaves of Begonia are satiny- green above, and traversed by dark-red veins on a reddish ground beneath. When plants naturally green become variegated, it is primarily a diseased state ; but this state can be, and is, frequently transmitted to the posterity of the plant by the art of the horticul- turist. Variegated plants have generally less vital energy than uniformly coloured ones. Plants of an acid or astringent nature often become very red in their foliage by the action of an acid, as the dock, Epilobium and Berberis. A most extraordinary change of colour has, however, been observed in a Selaginclla (S. muta- hilis) cultivated in the Royal Gardens at Kew. In the morning the fronds are green, but as the day advances they become pale, recovering gradually their colour by the following day. Dr 59° CLASSIFICATION OF COLOURS OF PLANTS. Hooker observed that in their pale condition the endochrome, or colouring matter of the cells, was contracted into a little pellet.' Changeable colours are also found in the corollas of flowering plants. For instance, that of Hibiscus mutabilis is white in the morning, pale-rose at mid-day, and bright-rose in the evening. Some white flowers {e.g., the white flowers of the margin of Chry- santhemum alpittian) redden as they fade. In these flowers, how- ever, we have the most varied and exquisite colours — adding im- mensely to the beauty of the plants. These colours also undergo remarkable variations. For instance, in the little English scorpion- weed {Myosotis scorpioides), and several others of its natural order {Boragifiacecs), the flower-buds are of the most delicate rose- colour, which turns to bright blue as they open ; and many yellow flowers, under the influence of light, become white. Numbers of red, blue, or purple ones are liable, from some unknown cause, to vary to white. Such varieties are sometimes propagated by seed, but can in general be kept up if the plant is propagated by cuttings, grafting, or by roots. Classification of Colours. — The researches of De CandoUe pri- marily, and in the second degree of Schiibler and Frank, have established the following classification of the colours of plants. They are divided into two series — Cyanic"^ (of which blue is the type), and Xanthic'^ (of which yellow is the type). From these proceed all the various tints, according to the following chromatic scale : — Red. \ Orange-red. I Orange. Ixanthic series of De Candolle (oxidised series of Orange-yellow. ( Schiibler and Frank). Yellow. Yellow-green. Green. Colour of leaves. Blue-green. Blue. Blue- violet. Violet-red. Red. [ Cyanic series, DC. (desoxidised series of Schiibler and Frank. ) When we examine the plant microscopically, we find that in general the colours of the cyanic series are in solution in the juice of the cells, while those producing the xanthic series and the green are in the form of granules, which are only modifications of chlorophyll. Exceptions to this rule, however, exist — according to Mohl and George Lawson — in the flowers of Strelitzia Regina and Salvia splendens, in both of which the colouring matter exists in a granular form. 1 Berkley, Introd. to Cryptogamic Dot., p. 563. 2. (cuom, blue. favflds, yellow RELATION OF FORM AND COLOUR. The different shades of the same colour in flowers are produced by the greater or less number of colourless cells interspersed through the substance of the coloured ones, and the different colours are often caused by layers of cells with one colour lying above another with a different colour {e.g., brown by red above green, orange by yellow above red, &c.) White is generally pro- duced by cells containing air. and this is also the cause of the white spots on some green or other coloured plants. The velvety appearance of many flowers and leaves is caused by the play of the rays of light on the epidermis, the superficial cells of which are raised into papillae (fig. 33, p. 53) ; and the metallic tint of the leaves of certain orchids is due to the action of light on prismatic cells containing air. The Relation of Form and Colour. — It would be neither just to the student, nor to the distinguished botanist, to whose labours we are indebted for them, to pass from this subject without noticing, however briefly, the beautiful researches of Professor Dickie of Aberdeen on the relations of form and colour.^ By means of patient research, conducted over a number of years, he has deduced some remarkable laws, which may be given seriatim. 1. In regular corollas the colour is tmiformly distributed, what- ever be the number of colours present—that is to say, the pieces of the corolla, being all alike in size and form, have each an equal proportion of colour. The common primrose {Primtda milgaris) is an example where the petals are all of one colour. In the Chinese primrose {Primula sinensis) there are two colours. Here the centre is yellow and the margin purple, but each has an equal proportion of colour. 2. In irregtilar flowers where the number 5 prevails, the odd piece is most varied in form, size, and colour; when only one colour is present, it is usually more intense in the odd lobe of the corolla. Where there are two colours, one of them is generally confined to the odd piece. Sometimes, when only one colour is present, and of a uniform intensity in all the pieces, the odd segment has spots or streaks of white. For instance, in the common laburnum there are four petals yellow, and the fifth yellow with purple veins. In the common red clover the odd piece is distinguished from the others by its darker purple veins. In the eyebright {Euphrasia officinalis) the corolla is generally purple ; the odd piece has a yellow spot. In the wild thyme the corolla is generally red-purple, with two pale spots on the odd piece. And in Ajuga reptans (common bugle), four divisions are purple, and the fifth has a yellow spot on the inner surface. It has also been pointed out, by various observers, that when a 1 Typical Forms and Special Ends in Creation, by Principal M'Cosh and Pro- fessor Dickie, 1857, p. 153. 592 RELATION OK FORM AND COLOUR. flower is of two colours, the one is always a complement of the other — e.g.. Primula farinosa, bcaring pale-lilac blossoms, " with yellow eyes powdered with silver farina." When there are three colours, the third is commonly white.^ 3. In certain Thalaniiflorous Exogetts (i. e., flowers where there is no adhesion between the whorls of the corolla, and where the stamens are hypogynous or inserted at the base of the ovary) wii/i imequal corolla, arising chiefly from difference in size of the petals, the largest are most highly coloured— e.g., the common horse-chest- nut. On each petal there is usually a crimson spot at the lower part ; the size of this spot and its intensity are in direct relation to the size of each petal — the two upper being largest, and the two lateral smaller, and the odd piece least of all, 4. Different forms of corolla in the same inflorescence often pre- sent differences of colottr, but all of the same for7n agree also in colour. The Compositae (Aster, daisy, &c.) illustrate this. Where there are two colours, the flowers of the centre, usually of tubular form, have generally one colour of uniform intensity. These of the circumference having a different form, agree in colour also — e.g., daisy, where the centre flowers are yellow, and all the ligulate or strap-like flowers of the ring or circumference are white, variegated with purple. A yellow centre with a purple margin is common in Compositae — e.g., Aster, Rudbeckia, &c. 5. The law of contrasts in the colours of the flowers is simpler in Monocotyledmis than in Dicotyledons. The flowers of Dicotyledons may be symbolised by the square or pentagon — four, eight, five, or ten being the prevalent numbers in the different whorls ; whereas, since three and six are generally found in the flowers of Monocotyledons, the triangle may ser\'e to symbolise such an arrangement. In conclusion, it may be stated that simplicity of figure corre- sponds with simpler contrast of colour in the Monocotyledons j while greater complexity of colour, and greater cojnplexity of struc- ture, are in direct relation to Dicotyledons. Is all this mere coincidence? Professor Dickie (than whom no man's opinion is entitled to more deference) thinks that it is not. The laws of beauty not being yet unfolded and detected, this author remarks that it is not possible to demonstrate scientifically that the relations we have been treating of are in accordance with a:rtistic principles. " Still the eye at once perceives, in regard to some of these arrangements, they are intended to enhance the beauty of the plant. Would not reason be offended if uniform flowers had not uniform colouring? And is there not propriety when, in an irregular flower, there is one petal standing by itself, 1 Gillman in Amer. Naturalist, 1870, p. 313. LUMINOSITY OF ROOTS, ETC. 593 that that petal should have more brilliant colours, that thus the flower may be tempered together, having more abundant honour in the parts which lacked, that there be no schism in the plant? " In all this there is an adaptation of the colour to the natural taste of man, and to the laws of colouring to which that taste has given, rise. For instance, in painting, a large portion of the ground is of a neutral colour; and in the grand canvas of nature, the ground- colours, if not neutral, are soft and retiring. The sky is not scar- let, nor the clouds crimson, nor the grass yellow, nor the trees decked with orange-leaves. The soil, on the contrary, is in most places a sort of brown ; the mature trunks of trees take a neutral tint ; the sky is soft blue, except where covered with grey clouds ; and the foliage of the earth is refreshing green. There is also a beauty in the way different plants grow together in association ; in a word, in nature we see the most exquisite harmony of colours in association — laws which have been only recognised by man in a late state of his civilisation, though ever existing in the vegetable world. If Mr Darwin's theory is true, then there can be nothing in this ; for he allows only utilitarianism, or descent, as at all concerned in the varieties of colour, &c., though to the artistic mind this is one of the objections to the doctrines of the eminent philosopher mentioned. In science, however, we can afford the indulgence of no aesthetic sentimentalism, and the doc- trine must stand or fall by facts. In the mean time, it will be enough that we state the facts, as generalised by this most emi- nent of Scottish botanists. LUMINOSJTY OF PLANTS. It has been long known that certain plants emitted light, which, for want of a better name, has been called phosphorescence. The numbers known to do so are rather numerous, and belong to differ- ent orders. Not to mention the vague rumours of fiery bushes which still float about in India among the modern Hindoos, as such stories did in former days among the old Hindoos and Greeks, there are facts, circumstantial and well confirmed, enough to record. Luminosity of Roots, &c.