- aoe ‘ Secor: ane ees gow net Arenas ae tne ee Sas ~ ALBERT R. MANN LIBRARY AT CORNELL UNIVERSITY British wild flowers considered in re Tama Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924001221559 ON BRITISH WILD FLOWERS CONSIDERED IN RELATION TO INSECTS. Mee See Fic. 44. Fic. 43. Fic. 48. Fic. 47. NATURE SERIES. ON BRITISH WILD FLOWERS CONS{[DERED IN ’ RELATION TO INSECTS. JN SIR JOHN J, LUBBOCK, Barrt., MP., DG, PukGS:, ETC. etre CHANCELLOR OF THE UNIVERSITY OF LOND« SECOND EDITION. WITH NUMEROUS [LL USTRATIONS. Zondon : MACMILLAN AND CoO. 1875. (Vhe Right of Translation ana Reproduction is Rese -ved.\ wah LONDON : R. CLAY, SONS, AND TAYLOR, PRINTERS, EREAD STREET HILL. PRE FACE, IT is not without much diffidence that I venture on the present publication. For though as an entomo- logist I have necessarily been long familiar with our common wild plants, I had made no serious study of Botany until recent researches brought prominently before us the intimate relations which exist between flowers and insects. My observations and notes on this subject were originally prepared with the view of encouraging in my children that love of natural history from which I myself have derived so much happiness, but it was suggested to me that a little book such as the present might perhaps be of use to others also. “Sprengel, in his admirable work, “Das entdeckte ak ete der Natur,” published as long ago as the year41793, was the first to show how much plants are dependent on the visits of insects, and to point out that the forms and colours of flowers are adapted to ensure, and profit by; those visits. His work, how- ever, did not attract the attention which it deserved, and our knowledge of the subject made little pro- gress until the publication of Mr. Darwin’s researches, to which I shall continually have occasion to refer. Dr. Hermann Miiller in his “Die Befruchtung der Blumen durch Insekten,” has brought together the observations of previous writers, and added viii PREFACE. to them an immense number of his own. Many other naturalists—for instance, Axell, Bennett, Del- pino, Hildebrand, Hooker, F. Miiller, and Ogle, have also published valuable memoirs on the subject, to which I shall frequently have occasion to refer; but to the works of Sprengel, Darwin, and Dr. H. Miiller Y am indebted in almost every page, and in spite of constant references, it is impossible for me ade- quately to acknowledge my obligations to them. In the systematic portion, I have followed Mr. Ben- tham’s excellent “Handbook of the British Flora.” As far as possible, I have avoided the use of technical terms, but some were unavoidable; refer- ences for these will be found in the Index, and I have aiso given a Glossary of the technical terms most fre- quently employed. I have to thank various friends who have been good enough to assist me, but especially Dr. Hooker and Mr. Busk, who have been so very kind as to look through my proofs. In conclusion, I must add that the subject is com- paratively new, and many of the observations have not yet stood that ordeal of repetition which they will no doubt experience. While, therefore, I believe that the facts will be found to be in the main correct, the inferences drawn from them must, in many cases, be regarded rather as suggestions than as well esta- blished theories. The whole subject is one which is most interesting in itself, and will richly repay those who devote themselves to it. Hicu Ems, Down, KENT, September, 1874. CONTENTS. PAGE LIST OF ILLUSTRATIONS . i é 3 - xl GLOSSARY . ‘ ‘ . . i z , xv CHAPTER 1. INTRODUCTION . - * ‘ $ . 2 I CHAPTER II. INTRODUCTION—(Continued) . . i é F 23 . CHAPTER III. DICOTYLEDONS. THALAMIFLORE . CT ee ee ee a 47 ‘ CONTENTS. CALYCIFLORZ. COROLLIFLORA . INCOMPLETA MONOCOTYLEDONS CHAPTER IV. CHAPTER V. CHAPTER VI. CHAPTER VIL. PAGH 78 108 157 LIST OF ILLUSTRATIONS, *,” In all the figures of flowers, unless otherwise specified, the letters refer to the same parts, viz. :—pistil, ~—style, 2’—stigma, s¢— stamen, /—filament, /—anther, a—petals, ~e—corolla, co— sepals, s.—calyx, ca—ovary, o—honeygland, 4—pollen, Zo. FIG. PAGER Geranium sylvaticum a I 1, Stigma of the Alder (after Axell) 9 2. Stigma of the Hop Fy A 9 3. Stigma of the Wheat i 55 9 4. Stigma of the Willow #8 3 9 5. Stigma of the Flax es ‘5 9 6. Stigma of Nuphar $5 ee 9 7. Section of Plantago major = 10 8. Section of Plumbago Europea ‘is % 10 g. Section of Poterium sanguzsorba Pe ag 10 10. Section of Sanguisorba officinalis ,, a 10 11. Mouth-parts of a Wasp 13 12, Front part of head of Bideopa seen i ‘halon: spt ihe mouth-parts extended (after Miiller) 14 13. Prosopis (after F. Smith) e 3 5 14 14. Mouth-parts of Polistes (after Miiller} . 14 15. Mouth-parts of Andrena, seen from below ,, Franee 15 16. Mouth-parts of Halictus 53 3 15 17. Mouth-parts of Panurgus fp x 15 18. Mouth-parts of Halictoides ve - 15 19. Mouth-parts of Chelostoma 53 ” 15 20. Head of Humble-hee (Bombus agrorum), with the mouth- parts extended (after Miiller) . 16 21. Left hind-leg of Prosopis ,, FA 17 22. Left hind-leg of Sphecodes ,, 5a 17 17 23. Sphecodes (after Westwood) xii LIST OF ILLUSTRATIONS. FIG. PAGE 24. Right hind-leg of Halictus (after Miiller) . aes RZ, 25. Left hind-leg of Panurgus banksianus ,, 55 . e. 28 26. Right hind-leg of Anthophora bimaculata ,, Se g = 58 27. Right hind-leg of Bombus scrimshiranus ,, se ‘ : 19 28. Right hind-leg of Hive-bee ” ” : - 19 29. Diagrammatic section of Arum . . : 3. 428 30. Pink in the first (male condition) . : : 30 31. Pink in the second condition, with mature diemas “ - 30 32. Thymus serpyllum, in the first condition, with ripe stamens (after Miiller) : “ : : : to Sam 33. Thymus serpyllum, in the second cantor: with mature stigma . af 34. Myosotis versicolor, young flower (iver Nature) : é eee | 35. Myosotis versicolor (older flower) . 31 36. Cleistogamous flower of Lamium amplexiraule ao Hilde. brand) : F 7 33 37. Section of ditto (after Hildebrand) 5 5 5 2! 333 38. Primula (long-styled form) . : : 3 3 ©, 33 39. Primula (short-styled form) . ; : : . és AO 433 40. Geranium pratense (after Bentham) : F - 36 41. Geranium pratense, young flower (after Hildebrand sy 37 42, Geoz~‘um pratense (older flower) ,, - " a 837 43. Matva sylvestris (after Sowerby) . : 3 . 40 44. Malva rotundifolia ,, ‘3 - 40 45. Stamens and stigmas of Malva eines latter Miiller) 4! 46. Stamens and stigmas of .Walva rotundifolia ,, < 41 47. LZpilobium angustifolium (after Sowerby) : . 42 48. Epilobium parviflorum 55 56 ; « 42 49. Corolla of—a, Geranium pratense; b, G. Dpbandieaie 3G G. molle; ad, G. pusillum . . F ‘ ; & AB 50. Lychnis vespertina (after Bentham) ‘ 45 51. A young flower of Delphinium elatum, seen frank in front, al after removal of the calyx (after Miiller) 52 2, Section of the same flower seen from the side ag ve 52 53. An older flower, seen from front, after removing calyx ,, wa 52 54. Section of the same flower, seen from the side Py 7 52 55. Flower seen from above ay is 54 56. Pistil with two stamens, after the visit of an insect ,, ae 54 57. Section of a flower of Viola canina . f . A « 59 58. Stamen of a flower of Violacanina . 5 . + 59 LIST OF ILLUSTRATIONS. . Polygala vulgaris (after Bentham) . Flower of Polygala vulgaris . Section of ditto . . Stellaria graminea (after Denchand ‘ . P ‘ - Young flower of Zropeolum major ‘ Flower of Zropwolum major in the second stage . Flower of Zropfeolum major in the third stage . Lotus corniculatus (after Bentham) . Flower of Lotus corniculatus seen from the ade at in i at (after Miiller) . Ditto, after removal of the cesited (after Miiller) . Ditto, after removal of the standard and wings ,, +6 . Ditto, after removal of one side of the keel ,, - . Terminal portion of Fig. 70 more magnified ,, 95 . Flower of Sweet Pea, in its natural position . Ditto. The wings are depressed, the stamens and pistil acuaied . Flower of Genista tinctoria unopened . a 76. Ditto, opened. : . . . Lythrum salicaria (after Bentian) . . i . Long-styled form of Lythrum salicaria (after Darwin) 3 . Mid-styled ditto 55 na . Short-styled ditto oF on . Drosera rotundifolia (after Bentham) . Two leaves of Dionzea : one open, one closed upon a fly Wild Chervil (Cherophyllum sylvestre) (after Bentham) . Flower of Wild Chervil in the first (male) state (after Miiller) Ditto, in the second (female) state . F ey $e . Chrysanthemum parthenium (after Bentham) 87. Floret of Chrysanthemum parthenium, just opened aller Ogle) 88. Ditto, somewhat more advanced an ie 89. Ditto, with the stigmas expanded sey Ge go. Section of bud of Campanula medium 7 ‘ gt. Section of a flower in the first (male) condition g2. Ditto, in the second (female) condition F ‘ ‘ 93. Flower of Erica tetralix (after Ogle) . : . . 94. Stamen of ditto yy 95 P . os i & 9s. Borago officinalis (after Bentham) . a ee : 96. Lulmonaria officinalis ,, 3 : , - ‘ F 97. Veronica chamedrys Pr i ‘ ‘ . Verbascum thapsus ag of , ‘ ‘ é LIST OF ILLUSTRATIONS. xiv FIG. PAGE 99. Scrophularia nodosa (after Bentham) . 136 too. Section of Digitalis purpurea (af er Ogle) 137 tor. Ditto, more advanced 137 102. Ditto, still more advanced . 137 103. Bartsia od mnitites (after Bentham) : 138 104. Ditto. Flower with a short pistil (after Miiller) . 139 105. Ditto. Flower with a long pistil ,, ” 139 106. Euphrasia officinalis (after Bentham) . 140 107. Flower of ditto . 140 108. Peticularis sylvatica (after Ogle). 142 109. Lamium album (after Bentham) . 144 110. Flower of ditto. . 145 111. Section of ditto. 