t Gornell University Library Ithaca, New York THE LIBRARY OF EMIL KUICHLING, C. E. ROCHESTER, NEW YORK THE GIFT OF SARAH L. KUICHLING 1919 ioe University Library TD 475.W26 “HAA 3 1924 005 018 688 ers. ans 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/cu31924005018688 MINUTE MARVELS OF NATURE showing internal structure stem, h Beec Actual diameter _ g Transverse section of youn & of an inch MINUTE MARVELS OF NATURE BEING SOME REVELATIONS OF THE MICROSCOPE EXHIBITED BY PHOTO-MICROGRAPHS TAKEN BY THE AUTHOR JOHN J. WARD NEW YORK T. Y¥. CROWELL AND CO PUBLISHERS 19o4 TO RICHARD HANCOCK Honorary Secretary of the “Birmingham Microscopists’ and Naturalists’ Union” | inscribe this slight intro- duction to one of Nature’s inexhaustible sources of wonder and fascinating interest as an appreciation of his knowledge, skill, kind sympathy, ana valued friendship AUTHOR’S PREFACE Most of the contents of this volume originally appeared in Good IVords, although chapter viii. was vublished in the Pad A/al/ Magazine, and chapter ix. in the English Lllustrated Magazine, while Fig. 142 with its letterpress, and Figs. 94 and 95 appeared in Anzmal Life. 1 have to acknowledge the courtesy of the proprietors of these several publications in permitting me to use them for the present volume. Each chapter has been revised and considerably enlarged, both in matter and illustration, while the last chapter, with the exception of its first two illustrations and the matter pertaining thereto, is entirely new. The purpose of this little volume is not to offer even an elementary text-book on microscopy, but rather to present a readable and popular descrip- tion of some of the innumerable minute wonders that abound in Nature. AUTHOR’S PREFACE To those readers who possess and use a micro- scope I trust that my work may increase their interest in the fascinating study ; while for those who do not the large number of illustrations will to some extent enable them to realise what the microscope reveals, and may, perhaps, create in them the desire to use it for themselves. And then if this volume is soon laid aside for works more advanced, it will indeed have done good service. The illustrations throughout are greatly magni- fied photographs or photo-micrographs made directly from the actual objects, excepting in a few instances where they are stated to be of natural size. The image of the minute object, as seen by the eye when looking into the microscope, is projected directly on to the sensitive photo- graphic plate, the camera occupying the position of the observer at the head of the microscope tube ; but to describe the numerous details of the work would be out of place here. With regard to the minute objects themselves, such as the various plant, insect, and animal dis- sections, it need hardly be said that considerable care is required to prepare them for photographic purposes. While using a large number of my own pre- parations, I have to acknowledge the kindness of Messrs. W. Watson and Sons, of 313 High AUTHOR’S PREFACE x1 Holborn, W.C., for permission to photograph their diatom preparations in Figs. 13 and 15; also of C. Baker, 244 High Holborn, W.C., for the use of all the preparations illustrated in chapter iii., except Figs. 44 and 52; and likewise of Mr. C. E. Burnell, of Henley, Shepton Mallet, for the use of the insect dissections shown in Figs. 120, 136, and 163; and lastly, of Mr. R. Hancock, of Handsworth, Birmingham, for the various pre- parations shown in Frontispiece and Figs. 27, 28, a9, 36, 104, 112, Tr, 118, 123, 124, 125, 127, 130, 144, 147, and 161. I am also greatly obliged to Mr. E. Kay Robinson for his most helpful revision and emendation of my work. J. J. W. CONTENTS CHAPTER I THE BEGINNINGS OF PLANT LIFE Microscopic plants on an old wooden fence—Only a small pro- portion of the world’s plants assume conspicuous forms— Sea-water coloured with minute plants—Difficult to find any natural condition of land or water free from plant life— Plants which swim freely about in water—Difficulties in distinguishing between the lower plants and animalcules— Desmids — Structure of ditto— Reproduction of ditto — Diatoms—Where found—Structure of ditto—The decora- tive markings and sculpturings of ditto— Rotten-stone” or “Tripoli”—Diatom deposits eventually form rocks—Varieties of forms assumed—Movements of diatoms—Revealing power of microscope—Man’s skill with the minute—Thread-like plants—Plants which show the first indications of a stem, and differentiation in its cell-structure—Gradual evolution from lower to higher life-forms ‘ : : . . Pp, 1-31 CHAPTER II GLIMPSES INTO PLANT STRUCTURE Green film encrusting