— The root-stock of a plant from the Ooraghum jungles, at the foot of the Madura Hills, near Tachoor in India, was exhibited in July 1845 at a meeting of the Royal Asiatic Society. It lost its phosphorescence when dry, but re- gained it when moistened; and this property was not lost by repeated experiment each time it was tried-— the slice of the root glowed with equal brilliancy. It is said that this plant has been long familiar to the Brahmins under the name of Jyotismati, 594 LUMINOSITY OF FLOWERS. and that the discovery of its phosphorescence was rhade by a "tuhseeldar" compelled to take shelter at night under a scrap of rock, when he was astonished to see a blaze of phosphoric light all over the grass in the vicinity. The Sanscrit authorities also refer to it. The late Colonel Madden found that perhaps one root in a hundred oi Anthistiria Anatherum was luminous at night during the rainy season in the Himalayas, vi'here it is found. Other grasses, such as species of Andropogoji, are reported to possess the same property ; and fakirs seek far and near for a plant they call " Sunee," which is rumoured to possess this quality also, in addition to the more mythical one of revealing the wonders of fairyland. Luminosity of Flowers— In 1845, the country around Simla in the Himalayas was filled with rumours that the mountains near Syree were illuminated nightly by some magical herb. Probably these rumours may be traced to the existence of luminosity in Dic- tanimcs Htmalayensis (Royle), or other species of the same genus, which is known to possess that property in its European representa- tive D. albus. Polianthes Ucberosa is rumoured, though doubtfully, to dart small sparks in great abundance, in a sult^-y evening after a thunderstorm, from such of its flowers as are fading. In regard to the phosphorescence of the Dittany, or Fraxinella, much doubt has been expressed ; but of late the matter has been experiment- ally set at rest by the observations of Dr Hahn,^ who remarks : " When the daughter of Linhasus one evening approached the flowers of Dictamnus albus with a light, a little flame was kindled without in any way injuring them. The experiment was after- wards frequently repeated, but it never succeeded ; and whilst some scientific men regarded the whole as a faulty observation or simply a delusion, others endeavoured to explain it by various hypotheses. One of them especially, which tried to account for the phenomenon by assuming that the plant developed hydrogen, found much favour. At present, when this hj'pothesis has become untenable, the inflammability of the plant is mentioned more as a curiosity, and accounted for by the presence of etheric oil in the flowers. Being in the habit of visiting a garden in which strong healthy plants of Dictamnus albus were cultivated, I often repeated the experiment, but always without success, and I already began to doubt the correctness of the observation made by the daughter of Linnseus, when, during the dry and hot summer of 1857, I re- peated the experiment once more, fancying that the warm weather might possibly have exercised a more than ordinary effect upon the plant. I held a lighted match close to an open flower, but again without result; in bringing, however, the match close to 1 Seemann's Journal of Botany, 1863. LUMINOSITY OF FLOWERS. 595 some other blossoms, it approached a nearly faded one, and sud.- denly was seen a reddish, crackling, strongly shooting flame, which left a powerful aromatic smell, and did not injure the peduncle.^ Since then I have repeated the experiment during several seasons; and even during wet, cold summers, it has always succeeded — thus clearly proving that it is not influenced by the state of the weather. In doing so I observed the following results, which fully explain the phenomenon : On the pedicels and pe- duncles are a number of minute reddish-brown glands, secreting etheric oil. These glands are but little developed when the flowers open, and they are fully grown shortly after the blossoms begin to fade, shrivelling up when the fruit begins to form. For this reason the experiment can succeed only at that limited period when the flowers are fading. Best adapted for the purpose are those panicles which have done flowering at the base, and still have a few blossoms at the top. The same panicle cannot be lighted twice. The rachis is uninjured by the experiment, being too green to take fire, and because the flame runs along almost as quick as lightning, becoming extinguished at the top, and diffus- ing a powerful incense-like smell." Various plants probably giVe forth inflammable matter, and it is probably for this reason that the natives of the Spice Islands are careful how they bring flame near particular trees. Mr R. Dowling,^ again, mentions the luminous appearance of the common marigold after a week of very dry weather in August. It occurred about 8 p.m., when a golden-coloured lambent light appeared to play from petal to petal of the flower, so as to make a more or less interrupted corona round its disc. It was less lurid as the light declined. Linnaeus, his daughter Christina Linnaeus, Linnaeus the younger, Haggren, Crome, Zawadski, Hagen, John- son, and the Duke of Buckingham, have contributed observations on this subject. The following plants have, in addition to those mentioned, been noted as luminous : Indian cress (Tropaolum majiis), the sunflower {Helianthtis anmms), the marigold {Calen- dula officinalis), African and French marigolds {Tagetes erecta and T. patiila), Martagon lily {Lilium chalcedonicum and L. bidbiferiim), poppy {Papaver orientale), haiiy red poppy {Papaver pilosum), Chrysanthemum {Chrysanthemum inodorwn), evening primrose {CEnothera inacrocarpa), Gorteria rigens, geraniums, and verbenas.^ Regarding the last-named plant, a correspondent of a horticul- tural journal* noted the luminosity very particularly in reference ' The late Professor Henslow made a similar observation. 2 Report of Brit. Assoc., 1843. 3 Edwin LankesttT in Gardeners' Chronicle, 1843, p. 691. ■« Gardeners' Chronicle, 1859, p. 604. 596 LUMINOSITY OF FLOWERS. to three scarlet verbenas, each about nine inches high and about a foot apart, planted in the border in front of his greenhouse, "As I was standing a few yards from them, and looking at them, my attention wAs arrested by faint flashes of light passing backwards and forwards from one plant to the other. I immedi- ately called the gardener and several members of my family, who all witnessed the extraordinary sight, which lasted for about a quarter of an hour, gradually becoming fainter, till at last it ceased altogether. There was a smoky appearance after each flash, which we all particularly remarked. The ground under the plants was very dry ; the air was sultry, and seemed charged with electricity. The flashes had the exact appearance of summer lightning in miniature. This was the first time I had seen any- thing of the kind, and having never heard of such appearances, I could hardly believe my eyes. Afterwards, however, when the day had been hot, and the ground was dry, the same phenomenon was constantly observed at about sunset, and equally on the scarlet geraniums and verbenas. In 1859 it was again seen. On Sunday evening, July 10 of that year, my children came running in to say that the 'lightning' was again playing on the flowers. We all saw it, and again on July 11. I thought that the flashes of light were brighter than I had ever seen them before. The weather was very sultry." The writer of these pages has also observed it frequently in TropcBolum, verbenas, and other plants, but cannot coincide with the theory of Allman and others that there is no real light, only an optical delusion. "Whatever may be the cause, we have to seek it elsewhere than in this Gordian solution of the question. There seems, however, more reason to believe that in mosses it may be due to simple reflection of light. ScMstostega pinnata, a moss inhabiting caverns and dark places in the south of England, has been observed to give forth an appearance of light ; but Bab- bington and Lloyd discovered that this luminous appearance was due to the presence of small crystals in its structure, which re- flected the smallest portion of the rays of light. In Germany it has been observed in another species of the same genus — S. osmundacea — by Funk, Brandenberg, Nees von Esenbeck, Horn- schuh, and Struve. By Bridel, Brideri, and Agardh the elder, it was attributed to the presence of a small Alga, Protococcus smaragdiniis, which inhabited the moss ; but Unger and Meyen have satisfactorily proved that " at certain seasons the cells of the moss assume a globular form, and being partially transparent, the light is refracted and reflected in such a way as to present a lumi- nosity on the surface of the vessels," Luminosity of Fungi. — Certain fungi have long been known to be luminous, this luminosity having been observed in various LUMINOSITY OF FUNGI AND SAP. 597 parts of the world ; and it has been generally found to be a species of Agaricus which has yielded the phenomenon— Agaricus oleaj-ius of the south of Europe, Agaricus Gardneri in Brazil, and by others in Australia, Amboyna, &c. The Rhizo- morphce, found in mines, are often so beautifully phosphorescent that one can see to read by the light given forth. A remarkable instance is recorded by the Rev. M. J. Berkley. A log of spruce of larch, 24 feet long, had the inside of its bark covered with a white byssoid mycelium. This was so luminous, that when wrapped in five folds of paper the light penetrated through all the folds on either side as brightly as if the specimen was exposed.^ Diseased potatoes, on being sliced, are sometimes seen to be luminous, pro- bably from the presence of a fungus causing the disease. A fungus, described by Drummond ^ as growing in the vicinity of the Swan River, gives out light enough to read by — the light being a bright-white glow, ceasing on the plant becoming dry ; one, growing on a palm in Brazil, and hence called by the inhabi- tants the " Flor de coca " — gives out a pale greenish-hued light.^ Decaying wood is often luminous from the mycelium of fungi creeping through its tissues. Tulasne* examined the luminosity of the Agaric of the olive without being able to explain it ; but Fabre, in a paper in the same journal, ascribes it to a temporary increase of oxidation. Luminosity of Sap. — The sap of some plants is also luminous. Mornay describes a tree in South America called " Cipo de Cuna- man," with a milky juice, which gives out in the dark a bright light. Martius also mentions that when Euphorbia phosphorea was wounded, the sap gave out a light. The same celebrated traveller and botanist refers to the observations of Senebier, who found that when an Arum was confined in oxygen gas, it gave out light as well as heat. The whole subject still requires inves- tigation. In the majority of cases it is probably due to increased oxidation in the tissues of the plant, though sometimes, as in Diciamnus, a volatile oil may be the cause.* 1 Gardeners' Chronicle, Sept. 21, 1872 ; with remarks of W. G. Smith in No. for Sept. 28. — Grevillea, i. 75. See also Gardeners' Chronicle, 1872, p. 1327. and 1874, p. 63. ^ Hooker's Journal of Botany, April 1842. " Gardner in Hooker's Journ of Bot., ii. 426. * Ann. des Sc. Nat., 1848, ix. 338. 5 For a good summary — for which we are indebted for some of the foregoing facts— see Science Gossip, 1871, p. 121 ; and Gardeners' Chronicle, 1871, p. 904. A tolerably complete bibliography of writings will be found in Schleiden's Principles, p. 542 ; or in Meyen's Physiologic, Bd. ii. 192. 