145 112. Salvia officinalis. Section of a young flower (ilies Ogle) 148 113. Ditto, visited by a Bee % 35 148 114. Ditto, older flower 5 ae 148 115. Stamens in their natural position 3 a 149 116. Stamens when moved by a bee 5 5 149 117. Teucrium scorodonia, in the first state 150 118, Ditto in the second state 150 119. Chenopodium bonus-henricus (after Bente 156 120. Orchis mascula 39 3 163 . Side view of flower, with all the petals and pa 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 (after Darwin) . Front view of flower, sath all sais an, petals decane except the labellum (after Darwin) . The two pollinia 8 Soe lad ‘i . Ophrys apifera (after Bentham) . Cephalanthera grandifiora ,, 5 . Listera ovata . Flower of Cypripedium flnigifi Bain. Front view . Ditto. Seen from the side . Side view of Catasetum saccatum, with all ibe sepals and petals removed except the labellum (after Darwin) . Section or ditto, with all the parts a little expanded ,, —,, 170 172 172 174 175 GLOSSARY, Anemophilous (p. 9) plants are those in which the pollen is carried to the stigma by the wind. Anther, that portion of the stamen which contains the pollen. Calyx (p. 23), the outer whorl of the flower. Cleistogamous species (p. 32), are those which, besides the usual con- spicuous flowers, have others which are smaller, and generally uncoloured. Corolla (p, 23), the second whorl of the flower. In most cases this is the coloured part. Dichogamous species (p. 24) are those in which the stamens and pistil do not mature simultaneously. Dictinous plants (p. 24), are those in which all the flowers are either male or female, that is to say, either contain stamens but no pistil, or pistil but no stamens. Dimorphous species (p. 25) are those in which there are two forms of flowers, differing in the relative position or length of the anthers and stigma. Dicecious species (p. 24) are those in which the stamens and pistils are situated not only in distinct flowers, but also on separate plants. Entomophilous plants (p. 9) are those in which the pollen is carried to the stigma by insects Epigynous, situated upon the ovary. Filament, the stalk of the anther. Ueterogamous plants are those which have male, female, and her- maphrodite fluwers, or any two of them united in one head. xvi GLOSSARY. Heteromorphous species are those in which there is more than one form of flower. Hypogynous, situated under the ovary. Moneecious species (p. 24) are those in which the stamens and pistils are in separate flowers, but on the same plant. Monomorphous species are those in which all the flowers resemble one another in the relative position of the stamens and pistil. Nectary, that part of the flower which secretes honey. Perigynous, situated around the ovary. Petals, the leaves of the corolla. Pistil, the central organ of the flower. It generally consists of one or more ovaries and stigmas ; the stigma is often raised on a stalk, called » style,” Polygamous species are those which have male, fema‘e, and hermaphro- dite flowers on the same or on distinct plants. Proterandrous plants (p. 24) are those in which the stamens come to maturity before the pistil. Proterogynous plants (p. 24) are those in which the pistil comes to maturity before the stamens. Sepals (p. 23) the leaves of the calyx. Stamens (p. 23) the parts of a flower which generally stand next the corolla, on the inner side. They usually consist of a stalk or filament, and an ‘‘ anther” containing the polien. Stigma (p. 23), that portion of the pistil in which pollen must be deposited in order to fertilise the flowers. Style, the stalk of the stigma, Trimorphous species are those in which there are three forms of flowers, differing in the relative position or length of the anthers and stigma. GERANIUM SYLVATICUM. ON BRITISH WILD FLOWERS CONSIDERED IN RELATION LO INSECTS: CHAPTER I.—INTRODUCTION. THE flowers of our gardens differ much in size and colour from those of the same species growing wild in their native woods and fields: this is due partly to cultivation, but still more to the careful selection of seeds or cuttings from those plants, the flowers of which show any superiority over the others in size or colour. Even amongst wild flowers, however, recent re- searches have proved that the forms and colours have 5 B 2 IMPORTANCE OF INSECTS [CHAP. been modified in a similar manner: the observations of botanists, especially of Sprengel, Darwin, and H. Miiller, have shown that the forms and colours of wild flowers are mainly owing to the unconscious selection exercised by insects, although no doubt the existence of a certain amount of colouring matter is, as we see in the autumn tints, in various fungi, seaweeds, &c., due to other causes. Sprengel appears to have been the first who per- ceived the intimate relations which exist between plants and insects; and Geranium sylvaticum (see p. 1) will always have an interest as being the flower which first led him to his researches. In the year 1787 he observed that in the corolla of this species there are a number of delicate hairs; and, convinced, as he says, that “the wise Author of Nature would not have created even a hair in vain,” he endeavoured to ascer- tain the use of these hairs, and satisfied himself that they served to protect the honey from rain. His attention having thus been drawn to the sub- ject, he examined numerous other flowers with great care, and was surprised to find how many points in reference to them could be explained by their rela- tions to insects. The visits of insects are of great importance to plants in transferring the pollen from the stamens to the pistil, In many plants the stamens and pistil are situated in separate flowers: and even in those cases where they are contained in the same flower, self-fer- tilisation is often rendered difficult, or impossible; sometimes by the relative position of the stamens and pistil, sometimes by their not coming to maturity at 1] TO FLOWERS. 3 the same time. Under these circumstances the trans- ference of the pollen from the stamens to the pistil is effected in various ways. In some species the pollen is carried by the action of the wind; in some few cases, by birds; but in the majority, this im- portant object is secured by the visits of insects, and the whole organisation of such flowers is adapted to this purpose. To the honey are due the visits of insects; the sweet scent and bright colours of the flowers attract them ; the lines and circles on the corolla guide them to the right spot; and, as we shall see, there are a number of curious contrivances all tending to the same object. But while Sprengel’s deep religious feeling thus gave him the clue which has thrown so much light on the origin and structure of flowers, the comparatively low conception of creative power which was in his time, and, indeed, until recently, prevalent, led him to assume that each flower was created.as we now see it, and prevented him from perceiving the real signifi- cance of the facts which he had discovered ; while the true explanation could scarcely have escaped him if he had possessed that higher view of creation which we owe to Mr. Darwin. Though he observed that in many species the stamens and pistil are not mature simultaneously, and that such plants there- fore cannot fertilise themselves, but are generally dependent on the visits of insects, he appears to have considered that these visits were arranged mainly in order to overcome the difficulty of fertilisation thus resulting ; and hence, perhaps, the oblivion into which his work, though so interesting and suggestive in B 2 4 SPRENGEL'’S OBSERVATION’. [c1raP. itself, so full of curious and carcful observations, was allowed to fall. For there is an obvious incon- sistency in the coexistence of two elaborate sets of arrangements, one tending to preclude, the other to effect, self-fertilisation; in supposing that in the first place the stamens and pistil were so arranged that the pollen of the one might not fertilise the other ; and, secondly, that elaborate contrivances were devised to promote the visits of insects, and compel them to transfer the pollen from the stamens to the pistil: a result which might have been ob- tained so much more simply by a slight alteration of the flower itself. It is the more remarkable that this did not strike Sprengel, because he expressly observes in one pas- sage that, “Die Natur nicht will dass irgend einer Zwitterblume durch ihren eigenen Staub befriichtet werden solle” (Nature does not wish that any com- plete flower should be fertilised by its own pollen). Yet though thus so near the truth, he failed to per- ceive the true importance of the visits of insects. Subsequent observers, though in some cases recog- nising the advantage of fertilising one flower by pollen from another, did not connect these observa- tions with Sprengel’s discoveries ; and our illustrious countryman Mr. Darwin was the first to bring into prominence the fact that the importance of insects to llowers consisted in their transferring the pollen—not inerely from the stamens to the pistil, but from the stamens of one plant to the pistil of another. While then from time immemorial we have known that flowers are of great importance to insects, it is 1] MR, DARIWIN’S OBSERVATIONS. 5 only comparatively of late that we have realised how important, indeed how necessary, insects are to flowers. For it is not too much to say, that if, on the one hand, flowers are in many cases necessary to the existence of insects ; insects, on the other hand, are still more indispensable to the very existence of flowers :— that, if insects have been in many cases modified anc adapted with a view to obtain honey and pollen from flowers, flowers in their turn owe their scent and colour, their honey, and even their distinctive forms to the action of insects. There has thus been an in- teraction of insects upon flowers, and of flowers upon insects, resulting in the gradual modification of both. If it be objected that I am assuming the existence of these gradual modifications, I must reply that it is not here my purpose to discuss the doctrine of Natural Selection. I may, however, remind the reader that Mr. Darwin’s theory is based on the following considerations :—1. That no two animals or plants in nature are identical in all respects. 