old fence consists of many hundreds of plants—Structure of these unicellular plant-atoms—Repro- duction of ditto—Red snow—Vegetable cells are the bricks which build up the pliant editice—Hairs on plants—The XIV All Sex CONTENTS velvety appearance of flowers’ petals, how it is produced— Vascular tissues— Monocotyledons — Dicotyledons—Tissue which forms new cells—The rough bark of trees—The age of trees, how it can be estimated—Varieties of stem structure— Stems and leaf-stalks—Structural botany uninteresting Pp. 32-57 CHAPTER II11 A GREEN LEAF life depends upon the activity of a certain grecn-coloured substance which is found in the tissues of leaves—The structure of a laurel leaf—The growing-point of a stem—- Variations in leaf structure—Chemical analysis of a green leaf—Great trees chiefly built up of carbon obtained from the atmosphere by green leaves—“ Fall” of leaves—Plants and animals dependent on each other—How leaves purify the air—Chlorophyll corpuscles—Plants not only supply us with oxygen, but all our food and innumerable home com- forts— Canadian woodland and forest—Chlorophyll the mainstay of life—Enormous quantities of carbon dioxide passed into the atmosphere daily ; : . Pp. 58-83 CHAPTER IV POLLEN, OR FLOWER-DUST exists as much amongst plants as animals—Male and female flowers of a begonia—Functions of coloured portions of flowers— Stamens from various flowers— Fertilisation of foxglove—Microscopic examination of pollen—Structure of the pollen-grain—Fertilisation—Various kinds of pollen— Enormous quantity of pollen produced—Showers of pollen falling in the streets of towns—Marvels of function carried on beyond the range of unaided human vision . Pp. 84-107 CONTENTS xv CHAPTER V ANIMAL-PLANTS AND SEA-WEEDS Sea-weeds have no strong branches to support their weight— Sea-weeds that are not sea-weeds—Animal-plants—The structure of ditto—Fossil species—Mediterranean corals— The polypes—Their resemblance to flowers and seeds— The hard red coral of necklaces, &c.—Polypes the builders and not man—Algz, or sea-weeds proper—Their structure-— Alge with hard and stony fronds—Lime-builders Pp. 108-131 CHAPTER VI INSECTS’ EGGS Eggs of insects present fascinating objects for microscopic inves- tigation—Maggots no longer supposed to be spontaneously generated from putrefying substances—Eggs of the common house-fly — Number of eggs deposited varies — Successive generations and production of living young--Aphides or “ereen-flies’””— The hover-flles—The lacewing-fly — The wonderful eggs of birds’ parasites—Structure of insects’ eggs —Eggs of butterflies and moths—Where found—Instinct of ~ the mother insect—Blunders made by insects in depositing their eggs—Varieties of form—What purpose the artistic and microscopic sculpturings may serve . : . Pp. 132-156 CHAPTER VII ANIMAL PARASITES All living animals pestered more or less by parasites adapted to prey upon them—Insects no more exempt than larger ani- mals—Hyper-parasitism—Parasites which require several XV1 CONTENTS hosts to complete their life-cycle—The sheep-tick—Various animal parasites, beneficial and otherwise—Study of parasites offers a prodigious field for scientific work . Pp. 157-183 CHAPTER VIII INSECT WEAPONS AND TOOLS Many insects which can inflict serious injury with their weapons —The gad-fly—Personal experience of the effect of its weapons— The malarial mosquito— The weapons of the wasp—The spider’s poison fangs and teeth—A fly’s foot— The foreleg of a diving beetle—Feathered oar of a water- boatman—Poison bag and sting of wasp—An insect armed with a bayonet—The saw-fly’s weapons—Every insect has some special weapons to suit its own particular purposes Pp. 184-206 CHAPTER IX MAY-FLIES AND THEIR NEIGHBOURS Insect life at the bottom of the pend—Aquatic insects spend the greater part of their lives beneath the water—The May- fly as the type of brief and ineffectual life—Their anatomy— Their graceful and buoyant movements—Life story—Extra- ordinary final emergence—The alder-fly—Caddis-flies—The wonderful cases built by the caddis-grubs—Dragon-flies— Mask of the dragon-fly larva—Strength of wings—Eating butterfly : : : Pp. 207-233 CHAPTER X WONDERFUL TEETH AND TONGUES The mouth of a snail is provided with teeth unlimited—Genera and species identified by the various characteristic dental CONTENTS xvi arrangements—Slugs which eat worms—Tongue or proboscis of the common blow-fly—Proboscis of hover-fly—Tongues of butterflies—Sap-sweeping tongue of the largest British beetle . : , . : ; ‘ : . Pp. 234-243 CHAPTER XI SIMPLE WONDERS OF THE MICROSCOPE Dust rubbed from the wings of a moth—Scales of moths and butterflies—Hairs of insects—Skins and scales