598 TEMPERATURE OF PLANTS. TEMPERATURE OF PLANTS. Though at the time of the flow of the sap the general tempera- ture of the tissues of the plant may be slightly raised, the range of heat is not great, and bears a tolerably exact ratio to the ordinary temperature of the surrounding atmosphere, soil, and fluid ab- sorbed. However, at the period of flowering, the temperature within the flower is much elevated. This is chiefly observed in the order Aracete. As early as 1777, Lamarck made observations on Arum Italicum, Mill. ; and subsequently these observations were repeated by Senebier on the common cuckoo-pint {Artini mac7ilatum), with a result which showed that at the period of flowering there was heat 9° above the atmosphere. Hubert, on placing a thermometer in the centre of several flowering speci- mens of Arum cordifolium, found it elevated 25° above the tem- perature of the air at the surface of the ground. Planchon found a thermometer thrust into the flower of Victoria regia, a water- plant, showed 6° above the temperature of the air. Similar observations have been made by Saussure, Schultz, De Vriese, Vrolik, Treviranus, Gartner, Brongniart, Goppert, Warming of Copenhagen, and others. The last-named botanist made his observations on a Brazilian species of Philodettdroii — P. Lwidii, Wrmg. He found that there was a series of calorific undula- tions which did not coincide with the time when the heat of the air was greatest. The greatest heat which Dr Warming observed was 39/4° Cent., showing a difference of i8^° between the tem- perature of the flower and the surrounding air.^ The cause of this increase of temperature is probably an in- creased absorption of oxygen, and formation of a large quantity of carbonic acid, which has also the effect of increasing the volume of the flowers.2 It has also been long known that seed when germinating, as they lie heaped in masses, as on a malting-floor, evolve a consider- able amount of heat, this evolution of heat not being connected, as Goppert showed, with fermentation, but with germination. Seeds of hemp, clover, Spergula, Brassica, &c. — all of different chemical composition — when germinating in quantities of about 1 Vidensk. Medd. fra den Naturhistoriske Forening i Kjob, 1869. See also Dutrochet, Comptes rendus, 1839, p. 695 ; Brongniart, Nouv. Ann. de Muse- um, iii.; Vrolik and De Vriese, Ann. des Sc. Nat., ser. 2, v. 134, and xi. 62; Van Beek and Bersgma, Obs. thermoelect. sur I'eldvation de temperature des fleurs de Colocasia odorata, 1838 ; Pfeffer, Sitzungsbericht, d. ges. z. Beforder- ung d. ges. Naturwissensch. z. Marburg, 6th Feb. 1863, S:c. 2 Rameux in Ann. des Sc. Nat., 1843; Schubler in Poggendorff 's Annalen, X.; Dutrochet, Ann. Sc. Nat. (ser. 2), t. xii.; Gardner in Trans. Linn. Soc, 1841, and Phil. Mag., 1842 ; and op. cit., ut supra. TEMPERATURE OF PLANTS : VEGETABLE NOSOLOGY. 599 a pound weight, become heated, when the surrounding atmo- sphere is at a temperature of 48°-66° to 59°-! 20° Fahr. Full-grown plants, when heaped on the floor and covered with bad conductors of heat, cause a rise of a thermometer placed among them of about from 2°-7°, and even (as in the case of Spergttla) as much as 22° above the temperature of the air. Indeed, plants standing alone show an evolution of heat from one-sixth to one-twelfth of a degree above the air.^ All these manifestations of increased temperature in germinat- ing seed probably point to an increased consumption of oxygen, and exhalation of carbonic acid. In vegetating organs, Mohl considers the source of heat different. " It is true," he says, " that oxygen is consumed and carbonic acid formed by all organs ; but since, on the whole, a greater quantity of carbonic acid is decomposed in the green-coloured organs than is formed in the remaining parts, more heat must be consumed than pro- duced in the respiratory process of vegetating organs. But the evolution of heat must be connected with the nutrient process ; for the plant forms its organic substance, if not wholly yet in great part, from gases and liquids. Since, then, the growth of the plant exhibits a daily exaltation, occurring about noon, it is quite in accordance that the evolution of heat also should occur in increased degree at the same time." This seems reasonable. The experiments made regarding the temperature of trees by boring holes in them, and inserting long-tubed thermometers, are contradictory, owing to many disturbing causes of error. Yet the rule is, that their temperature is higher in the vvinter and lower in the summer in the tree than in the surrounding atmosphere. Wood in its longitudinal direction is a good, but across its fibres it is a bad, conductor of heat.^ VEGETABLE NOSOLOGY AND TERATOLOGY. Vegetable nosology, or the diseases to which plants are subject, is a long and intricate subject. Fortunately, however, it does not ^ Dutrochetin Ann. des Sc. Nat., ii. 77 (1839). 2 See Schleiden's Principles, p. 541 ; Meyen's Physiologie, Bd. ii. 164 ; Hai- der, Beobrachtungen uber die Temperatur der Vegetabilien, 1826 ; Neuffer, Untersuch. iiber die Temperaturer underungen der Vegetabilien, 1829 ; De la Rive and De Candolle's Poggendoiff's Annalen, Bd. xiv. s. 590 ; Sachs' Hand- buche, s. 48 et seq. : (for many original observations) Flora, 1864, s. 5 ; and Jahrb. f. \viss. botan. , ii. (1868) 328; Villari Poggendorff's Annalen, 1868, Bd. 133, s. 412 ; De Vriese, Archives Nderlandaises, t. v. (1870) ; De Candolle in Biblioth. Universelle, 1863; Koppen, Warme und Pflanzenwachsthum, 1870 (teste Sachs); Goppert, Bot. Zeit., 1871, Nos. 4 and 5 ; and Bibliog. in Sachs' Lehrbucii, ed. 1873 (" Allgemeine Lebensbedingungen der Pflanzen," s. 632 et seq.) 6oo VEGETABLE NOSOLOGY AND TERATOLOGY. call for discussion in a work of this kind, coming under the department of horticulture and arboriculture ; and therefore, though a legitimate subject of study by the scientific botanist, is not yet a part of botanical science, any more than is the cultiva- tion and conservation of living plants. Disease may be defined as that state of the organism in which all the organs are not perform- ing their functions in accordance with nature. The causes of these diseased conditions in plants may be classed as follows : i. Parasitic fungi and other plants, sucli as dodder attacking the tissues. 2. Insects causing galls and fissures in the leaves and bark, as well as wounds of any description. 3. Poisonous gases in the air or soil, as well as any poisonous material so placed as to affect the nutrition. 4. Atmospheric or other conditions, so affecting the plant as to alter the conditions of nutrition by giv- ing a redundancy or deficiency of air, light, moisture, warmth, &c. Under these four heads most of the diseases of plants find a place. Vegetable Teratology is that portion of the subject which takes cognisance of deformities and abnormalities of growth, and is not properly disease any more than abnormalities in the animal organism are ; nor, when such abnormalities do not injuriously affect the reproductive or nutritive powers of the plant, are they productive of disease. These teratological variations we have noted, so far as was necessary, while studying the normal condi- tions of the organs affected.^ With Masters, we may divide the phenomena of teratology into four sections : i. Deviation from the ordinary arrangement, com- prising (a) union of parts (cohesion and adhesion) ; 0) indepeiid- etice ofo7'gatis (fission, dialysis, solution) ; (y) alter attoji of position (displacement, prolification, heterotaxy, heterogamy (p. 407, 418), alteration in the direction of organs). 2. Deviations from ordinary forms, comprising (a) strasimorphy (persistence of juvenile forms) ; O) pleiomorphy (irregular peloria) ; (y) metamorphy (phyllody, metamorphy of the floral organs) ; (8) heteromorphy (deformities, polymorphy, alteration of colours). 3, Deviations from ordinary number, — (a) increase of number of organs (multiplication of axile organs, inflorescence, multiplication of foliar organs) ; (/3) diminished number of organs (suppression of axile organs, sup- pression of foliar organs). 4. Deviations from ordinary size and consistence, — (a) hypertrophy (enlargement, elongation, enation) ; (/3) atrophy (abortion, degeneration). 1 There are various works treating of this subject ; but the most recent, as well as the ablest and most exhaustive, is Dr Maxwell Masters's Vegetable Ter- atology (Ray Society, 1869), to which the student is referred. 6ot INDEX AND GLOSSAEY, Aberrant, differing from the customary structure. Abiogenesis, or "spontaneous " generation, in wliicli cells are supposed to originate from inorganic or dead matter. Absorption of nutriti\'e fluid, 239. Acaulescent plants, 71. Accrescent, gi'owing after flowering. Accumbent, leaning or lying against an- other plant or body. Acenacil'orm, scimitar-shaped. Acephalous, "headless," when the style is lateral, and therefore does not surmount the ovaiy. Acerose, needle-shaped. Acervuli, little heaps or clusters. Acetabuliform, cup-shaped. Acetic acid, 216. Acheillary, having the labellum (in an orchid) undeveloped. Achene, 483. Achlamydenus, 299. Acicular (see Acerose). Acotyledonous, 73. Acotyledons, stem of, 98. structure of root, 135. Acrocarpous, with a terminal fructification. Acrogenous stem, 73, 74, g8. course of sap in, 274. Acrospire, the first sprouting leaves or " braird" of com. Acuminulate, shortly acuminate or taper- pointed. Adesmy, division or splitting of an organ usually entile. Adnation, 380. Adverse, opposite. Aerophytes, plants growing entirely In, and deriving their noiu-ishment from, the air. ^Equilateral, equal-sided. iEruginose, the coloui' of verdigris. ^Estivation, 372. iEterio, 494. Agglomerate, heaped together. Aggregate (see Agglomerate). Air, as supplying food to plants, 259. Alabastrus, a flower-bud. Alfc, 310, 311. Albescent, growing white. Albicant, growing whitish (much the same as Albescent). Albinism, a pale or whitish condition, owing to the absence or non-develop- ment of chlorophyll Albumeji, 218, 503. Albuminoid or proteine bodies, 217. Alburnum, 86. Aleotorioid, filiform. Aleuroue, 28, 29, 218. Alkaloids, 220. Alliaceous, smelling like garlic, 589. Aluminium, 222. Alveolate, with "alveolfe" or sockets, honey-combed. Amentum, 394. Ammonia , 224. Amnios, sac of, 410. Amphicari^ous, having two kinds of traits. Amphisarca, 493. Amplexus, same as Equitant. AmpuUaceous, like an "ampulla," bladder or flask. Amyloids, 212. Anantherum, filament without an anther. Anberry, a diseased warty condition of the roots of Crucifei-a;, caused by tlie attacks of insect-larvae. Andrcecium, 319. development of, 371. regularity or irregularity of, 321. Androgynism, a change from a dioecious to a monoecious condition. Androgynous, having male and female fiowers on the same inflorescence. Androphores, 323, 324. Anemophileae, 455. Anfractuose, presenting sinuosities (anthers of Cucurbitaceie). Angieuchyma, 41. AngiUar divergence, 183, 185. Anicipital, two-edged and flattened. Anisomerous, unsymmetrical. Anistemonous, 320. Aunotinous, literally a year old, when the other shoot of the last year is rendered visible by an iuteiTuption at the point where it joins the previous growth. Annuals, 294. Annulate, ringed. Anomalous stems, exogenous, in. Aateposition, 380. Anther, 279, 319, 327. — ■ apijendages of, 32s. attachment to filament, 331. colour of, 329. dehiscence, 326, 327. development of, 343, 344. distractile, 330. 