2. That the offspring tend to inherit the peculiarities of their parents. 3. That of those which come into existence, only a certain number reach maturity. 4. That those which are, on the whole, best adapted to the circum- stances in which they are placed, are most likely to leave descendants. Now, applying these considerations to flowers ; if it be an advantage to them that they should be visited by insects (and that this is so will presently be shown), then it is obvious that those flowers which, either by their larger size, or brighter colour, or sweeter scent, or greater richness in honey, are most attractive to 6 USES OF INSECTS TO PLANTS. — [CHAP. insects, will, ceceris paribus, have an advantage in the struggle for existence, and be most likely to per- petuate their race. Every garden indeed is a sufficient proof that in size and colour, flowers are susceptible of great modifications; and insects, unconsciously produce changes similar to those which man effects by design. Insects are useful to plants in various ways. Thus, a species of acacia mentioned by Mr. Belt,! if unpro- tected, is apt to be stripped of its leaves by a leaf- cutting ant, which uses the leaves, not directly for food, but, according to Mr. Belt, to grow mushrooms on. The acacia, however, bears hollow thorns, and each leaflet produces honey in a crater-formed gland at the base, and a small, sweet, pear-shaped body at the tip. In consequence, it is inhabited by myriads of a small ant, Pseudomyrma bicolor, which nests in the hollow thorns, and thus finds meat, drink, and lodging all provided for it. These ants are con- tinually roaming over the plant, and constitute a most efficient body-guard, not only driving off the leaf-cutting ants, but even in Mr. Belt’s opinion, ren- dering the leaves less liable to be eaten by herbivo- rous mammalia. The principal service, however, which insects per- form for plants is that of transferring the pollen from one flower to another. : I will not now enter on the large question why this cross-fertilisation should be an advantage; but that 1 F, Miller has observed similar facts in Sta. Catharina. (Mature, vol. x, p. 102.) L] IMPORTANCE OF CROSS-FERTILISATION. 7 it is so has been clearly proved. Kolreuter speaks with astonishment of the “statura portentosa” of some plants thus raised by him; indeed, says Mr. Darwin (“Animals and Plants under Domestication,” ch. xvii.), “all experimenters have been struck with the won- derful vigour, height, size, tenacity of life, precocity, and hardiness of their hybrid productions.” Mr. Darwin himself, however, was, I believe, the first to show that if a flower be fertilised by pollen from a different plant, the seedlings so produced are much stronger than if the plant be fertilised by its own pollen. I have had the advantage of seeing several of these experiments, and the difference is certainly most striking. For instance, six crossed and six sclf- fertilised seeds of Jpoma@a purpurea were grown in pairs on opposite sides of the same pots; the former reached a height of 7 ft, whilc the others were on an average only 5 ft. 4 in. The first also flowered more profusely. It is moreover remarkable that in many cases plants are themselves more fertile if sup- plied with pollen from a different flower, a different variety, or even, as it would appear in some instances (in the passion flower, for instance), from a different species. Nay, in some cases pollen has no effect whatever unless transferred to a different flower. Fritz Miiller has recorded some species in which pollen, if placed on the stigma of the same flower, has not only no more effect than so much inorganic dust; but, which is perhaps even more extraordinary, in others, he states that the pollen placed on the stigma of its own flower acted on it like a poison. This he noticed in several species: the flower faded and 8 TRANSFERENCE OF POLLEN [CHAP. fell off; the pollen-grains themselves, and the stigma in contact with them, shrivelled up, turned brown, and decayed; while other flowers on the same branch, which were not so treated, retained their freshness. The transference of the pollen from one flower to another is, as I have already mentioned, effected principally either by the wind or by insects. In the former case the flower is rarely conspicuous; indeed Mr. Darwin finds it “an invariable rule that when a flower is fertilised by the wind it never has a gaily- coloured corolla.” Conifers, grasses, birches, poplars, &c., belong to this category. In such plants a much larger quantity of pollen is required than where fertilisation is effected by insects. Everyone has observed the showers of yellow pollen produced by the Scotch fir. It is an advantage to these plants to flower before the leaves are out, because the latter would gteatly in- terfere with the access of the pollen to the female flower. Hence such plants, as a rule, flower early in the spring. Again, in such flowers the filaments of the stamens ate generally long, and the pollen is less adherent, so that it can easily be detached by the wind, which would manifestly be a disadvantage in the case of those flowers which are fertilised by insects. On the other hand, it is an advantage tu most seeds to be somewhat tightly attached, because they are then only removed by a high wind which is capable of carrying them some distance, I say “to most” because this does not apply to such seeds as those of the dandelion, which are specially adapted to be carried by the wind. 1] BY WIND AND INSECTS. 9 Again, as Mr. Darwin has pointed out, irregular flowers appear to be almost always fertilised by insects. Wind-fertilised flowers, moreover, generally have the stigma more or less branched or hairy, which evidently tends to increase its chance of catching the pollen. Figs. 1 to 6, taken from Axell’s work, illustrate Fic. 1. Stigma of the Alder. Fic, 2.—Of the Hep. Fic 3.—Of the Wheat; which are anemophilous. Fic. 4.—Of the Willow. Fic. 5.—Of the Flax. Fic. 6.—Of Nuphar ; which are entomophilous. this difference. In the alder (Fig. 1), the hop (Fig. 2), and wheat (Fig. 3), the pollen is wind-borne, whence they have been termed by Delpino “ axemophilous ;” while in the willow (Fig. 4), the flax (Fig. 5), and nuphar, (the yellow water lily) (Fig. 6), it is carried by insects, whence such plants have been termed “ entomophilous.” fe) WIND-FERTILISED FLOWERS. [cHapP. Even in nearly allied plants this difference is well marked, in illustration of which Axell gives the following figures taken from Maout and Decaisne’s “Traité générale de Botanique”:—Fig. 7 represents -a section of a flower of Plantago major, which is wind-fertilised ; Fig. 8 of an allied species, Plambago Pic. 7. Fic. 8. VE Giptd Venema Hew —o! suopdotaamaele Europea, which is insect-fertilised. Again, Fig. 9 re- presents a section of Poterium sanguisorba, which is wind-fertilised ; Fig. 10 of the nearly allied Sanguz- sorba officinalis, which is fertilised by insects. 1.] COLOUR, SCENT, AND HONEY. 1 It is an almost invariable rule that wind-fertil- ised flowers are inconspicuous; but the reverse does not hold good, and there are many flowers which, though habitually visited by insects, are not brightly coloured. In some cases, flowers make up by their. numbers for the want of individual conspicuousness. In others, the insects are attracted by scent; indeed, as has already been mentioned, not only the colour? of flowers, but the scent also, has no doubt been greatly developed through natural selection, as an attraction to insects. But though bright colours and strong odours are sufficient to attract the attention of insects, something more is required. Flowers, however sweet-smelling or beautiful, would not be visited by insects unless they had some inducements more substantial to offer. These advantages are the pollen and the honey; although it has been sug- gested that some flowers beguile insects by holding out the expectation of honey which does not really exist, just as some animals repel their enemies by resembling other species which are either dangerous or disagreeable. The honey is secreted, sometimes by one part of the flower, sometimes by another; and great variations may be found in this respect even within the limits of a single order. Thus in the Ranunculacee the honey glands are situated on the calyx, in certain Pzonies; on the petals, in buttercups and hellebore; 1 In confirmation of this it is stated that when insects are excluded, the blossoms last longer than is otherwise the case ; that when flowers are once fertilised, the corolla soon drops off, its function being per- formed, 12 BEES AND COLOURS. [CHAP. on the stamens, according to Miiller, in Pulsatilla ; and on the ovary, in Caltha. The pollen, of course, though very useful to insects, is also essential to the flower itself; but the scent and the honey, at least in their present development, are mainly useful in securing the visits of insects, though the honey is also sometimes of service in causing the pollen to adhere to the proboscis of the insect. That bees are attracted by, and can distinguish, colours, was no doubt a just inference from the observations on their relation to flowers, but I am not cognisant of any direct evidence on the subject. I thought it therefore worth while to make some experiments; and a selection from them will be recorded in the forthcoming volume of the Journal of the Linnean Society. I placed slips of glass with honey, on paper of various colours, accustoming different bees to visit special colours, and when they had made a few visits to honey on paper of a par- \ticular colour, I found that if the Papers were trans- posed the bees followed the colour. But if flowers have been modified with reference to the visits of insects, insects also have in some cases been gradually modified, so as to profit by their visits to flowers. This is specially the case with reference to two groups of insects, namely, Bees and Butter- flies, which have been specially studied by H. Miiller with reference to this point; and from his works the following facts are mainly taken. Although the whole organisation of the insect might be said to have reference to these relations, still the parts which have been the most profoundly altered are the mouth 7 lL] ADAPTATIONS OF INSECTS TO FLOWERS. 