of fishes— Feathers of birds—Varieties in birds’ feathers, and why they vary—Hairs of mammals—Hairs are modified skin structures ---Human hair— Hair sections—Conclusion . Pp. 244-264 INDEX ; : 3 ‘ a : : ; . Pp. 265-272 b + WN H Now Ww NW bo ay LIST OF ILLUSTRATIONS PAGE Transverse section of beech twig . : . Frontispiece . Unicellular piants multiplying 3 - Desmids (Closteriuim lunula) : 5 . Desmids (Micrasterias denticulata) . ‘ F 2 : 7 . Diatoms grouped. ‘ ‘ : , . ; ‘ 10 . Diatoms ona dark ground . ; , : : 12 . Diatoms dredged from the Atlante : : . ‘ 14 . Diatoms common in ponds and lakes. ‘ : ‘ 15 . Diatom-chains ‘ : : 16 . Selected diatom patie deserts hpenbon git) : : 17 . Central portion of diatom group, Fig. 4 ‘ : : 18 . Selected diatoms from group, Fig. 10 . = : ‘ 1g Selected diatoms from group, Fig.4 . : : : 20 . Artistic arrangement of diatoms . ‘ ‘ ; z au . Central portion of diatom group, Fig. 13 ‘ : ‘ 23 . Another artistic arrangement of diatoms .. : : 24 . Central portion of group, Fig. 15. ; 5 : : 26 . Thread-like plants (Spirogyra) : 5 : . P 28 . Volvox globator F : . : é ; 29 . Freshwater alga (Drapar alata : : : ‘ : 30 . Freshwater alga (Batrachospermunt) : F : : 31 . Alga on damp tence ‘ : : ; ’ : : 33 Vegetable cells of apple. F ; : ‘ ‘ : 35 . Hairs from flower of pansy. : ‘ : ‘ 37 . Cells from surface of geranium iid , : , : 38 . Scales from fern frond . F ‘ ‘ ; 39 . Vascular tubes in stem of bracken ir : : ‘ 40 XX ric. ar. 25. 29. LIST OF ILLUSTRATIONS Section of sarsaparilla stem Section of sycamore stem Section of clematis stem Section of date-palm stem Section of pillwort stem . Section of marestail stem Section of club-moss stem Section of rush stem Section of ivy stem ‘ Section of Brazilian liana stem Section of mid-rib of rhododendron le sa Section of pine leaf , Section of blade of laurel leat Section of mid-rib of laurel leaf Section of blade of sunflower leaf Section of mid-rib of sunflower leaf The growing-point of a stem . Section of blade of deadly nightshade ie Section of stonecrop leaf Section of pine leaf. : Section of blade of water-lily eee, Section of blade of Indian corn leaf . Transparent leaves of a moss Section of the base of a Virginian creeper’s ent stall . Breathing pores or ‘‘stomata”’ of monkey-puzzle leaf . *Stomata” of tulip leaf 3 Central portion of male begonia flower . . Central portion of female begonia flower Stamens from various flowers ». The tubular corolla of foxglove opened Pollen grains falling from stamens of mallow Spiny pollen grains of hollyhock Ripe stamens of mallow flower Section of anther of a lily . Compound pollen grains . Sections of pollen grains Stigma of evening primrose with pollen habe: Ss LIST OF ILLUSTRATIONS . Pollen from evening primrose . Triangular pollen grains . Reticulated pollen grains . Pollen of Monarda. . Pollen of vegetable marrow . . Pollen of pine . Animal-plants 2 . Branches of an animal- plant . A coralline animal-plant ? . Animal-plant cells arranged in a leaf- ties manner . Fossil zoophytes 5. Section of limestone . Animal-plant feeding . Section of fossil corals . . Branches of a tiny sea-weed. . Sea-weed scattering its spores . Tip of frond of delicate sea-weed . Sea-weed discharging its capsule of spores . . Sea-weed with stony foliage . . Another sea-weed with stony beemalies . Stony sea-weed with its companion stone-masons . Eggs of the common house-fly . An egg of a hover-fly . Eggs of parasite of the ground heenbill . Eggs of parasite of Australian mallee-bird . . Eggs of parasite of turkey of Japan . Eggs of fowl parasite . Eggs of pheasant parasite . Eggs of peacock parasite . Eggs of moth on cabbage leaf . Eggs of Privet Hawk-Moth (natural size) 95- . Eggs of Currant Moth . Eggs of Blue Underwing Moth Eggs of Privet Hawk-Moth (magnified) Eggs of Gray Chi Moth . Eggs of Small Emerald Moth 100, Egg of the Brown Hair-streak Butterfly XX1 PAGE IOI 102 103 104 105 106 IIO III 1L2 113 sage T16 117 120 122 123 124 125 127 129 130 134 137 139 140 I4I 142 143 144 145 146 147 148 149 150 151 152 oXU FIG, TGs 102. 103. 104. 105. 100. 107. 108. 10g. L LO. LIST OF ILLUSTRATIONS Eves of the Small Tortoiseshell Butterfly Evgs of the Common Meadow-brown Butterfly Eges of the Small Copper Butterfly Parasite of tortoise Parasite of humble-bee Parasite of humble-bee, fore- pants Beetle and parasite Pincer of beetle parasite Parasites of house-fly A sheep tick : Foreparts of sheep tick Parasite of pig Parasite of ostrich Parasite of crow Parasite of pigeon . Parasite of tawny owl Parasite of pike Parasite of polecat Parasite of bat Lancets and blood-suckers at oe fly Tip of gad-fly’s lancets . . Tip of gad-fly’s blood-sucker Another view of the gad-fly’s mouth Mouth-weapons of the female mosquito Head of male mosquito Mouth of wasp Mouth of spider Foot of fly Foreleg of a water- beaile Feathered oar of water-boatman . Poison-bag and sting of wasp Ege-depositor of an ichneumon fly Another insect bayonet Ichneumon fly’s toot : : : Ichneumon fly which lays its eggs in * blight ” . Tip of saw of saw-fly The saw-fly’s weapons . LIST OF ILLUSTRATIONS XX11 FIG. PAGE 138. The caterpillar’s many-hooked foot. : : . 