602 INDEX AND GLOSSARY. Antlier, position of, &c. , 326. shape of, 325. structure of, 330. union of lobes of, 326. union of, 327, 328. Authodiuni, same as Capitulum. Antliopliorc, 286. Antliotaxis, 391. Antipatliies and sympathies of plants, 141. Aphyllous, 146. Aphylly, when leaves are suppressed. Apiculate, terniinating in a short apex or point. Apiculus, a short point or apex. Apocarpous, 348, 465. Apostasis, separation of the whorls of leaves or floral coverings by an unusual length of the internodes. Applanate, flattened out horizontally. Apposite, iJlaced side by side. Apterous, wingless. Arachnoid, spider-web-like. Arborescent, 73. Ai-eolate, divided into " areote," or little spaces or cavities. Arillode, 501. Ai'illus, 501. Aristate, having a beard or avra like the gi-ain of barley. Aristolochiaceffi, anomalous stems of, 114. Arrest or defect in development, 379. Arsenic, 221. use of, in the plant, 233. Articulate, joiuted- Ai-ticulation of leaves, 196. Ascidia as leaves, 158. AsclepiadaceiE, fertilisation of, 450. Ash, ingredients of plants, 221. Ash, varying proportions of, 224-226. ingredients, absorption of excess of, 233. how they exist in plants, 234. Assimilation, 270-272. Assurgent, rising upward in a cui've. AstoniouR, without mouth or aperture. Atractenchyma (see Prosenchyma). Atrophy, 600. Autonomous, complete in themselves, ap- plied to perfect plants. Autophyllogeny, one leaf gi-owing on an- other, 199. Avenine, 218. Awn, an "arista" or beard (sec Ai'istate). Axis, ascending, 71. primary, 78. secondary, 78. tertiary, 78. Axophyte, 71. Bacca, 491. Baiausta, 493. Bark, 89. variations in sti'ucture of, 93. Barren, applied to a flowerless shoot. Baryta, use of, in the plant, 232. Basifugal development, i6i. Basigynium, 350. Basipetal development, 161. Bast-tissue, 40. Bast-layer, 89. Bauliiniaj anomalous stems of, 115. Bicarinate, two-keeled (the bl In all such compound words signifying " two "). Biennials, 295. Bignoniacea;, anomalous stems of, 112. Bilocular, 475. Biogenesis, production of living cells from similar cells of the same nature ])re- existing. Bivalvular, 478. Blastema, 71. Bossed, with a boss or central elevation (see Umbonate). Botanometry, 181. Botany, i. agi-i cultural, 5. economical, 5. geogi-aphieal, 5. horticultural, 5. industrial, 5. medical, 5. palaiontological, 5. physiological, 4. Bothrenchyma, 48. Braohiate, when opposite branches are de- cussate. Bracteoles, 288. Bracts, 287. conversion into stamens, 286. forms of, 287, 289. gamophyllous, 289. polyphyllous, 289. Branches, 72. Branching, 78. Branchlets, 72. Bromine, 221. Bryophyllum, &c., 181, 200. Buds, 74. adventitious, 77. flower, 77. foliaceous, 77. fulcrar, 77. lateral, 74. mixed, 77. stipular, 77. tenninal, 74, 76, 77. wood or lealing, 77. Bud-scales, 77. Buds on roots, 124. Bulblets, 109. Bulbs, 107-109. uses of, 109, no. Bimdles, vascular, 50. Bursiculate, purse-like. C^NANTHIXJM, 397. Csenilescent, more or less sky-blue (same as Coerulescent). Csesious, bluish-grey. Cajspitose, gi-owth in tufts. Csespitulose, a diminutive of casspitose. Cafleine, 220. Caloarate, spurred. Calceolate, slipper-shaped. Calcium, 222. Calcimn carbonate, 223. sulphate, 223. ishosphate, 223. Calcivorous, eroding or "eating into" a limestone rock. Calicula, 290, 291. Calycauthemy, the conversion, wholly or partially, of scimls into ijetals. INDEX AND GLOSSARY. 603 Calycine, belonging to tlie caljTC. Calycoid, calyx-like. Calypliyomy, abnormal adliesion of the calyx to the corolla. Calj-x, 279, 299- absence or presence of, 305. accrescent, 302. colour of, 304. development of, 371. dialysepalous, 303, 304. duration of, 301. gamosepalous, 303, 304. niai'cesceut, 301, 302. of rose, 302. of winter cherrj% 302, 417. peculiar forms of, 304, 305. — regular or irregulai', 302. use of, 306. Cambium, 81, 8g, 274, 275. Campylospennous, when the endosperm is ciu'ved at the margin so as to form a longitudinal groove or fiUTOw. Canaliculate, channelled. Canals, air-bearing, 31, 32. intercellular, 15. Cancellate, resembling lattice-work. Cane, sugar, 214. Canescent, hoary-grey. Capillary, thread-like. attraction as aiding ascent of sap, 249. Capitulum, 396. disc of, 396. foveolae of, 396. radius of, 396. Caprification, fertilisation of the flowers of the fig, &c., by insects as well as by arti- ficial means. Capsule, 488. Carbon, 209. Carbonates in ash of plants, 222. Carcenile, 484. Carpel, 279, 348, 349. formation of, 362, 385. Carpology, 481. Caruncle, 502. Carj'opsis, 484. Caseine, 218. Cassideous, helmet-shaped, applied to pet- als or sepals. CatacoroUa, " a second corolla, formed in- side or outside the fruit." Cataphyllaiy, enclosing true leaves. Caudex, 72. Caulescent, growing on a stem. plants, 71. Caullcle, 510. Cell, 8, 9. contents of, 19. elongated cylindrical, 13. — — formation, original, 34. form of, 9, 10. fusiform, 13. gemmation of, 36. growth, 36. gyration in, 20, 269. increase of, 33. large, 33. liquid, 22. multiplication, 35. nucleus, 22. structure of, 33. Cell, theories of, 34, 35. Cell-wall, 16, 33. 34- mancings on, 17. Cellular tissue, 9, 10. lacunas in, 31. Cellulose, 17. group, 212. Cellulaj clathratiE, 265. conductrices, 265. Cenauthy, suppression of the essential or- gans (stamens and pistils) in a flower. Cephalodine, forming a head. Ceriferous, jiroduciug wax. Chalaza, 364, 497. Chemistry, vegetable, 4. of plants, 209. Chlorides in ash of plant, 223. Chlorine, 221. use of, in the plant, 230. Chlorophyll, 23-25, 219. Chlorosis, loss of colour'. Cliorosis, 378. Chromatism, an abnormal colouring of plants. Chromism (see Chromatism). Chromule, any other colouring matter than green ; the colouring matter of petals. Chroolepoid, made up of small yeUow scales. Cinchonine, 220. Cinenchynia, 41. Cinereous, ash-coloured. Cineres cent, approaching ash-colour or grey. Circinate, 163. Circulation, 244. descending sap, 263. doubts as to, 266. Circumscription, the outline or boundary of an organ. Cirrhi, 176. Cirrhiform, tendril-shaped. Cistome, mouth of stomata (same as Os- tiole). Citric acid, 216. Citrine, yellow-green. Cladodia, 79. Classification, 5. Cleistogenous flowers, 459. destines, cells containing raphides. Climbers, leaf, 580. CUmbing plants, 579. Clostres, 13. Coalescence, 378. Coarctate, closely pressed together. Coccospheres, 2. Cochlear, snail-shaped. Coelosperm, applied to a seed in which the endosperm is curved, so that the base and apex apjiroach. Coleorhiza, 129. CoUmn, 74. Colocasia odorata, movement of leaves of, 563. Colours, 589. classification of, 590. • relation of, to form, 591. Colouring matter in leaves, 198, 199. Colpenchyma, waved, sinuous cells, 52. Columella, 478. Coma, the tuft of hairs terminating certain seeds. Combinations possible In the plant, 224. 6o4 INDEX AND GLOSSARY. Comose, ending In hairs. Compass plnnt, movements of leaves of, 562. Concatenate, cliained together. Conceptaculura, 490. Concolorous, of tlie same or similar colour. Conduplicate, 162. Cone, 396, 494. Confluent, gradually united so as to form one body. Conglobate, united so as to form a rounded balL Conglomerate, huddled together. Conglutinate, soldered or glued together in heaps. Conlferae, discs on fibres of, 3^. anomalous stems ot, m. Connective, 324, 329, 330. Connivent, having the points turned in— commonly appUed to two organs which arch so as to meet above. Consolidation, 380. Constants in iihyllotaxis, 193, 194. Constituents of plants, volatile and non- volatile. Contabescence, an abnonnal condition of the stamens, in which they are defective. Contortuplicate, turned back on itself. Convolute, 163. Copper, 222. use of. in the plant, 233. Coralliform, like coral in form. Coriaceous, leathery. Cork, 91, 92. Corm, 106. CoroUa, 279, 299, 306. ■ anomalous forms of, 312, 315, 316. appendages of, 313. — bilabiate, 315. campanuJate, 314. caryophyllaceous, 310. colour of, 316. cruciform, 309. develojjment of, 371. dialypetalous, 308. digitatiform, 316. dvu'ation of, 316. forms of gamopetiilouS, 314. gamopetalous, 308, 312, 314, 315. globose, 314. hypocrateriform, 314. inftxndibuliform, 314. irregular dialypetalous, 310, 311. labiate, 314. ligidate, 315. • liliaceous, 310. of Leguminosfe, 310. ovoid, 314. regular dialypetalous, 309, 310. ringent, 315. rosaceous, 309. • saccate, 315. ■ stellate, 314. tubular, 314. unilabiate, 315. union of stamens with, 313. urceolate, 314. uses of, 317. Corona, 313. Corpuscles, 415. Corydaliuc, resembling the flower of Cury- dalis. Corymb, 398. — comi)Ound, 399, 400. Costato, applied to leaves which have a single rib. Cotton, 500. Cotyledons, 73, S"-Si4- Cremocarj), 484. Criljriform vessels, 265. Cril)rose, jiierced with little openings. Crinite, bearded. Crops, rotation of, 236. Cruciate, in the form of a cross. Crara, tlie legs or divisions of a forked tooth. Crustaceous, hard and brittle. Cryptoganiia, 553. Crystals in cells, 29, 31. Cucullate, hooded. Culm, 72. Cuniculate, traversed by a long passage or aperture. Cupula, 2pi. CuiTents in cells, speed of, 20. Curviserial leaves, 190. Cuticle, 51. CyanophyU, 219. Cycadaceee, anomalous stem of, iii. Cycle in phyllotaxis, 183. various series, 191. Cyclogens, 87. Cyclosis, 44. Cylindrenchyma, tissue made up of cylin- drical cells. Cyme, 400. biparous, 40. contracted, 402. dichotomous, 401, 402. heUcoid, 402. monotomous, 402. scorpioidal, 402. trichotoraous. 401, 402. — miiparous scorpioidal, 40. Cymule, 403. Cynarrhodum, 465, 494. CystoUthes, 30. Cytoblast, 33. Cytogenesis, 33. D/EDALENCHYMA, 38. Decandrous, 320. Deduplication, 378. Degeneration, 380. Dehiscence of anthers, 326, 327. circumcissal, 480. elastic, 480. loculicidal, 479. ■ of fruit, 477. of unilocular fi'uits, 480. ! porous, 478. septicidal, 478. septifragal, 479. valvular, 479. Dehiscent, 477. Deltoid, triangular in shape, like the Greek letter A. Demi-equitant, 163. Dendritic, branched like a tree. Denudate, a hairy surface deprived of hairs or down. Depauperate, impoverished, Deperdition, 259. Deplanato, flattened. INDEX AND GLOSSARY. 605 Denna, 51-53. Descriptive terms of leaves, 201-208. of root, 142-144. of stem, 117-122. Dextrine, 213. Diaehyniii, tlie parenchyma of leaves. Diadeiphous, 324. Diagrams, 376, 377, 379. Dialysis, sejiaration of parts usually united. Diamesogamous grasses, 455. Diandrous, 320. Diaphanous, almost transparent. Diaphragm, a dividing partition. Diaphysis, abnormal prolongation of tlie inflorescence. Dichisma, 490. Dichlamydeous, 299. Dichogamy, 432-437- Dicotyledonous, 73, 74. Dicotyledons, annual structure of stem of, 93- general structure of root, 133- Diffusion, membranous, 36. of liquids, 251. DigjTious, 349. Dimorjohism, 428-432. uses of, 432. Dioecious flowers, 282. Diceciously-hermaphrodite, a term applied to flowers which are hermaphrodite, but yet in none of which are both the stamens and pistils perfect. In one flower the stamens may be perfect and the petals imperfect, and vice versa. Dionfea, irritability of, 573. Dipetalous, having two petals (the prefix di in this and other similar compound words signifying " t^vice " or "two "). Diplostemonous, 320. Disc, 388. Disciform tissue, 39. pith, 81. Discrete, separate, distinct. Discs in form of St Andrew's cross, 40. Dissepiments, 351, 352, 475. true and false, 352, 353. Distichous jihyUotaxis, 184. Divaricate, straggling. Divergence, angiUar, 183, 185. Dodecandrous, 320. Drosera, iiTitability of, 575. Dmpe, 490. Ducts, closed, 49. Duramen, 86. Ebracteated, 293, 294. Egranulose, without granules (the prefix c in this as in other similar comijound words meaning ' ' without "). Elaters, 15. Embryo, 411, 506. connection with endospenn, 509. development of, 413, 414. general character of, in dicoty- ledons, 518. general character of, in mono- . cotyledons, 518. origin of, 411. position and relations of, 506- 508. — sac, 410. Kmulsine, 218. Enanation, excessive development. Endocarp, 474. Endogenous stem, 73, 94. ' anomalous, 116. course of sap in, 274. structure of, 94-97. Endophlceum, 89. Eudorhizal, 129. Endosmose, 36, 249. Endosperm, 503. connection between it and embi-yo, 509. presence or absence of, 505. varieties of, 504, 505. Endostome, 363. Endothecium, 330. Enneandrous, 320. Epanody, an abnormal condition, when an irregular flower reverts to a regular form. Epiblema, 53. Epicarp, 474. Epiclinal, on the receptacle or disc (the prefix epi meaning " upon "). Epidermis, 51, 92. Bpigynous, 332. Epipetalous, 332. Epiphloeodal, on the sm-face of the bark. Epiphloeum, gi. Epistrophy, an abnormal condition, in which a monstrous or variegated form returns to its normal condition. Epithelium, 53. EisUcate, not plaited. Equisetaceae, stem of, 100. Equitant, 163. Erose, gnawed or bitten — i.e., with the serratures so irregular as to seem as if they had been formed in that manner. Eruinpent, breaking out. Etoliated {see Albinism). Eustathe, 16. Evaporation from the leaves, 249, 250. insensible, 259. Evittatated, without vittae. Exasperate, clothed mth hard, stiff, short points. Excrescences, warts or knaurs seen on tree- stems. .Excretions, 141, 267. Exeurrent, applied to the central stem of a tree with the branches surrounding it. Exhalation, in the form of drops, 261, 262. Exine, 339. Exogenous stem, 73. Exophloeum, 91. Exorhizal, 128. Exosmose, 36. Bxostome, 363. Exothecium, 330. Ex-tine, 339. Fasciation, union of parallel branches or stem, so as to form a flattened form. Fascicle, ^02. Fat and oils, 217. Ferns, stem of, 98. tree, 72. Fertilisation, 406. by aid of the wind, 431. by means of insects, 437-442. consecutive phenomena, 416. essential process of, 408. 