13 and the legs. If we are asked why we assume that in these cases the mouth and legs have been modified, the answer is, that they depart greatly from the type found in allied insects, and that be- tween this original type and the most modified examples, various gradations are to be found. The mouth of an insect is composed of (1) an upper lip (Fig. 11a), (2) an under lip (Fig. 11d) (3) a pair of anterior jaws or mandibles (Fig. 11 4), and (4) a pair of posterior jaws or maxille (Fig. I1¢). These two pairs of jaws work laterally, Fic. 11.—Mouth-parts of a Wasp a, labrum or upper Jip ; 4, mandibles ; ¢, maxille ; d, labium or lower lip; 2, palpi. that is to say, from side to side, and not, as in man and other mammalia, upwards and downwards. The lower lip and maxilla are each provided with a pair of feelers or palpi (Fig. 11, ¢ and d, x). The above figures represent the mouth parts of a wasp, in which, as is very usually the case, the mandibles are hard and horny, while the maxilla are delicate and mcm- branous, In the different groups of insects, these organs present almost infinite variations. 14 MOUTH OF WASP. [CHAP. Fig. 12 represents the mouth parts of a bee, Prosopis (Fig. 13), seen from below; # d@ being the mandibles ; pm, the palpi of the maxille /a, pt, those of the lower lip. The bees belonging to this genus construct their cells in sand, or in the centre of dry bramble sticks, lining them with a transparent mucus, which they smooth down with their trowel- like lower lip (Fig. 12 ), and which hardens into a thin mem- Fic. 12.—Front part of head of brane (Smith “ Catalogue of Prosopis, seen from below, s 75 with the mouth- parts. ex” Brit. Hymenoptera,” p. 7). lee: frtabisl palpisy, ‘That the mouth of Prosopis maxillary palpi; rt, men- z “ tum; sé, stipes; ma, man- probably represents the condi- dibles ; c, cardo; 0, eye. . tion of that of the ancestors of the Hive-bees, before their mouth-parts underwent spe- cial modifications, may be inferred from the fact that the same type occurs in allied groups, as is shown in Fig. 14, which represents the mouth of a wasp (Polistes) Fic. 13.—Prosopis. Fic. 14.—Mouth-parts of Polistes. also seen from below. We may therefore consider that Prosopis shows in this respect no special adap- tation for the acquirement of honey, and in fact, 1.] MOUTH OF SOLITARY BEES. 15 though the bees belonging to this genus feed their young on honey and pollen, they can only get the Fic. 15. Fic. 16. Fic. 17. Fie. 18. Fic. 19. Fia. 15.—Mouth-parts of Andrena, seen from below—fz, paraglosse ; //, ligula ; p!, labial palpi; fr, maxillary palpi; me, mentum ; sé, stipes; ¢, cardo ; 9, eye. Fic. 16.—Of Halictus. Fic. 17.—Of Panurgus. Fic. 18.—Of Halictoides. Fic. 19.—Of Chelostoma. former from those flowers in which it is on the surface. In Andrena (Fig 15), Halictus (Fig. 16), 16 MOUTH OF HUMBLE-BEE. [CHAP. Panurgus (Fig. 17), Halictoides (Fig. 18), and Chelos- toma (Fig. 19), we see various stages in the elon- gation of the lower lip, until at length it reaches the remarkable and extreme form which it now presents in the hive and humble bees (Fig. 20), and Fic 20.—Head of Humble-bee (Bombus agrorum), with the mouth-parts extended. fa, paraglosse ; /, ligula; Ad, labial palpi; fm, maxiliary palpi; /a, lamina of ditto; a, mentum ; sé, stipes ; 2d, mandibles; ¢, cardo ; 0, eye. which enables them to extract the honey from almost all our wild flowers. No bees, however, have the proboscis so much elongated as is the case with some butterflies and .moths; perhaps, as Hermann Miiller has suggested, because the 1] HIND-LEGS—PROSOPIS, SPHECODES. 17 necessity of using their mouth for certain domestic purposes has limited its specialisation in this parti- cular direction. If, again, we examine the hind-legs of bees, we shall find gradations similar to those already men- tioned in the lower lip. In Prosopis (Fig. 21) they do not differ materially from those of genera which supply their young with animal food. Portions of the leg, indeed, bear stiff hairs, the original use of Fic, 2r. Fic. 23. Fig 24. Fic, 21.—Left hind-leg of Prosopis. Fic. 22.—Left hind-leg of Sphecodes. Fic. 23.—Sphecodes. Fic. 24.—Right hind-leg of Halictus. which, probably, was to clean these burrowing insects from particles of sand and earth, but which in Pro- sopis assist also in the collection of pollen. Fig. 22 represents the hind leg of Sphecodes (Fig. 23), a genus in which the tongue resembles in form that of Halictus. Here we see the hairs decidedly more developed, a modification which has advanced still further in Halictus (Fig. 24), in which the de- c 18 HALICTUS, PANURGUS, ANTHOPHORA. [cHAP. velopment of the hairs is most marked on fhose seg- ments of the hind legs which are most. conveniently situated for the collection and transport of pollen. In Panurgus, the same change is still more marked (Fig. 25) and the pollen-bearing apparatus is confined to the tibia, and first segment of the tarsus, a differen- tiation which is even more apparent in Anthophora (Fig. 26). In all these bees the pollen is simply en- tangled in the hairs of the leg, as in a brush, but there Fic. api Nee or Panurgus Fic. es poe Antho- are other genera, of which the humble bees and the hive bees are the only British representatives, which moisten the pollen with honey, and thus form it into a sticky mass, which is much more easy to carry, and is borne not round the leg, but on one side of it. In the Humble-bee (Bombus, Fig. 27) for instance, the honey is borne on the outer side of the hinder tibiz, which are flattened, smoothed, and bordered by a row of stiff curved hairs, thus forming a sort of 1] BOMBUS, APIS—HAIRS ON BODY. 19 little basket.. Lastly in the Hive-bee (Fig. 28) the adaptation is still more complete, the hairs on the first tarsal segment are no longer scattered, but are arranged in regular rows, and the tibial spurs, inherited by Bombus from far distant ancestors, have entirely disappeared. In some bees the pollen is collected on the body, and here also we find a remarkable gradation from Prosopis (Fig. 13) which has only simple hairs like a «tlie Oe i} a , Bryonia dioica Halictoides | Species of Campanula. Andrena hattorfiana ES Scabiosa arvensis. Cilissa melanura | ./ ©). Lythrum Salicaria. Macropis labiata iz Lysimachia vulgaris. Osmia adunca ” \ Echium. Another remarkable peculiarity of plants, which may I think possibly have reference to their rela- ‘tions with insects, is the habit of “sleeping,” which ‘characterises certain species. Many flowers close their petals during rain, which is obviously an advantage, since it prevents the honey and pollen from being spoilt or washed away. Every- body, however, has observed that even in fine weather _certain flowers close at particular hours. This habit of going to sleep is surely very curious. Why should flowers do so? In animals we can understand it; they are tired and require rest. But why should flowers sleep? Why should some flowers do so, and not others? Moreover, different flowers keep different hours. The Daisy opens at sunrise and closes at sunset, whence 22 SLEEP OF FLOWERS. (CHAP. I. its name “day’s-eye.” The Dandelion (Leontodon Taraxacum) is said to open about seven and close about five; Avenaria rubra to be open from nine to three ;1 Nymphaea alba from about seven to four; the common Mouse-ear Hawkweed (Hieracium Pilosella) from eight to three; the Scarlet Pimpernel (Aza- gallis arvensis) to waken at seven and close soon after two; Tragopogon pratensis to open at four in the morning, and close just before twelve, whence its English name, “John go to bed at noon.” Far- mers’ boys in some parts are said to regulate their dinner-iime by it. Other flowers, on the contrary, open in the evening. Now, it is obvious that flowers which are fertilised by night-flying insects would derive no advantage from being open by day ; and on the other hand, that those which are fertilised by bees would gain nothing by being open at night. Nay, it would be a distinct dis- advantage, because it would render them liable to be robbed of their honey and pollen, by insects which are not capable of fertilising them. I would venture to suggest, then, that the closing of flowers may have reference to the habits of insects, and it may be observed also in support of this that wind-fertilised flowers do not sleep; and that some of those flowers which attract insects by smell, emit their scent at particular hours; thus, Hesperis matronalis and Lychnis vespertina smell in the evening, and Orchis bifolia is particularly sweet at night. 