266 139. Portion of wing of May-fly . ‘ , , F . 210 140. Larva of May-fly . : ‘ ‘ ‘ ; ; » CBS 141. Exuvium of May-fly . 2 ; : 3%. 42 2 iby, 142. Final emergence of May-fly . : : ; . 216 143. May-fly (natural size) . : : ’ : : . 218 144. An alder-fly 21g 145. Eggs of alder-fly 220 146. Larva of alder-fly . 221 147. A caddis-fly 222 148. A caddis-worm £23 149. Specimens of caddis-cases tacked sie) Dog 150. End of body of caddis-larva. 226 151. A dragon-fly (natural size) 227 152. Larva of dragon-fly ; 228 153. Head of the larva of a dragon-fly 230 154. Tips of wings of dragon-fly : : : . 231 155. The face of adragon-fly ‘ : F : » 232) 156. Palate of edible snail . } : ; ; . - 335 157. Teeth of edible snail. , . « 236 158. Palate of snail showing different foie of teeth ‘ 5 O39 159. Palate of slug : ‘ d ‘ : : : . 238 160. Proboscis of blow-fly . : 3 : 4 ‘ i 280 161. Proboscis of hover-fly . : i : . ; . 240 162. Tongue of a butterfly . : : : : : 2 RYT 163. Tongue of stag-beetle . 4 : 5 ; . Bye. 164. Scales or dust from wing of stl, : : : 245 165. Scales on butterfly’s wing, im situ : : : . 246 166. Hairs of “woolly-bear” caterpillar. : : 3 yy 167. Hairs of a humble-bee . 3 : ‘ : , - 248 168. Leg of a tiger-moth ; , : : : : > 249 16g. Skin of dog-fish . F . ‘ : 5 : 2 B50 170. Skin of sole. : ‘ . ' : : ‘ ~ 252 171. Skin ofeel . . ‘ . ‘ : . B52 172. Scale removed from et. sida. é ‘ ‘ : « 3853 173. Scale removed from gold-fish ; : , ‘ i Baap 174. Feather of humming-bird . a “ ; ‘ 255 XXIV LIST OF ILLUSTRATIONS FIG. 175. 176. 7%. 178. 179. 180. ISt. T82; 153 184. Feather of condor . Feather of ostrich Feather of emu Feather of owl Section of mouse-skin Mouse hair : P ‘ Shavings from human beard. Sections of whisker-hairs of lioness Sections of hairs of American peccary Sections of tail-hairs of African elephant No oN N |S wa tn we & Ce co Da O~I nN CHAPTER I THE BEGINNINGS OF PLANT LIFE Art the end of my garden, facing full south, stands an old wooden fence. Nothing could appear more thoroughly and completely dead than a paling which is beginning to decay; but if you will come with me to the fence I will show you more living plants than you could observe in a bird's-eye view of the whole of Kew Gardens. Many of us think of “ plants” only as the Howering plants which are put in our garden, and we should see no absurdity in remarking that a flower-bed contained ‘ more weeds than plants ;” while very few would enumerate more than trees, shrubs, herbs, grasses, ferns, and mosses as classes of plants. Yet only a very small proportion of the world’s plant life, so far as numbers go, assumes these prominent forms. The sea, for instance, is sometimes conspicuously tinged in large patches, upon which inexperienced passengers gaze in wonder from the steamer’s deck, by plants. You may fill a tumbler with the A 2 MINUTE MARVELS OF NATURE coloured sea-water, and no matter how closely you look, it still seems only coloured water. But the colour is due to incalculable multitudes of tiny plants, living their separate sea-lives as completely as the great whale himself. In the same way a coloured stain will creep over damp walls, the bark of trees, or this old fence of mine, where myriads of microscopic plants are congregating together and multiplying very rapidly. For the infinite variety of form and habit that plant life assumes adapts it to flourish in sites where life of any kind might have seemed im- possible. Leathery and powdery plant-incrusta- tions cling to the hardest rocks and stoniest soils ; vegetable moulds take up their abode on almost every perishable article ; trees and ships are often completely destroyed by a plant multitude known as ‘“dry-rot” ; while smut, rust, bunt, and other familiar forms of parasitic fungi, prey upon living plants to such an extent as to spoil and destroy whole crops of grain or fruit. What seems worse still is that many of them not infrequently invade the organs of living animals, and are the known causes of many diseases. A single drop of pond, river, or sea water will often reveal multitudes of varied plant forms; and, in short, it is difficult to point to any natural condition