6o6 INDEX AND GLOSSARY. Fertilisfttion, historj' of opinion regarding, 411, 412. of grasseB, 452. of Gynino8])ennie, 407. of orchids, 442. of tlic A8elei)iadaoea3, 450. of \vater-i)lanl.s, 459. of winter- lloweriiig plants, 456. ])reparatory ])Iienomena, 406. resume of, 416. summary of modes of, 462. Fibres, 13. FibrilliB, tlie finer thread-like subdivisions of roots. Pibrocellular, 45. Fibrous layer of anther, 330. Fibrovascular, 45. Filament, 279, 319, 322. adnate, 331. apiclfixed, 331. appendages of, 323. attachment of anther to, 331. innate, 331. • shape of, 322, 323. versatile, 331. Fimbriated, fringed. First crosses aud hybrids, sterility of, 425. Flax, 500. Plexuose, waved in a zigzag form. Flocci, hairs or thread, in appearance like wooL Flower, 279. chloranthous, 387. clelstogenous, 459. development of, 371. dioecious, 282. double, 386. hermaphrodite, 281. metamorphosis of, 383. • monoecious, 281, 282. neutral, 282. opening and closing of, 566. pistillate, 280. polygamous, 282. semi-double, 386. staminate, 280. symmetry of, 376. unisexual, 281. Flowering, 294-298. different periods of, 567. Fluid, transference from cell to cell, 36. nutritive, absorption of, 239. Fluorine, use of, in the plant, 232. Follicle, 484. Forcipitate, pincer-shaped. Form, connection with coloui', 59. Fovilla, 340. chemical composition of, 341. movements in, 340. Fruit, 464. apex of, 473. base of, 473. classification of, 481. ■ dehiscence of, 477. general remarks on, 465. Lindley's classification of, 482. Masters' classification of, 482. monothalmic, 483. ' organic sutnmit' of, 473. parts of the fiower adherent to, 465. polytiialmic, 483, 494. Fruit, ripening of, 468-473. structure of, 473. Fulcra, 77. Fuliginous, smoke-coloured. Fungi, resjjiratioii of, 254. Funiculus, 364, 496. Purfuraceous, scurfy. Gases, poisonous, effect on plants, 257. Galbulus, 494. Gemmule, 74, 510. Genus, the smallest assemblage of species wliicli have cliai-icters in common, and therefore grouped under one "generic" name. Geotropism, movements of leaves or flowers towards the earth. Germination, 522. act of, 527. artificial aids to, 537. chemical physiology of, 539- 543- conditions necessary to, 528- 536. time required for, 536. Glands, 65. Glandular tissue, 39. Glans, 484. Glebulee, masses in appearance like crumbs. Gliadine, 218. Glochidiate, barbed like a fish-hook. Glomerule, 402. Glossology, 5. Glucose, 214. Glucosides, 220. Glume, 293, 294. Glumella, 293, 294. Glumellula;, 293. Gnetaceae, anomalous stems of, iii. Grafting, 544. advantages of, 545. conditions necessary to, 546. Grape-sugar, 214. Grasses, fertilisation of, 452. Grossification, gro^vth or swelling of the ovary after fertilisation. Gums, 213. Gutta-percha, 44. Gymnaxony, an abnormal condition of the ovary in which the placenta protrudes through it. Gymnosi^ermjB, 515. Gymnospermous plants, fertilisation o^ 407. Gynantherous, an abnormal condition of the flower in which, the stamens are con- verted into pistils. GjTicecium, 348. Gynophore, 286, 350. Gyration in cells, 269, 270. cause of, 20, 21. Gyrose, marked with wavy lines. Habit, general appearance of a plant Habitat, place where a plant is found in its wild stiite. Hairs, 50, 60. . classification of, 64. glandular, 61. nettle, stinging-hairs of, 62, 63. Halophytes, ]ilants of salt marshes, contain- ing soda salts. Hamulose, covered with little hooks. INDEX AND GLOSSARY. 607 Hnniulus, a liooked bristle. HiUistoriuiu, sucker-like rootlets of plants, like the worz, dodder, &c. Hiizel, development of flower of, 395' Heat, eftect of, on evolution of oxygen, 255. Hedysarum, movements of, 560. Helioti'opic plants, 563. Heliotropism, movements of leaves or flowei-s towards the sun, 563. Heptandi'ous, 320. Herbs, 72. Hermaphrodite flowers, 281. Hesperidium, 492. Heterocephalous, applied to a plant bear- ing separately heads of male and female flowers. Heterodronious spiral, 190. Heterogamy, 407, 418. Heteromorphic, appUed to the forms of flowers which, like the dimorijhic and trimorphic fonns of Primulas, are distin- guished only by a difference in the rela- tive length of the stamens and pistils. Heteromorphy, 600. Heterophylly, variation in the external form of leaves. Heterorhizal, 135. Heterotaxy, deviation of organs from ordi- nary arrangement or position. Hexagionenchyma, 11. Hexandrous, 320. Hidden-veined, applied to veins concealed in the substance of succulent leaves. Hilum, 364, 496. Hippocrepiform, horse-shoe-shaped. Histology, recapitulation of, 66, 67. 3- Homocarpous, with all the fruits of an in- fructescence alike. Homodromous spiral, 190. Homogamous, 418. flower, 418. Homogamy, 432. HomomoriJhy, with the disc (or tubular) florets of the capitulum of a composite plant become ligulate, like those of the periphery. Homoplasmy, 557, 558. Hose in hose, a horticidtural term signify- ing that the calyx has taxen the form of a corolla, so as to give the appearance of two coroUiE, one within the other. Hybemacula, 74. Hybridism and grafting compared, 424. uses of it, 423, 424. Hybridity, 418, 419. difficulties in understanding, 426. Hybrids, cultivated, 428. Hydrogen, 210. Hydi-ophileiE, 455. Hydrophytes, plants living entirely in the water. Hygrometric plants, 567. Hygrophanous, applied to any substance which is diaphanous when moist, but opaque when dry. Hypertrophy, 600. Hypocotyle, 106. Hypogj-nou.s, 331. Hypophloeodal, under the epidermis of the bark. Hyiiophyllous, on the under sm-face of a leaf Plypostasis, 413. Hysterojihytes, plants, like fungi, living on dead or living organic matter. Illegitimate unions, 429. Imbibition as aiding ascent of the sap, 251. Imbricate, 163. Imperforate, without a tenninal opening. Inarticulate, unjointed. Incanescent, hoary in appearance. Incomplete, destitute of some organ. Incrassate, thickened. Indehiscent, 477. India-rubber, 43, 44. Iiuliunentum, a hairy covering. Induplicate, 163. Indusium of Goodeniaceee, 360, 361. Induvial calyx of winter cherry, 302, 417. Induviiun, 302. Inembryonate, without an embryo. Inenchyina, 19. Inflorescences, 391, 392. anomalous, 404, 405. . axiUary, 394. centrifugal, 392. centripetal, 392. definite, 392. indefinite, 392. mixed, 403, 404. Infructescence, 494. Inorganic matter not absolutely necessary as food for jilants, 239, 240. Inosculation, gi-afting or budding. Insects, fertilisation by means of, 437. Integuments, variation in number of, 367. Intercellular canals, 15. substance, 15. Intercrossing, good effects of, 426. Internode, 74. Intine, 339. Intracai-peUary, among or interior to the carpels. Intrafoliaceous, within the axil of a leaf. Innltne, 28, 213. Involute, 163. Involucre, 289. caliculated, 289. imbricated, 289. scaly, 289. superimposed, 289. Iodine, 221. use of, in the plant, 232. Iron, 222. use of, in the plant, 229. Irregularity in development, 380. Irritability, vegetable, 571, 583. Isooandrous, 320. Isosteraonous, 320. Keel, 311. Knaurs, 117. Labellum of orchids, movements of, 561. Laciniolate, consisting of very minute lacinia;. Lacinula, the incurved point of the petals of Umbelliferfe. Lacunre in cellular tissue, 31, 32. Lageniform, florescence flask-shaped. Lamina, 147, 149. 6o8 INDEX AND GLOSSARY. Lamiginose, clothed with woolly-looltiiig • liairs. Latex, 42, 43. r iiioveineiits of, 44, 45, 269, 270. Laticiferous vessols, 41-43. Layei-s, limitation of uiimial, 89. Leader, jn-iiuary or terminal sliool of a tree. Leaf, 146. accessory or luodillcd parts of, 189. articulation of, 196. autumnal colour of, 198. buds, 161. climbers, 580. death of, 197. deviation IVom normal structure, 156. diu'ation of, 195. excretions, 269. fall of, 196. microscopic anatomy of, 152. modification of, 201. normal histology of, 153-156. teratology of, 199. uses of, 194. Leaflets and lobes of leaves, development of, 160. Leaves, adnata, 195. adventitious, 200. alternate, 182. as ascidia, 158. caducous, 196. compound, 169. cornute, 200. curviserial, 190. deciduous, 196. development of, 159. digitate, 171. • digitately peltate, 172. digitately pinnate, 172. distichous, 182. equitant, 175. evergreen, 195. fascicled, 192. fonns of, 168, 202. fugaoeous, 195. general structure of, 147. irregularity in ajapearance of, 199. marcescent, 196. mai-gin of, 168, i6g. movements of, in water, 563. opposite, 182, 191. palmate, 171. pinnate, 169. pitcher-plants, 177. as prickles, 146. producing buds on tlie edge, 181. rectiserial, 190. return of, 562. simple, 169. as spines, 177. succession of compound and simple, 173- • succulent, 175. — succulent plants, 156. as tendrils, 176. terms used in descriljing, 201, 208. transition from, to sepals and. pet- als, 384. tristichous, 183. unsymmetrical, 175. variability of, 173. Leavcri, \'aried size, 146, 147. verticjil, 175. vcrticillate, 182, 191. • of water-jtlants, 157. witli no distinction of lamina and ]>etiole, 175. L(!gitimate unions, 428. Legume, 486. Legumine, 218. Lenticels, 58, 59. Lentiginose, carved with numerous fleck- . like ilots. Leucophyll, 220. Lianas, 136. Liber, 89, 90. Lignine, 17, 87. Ligniriose, 87. Lignone, 87. ^ Limb, 312. Lime, excretion of, on Saxifraga Aizoon, 31- Limitate, bounded by a markedly distant line. Linguaiform, tongue-shaped. Lmgulate (same as Linguaform). Lingulifonn(same as Linguaeform). Liquids, diffusion of, 251. Lithium, use of, in the plant, 232. Locnlaments, 349, 351, 475-477. Lodiculse, 293. Loraentum, 487. Luminosity of flowers, 593. of plants, 593. of roots, 593. of sap, 597. Lycopodiaeese, stem of, 100. MACROPHYLLiirE, coiisistiug of elongated extended leaflets. Magnesium, 222. Malic acid, 216. Malpighiacese, anomalous stems of, 113. Maltose, 214. Mamma;form, resembling a mamma or teat. Manganese, 222. use of, in the plant, 229. Mannite, 214. Marginate, applied to the calyx when the border is of a difl'erent texture to the blade — i.e., in the form of a rim. Markings, annular, 19. on ceU-wdll, 17. punctated, i8. reticulated, 19. simple, 18. • spiral, 19. thickened, 18. — transverse bars, 19. Mastoid, teat-like. Medullaiy sheath, 84. Meiophylly, sujjpression of one or more leaves in a whorl. Meiostemonous, 320. Meiotaxy, 320. Menispermacea% anomalous stems of, 114. Merenohyma, 10. Mericarps, 484. Mesocarp, 474. Mesoderm, 91. Mesophloium, 91. INDEX AND GLOSSARY. 