1 In my own observations the opening and closing was more gradual and more dependent on the weather than I should have expected from the statements quoted above, LYTHRUM SALICARIA. CHAPTER II. I NOW pass to the structure and modification of flowers. A complete flower consists of (1) an outer envelope or calyx, sometimes tubular, sometimes con- sisting of separate leaves called sepals; (2) an inner envelope or corolla, which is generally more or less coloured, and which, like the calyx, is sometimes tubular, sometimes composed of separate leaves, called petals ; (3) of one or more stamens, consisting of a stalk or filament, and a head or anther, in which the pollen is produced ; and (4) a pistil or an ovary, which is situated in the centre of the flower, and contains one or more seeds or ovules. The pistil consists of a stalk or s¢y/e,; and a stigma, to which the pollen must find its way in order to fertilize the flower, and which 24 THE PARTS OF A FLOWER. [CHAP. in many familiar instances forms a small head at the top of the style. In some cases the style is absent, and the stigma is consequently sessile. Thus, the pistil is normally surrounded by a row of stamens, and it would seem at first sight a very simple matter that the pollen of the latter should fall on the former. This in fact does happen in many instances, and flowers which thus fertilize themselves have evidently one great advantage-— few remain sterile for want of pollen. Such cases, however, are much less frequent than might at first be supposed, and there are three prin- cipal modes by which self-fertilization is prevented. Firstly, in many species, the stamens and pistil are situated in different flowers; such species are called diclinous ; when the male and female flowers are on the same plant, they are termed mona@cious ; when on different plants, diacious. Secondly, in other instances, as was first discovered by Sprengel, though the stamens and pistil are both situated in one flower, they are not mature at the ‘same time, and the pollen, therefore, cannot fertilize the stigma. These plants are called adichogamous. Sometimes, as in the Arum, the pistil matures before the anther, and these plants are called proterogynous ; but much more frequently the anther matures before the pistil ; and such plants are called proterandrous. Thirdly, there are some plants in which, as was first discovered by Mr. Darwin, the same obiect is secured by the existence, within the limits of the same species, of two or more kinds of flowers, differing in the rela- tive position of the stamens and pistil, which are so placed as to favour the transference by insects of the 1.] MODES OF CROSS-FERTILISATION. 25 pollen from the anther of the one form to the pistil of the other. These plants are termed /eteromorphous ; some of them have two kinds of flowers, and are called dzimorphous ; while others have three forms, and are called ¢rzmorphous. But even in plants which belong to none of these categories we find minor modifications which tend to prevent self-fertilization ; and Mr. Darwin is pro- bably right in his opinion that no plant invariably fertilizes itself. Thus in some species where the stamens surround the pistil, and which might, there- fore, be supposed to be arranged in such a man- ner as to ensure self-fertilization, the anthers do not open towards the pistil, but on the sides, and by no means therefore in a favourable position with reference to the transference of the pollen. In most, if not all the Cruciferz, the anthers in young flowers have the side which opens turned towards the pistil ; but be- fore the anthers come to maturity. they twist them- selves round, so as to turn their backs to the. stigma. Again, in pendent flowers, where the pistil hangs below the anthers, the stigmatic surface is never the upper one, which would catch any falling pollen; but on the contrary, the lower one, which could hardly be touched by the pollen of the same flower, but which is so placed as to come in contact with any insect or other body approaching the flower from below. It is also probable that many cases will be found to exist, in which, though the pollen necessarily comes in contact with the pistil of the same plant, fertilization does not take place. However improbable this might @ priori appear, it is nevertheless said by Hildebrand 26 TRANSFERENCE OF POLLEN. [CHAP. to be the case in Corydalis cava and Pulmonaria (Fig. 96), by Gartner in Verbascum nigrum (Fig. 98), and Lobelia fulgens ; by Scott in Primula verticillata, Oncidium, &c. Other cases are recorded in which plants are more or less insusceptible of fertilization by their own pollen. Moreover, even where plants are capable of self-fertilization, the pollen from another flower is often more effective than their own, whence it fol- lows that if a supply of pollen from another plant be secured, it is comparatively unimportant to ex- clude the pollen of the plant itself; for in such cases the latter is neutralized by the more powerful effect of the former. Everyone who has watched flowers, and has ob- served how assiduously they are visited by insects, will admit that these insects must often deposit on the stigma pollen brought from other plants, generally those of the same species; for it is a re- markable fact that in most cases bees confine them- selves in each journey to a single species of plant; though in the case of some very nearly allied forms this is not so; for instance, it is stated, on good authority, that Ranunculus acris, R. repens, and R. bulbosus, are not distinguished by the bees, or at least are visited indifferently by them, as is also the case with two of the species of clover, Trifolium Jragiferum and T. repens. Even in the simplest and most regular flowers, where the stamens surround the pistil, and both are mature at the same time, insects may visit the flower, and yet not fertilise it with its own' pollen, because 11] DICLINOUS PLANTS. 27 they touch the anther with one side of the proboscis and the stigma with the other. There are, however, in flowers a great many admirable and beautiful contrivances, tending to prevent the fertilization of a flower by its own pollen; in consequence of which insects habitually carry the pollen from the anthers of one flower to the stigma of another. As already mentioned, there are three principal modes in which self-fertilisation is prevented. Firstly, by.the stamens and pistil being situated in different flowers, either on the same plant, or, more commonly, in different plants. These differences form the char- acteristics of the classes, Moneecia, Dicecia, and Poly- gamia, of Linnzus ; but it is obvious that such classes are not natural, since we have in very nearly allied species, even within the limits of what is generally considered a single genus, cases in which the one is diclinous, that is to say, has the stamens and pistil in separate flowers, while in the other, the flowers contain both. Secondly, in other cases, the self-fertilization of plants, as was first observed by Sprengel in Zpilobium angustifolium in the year 1790, is guarded against by the fact that the stamens and pistils do not ripen at the same time. In some few cases the pistil ripens before the sta- mens ; these species are calied “proterogynous.” Thus the Aristolochia has a flower which consists of a long tube with a narrow opening closed by stiff hairs which point backwards, so that it much resembles an ordi- nary eel-trap. Small flies enter the tube in search of honey, which from the direction of the hairs they can 28 DICHOGAMOUS PLANTS. [CHAP ‘do easily, though on the other hand, from the same cause, it is impossible for them to return. Thus they are imprisoned in the flower; gradually, however, the pistil passes maturity, and the stigma ceases to be capa- ble of fertilisation, while the stamens ripen and shed their pollen, by which the flies get thoroughly dusted. Then the hairs of the tube shrivel up and release the prisoners, which carry the pollen to another flower. Again, in the common Arum, we find a somewhat similar mode of fertilisation. The well-known green leaf, as shown in the annexed diagrammatic figure (Fig. 29), encloses a central pillar which sup- ports a number of stigmas (Fig..29, s¢.) near the base, and of anthers (2) some- _ what higher. Now in this case nothing would at first sight seem easier or more natural than that the pollen from the anthers should fall on, and fertilise, the pistils. This, however, is not what occurs. The stigmas mature before the anthers, and by the time the pollen is shed, have become incapable of fertilisation. It Fic, 29 —Diagram- is impossible, therefore, that the plant Aun. ‘Ebsirs: should fertilise itself. Nor can the pol- Cae * len be carried by wind. When it is shed it drops to the bottom of the tube, where it is so effectually sheltered that nothing short of a hurricane could dislodge it; and although Arum is common enough, still the chances against any of the pollen so dislodged being blown into the tube of another plant would be immense. 1] ARUM, ARISTOLOCHIA. 29 As, however, in Aristolochia, so also in Arum, small insects which, attracted by the showy central spadix, the prospect of shelter or of honey, enter the tube while the stigmas are mature, find themselves imprisoned, by the fringe of hairs (Fig. 29, 4), which, while per- mitting their entrance, prevent them from returning. After a while, however, the period of maturity of the stigmas is over, and each secretes a drop of honey, thus repaying the insects for their captivity. The anthers then ripen and shed their pollen, which falls on and adheres to the insects. Then the hairs gradually shrivel up and set the insects free, which carry the pollen with them, so that those which then visit another plant can hardly fail to deposit some of it on the stigmas, Sometimes more than a hundred small flies will be found ina single Arum. In these two cases there is obviously a great advantage in the fact that the stigmas arrive at maturity before the anthers, Our common Scrophularia nodosa, some species of Plantago, &c., are also proterogynous, but these cases are comparatively rare. On the other hand those in which the anthers come to maturity before the pistil are much more numerous. To the category of these plants, which are called prose- randrous, belong some species of Thyme, Pinks, Epilo- bium (Figs. 47, 48), Geranium (Fig. 40), Malva (Figs. 43, 44), (Mallow), Impatiens, Gentians, many of the Labiate, the Umbellifers, most of the Composites, of the Lobeliacee, and Campanulacez. In fact, the greater number of flowers which contain both stamens and pistil, are more or less proterandrous. 