of land or water THE BEGINNINGS OF PLANT LIFE 3 that is free from plant life. Its germs, or spores, fill the air we breathe and are consumed in all the food that we eat. The very ground we stand upon may be built up of tiny plants, as [ will show later. While mentioning fungi, moulds, and other Fig. 1. Microscopic unicellular plants, multiplying by division of their cells parasitic organisms as being representative of plant life, it is not my purpose here to consider this class of plants, but rather those which may be regarded as leading the way to the higher plants, by their possession of the important green colouring-matter known as ‘‘ chlorophyll,” or its 4. MINUTE MARVELS OF NATURE equivalent; of which I will speak in a later chapter. Almost all damp situations and standing waters, such as rain-water cisterns, drinkin -troughs, wet ditches, ponds, &c., will provide examples of minute alge, or the earlier forms of plant life. And these, like the green film on the fence, will be mostly unicellular plants—each microscopic cell constituting an individual plant, which eventually divides into two or four similar cells, with the same power of division (see Fig. 1). Sometimes the newly formed cells have long cilia, with which they swim freely about in water ; and stagnant ponds often owe their green hue to myriads of these active green cells swimming gaily about within them. When shown under the microscope. perhaps the last thought that would occur to the inexperienced observer would be that these wonderful little organisms are plants at all ; and as there are large numbers of lowly plant forms that can move about in water, and are almost invariably found in company with minute animalcules similarly endowed, even experts are often puzzled to decide to which kingdom the tiny living forms belong. So it comes about that many of these organisms have been bandied about by learned scientists from the Animal to the Vegetable Kingdom and back again, until the THE BEGINNINGS OF PLANT LIFE 5 ordinary student scarcely knows where to locate them. In recent years, however, a better understand- ing has been arrived at with regard to the more Fig. 2. Desmids (Closter?um lunula), or unicellular plants, found in standing waters. Actual length about ;)5 of an inch familiar forms, since a large number of these gaily swimming organisms have been shown con- clusively to belong to the Vegetable Kingdom. Fig. 2 shows a number of the singular uni- cellular plants which are called ‘desmids.” These are minute fresh-water alga, of a beau- tiful green colour and numerous diverse forms. 6 MINUTE MARVELS OF NATURE Every moderately clear pool or ditch will provide examples of these interesting plants, and they especially abound in ponds which lie in exposed and bleak situations. The species in the illustra- tion is characterised by its crescent-like form. Each cell is free and able to move about in the water by a curious, feeble movement, and if kept in a glass vessel they all move slowly to the side next to the light and congregate there. For a period of over twelve months I kept a large quantity of these desmids propagating in a common glass jar, having accidentally gathered a few attached to some of the common duckweed which floats on ponds. Desmids, like other green piants, evolve oxygen in sunlight ; and so, together with the duckweed, which also multiplied in the glass jar, the water was kept fairly pure, and the desmids increased at sucha rate as to completely line the sides of the lass vessel with a film of bright green colour. A desmid cell possesses a thin outer coating or cell-wall, sometimes adorned with spiny projec- Oo co) tions or markings. Surrounding this, a trans- parent film of gelatinous matter is recognisable, although sometimes only by its preventing the cell-wall from touching external objects. Inside the cell-wall proper is a layer of colourless proto- plasm, which encloses the mass of green-coloured THE BEGINNINGS OF PLANT LIFE 7 living substance of the cell or plant. As these plant cells all show more or less clearly a line of division in the middle, they might seem to be two separate cells joined together; but such is not the case, each desmid being but one cell. When reproduction is about to take place, the Fig. 3. Other forms of desmids, chiefly A/?cras- terias denticulata. Actual length about +}, of an inch contents of the cell divide into the two halves, which seem to draw away from each other, and so become constricted towards the centre, and finally break away. Each irregular half then soon develops the symmetrical crescent shape. The above example (Fig. 3) is taken from 8 MINUTE MARVELS OF