609 Mesosperm, 498. JlcsoUiecium, 330. Metals, salts of, found in the nsli of plants, 272. Metamorphosis, 383. history of, 383. retrograde, 387. Jletapectic acid, 216. Metaphery, displacement of organs. Micropyle, 364. Midrib, 147, 149. Mimicry, 557, 558. Mimosa, irritability of, 571. Mineral ingi-edients of plants, uses of, 227. summary of use of, 233. Mitriform, conical or mitre-shaped. Monandrous, 320. MonocarpijB, 551. Monochlamydeous, 299. Monocotyledons, 73. development of roots of, 129. perianth of, 317. stem of, 94. structure of root, 134. — — theoretical structure of the stem of, 97. Monodelphous, 324. Monoecious flowers, 281, 282. Monogynous, 349. Monosis, the isolation of one organ ft'om the rest. Monothalmic fruits, 483. Morphology, 4. Morphosis, order or mode of development of any organ or organs. Movements, automatic, of plants, 560. free, of plants, 559. Mucidine, 218. Mucro, a short, sharp, terminal point. Multijugate, with many pairs of leaflets. Multilocular, 476. Multiplication, merismatic, 35. free, within another cell, 36. of parts of floral envelopes, 377- Murlcate, with hard tubercles. Muticous, destitute of a tenninal point. Nectaeies, 389. Nephroideous, kidney - shaped (same as Reniform). Nerviamphipetate, 396. Neutral flowers, 282. Nicotine, 220. Nigrescent, in colour approaching to black. Nitrates in ash of jilants, 223. Nitric acid, 219, 224. Nitrogen, 210. Node, 74. Non-metallic substances, 221. Non-volatile ingredients of plants, 221. Nosology, vegetable, 599. Nucleolus, 22. Nucleus of cell, 22, 23. of seed, 501. Nut, 484. Nutrition, 6, 70, 238. OcELLATED, " Iikc thc cyc ; " a round spot of one colour .surrounded with a ring of auother colour. 2 ( Ochroa, 151. Ochroloucous, a pale ochry colour. Octandrous, 320. Octofarious, in eight directions. Odours, 586. classification of, 588. Ofl"set, 107. Oleino, 217. Orchid, flower of, 318. anatomy of the flower of, 442. fertilisation of, 442-444. labellum of, movements of, 561. morphology of the flowcacB of, 443, 445- Organogenesis, 4. Organography, 3. Orthogamy, 406, 418. Ostiole, 54. Ovary, 348, 350. attachment of, 353. dissepiments of, 350. free, 400. inferior, 400. loculaments of, 350. shape, 350. superior, 400. Ovenchyma, oval cellular tissue, 10^ Ovules, 363. amphitropal, 365. anatropal, 365. ascending, 366. camptotropal, 365. campylotropal, 364. collateral, 366. definite, 363. exceptional structure of, 36.6, 367. fertilisation of, 406. hemitropal, 365. heterotropal, 365. horizontal, 366. indefinite, 363. length of time taken to fertilise, 408. lycotropal, 365. naked, 367. nucleus of, 363. orthotropal, 364. pendulous, 366. position in ovary, 366. relation of poles of, to each other, 364- semianatropal, 365. . solitary, 363. structure and development of, 363. superimposed, 366. suspended, 366. variations in form of, 367. Oxalic acid, 216. Oxygen, 210. PagiN/e; 147. Pateo-phytology, 5. Palea, 293. Paleolee, 293. PaUescent, growing pale. Palms, growth of, 96. Panicle, 400. Pappus, 300. Parenchyma, 146, 154. branched, 12 niuriform, 11. polyhedral, 10. rounded, 10. 6 Id INDEX AND Parenchyma, stellate, 12. tubular, 11. Parietes, walls— applied to sides of ovary, &c. Parthenogenesis, 460. Patent, spreading. Poetic acid, 215. Pentose, 215. group, 215. Pectosic acid, 215. Pedatisect, when the veining of a leaf is pedatifid, and the lobes extend nearly to the midrib. . Peduncle, 279, 283-287. Peloria, 315. Pentadelphous, 324. Pentandrous, 320. Pentastichous phyllotaxis, 184. Pepo, 492. Percurrent, running through the entire length. ■ Perennials, 295. Perianth, 293, 299. of Monocotyledons, 317. ' of orchids, 318, 442-444. Perianthelium, 293. Pericarp, 473. Pericarpoidal, 291. Pericladium, 148. Periclinium, 288. Periderm, 91, 93. Perigone, 293, 299. Perigynium, the membranous covering of the pistil of sedges, 305. Perigynous, 331. Periphoranthium, 288. Peristachyum, 293. Peristomatic, around the stomata. Peronate, with a mealy or woolly coat. Pertusate, pierced at the apex. Petalody, 335. Petals, 306. anatomy of, 308. number of, 307. transition from leaves to, 384, 385. Petiole, 147, 148. development of, 161. PhiBnogamous, 553. Phanerogamise, 553. Phanerogamous, applied to flowering plants (same as Phsenogamous). Phloridzine, 220. Phosphates in ash of plants, 223. Phosphorus, 210. Phycostema, 390. Phyllodia, 151, 152. Phyllody, 600. Phyllomania, 199. Phyllomorphosis, 174, 175. Phyllomorpliy, same as Phyllody. Phyllophor, terminal bud or growing point in palms. Phyllotaxis, 181. abnormal, 193. . ■ constancy or irregularity of, 192. ■ denominator and numerator of, 185. high series of, 184. recapitulation, 193. Phyto-geography, 5. Phytology, i. GLOSSARY, Pileorhiza, 131, 133. Piiienchyina, 11. Pinite, 215. Pistil, 279. formation from leaf, 386. morphology of, 368-370. Pistillate, 280. Pistils, prafloration of, 375. Pitcher-plants, 177-181. Pitcher-shaped leaves, 177-181. Pith, 82. Placenta, 348, 352, 362. abnormal, 356. Placentation, axillary, 355. free central, 355. parietfil, 355. Plants, annual, 547. biennial, 547. comijosition of, in successive stages of growth, 234. dead, season of, 247. death of, 550. distinguishing characteristics from animals, i, 2. increase of, 273-276. life, general phenomena connected ynth, 556. longevity of, 547. perennial, 547. single-celled, 14. sleep of, 568. spirally twining, 579. succulent, leaves of, 156. temperatiu-e of, 598. ultimate constituents of, 209. volatile parts of, 209, 211. with irritable leaves, 577. Platyphyllous, broad-leaved. Pleiomorphy, renewed growth of the ar- rested parts in irregular flowers, 600. Pleiophylly, 199. Pleiotaxy, 321. Pleiotrachea, 46. Pleurenchyma, 38. Plica, undue development of small branch- lets, giving rise to the appearance of large bunches, as in birch, hornbeam, &c. Plicate, 162. Plimiule, 510. Podogynium, 287, 350. Podosperm, 364. Pollen, 336, 337. of Asclepiads, 346, 347. of aquatic plants, 340. colour of, 347. development of, 343, 344. mother-cells of, 344. grains, compound, 345. of coniferte, 345. of evening primrose, 345. . slits and pores on, 341-343. shape of, 337. variation in number of coats of, 339, 340. of orchids, 346, 347, 446. how gets access to the stigma, 406. length of time taken to penetrate stigma, 408, 409. size, 338. solid, 346. structure, 339. superfluous quantity of, 407. INDEX AND GLOSSARY. 6ll Pollen, vitality of, 347. tube, I'uiictions of, 412. rate of gro>vth of, 409. PoUinia, 346, 347. Polyaiidrous, 320. Polycladv, same as Plica. Polycotyiedony, accidcxital increase m tne niunber of the cotyledons. Polydelphous, 324. Polygamous flowers, 282. Polj-gynoiis, 349. Polyinerous, of many parts. Poljnnoriihy, existence of several forms of the same organ in a plant, as the vari- ously formed leaves in many plants. Polyjihylly, increase of the number of or- gans in a whorl, 200. Polystemonous, 320. Polythalmic fi-uits, 483, 494. Pome, 491. Porosity of tissues, 251. Potassium, 221. chloride, 223. phosphate, 223. Prsefloration, 372. cochlear, 374. convolutive, 372. corrugated, 374. imbricative, 372. induplicative, 374. by juxtaposition, 372. open, 374. quincuncial, 372. reduplicative, 374. by superposition, 372. supervolute, 374. twisted or contorted, 373. vexillai-y, 373. Praefoliation, 162. in different orders, &c., 164. Premorse, bitten off, terminating abniptly. Primine, 363. Primordial vesicle, 33, 34. Prismenchyma, 11. Proembryo, 414. Proliferous, an unusual development of parts. Propagulum, a runner ending in a germin- ating bud. Prosenchjmia, 13, 38. Protandry, 433. Proteine, 34. Protogyny, 433. Protoplasm, 19, 20, 33. Proximate principles, 211. Pruinose, like hoar-frost — applied to an organ covered with granular secretions of that appearance. Pulvinate, cushion-like. Punctations on fibres, 39. Punctum Vegetationis, 74. Putamen, 474. Pyrenodeous, wart-like. Pyrenodine, same as Pyrenodeous. Pyxis, 490. QUADRILOCULAR, 476. Quadrivalvular, 478. Quaquavcrsal, directed evei-y way. Quartine, 366. Queroite, 215. Quinine, 220. Quinquefarious, in five directions. Quinquovalvular, 478. Raceme, 398. compound, 398. corymbose, 399. Rachis, 98. Radicle, 509. Ramenta, membranous scurl on siu'face of leaf, &c. Ramification, 78. Ramulus, a small branch. Raphe, 497. Rapliides, 29, 31. in screw-pine, 30. Rays, medullary, 81, 83. Reciprocal crosses, 422. Reolinate, 162. Recrudescence, the production of a young shoot fi-om tlie tip of a ripened spilce of a seed. Rectiserial leaves, igo. Regma, 490. Regularity of flower, primitive, 381. Replum, 487. Reproduction, 6. Resins, 217. Respiration, 252. chlorophyll in, 254. in darkness, 253. nocturnal, 254. in non-oxygenated air, 257. Reticulum, fibrous debris at the base of the petioles of some palms. Retiform, like a net. Revolute, 163. Rhizome, 102. Rhizomorphoid, root-like in shape. Rhizotaxis, 130, 131. Rigescent, of a stiflish consistence, or get- ting stiff. Rimose, with chinks or cracks. Root, 124. buds, 124. cUmbers, 583. crown of, 71. development of, 128. elongation of, 130. excretions, 267, 268. fibrous, 129. as a floating organ, 140. length of, 125-127. as a magazine of nutriment, 140. as an organ of absorption, 138. as an organ of fixation, 137. as an organ of respiration, 139. "parting," 107. special direction of, 564. structure of, 131. summary of description, 144. technical terms used in describing, 142-144. Roots, adventitious, 135. deciduous, 137. as discs, 125. excretion of, 141. as fulcra, 124, 125. functions of, 137. luminosity of, 593. selective power of, 242-244. as suckers, 125. Rootstock, 102. 