30 PINKS, THYME. [CHAaP. Fig. 30 represents a flower of the Pink in the first, or male condition. The stamens are mature, and pro- ject above the disk of the flower, while the pistil is still concealed within the tube. On the other hand Fig. 31 represents the same flower in a more advanced condition ; the stamens have shrivelled up, while the pistil now occupies their place. Again, Fig. 32 represents a flower of the Thyme (Thymus serpyllum) and shews the four mature sta- mens, aa, and the short, as yet undeveloped pistil, /. OY wy yf Fic. 30.—Pink in the first (male) Fic. 31.—Pink in the second conaiuun, condition. with mature stigmas. Fig. 33, on the contrary, represents a somewhat older flower, in which the stamens are past maturity, while the pistil, #, on the other hand, is considerably elon- gated, and is ready for the reception of the pollen. Here it is at once obvious that insects alighting on the younger (male) flowers would dust themselves with pollen, some of which, if they subsequently alighted on an older flower, they could not fail to deposit on I] THYME, MYOSOTIS. 31 the stigma.! In some cases flowers which are first male and then female, are male on the first day of st. Fic. 32.—Thymus serpyllum, in the Fic. 33.—Thymus serpyllum, in the first condition, with ripe stamens. second condition, with mature stigma, Sti Fic. 34.—Myosotis versicolor (young Fic. 35.—Myosotis versicotor (older flower). flower). opening, female on the second. In others the period t In the Thymes there are likewise some small flowers which contain no stamens. DIMORPHOUS PLANTS. [cHaP. we tS is longer. Thus Nigella, according to Sprengel, is male for six days, after which the stigma comes to’ maturity and lasts for three or four. (Das entdeckte Geheimniss der Natur, p. 287.) Fig. 34 represents a flower of AZyosotis versicolor (a species often known as the Forget-me-not), when just opened. It will be observed that the pistil projects above the corolla and stamens, so that it must be first touched by any insect alighting on the flower. Gradually, however, the corolla elongates, carrying up the stamens with it, until at length they come opposite the stigma, as shown in Fig. 35. Thus, if the flower has not already been fertilised by insects, it is almost sure to fertilise itself. I now pass to the third of the principal modes by which self-fertilisation is prevented. In the flowers hitherto described, while the several species offer the most diverse arrangements, we have met with no differences within the limits of the same species, ex- cepting those dependent upon sex. But there are other species which possess flowers of two or more kinds, sometimes, as in the violet, adapted to dif- ferent conditions, but more frequently so constituted as to ensure cross-fertilisation. In some of the violets (V. odorata, canina, &c.), besides the blue flowers with which we are allso familiar, there are other, autumnal, flowers almost without petals and stamens; which indeed have scarcely the appearance of true flowers, but in which numerous seeds are produced. “ Cleis- togamous” flowers, as these have been called, occur also in Lamium amplextcaule (Figs. 36 and 37), Oralis acetosella, Trifolium subterraneum, and other plants 11.] CLEISTOGAMOUS FLOIWERS. 335: belonging to very different groups. They were, I believe, first observed by Dillenius in Ruellia (Hortus Elthamensis, v. ii. p. 239). As, however, they have no Fic. 36.—Cleistogamous flower of Fic. 37.—ectiun of ditto. Lamiun amplexicaule. relation to our present subject, I shall not now dwell upon them. I pass on, therefore, to the genus Primula. If a numer of specimens of primroses or of cowslips be x 250 Fic. 38.—Primula (long-styled form). Fic. 39-—Primula (short-styled form). examined, we shall find that about half of them have the pistil at the top of the tube, and the stamens half-way down (as is shown in Fig. 38), D 34 HETEROMORPHOUS FLOWERS. (CHAP. while the other half have, on the contrary, the stamens at the top of the tube, and the pistil half- way down (as shown in Fig. 39). Corresponding differences occur in Polyanthus and Auricula, and have long been known to gardeners, and even to schoolchildren, by whom the two forms are distin- guished as “thrum-eyed” and “ pin-eyed.” As already mentioned, plants which present these differ- ences are known as Heteromorphous (in opposition to those which are Homomorphous, or have only one kind of flower), while those with two forms are called Dimorphous, those with three, Trimorphous. Sprengel himself had noticed a case of Dimorphism in Hottonia, and shrewdly observed that there was probably some reason for it, but was unable to suggest any explanation. In Lythrum the existence of different forms had been observed by Vaucher in 1841, and in the genus Oxalis by Jacquin, who regarded them as indicative of different species ; but it was reserved for the genius and perseverance of Mr. Darwin to explain (Jour. Linn. Soc. 1862, p. 77) the significance of this curious phenomenon, and the important part it plays in the economy of the flower. Now that Mr. Darwin has pointed this out, it is sufficiently obvious: An insect thrusting its proboscis down a primrose of the long- styled form (Fig. 39) would dust its proboscis at a part which, when it visited a short-styled flower (Fig. 40), would come just opposite the head of the pistil, and could not fail to deposit some of the pollen on the stigma. Conversely, an insect visiting a short-styled plant, would dust its proboscis at a I1.] PRIMROSE. LYTHRUM. 35 part further from the tip ; which, when the insect sub- sequently visited a long-styled flower, would again come just opposite to the head of the pistil. Hence we see that by this beautiful arrangement, insects must carry the pollen of the long-styled form to the short-styled, and vice versd. There are other points in which the two forms differ from one another ; for instance, the stigma of the long- styled form is globular and rough, while that of the short-styled is smoother, and somewhat depressed. The pollen of the two forms (Figs. 38 and 39) is also dissimilar; that of the long-styled being con- siderably smaller than the other—z,%,y of an inch in diameter against 3937, or nearly in the proportion of three to two; a difference, the importance of which is probably due to the fact that each grain has to give rise to a tube which penetrates the whole length of the style, from the stigma to the base of the flower ; and the tube which penetrates the long-styled pistil must therefore be nearly twice as long as in the other. Mr. Darwin has shown that much more seed is set, if pollen from the one form be placed on the pistil of the other, than if the flower be fertilised by pollen of the same form, even taken from a dif- ferent plant. Nay, what is most remarkable, such unions in Primula are more sterile than crosses between some nearly allied, though distinct species of plants. The majority of species of the genus Primula appear to be dimorphous, but this is not the case. (Scott, Proc. Linn. Soc. v. viii. 1864, p. 80.) Mr. Darwin has since pointed out (Jour. Linn, D2 36 HETEROMORPHOUS GENERA. [cHAP. Soc. 1863) that several species of Linum are dimorphous, in the same manner as those of Primula ; and has shown that the existence of three forms in Lythrum (Figs. 77—80) already observed by Vaucher, is to be explained in the same manner. I shall refer to this case more in detail when we come to that family. Nor are these by any means the only cases of Heteromorphism now known. I have already Fig. 40.—Geranium pratense. mentioned that of Oxalis, and Hildebrand gives the following list of genera as containing Heteromorphous species, viz., Hottonia, Primula, Linum, Lythrum, Pulmonaria, Cinchona, Mitchella, Plantago, Rhamnus, Amsinckia, Mertensia, Ieucosmia, Drymospermum, Menyanthes, and Polygonum. It will be observed that these genera belong to very different groups, while on 1] MOVEMENTS OF STAMENS AND PISTIL. 37 the other hand, in several cases, as in Primula itself (Scott, Proc. Linn. Soc. vol. viii.), we find monomor- phous and heteromorphous species in the same genus. Another point of great interest, is the spontaneous movement of the stamens and pistil in dichogamous plants, first observed by Kolreuter in Ruta graveo- lens ; he, however, supposed that the object was to bring the stamens in contact with the pistil; whereas the real advantage, as Sprengel pointed out, is that Fic. 41.—Geranium pratense (young Fic. 42.