NATURE other species of desmids which present a some- what different method of reproduction. Instead of breaking away and subsequently acquiring a complete shape, the two halves remain together, but gradually develop at their line of junction, two little rounded discs touching each other at the edge, which gradually become larger and push each other further apart, until, finally, the indentations round the desmid’s edges appear, after which the two halves become detached as perfect desmids. There are other and more complicated methods of reproduction and cell division even with this same Micrasterias ; but these need not concern us here, though they show that even these lowly, single- celled plants gradually approximate in structure and methods of reproduction to higher and more complicated forms. And it should also be ob- served with regard to these delicate and beau- tiful organisms, how frequently symmetry and regularity of form prevail. But this we will consider more in detail hereafter. Meanwhile let us glance at some of the most extraordinary forms of the invisible vegetable world—tiny unicellular plants of almost un- imaginable minuteness, called ‘* diatoms.” These microscopic and wonderful alge are abundantly distributed in nature. Wherever THE BEGINNINGS OF PLANT LIFE 9g exposed water is to be found, diatoms may be looked for, whether it be stagnant or running, salt or fresh, warm or cold. Even the melting snow on the summits of the highest mountains, or the water that lodges in your rain-water spout, frequently contains diatoms in abundance. As the water evaporates, these invisible plant particles become dry, and by reason of their lightness and tenuity get wafted, still alive, from one region to another by the high winds. The hottest sun and bitterest cold does not affect their vitality. As the air calms they settle down again, and after months of frost or scorching sun, given moisture and sunlight, they again rapidly multiply, and so become distributed everywhere. When considering the desmids I mentioned that the cell-walls sometimes developed spines or markings on their surface. Now diatoms present most extraordinary and remarkable features in this respect. Each little vegetable cell that constitutes a diatom has the power to absorb from the surrounding water that chemical com- bination termed “silica” or flint, a small proportion of which exists dissolved in most natural waters. The silica which it thus appropriates becomes deposited regularly on the cell-wall, and so the single vegetable cell becomes clothed with an almost indestructible finty armour. But this is 10 MINUTE MARVELS OF NATURE not all; one side of the shell or frustule becomes slightly larger than the other, and fits over the smaller, after the manner of the halves of a pill- box or canister. On the surfaces of these flinty shields deli- cately carved and chased symmetrical markings Fig. 4. An arranged group of the cleaned shells, or shields, of the tiny plants called ‘‘ diatoms.” The actual group measures ;'; of an inch in diameter are revealed when considerably magnified. An arranged group of these tiny and wonderful shields is shown in Fig. 4. As this group measures only one-twelfth of an inch in diameter, it will be understood that the shields are considerably magnified, although but THE BEGINNINGS OF PLANT LIFE 11 the faintest indications of their fascinating sculp- turings are visible. The refined nature of some of the markings of diatom valves defied the powers of the best microscopes for many years, and even with the finest of modern lenses most skilful manipulation is required to bring out their details of structure. In fact, the more delicate forms are used by the makers of microscopes for testing the accuracy of their work. A very remarkable fact regarding these minute sculpturings is that frequently, as the magnify- ing power is increased, new and_ unsuspected details of structure become visible. What were minute rows of dot-like spaces reveal, when enormously magnified, other perforations and sculpturings within them of equal beauty and symmetry. And, when we have exhausted the powers of our best optical instruments, who knows what lies beyond? If unsuspected marvels of fascinating minuteness have been revealed with the advance of modern instruments, one cannot help wondering where this decoration ends. The methods by which these tiny plants construct their almost in- destructible shells defies all attempts to explain ; and in saying ‘‘almost indestructible” [ am well within the mark, for these silicious frustules, or 12 MINUTE MARVELS OF NATURE valves, resist putrefaction almost indefinitely ; and as the