6X2 INDEX AND GLOSSARY. Rotation of crops, 236. Rubidium, 222. use of, in the plant, 232. Rubiginose, reddish. Rufescent, approaching to reddish brown. Rufous, red-brown in colour. Rugose, wrinkled. Rugulose, diminutive of Rugose. Runner, 107. Rytidom, 91. Saccate, bag-shaped. Sacciform, like a bag. Salicine, 220. Samara, 484. Sap, 241. ascent of, 244. autumn, 247. causes of ascent, 248. causes which accelerate or retard as- cent of, 245. composition of, 244. continuous ascent of, in tropics, 248. course in acrogenous stems, 274. course in endogenous stems, 274. descending, 263. descending path of, 264, 265. force of ascent, 241. ( how absorbed, 242. lateral movements of, 247. luminosity of, 597. path of ascent, 246. rapidity of ascent, 241. Sapindacese, anomalous stems of, 112. Sarcocarp, 474. Sarcoderra, 498. Sarcosperm, 498. Sarmentum, slender woody stem of climb- ing plants. Saxicolous, growing on rocks. Scales, 60. of corolla, 311, 312. Scape, 109. Scalpelliform, shaped like a scalpel Sclerenchyma, a name applied by Mittenius to the thickened parenchyma and prosen- chyma found in the stems of ferns and other vascular cryptogams, and which in Equisetaceee, at least, is probably a part of the cortical tissues, rather than of the fibro-vascular bundles. Sclerogen, 17. Sclerotoid, having the form and consistence of one of the genus Sclerotium. Scobiform, applied to small sawdust-look- ing seeds. Sebuliform, thread-like. Secretions, 267. Sectile, easily cut into pieces. Secund, having all the flowers or leaves turned to one side. Secundine, 363. Seed, 496. — - descriptive terms applied to, 497, 498. dwarfed or light, 526. growth of, 520. hairs of, 499. how scattered, 495. naked, 515. proper depth for sowing, 538. ripe, 521. ripening of, 520. Seed, results of long-kept, 525. structure of, 498. — teratology, 543. umipe, 526. value as regards density, 527. vraigs of, 501. Sensitive plant, 571. Sepalody, reversion of petals into sepals. Sepals, 279, 299. form, 299. hooded, 300. ■ mode of insertion, 301. • ^ morphology of, 301. nervation, 299, 300. spurred, 300. ■ • transition from leaves to, 384. Septa, 351. Septulse, diminutive of Septa. Sheath of leaf, development of, 161. Shoots, 107. Shrubs, 72. under, 72. Silica, uses of, in the plant, 230, 231. Silicon, 221. Silieula, 457. Siliqua, 487. Sleep of plants, 568. Sobol, 103. Soda and potash, use of, in the plant, 227, 228. Sodium, 221. chloride, 123. phosphate, 223. sulphate, 223. Soleseform, slipper-shaped. Somatia, 340, 341. Sorosis, 494. Spadix, 395. Spathe, 291. Spathelle, 292. Speiranthy, the occasional twisted growth of the parts of a flower. Spermoderm, 498. Spheerenchyma, 10. ■ Sphalerocarpium, 491. Spike, 394. Spikelet, 293, 395. Spines, no. Spirals, dextrorsal, 186. generating, 186-190. heterodromous, 190. homodromous, 190. • how to determine by aid of secon- dary, 187-189. • primitive, 186. ■ secondary, 185, 186. secondary convergence of, 193. sinistrorsal, 186. Spongioles, 132. Spores, 14, 73. Squamose, rough with projecting or deflexed scales. Squamulffi, 293. Stamens, 319. adhesion of, 322. declinate, 333. definite, 320. didjTiamous, 321. epigynous, 332. epipetalous, 332. exserted, 333. formation of, 385. INDEX AND GLOSSARY. 613 Stamens, general structure of, 329. hypogynous,33i. included, 333. indefinite, 320. insertion of, 313, 331. irritability, 578. morphology of, 336. number of, 319, 320. perigynous, 331. prsefloration of, 375. relation of niunber to number of petals, 333, 334. relative lengths of, 321. situation of, in regard to petals and sepals, 322. tetradynamous, 321. union of, 323. Staminate, 280. Staminodia, 334, 335. Standard, 311. Starch, 25-28, 212. Stearine, 217. Stem, 71. absence or existence of, 71. acaulescent, 116. acrogenous, 73, 198. anomalous, of Aristolochiaceae, 114. Bauhinia, 115. ■ Eignoniacese, 113. Coniferse, m. ■ Cycadacese, m. endogenous, 166. Euonymus tingens, 116. Gnetacese, m. Lathrsea clandestina, 116. Malpighiace*, 113. Melampyrum, 116. Menispermacese, 114. Myzodendron, 116. ■ Pisonia, 116. '■ Sapindacese, 112. Stauntonialatifolia, 116. branching of, 78. consistence of, 72. development of, 80. division of, according to structure, 73. endogenous, 73. ■ epidermis of, 92. of Equisetacese, 100. exogenous, 73. of ferns, 98. fleshy, 79. of Lycopodiacese, 100, loi. size of, 82. special directions of, 564. structure of, 80. subterranean, 102. summary of description, 122. technical terms usedin describing, 117- 122. teratology of, 116, 117. twining, 78, 79. uses of, 94. Stenophyllous, narrow-leaved. Sterility, degrees of, 419. laws governing, 421-423. Stigma, 279, 348. divisions of, 360. falsely so called, 361. papillse of, 360. shape of, 360. Stigma, structure of, 362. unilateral, 360. Stigmas, irritability of, 578. Stipe, 72. Stipitiform, resembling a stalk or stem. Stipules, 149-151. development of, 160. Stomata, 54. absence of, 55. development of, 55. number of, 55-57. of oleander, 55. use of, 57. Strasimorphy, deviation of form arising from arrest of growth, 600. Strigose, covered with sharp rigid hairs. Strobilus, 494. Strombuliform, twisted with a long spire. Strophiole, 502. Style, 279, 348, 349, 357. attachment of, to anther, 358. caducous, 358. collecting hairs of, 360. gynobasic, 358. persistent, 259. — — a process of the placenta, 359. shape of, 357. structure of, 362. Stylopodium, 388. Substance, intercellular, 15. Sucker, 107. Sucrose, 214. Suffrutescent, 73. Sulfruticose, 73. Sulcate, furrowed. Sulphates in ash of plants, 223. Sulphur, 210. " Sun-dews," irritability of, 575. Superposition, 380. Supertuberation, the producing of young potatoes from the old ones while still growing. Suppression, 379, 380. Surculus, 107. Suspensor, 413. Sutural lines, 478. Suture, dorsal, 478. Suture, ventral, 478. Syconus, 397, 494. Symmetry, 376. causes of variation and altera- tions, 377-379- dimerous, 371. pentamerous, 376. trimerous, 376. variations and alterations in, 376, 380. Sympathies and antipathies of plants, 141. Symphoricarpous, bearing fruits clustered together. Symphysandrous, 328. Sympodial, 403. Sympodium, 403. Synacmy, 432. Synantherous, 328. Synanthy, the adhesion of several flowers. Syncarpous, 348, 349, 465. Syncarpy, the adhesion of several fruits (an abnormal condition). Syngenesious, 328. Synophty, adhesion of several embryos. Synspermy, 543. 6i4 INDEX AND GLOSSARY. TA^fNIN, 220. Tftp-VOOt, I2Q. Tai'tiivic aciil, 216 Taxology, 5. Tiixonomy, 5. Togmen, 364, 498. appendages of, 499. Teniperatiu'o of i)lants, 598. Tondril-beuring i)lants, 581. Tendrils, no. Teratology, 4, 600. Tercinc or cliorion, formation of, 366. Terminology, 5. Terms used in describing leaves, 201-208. used iiidescribing the stem, 117-122. technical, used in describing the root, 142-144. Testa, 364. Tetradynamous, when of six stamens two are longer than the others. Tetragynous, 349. Tetrandrous, 320. Thalamiflorous, having the petals and stamens inserted on the thalamus or receptacle. Thalamus, 283. TheciE, 324. bilocular, 324. quadrilocular, 325. Thecaphore, 287, 350. Theniscoid, shape of a watch-glass. Theobromine, 220. Throat, 312. Thyrsus, 398, 400, 404. Tissue, bast, 40. Tissues, classification of, 14. Titanium, 221. use of, in the plant, 232. Tomentose, "do^v^ly," with short hairs. Torulose, when a cylindrical body is swol- len and constricted alternately. Torus, 283. Tracheary vessels, 45, 46. Trachenchyma, 45. Transpiration, 259. Tree-ferns, 72. Trees, aged, 548-550. Triadelphous, 324. Triaudrous, 320. Trigj'nous, 349. Trimorphism, 428-432. uses of, 432. Trioeciously-hermaphrodite, the same as Trhnorphic. Tristichous phyllotaxis, 183. Trivalvular, 478. Trunk, 72. Tryma, 490. Tube of corolla, 312. Tuber, 103-105. Tubes, cribriform, 43. Twigs, 72. Twisted, 163. -Tylosis, 49. Umbel, 499. comijound, 400. Umbellules, 399. Umbraouliform, umbrella-shaped. Unilocular, 475. Unisexual flowers, 281. UtricU,, 484. Uva, 491. Valvate, 163. Valves, 478. Varieties and their mongrel offspring, fer- tility of, when crossed, 426. Vascular tissue, 38. Vaseuluni, a pitcher-sliaped leaf (much the same as Aseidium) ; a box for collectiiig plants in. Vegetable acids, 216. Vegetable organic compounds, 211. Veins, 149. Venation, 164. and branching, correspondence between, 166, 167. different kinds, 165, 166. Venus' fly-trap, 573. Vernation, 162. Vertici Is of flowers, relation of, to each other in praifloration, 374, 375. Vesicle, genninal, 413. embryonal, 413. Vesicles, antipodal, 415. Vessels, annular, 47. barred, 47. dotted, 48. imperfectly barred, 47. punctated, 47. reticulated, 47. scalariform, 45. spiral, 47. tracheaiy, 45. transitory, 50. Vexillum, 310. Virescence, the act of a plant growing green by the development of chlorophyll. Virescent, approaching green in colour. Vitality, duration of, in seed, 552-554. Viticula, the trailing stem of a jjiant, like a cucumber, &c. Vittse, narrow oil-bearing canals in fruits of Umbelliferse. Volatile parts of plants, 209. Water, 211. plants, leaves of, 157. fertilisation of, 459. respiration of, 255, 256, 258. Waving of tree, 251. Whorls, floral, relation to the axis, 381. Wind as a fertilising agent, 451. Winter - flowering plants, fertilisation of 456- Winter cheiTy, calyx of, 302, 417. Wood, 85. causes of diff'erent qualities of, 86. chemical composition of, 87. formation of annual zones of, 87. Woody fibre, 38, 39. Xanthophyll, 219. XiphophyUous, having ensiform or sword- shaped leaves. Xylocarp, a hard woody fruit. Zinc, 222. use of, in the plant, 283. Zoi'diophileiv,, 455. Zoospores, 14. EDUCATIONAL WORKS PUBLISHED BY WILLIAM BLACKWOOD & SONS, EDINBURGH AND LONDON. ♦ English Language. AN ETYMOLOGICAL AND PRONOUNCING DICTIONARY OF THE ENGLISH LANGUAGE. Includ- ing a very copious selection of Scientific, Technical, and otheV Terms and Phrases. Designed for use in Schools and Colleges, ■ and as a Handy Book for General Reference. By the Rev. James Stormonth, and the Rev. P, H. Phelp, M.A. Crown 8vo, pp. 760, 7s. 6d. THE SCHOOL ETYMOLOGICAL DICTIONARY AND WORD-BOOK. Combining the advantages of an ordinary Pronouncing School Dictionary and an Etymological SpelHng-Book. By the Rev. James Stormonth. Fcap. 8vo, pp. 254, 2s. ENGLISH PROSE COMPOSITION : A Practical Manual for Use in Schools. By James Currie, M.A., Principal of the Church of Scotland Training College, Edinbtirgh. Ninth Edition, is. 6d. 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A MANUAL OF MODERN GEOGRAPHY, Mathe- matical, Physical, and Political. By the Rev. Alexander Mackay, LL.D., F.R.G.S. Crown 8vo, pp. 676. 7s. 6d. This volume — the result of many years' unremitting application — is specially adapted for the use of Teachers, Advanced Classes, Candi- dates for the Civil Service, and proficients in geography generally. twenty-koukth thousand. ELEMENTS OF MODERN GEOGRAPHY. By the Same. Thirteenth Edition, revised to the present time. Crown 8vo, pp. 300. 3s. The 'Elements' form a careful condensation of the 'Manual,' the order of arrangement being the same, the river-systems of the globe playing the same conspicuous part, the pronunciation being given, and the results of the latest census being uniformly exhibited. This volume is now extensively introduced into many of the best schools iu the kingdom. sixty-second thousand. OUTLINES OF MODERN GEOGRAPHY: Fif- teenth Edition, revised to the present time. By the Same. i8mo, pp. 112. IS. These ' Outlines ' — in many respects an epitome of the ' Elements ' — are carefully prepared to meet the wants of beginners. The arrange- ment is the same as in the Author's larger works. Minute details are avoided, the broad outlines are graphically presented, the accentua- tion marked, and the most recent changes in political geography ex- hibited. forty-first thousand, revised to the present time. FIRST STEPS IN GEOGRAPHY. By the Same. iBmo, pp. 56. Sewed, 4d. In cloth, 6d. GEOGRAPHY OF THE BRITISH EMPIRE. From ' First Steps in Geography.' By the Same. 3d. Agriculture. CATECHISM OF PRACTICAL AGRICULTURE. By Henry Stephens, F.R.S.E., Author of the 'Book of the Farm.' A New Edition. With Engravings, is. PROFESSOR JOHNSTON'S CATECHISM OF AGRICULTURAL CHEMISTRY. A New Edition, edited by Professor Voelcker. With Engravings, is. PROFESSOR JOHNSTON'S ELEMENTS OF AGRICULTURAL CHEMISTRY AND GEOLOGY. A New Edition revised and brought down to the present time, by G. T. 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EngUsh Journal of Education.— Of all the Manuals on Geography that have come under our notice, we place the one whose title is given above in the first rank. For fulness of information, for knowledge of method in arrange- ment, for the manner in which the details are handled, we know of no work that can, in these respects, compete with Mr Mackay's Manual. ELEMENTS. A. KEITH JOHNSTOK, LL.D., F.R.S.E., F.R.G.S., H.M. Geographer for Scotland, Author of the ' Physical Atlas,' &c. &c.