—Geranium pratense (older flower). Five of the stamens are flower). The stamens have retired, erect. and the stigmas are expanded. in consequence the stamens and pistil successively occupy the same spot in the flower, and thus come in contact with the same part of the insect. For instance, in Geranium pratense (Fig. 40), when the flower first opens, the stamens lie on the petals, at right angles with the upright pistils. As, however, they come to maturity they raise themselves (Fig. 41 a), parallel and close to the pistil (Fig. 41 4), which, however, is not as yet capable of fertilisation. After they have shed their pollen, they return to their original position (Fig. 42), 38 AQUATIC PLANTS. POLLEN. (CHAP, and the stigmas unfurl themselves. More or less similar movements have been observed in various other flowers. Thus the anthers of the Foxglove (Digitalis purpurea) (Figs. 100-102), which are at first transverse, become longitudinal as they ripen. In aquatic plants, the blossoms habitually come to the surface. In Valisneria spiralis the female flower has a long spiral stalk which enables it to rise to the top of the water. The male flowers which are small, very numerous, and attached lower down, separate themselves altogether from the plant, rise to the surface, and fertilise the female flowers, among which they float. When this is effected, the spiral stalk of the female flower again contracts, and draws it down below the surface. While the follen grains from each flower agree very closely with one another, those of different species differ greatly in form, size, character of surface, &c. Doubtless there are reasons for these differences, but the subject is one with reference to which we have as yet very little information. According to Sprengel, the pollen of wind-fertilised flowers is drier, and therefore more easily carried by the wind, than that of most insect-fertilised flowers. I say of most, because in some cases, for instance in the violet, as will be shown presently, it is as necessary that the pollen should separate readily from the anthers, as in wind-fertilised flowers. Mr. Bennett states that the pollen of wind-fertilised flowers is generally spherical ; while that of insect- fertilised flowers is usually furrowed, the furrows running along the longer axis of the grain. i1.] FORM AND QUANTITY OF POLLEN. 39 In Dimorphous species the pollen of the short- styled form is generally larger than that of the long- styled form, but in Linum, according to Hildebrand, (“Die Ges. Verth. bei den Pflanzen,” p. 37) it is of the same size in both forms. In Faramea, another Dimorphous group, the sur- face of the pollen grains is different in the two forms (Thomé, “ Das Gesetz der vermiedenen Selbstbe- fruchtung bei den hdheren Pflanzen,” 1870), the smaller grains of the long-styled form being smooth, while those of the short-styled form are studded with small points ; in consequence of which the pol- len-grains are less easily detached from the anther ; this difference possibly has reference to the different position of the two forms; the smooth ones being sheltered by the flower; while the larger pollen- grains, which are produced in the anthers of the long stamens, and are therefore more exposed to the wind, are, in consequence of their roughness, less liable to be blown away and wasted. According to D, Miller (Bot. Zeit, 1857) the pollen of the small flowers of Viola elatior and V. lancifolia is minute and round. Herr von Mohl, however, found no difference between the pollen of the large and small flowers in V. mirabilis (Bot. Zeit., 1863). The number of grains in these flowers is very small. So also in the cleistogamous flowers of Oxalis acetosella, there are not above two dozen pollen-grains in each of the five larger anthers, and one dozen in each of the five smaller ones, The ovules are abuut twenty in number. It is interesting to nutice that the contrivances by 40 GEOLOGICAL ANTIQUITY OF FLOWERS. [cHapP. which cross-fertilisation is favoured, or ensured, are probably of very different geological antiquity. Thus as Miiller has pointed out, the special peculiarities of the Umbelliferze and Composite have been inherited respectively from the ancestral forms of those orders ; those of Delphinium, Aquilegia, Linaria, and Pedicu- laris, from the ancestral forms of the respective genera; those of Polygonum Fagopyrum, P. Bistorta, Lonicera Caprifolium, &c., from the ancestors of those species; while in Lyszmachia vulgaris, Rhinanthus Fic. 43.—Malva sylvestris. Fic. 44.—Afalva rotundifolia. Cristagalli, Veronica spicata, Euphrasia Odontites, and E. officinalis, we find that differences have arisen even within the limits of one and the same species. Among other obvious evidences that the beauty of flowers is useful to them, in consequence of its attract- ing insects, we may adduce those cases in which the transference of the pollen is effected in different manners in nearly allied plants, sometimes even in different species belonging to the same genus. U.] DIFFERENCES BETWEEN ALLIED SPECIES. 41 Thus, as Miiller has pointed out, Alalva sylvestris (Fig. 43) and ALalva rotundifolia (Fig. 44), which grow in the same localities, and therefore must come into competition, are nevertheless nearly equaily common. In both species the young flower contains a pyramidal group of stamens which surround the stigma, and produce a large quantity of pollen, which cannot fail to dust any insect visiting the flower for the sake of its honey. In Malva sylvestris (Fig. 43), where the branches of the stigma are so arranged (Fig. 45), that the plant cannot fertilise itself, the petals are large and conspi- cuous, so that the plant is visited by numerous insects; Fic. 45.—Stamens and stigmas of Mfu/va Fic. 46.—Ditto of Malva rotundifolia, sylvestris. E while in Malva rotundifolia (Fig. 44), the flowers of which are comparatively small and rarely visited by insects, the branches of the stigma are elongated and twine themselves (Fig. 46) among the stamens, so that the flower can hardly fail to fertilise itself. Another remarkable instance occurs in the genus Epilobium, which is, moreover, specially interesting, because in £. angustifolium, as 1 have already men- 42. RELATION OF THE SIZE OF FLOWER [cuap. tioned, the curious fact was first noticed that the pistil did not mature until the stamens had shed their pollen. E. angustifolium (Fig. 47) has conspicuous purplish- red flowers, in long terminal bunches or racemes, and is much frequented by insects; E. parviflorum (Fig. 48), on the contrary, has small solitary flowers, and is seldom visited by insects. Now, tothe former species the visits of insects are necessary, since the stamens ripen before the pistil, and the flower has consequently lost the power of self-fertilisation. In the latter, on the contrary, the stamens and pistil come to maturity at the same time, and the flower can therefore Fic. 47.—LZ£filobium angustifolium, Fic, 48.—Epilobum parvifiorum. fertilise itself. It is, however, no doubt sometimes crossed by the agency of insects; and indeed I am disposed to believe that this is true of all the flowers which are either coloured or sweet scented. The genus Geranium also affords us an instructive example. There are a number of species which, as will be seen in Fig. 49, differ much in the size of the flowers, Thus those (Fig. 49 @) of Geranium pratense 11.] TO THE DEPENDENCE ON INSECTS. 43 (Fig. 40) are nearly twice as large as those of G. pyre- naicum (Fig. 49 6), which again are much larger than those of G. molle (Fig. 49 ¢), while those of G. pusillum (Fig. 49@) are still smaller. These differences of size appear to be connected with other remarkable differences between these species. Fig. 41, as already mentioned, represents a flower of G. pratense when first opened. Five of the stamens have raised them- selves and stand upright, and surround the still immature pistil, When they have shed their pollen they sink back and shrivel up, when the other five raise themselves. At a later stage these in their turn fall back and shrivel up ; but the stigma does not become ma- ture (Fig. 42), until all the stamens xe have shed their pollen. Under these circumstances G. pratense has lost &G the power of self-fertilisation, and is absolutely dependent on the visitsof a¢ & insects. Fic. 49.—Corolla of—a, G. pyrenaicum (Fig. 49 6) is also pro- eel rita terandrous; but while in G. pratense By een a Gee the pistil is not mature until the sta- mens have shed all their pollen and fallen back, in G. pyrenaicum the second series of stamens are still upright when the stigmatic lobes unfurl ; the flower is consequently less absolutely dependent on insects, and we see that the corolla is much smaller. In the third species, G. molle (Fig. 49 ¢), the pistil matures before the second series of stamens, and the corolla is still smaller ; while in G. pusillum (Fig. 49 2) 44 LINES AND MARKS ON FLOWERS. [cHap. the pistil matures before any of the stamens. Thus then these four species may be arranged in a table as below :— GERANIUM PRATENSE. GERANIUM PYRENAICUM. GERANIUM MOLLE, GERANIUM PUSILLUM. Flower large. as) First exclusively Flower smail. First exclusively Flower smaller. First exclusively Flower smallest. First exclusively male, then ex- | male,thenher- | male,thenher- | female, soon clusively fe-| maphrodite. maphrodite. becoming her- male. maphrodite. Incapable of self- |Generally fertil- |Often self-fertil- |Generally _ self- fertilization. ised by insects. | ised. fertilised. Indeed, though further observations on the point are no doubt required, it would seem that, asa general rule, where we find within the limits of one genus some species which are much more conspicuous than others, we may suspect that they are also more dependent on the visits of insects. Sprengel also suggests, and, as it would appear, with reason, that the lines and bands by which so many flowers are ornamented have reference to the _ position of the honey ;! and it may be observed that these honey-guides are absent in night-flowers, where of course they would not be visible, and would there- fore be useless, as, for instance, in Lychnis vespertina (Fig. 50), or Szlene nutans. Night-flowers, moreover, 1 I did not realise the importance of these guiding marks until, by experiments on bees, I saw how much time they lose if honey, which s put out for them, is moved even slightly from its usual place. 1.) ZALPORTANCE OF INSECTS TO FLOWERS. 