— There is no work of the kind in this or any other language, known to me, which comes so near my ideal of perfection in a school-book, on the important subject of which it treats. In arrangement, style, selection of matter, clearness, and thorough accuracy of statement, it is without a rival ; and knowing, as I do, the vast amount of labour and research you bestowed on its production, I trust it will be so appreciated as to insure, by an extensive sale, a well-merited reward. G. BICKERTON, Esq., Edinburgh Institution.— I have been led to form a very high opinion of Mackay's ' Manual of Geography ' and ' Elements of Geo- graphy,' partly from a careful examination of them, and partly from my expe- rience of the latter as a text-book in the Edinburgh Institdtion. One of their most vahiable features is the elaborate Table of River-Basins and Towns, which is given in addition to the ordinary Province or County list, so that a good idea may be obtained by the pupil of the natural as well as the political relationship of the towns in each country. On all matters connected with Physical Geography, Ethnography, Government, &e., the information is full, accurate, and well digested. They are books that can be strongly recommended to the student of geography. RICHARD D. GRAHAM, English Master, College for Daughters of Ministers of the Church of Scotland and of Professors in the Scottish Universities. — No work with which I am acquainted so amply fulfils the con- ditions of a perfect text-book on the important subject of which it treats, as Dr Mackay's 'Elements of Modern Geography.' In fulness and accuracy of de- tails, in the scientific grouping of facts, combined with clearness and simplicity of statement, it stands alone, and leaves almost nothing to be desired in the way of improvement. Eminently fitted, by reason of this exceptional variety and thoroughness, to meet all the requirements of higher education, it is never without a Uving interest, which adapts it to the intelligence of ordinary pupils. It is not the least of its merits that its information is abreast of all the latest developments in geograi)hical science, accurately exhibiting Ijoth the recent political and territorial changes in Europe, and the many important results of modern travel and research. Spectator. — ^The best Geography we have ever met with. 4 WILLIAM BLACKWOOD AND SONs' Geology. " Feio of our handbooJcs of popular science can be said to have greater or viore decisive merit than those of Mr Page on Geology and I'alceontology. They are clear and vigorous in style, they never oppress tlie reader with a ■pedantic display of learning, nor overwhelm him with d pompous and super- Jluous terminology ; and they have the happy art of taking him straightway to the face of nature herself, instead of leading him by the tortuous and bewild- ering paths of technical system and artificial classification."— Satuidny lie- view. INTRODUCTORY TEXT-BOOK OF GEOLOGY. By David Page, LL.D., Professor of Geology in the Durham University of Physical Science, Newcastle. With Engravings on Wood and Glossarial Index. Tenth Edition. 2S. 6d. "It has not been our good fortune to examine a text-book on science of ■which we could express an opinion so entirely favourable as we are enabled to do of iMr Page's little work." — Athenceum. ADVANCED TEXT-BOOK OF GEOLOGY, De- scriptive AND Industrial. By the Same. With Engravings, and Glossary of Scientific Terms. Fifth Edition, revised and enlarged. 7s. 6d. " We have carefully read this truly satisfactory book, and do not hesitate to say that it is an excellent compendium of the great facts of Geology, and writ- ten in a truthful and philosophic spirit." — Edinburgh Philosophical Journal. " As a school-book nothing can match the Advanced Text-Book of Geology by Professor Page of Newcastle." — Mechanics' Magazine. 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" Of singular merit for its clearness and trustworthy character." — Standard. GEOLOGY FOR GENERAL READERS. A Series of Popular Sketches in Geology and Palaeontology. By the Same. Third Edition, enlarged. 6s. " This is one of the best of Mr Page's many good books. It is written in a flowing popular style. Without illustration or any extraneous aid, the narra- tive must prove attractive to any intelUgeut reader." — Geological Magazine. EDUCATIONAL WORKS, 5 HANDBOOK OF GEOLOGICAL TERMS, GEO- LOGY, AND PHYSICAL GEOGRAPHY. By the Same. Second Edition, enlarged. 7s. 6d. " The only dictionary of Geology in the English language— modem in date, and exhaustive in treatment."— iJeyiew. CHIPS AND CHAPTERS. A Book for Amateurs and Young Geologists. By the Same. 5s. THE PAST AND PRESENT LIFE OF THE GLOBE. With numerous Illustrations. By the Same. Crown 8vo. 6s. THE PHILOSOPHY OF GEOLOGY. A Brief Re- view of the Aim, Scope, and Character of Geological Inquiry. By the Same. Fcap. 8vo. 3s. 6d. "The great value of Mr Page's volume is its suggestive character. The problems he discusses are the highest and most interesting in the science — those on which it most becomes the thinkers and the leaders of the age to make up their minds. The time is now past for geologists to observe silence on these matters, and in this way to depreciate at once the interest and im- portance of their investigations. It is well to know that, however they may decide, questions of high philosophy are at stake, and therefore we give a hearty welcome to every book which, like Mr Page's, discusses these questions in a fair and liberal spirit." — Scotsman. Physical Geography. INTRODUCTORY TEXT-BOOK OF PHYSICAL GEOGRAPHY. With Sketch- Maps and Illustrations. By David Page, LL.D., Professor of Geology in the Durham Univer- sity of Physical Science, Newcastle. Sixth Edition. 2S. 6d. " The divisions of the subject are so clearly defined, the explanations are so lucid, the relations of one portion of the subject to another are so satisfactorily shown, and, above aU, the bearings of the alUed sciences to Physical Geography are brought out with so much precision, that every reader will feel that diffi- culties have been removed, and the path of study smoothed before him." — Athenceum. "Whether as a school-book or a manual for the private student, this work has no equal in our Educational literature." — Iron. ADVANCED TEXT-BOOK OF PHYSICAL GEO- GRAPHY. By the Same. With Engravings. Second Edition. SS. " A thoroughly good Text- Book of Physical Geography." — Saturday Review. " It is not often our good fortune to meet vrith scientific m'anuals so cheap and so excellent in matter, and so useful for the practical purposes of educa- tion, as this admirable work, which is beyond all question the best of its kind." —Evening Standard. EXAMINATIONS ON PHYSICAL GEOGRAPHY. 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" An excellent and comprehensive compendium of French history." — National Review. FACTS AND DATES; or. The Leading Events in Sacred and Profane History, and the Principal Facts in the Various Physical Sciences : the Memory being aided throughbut by a Sim- ple and Natural Method. For Schools and Private Reference. By the Rev. Alex. Mackay, LL.D., F.R.G.S., Author of 'A Manual of Modern Geography,' &c. Second Edition, crown Bvo, pp. 336. 4s. THE LIFE AND LABOURS OF THE APOSTLE PAUL. A continuous Narrative for Schools and Bible Classes. By Charles Michie, M.A. Fcap. 8x0, cloth, is. " The details are carefully collected and skilfully put together, and the out- come is a succinct, yet clear and comprehensive, view of the life and labours of the great Apostle. The story of Paul's Ufe, so replete with spirit-stirring incidents, is told in a manner extremely well fitted to arrest the attention of advanced pupils, and we can with confidence commend this little work as an admirable text-book for Bible-classes. The narrative is enriched by foot- notes, from which it is apparent that Mr Michie is well posted up in the litera- ture of the subject. These are subjoined without any pretence or parade of learning, and only when required to elucidate or illustrate the text. The map at the close will enable the reader to trace the course of the Apostle in his various missionary tours. We give this handbook our warm commendation : it certainly deserves a wide circulation." — National Education Gazette. 8 WILLIAM BLACKWOOD AND SONS* IMPEOVED EDITIONS. School Atlases. By A. KEITH JOHNSTON, LL.D., &c. Author of the Royal and the Physical Atlases, &c. ATLAS OF GENERAL AND DESCRIPTIVE GEO- GRAPHY. 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This work has been constructed for the purpose of placing in the hands of the public a useful and thoroughly accurate Atlas of Maps of Modern Geography, in a convenient form, and at a moderate price. It is based on the ' Royal Atlas,' by the same Author ; and, in so far as the scale permits, it comprises many of the excellences which its prototype is acknowledged to possess. The aim has been to make the book strictly what its name imphes, a Handy Atlas — a valuable sub- stitute for the ' Royal,' where that is too bulky or too expensive to find a place, a needful auxiliary to the junior branches of families, and a vade mecum to the tutor and the pupil-teacher. EDUCATIONAL WORKS. 9 Keith Johnston's Atlases. EXTRACTS FROM OPINIONS OF THE PRESS. SCHOOL ATLASES. " They are as superior to all School Atlases within our knowledge, as were the larger works of the same Author in advance of those that preceded them." — Educational Tivies. "Decidedly the best School Atlases wa have ever aeen."— English Journal of Education. "... The 'Physical Atlas' seems to us particularly well executed. . . . The last generation had no such help to learning as is afTorded in these excellent elementary Maps. The ' Classical Atlas ' is a great improve- ment on what has usually gone by that name ; not only is it fuller, but in some cases it gives the same country more than once in diiferent periods of time. Thus it approaches the special value of a historical atlas. The ' General Atlas ' is wonderfully full and accurate for its scale. . . . Finally, the ' Astronomical Atlas,' in which Mr Hind is responsible for the scientific ac- curacy of the maps, supplies an admitted educational want. No better com- panion to an elementary astronomical treatise coiild be found than this cheap and convenient collection of maps." — Saturday Review. " The plan of these Atlases is admirable, and the excellence of the plan is rivalled by the beauty of the execution. . . . The best security for the accuracy and substantial value of a School Atlas is to have it from the hands of a man like our Author, who has perfected his skUl by the execution of much larger works, and gained a character which he will be careful not to jeopardise by attaching his name to anything that is crude, slovenly, or superficial." — Scotsman. "This Edition of the ' Classical Atlas' is so much enlarged and improved as to be virtually a new work, surpassing everything else of the kind extant, both in utility and beauty."— .IfTienoeMJn. THE HANDY ROYAL ATLAS. "Is probably the best work of the kind now published."— Kmes. "Not only are the present territorial adjustments duly registered in all these Maps, but the latest discoveries in Central Asia, in Africa, and America, have been delineated with laborious fidelity. Indeed the ample illustration of recent discovery, and of the great groups of dependencies on the British Crown, renders Dr Johnston's the best of all Atlases for English use."— Pafi Mall Gazette. " This is Mr Keith Johnston's admirable Royal Atlas diminished in bulk and scale so as to be, perhaps, fairly entitled to the name of ' Handy,' but still not so much diminished but what it constitutes an accurate and useful general Atlas for ordinary households."— 5pec(a