45 are generally pale; for instance, Lychuis vespertina is white, while Lychuis diurna, which flowers by day, is red. I have been good-humouredly accused of attacking the Bee, because I have ventured to suggest that she does not possess all the high qualities which have been popularly and poetically ascribed to her. But if scientific observations do not altogether support the Fic. 50.—Lychais vespertina. moral and intellectual eminence which has been ascribed to Bees, they have made known to us in the economy of the hive many curious peculiarities which no poet had dreamt of, and have shown that bees and other insects have an importance as regards flowers which had been previously unsuspected. To them we owe the beauty of our gardens, the sweet- ness of our fields. To them flowers are indebted for their scent and colour; nay, for their very existence, 46 IMPORTANCE OF INSECTS TO FLOWERS. {cu. 11. in its present form. Not only have the present shape and outlines, the brilliant colours, the sweet scent, and the honey of flowers, been gradually developed through the unconscious selection exercised by insects ; but the very arrangement of the colours, the circular bands and radiating lines, the form, size, and position of the petals, the relative situations of the stamens and pistil, are all arranged with reference to the visits of insects, and in such a manner as to ensure the grand object which these visits are destined to effect. LYCHNIS VESPERTINA. CHAPTER III. DICOTYLEDONS. THALAMIFLOR&. In the preceding chapters I have endeavoured to give a general sketch of the relations existing between flowers and insects. I shall now proceed to de- scribe particular instances more in detail, following in general the classification adopted in Mr. Bentham’s admirable “ Handbook of the British Flora,” from which also many of my facts and illustrations have been borrowed. I propose to go through the English Flora, in the order of Mr. Bentham’s work, calling at- tention to those facts, bearing on our present subject, which strike me as most interesting. The present chapter is devoted to the thalamifloral division of the Dicotyledons. 48 CLASSIFICATION OF PLANTS, [CHAP. The vegetable kingdom may be divided into flowering and flowerless plants; while flowering plants again fall.into two divisions, known as Dicotyle- dons or Exogens and Monocotyledons or Endogens. Dicotyledonous or exogenous plants are those in which, when the seed germinates, the “plumule” or bud arises between two ‘rarely more) seed-leaves or cotyledons of the embryo, or from a terminal notch. Tn this class the leaves have their nerves branched, forming a sort of network, as in the oak, beech, clover, violet, &c. In their growth they increase by forming new woody tissue over the old, whence the term “Exogenous.” In a Dicotyledonous or exo- genous tree, therefore, we find a number of con- centric circles, each representing a period of growth, and indicating, though roughly, its age in years. Monocotyledonous or endogenous plants, on the con- trary, are those in which the plumule or bud is de- veloped from a sheath-like cavity on one side of the cotyledon. The leaves have parallel nerves, as for instance in grasses, orchids, lilies, palms, &c. In a cross-section the wood shows no concentric circles, but consists of bundles of woody fibre irregularly imbedded in cellular tissue. Both these classes have flowers, Cryptogams, on the contrary (ferns, mosses, sea- weeds, lichens, fungi, &c.), have no flowers, and multiply by bodies called spores. That the colour of the corolla has reference to the visits of insects is also well shown by the case of those flowers, which—as, for instance, the ray or outside florets of Centaurea—have neither stamens nor pistils, UL] CLASSIFICATION OF DICOTYLEDONS. 49 and merely servé, therefore, to render the flower-head more conspicuous. The calyx, moreover, is usually green; but when the position of the flower is such that it is much exposed, it becomes brightly coloured, as, for instance, in the Berberry or Larkspur The above characters, though true in the main, do not hold good in all cases, For instance the genus Arum, though a Monocotyledon, has reticulated nerves, but its stem is endogenous, and its embryo has only one cotyledon. The class of Dicotyledons is divisible into four sub- classes, which may be thus characterised :— Thalamifiore. Petals distinct from the calyx and from each other, seldom wanting. Stamens usually hypogynous (ze. attached under the ovary), so that if the calyx be torn away the stamens remain. Calycifiore, Petals usually distinct. Stamens perigynous (ze. attached round the ovary), or epigynous (ze. placed upon the ovary). Corollifiore or Monopetale. Petals united (at least, at the base) into a single corolla. Incomplete or Monochlamydee. Perianth or floral envelope, really or apparently simple; or none. These subclasses may be tabulated as follows :— single ornone . . . . . . . « ~- Monochlamydez, corolla of united petals. . . . Corolliflora:. Perianth ( ("= hypo- Thalamiflorz. double | corolla of dis- gynous tinct petals stamens perigy- nots or epigy- Calyciflorae, nous .. . i E 50 RANUNCULUS, CLEMATIS. [cHap. RANUNCULACEA, This order contains fourteen British genera, in- cluding the Clematis, Ranunculus (Buttercup), Ane- mone, Columbine, Hellebore, Larkspur, Peony, &c. In the Buttercup (Ranunculus acris), the anthers commence to discharge their pollen, as soon as the flower opens, beginning from the outside. The stigmas, however, are not as yet mature, nor do the _ stamens open on the side which is turned towards them, but on the contrary, on their edges; moreover as each stamen ripens, it generally turns outwards. The result of this is that bees and other insects, which visit the flowers in searcn of honey, are almost sure to dust themselves with pollen; which they carry away with them, and are then very likely to deposit it on another flower. The stigmas are mature before the inner stamens have shed all their pollen, and self- fertilisation must often take place, both by means of the small insects which may almost invariably be found wandering about the flower, and because the inner stamens often touch some of the stigmas. Larger insects, however, which fly from flower to flower, must habitually carry the pollen from the younger flowers, and deposit it on the stigmas of those more advanced. Clematis recta produces no honey, but is visited for the sake of the pollen. It is proterandrous (see p. 24), but not very decidedly so; for as in other flowers which do not produce honey, if the stamens had shed all their pollen before the pistil came to maturity, 111.] CALTHA, HELLEBORUS, ANEMONE. 51 insects would cease to visit the flowers before the stigma had attained maturity, and had thus become susceptible of fertilisation. Like Clematis, 7halictrum produces no honey. The petals are absent, and the sepals minute, but the stamens are numerous and brightly coloured. Caltha palustris has large yellow sepals, but no true petals. In the /el/ebore also the petals are minute, but secrete honey. The species of this genus are said by Hildebrand to be proterogynous (see p. 24). In Anemone nemorosa the colouring is given not by the corolla, but by the calyx. The flower does not appear to produce honey, but bees are said to pierce the base of the flower, and lick the sap. Delphinium (the Larkspur) is a very interesting genus. The D. elatum (Figs. 5t1—54) has been well described by H. Miller. The five sepals are brightly coloured ; the upper one is produced into a long spur (x x). The two upper petals are also produced into spurs which lie within the former, and secrete honey. In order to reach this it is necessary for the bee to press its proboscis between the upper and lower petals, through the interval (Figs. 51, 53 7). The lower wall of this orifice is in front closed by the lower petals (Figs. 51, 53 fe pe), which are turned upwards and sideways, so as to form the lower wall of the orifice leading to the nectary, and to cover the stamens and pistils. Immediately behind the entrance to the tube, however, these petals contract so as to leave a space (2). The stamens (a) and pistil lie below this space, and as the stamens ripen, they successively raise themselves, and their anthers pass through this space, as shown in E 2 £2 DELPHINIUM. (CHAP. 7 Fig, 51 a’, so that the proboscis of the bee, in passing down to the honey can hardly fail to come in contact with them. After shedding their pollen, they turn down again, and when each anther has thus raised itself and again retired, the pistil in its turn takes pos- Fic. 51. Fic. 54 Fic. 53. Fic. 52. Fig. 51.—A young flower of Delphinium elatum, seen from the frout, and after re- moval of the calyx. Fic. 52.—Section of the same flower seen from the side. Fic. 53.—An older flower, seen from the front, after removing the calyx. Fic. 54.—Section of the same flower, seen from the side. session of the place, as shown in Fig. 53, and 54 st; and is thus so placed, that a bee which has visited a younger flower and there dusted its proboscis, can hardly fail to deposit some of the pollen on the 111] RANUNCULACEZ. 53 stigma. Fig 51 represents a young flower seen from the front, and after the removal of the calyx ; it shows the entrance leading to the nectary, in which are seen the heads of two mature stamens, a’, while the others, aa, are situated in a cluster below. Fig. 52 represents a section of the same flower. Fig. 53 represents a somewhat older flower, in the same position as Fig. 51. In this case the stamens have all shed their pollen and retired, while the stig- mas s¢, on the contrary, have risen up, and are seen projecting into the space m. Fig. 54 represents a side view in section of this flower.