organisms multiply very rapidly by sub- division, and keep falling in a steady shower to the bottom of the water as they perish, layers of these Fig. 5. Some diatoms (Péznxularia nobilis) shown ona dark ground to illustrate their glassy nature. Individuals vary in length from ,), to ;}; of aninch glass-like shells gradually result in considerable deposits of solid flinty material which resists acids and even the dull red heat of an ordinary fire. The familiar polishing material ‘ rotten-stone” or ‘ Tripoli,” large deposits of which occur in Bohemia and other parts of the world, is a soft friable rock which chemically is almost pure silica; but the microscope reveals the fact that it is not THE BEGINNINGS OF PLANT LIFE 13 ordinary silica, but is built up of the tiny and beautiful silicious shields of diatoms. And as the forms found in rotten-stone are characteristic of fresh-water species, we conclude that where the deposits are found lakes or marshes existed in previous ages. In long periods of time, by the slow percolation of water, these diatomaceous deposits (a minute speck of a diatom deposit composed almost entirely of one species is shown in Fig. 5) are slowly dissolved and then redeposited as a hard opal-like rock. Thus these apparently insignificant plant atoms, by their vast numbers and rapidity of multiplication, play most important parts in the formation of the earth. The city of Richmond, in Virginia, is said to be built on a stratum of di- atoms 18 feet thick. Estuaries and harbours are frequently considerably shallowed by the accumu- lation of these flinty deposits, and the surface and ooze of many seas reveal diatoms in abundance. Fig. 6 shows diatoms dredged from the Atlantic by the Challenger at a depth of 1990 fathoms, or just over 24 miles. The variety of forms assumed by the frustules, or shields, are as varied as their surface markings, and quite beyond description. The most familiar species found in ponds assume the long oval or boat-shaped forms, such as those shown in 14. MINUTE MARVELS OF NATURE Figs. 5 and 7, and many are extremely delicate ; but all alike possess their characteristic wrink- Fig. 6. Diatoms dredged from the Atlantic at a depth of about 2} miles lings, dottings, and markings, when highly magni- fied. It is extremely interesting to watch the peculiar gliding movements of some of these boat-shaped THE BEGINNINGS OF PLANT LIFE 15 atoms. Without any visible effort or means of propulsion they slowly glide in a straight line through the water, and should anything obstruct their passage they make no effort to round it, but without turning reverse their motion and glide backwards, apparently on the same straight track on which they came, often repeating the move- ment several times as if unconvinced that the path was impassable. Other common forms do not lead such a free 16 MINUTE MARVELS OF NATURE Fig. 8. Chains of diatoms in their natural state adhering to a larger microscopic alga, magnijied life, but remain attached, and form chains of somewhat oblong or square frustules, each ad- hering to the other at the corners, the chains ulti- mately being fastened to, or intermixed with, other THE BEGINNINGS OF PLANT LIFE 17 and larger aleze or aquatic weeds. Fig. 8 shows an example of diatom chains in their natural situa- Fig 9. An individual diatom-shield (fvachnotdiseus Ehrenbergit) itumensely magnified tions, clinging to a much larger alga, although the portions shown of this are really microscopic. Others develop foot-stalks, by means of which they attach themselves to stones, &c., and so form little groups or clusters. b 18 MINUTE MARVELS OF NATURE The beauty of the markings of the frustules cannot be readily seen in the living diatoms ; but the skeleton shields, when cleansed of their living matter by heating to red heat or dissolving by Fig. 10. The central portion of the group of silicious diatom-shields shown at Fig. 4, more highly magni- fied. nitric acid and magnified, reveal to perfection their wonders of symmetrical precision and minuteness. One of the cleaned shields from a marine form is exhibited in Fig. 9. Two hundred of these, placed edge to edge, would scarcely extend one inch ; yet this is a very large form, comparatively speaking. The lines and markings on some species are estimated at about 1-76,oooth of an inch ig. 11. A fewselected diatom-shields from the central portion of Fig. 10 again shown under increased magnifying power 20 MINUTE MARVELS OF NATURE apart, so that a hair from the human-head cut longi- tudinally into 4oo thin slices would approximately fill the spaces between 400 of these marks, We cannot here even glance at the life history ‘ig. 12. Several diatom forms from the top central edge of Fig. 4 immensely magnified and methods of reproduction of these lowly and beautiful unicellular plants. The subject is so great and their species are so numerous that we should require a separate chapter; so I must be content to call attention to their beauties, which show that the lowest and most minute forms of plant life present no less wonderful intricacies of structural detail than the highest and largest. ged in an artistic manner within Fig. 13. A group of cleaned diatom-shields arran L of an inch in diameter rd a circle actually measuring only 22 MINUTE MARVELS OF NATURE As an instance of the revealing power of the microscope, I will again call my readers’ attention to Fig. 4, and ask that it may be compared with Fig. to, which represents the central portion of the same group still more highly magnified, showing how further details of structure are brought out by the increased magnifying power. And again in Fig. 11 a few forms selected, but rearranged, from the centre of Fig. 10, are shown under considerably greater magnifying power. Fig. 12 shows another combination immensely magnified from the top central edge of Fig. 4 group, the members of which can readily be identified by their relative positions. These will serve to give an idea of the beautiful and wonderful frustules or shells of diatoms. It may occur to those who study these illustra- tions how beautifully these diatom shields stand apart in the groups, or how prettily they are arranged, It is true that they have been arranged in these forms. Here we get an instance of man’s skill with the minute, for all these diatoms have been individually selected as per- fect forms, and carefully placed in their relative positions. Fig. 13 shows a beautiful group of diatom valves, arranged in a symmetrical and artistic manner by one skilled in this work. The actual group roup Fig. 13, again more highly The central portion of the gr Fig, 14. ified magni Fig. 15. Another diatom group, also arranged within a circle of 4 of an inch in diameter THE BEGINNINGS OF PLANT LIFE 25 measures one-eighth of an inch in diameter, every individual specimen having been placed within this small compass. This is truly very wonderful work ; but when we magnify these exquisite atoms and see their marvellous, symmetrical patterns, thousands of times smaller yet perfect withal, we see how insignificant man’s most clever and ingenious efforts become in comparison with Nature’s humblest works. The central portion of this prettily arranged group is shown more highly magnified in Fig. 14 ; and to exhibit the infinite variety of form and design in these fascinating plant atoms, another wonderful group is illustrated in Fig. 15, which also is arranged within a circle one-eighth of an inch in diameter, while a portion from near the centre of this is again further magnified in Fig. 16. In conclusion, we may glance at a few forms of algae that show a further advance in plant form ; that is, an advance on the single cell. We take from almost any pond some of the common green slime almost invariably found in such localities. On examining this material we find long strings or threads of vegetable cells, all alike and joined together, as is shown in Fig. 17. When these thread-like plants are about to propagate or multiply, corresponding cells in Fig. 16. A portion from near the centre of group Fig. 15, more highly magnified THE BEGINNINGS OF PLANT LIFE 27 individual threads, as they rest beside each other, throw out tiny tubes which eventually meet. The cell-walls between them then dissolve, and the contents of one cell pass into the other. This process is shown taking place in our illustration ; and it results in the formation of a spore for a future plant, which by subdivision of its primary cell becomes a thread-like plant like its parents. From this stage in plant life a gradual evolution of form and specialisation of cells begins to take place, and in forms slightly higher in the scale certain cells are told off to attach those simple- celled plants to fixed objects, and so we get the first indications of the roots of the higher plants. It does not follow, however, when plants are composed of a number of cells, that they necessarily give up the habit of free movement. At Fig. 18 is shown an example of one of the most beautiful and interesting examples of pond alge. This little plant is just visible to the eye as a tiny green rolling sphere. When viewed by the microscope, other smaller spherules can be seen within, through its transparent walls. The surface wall of the sphere is covered with a delicate network of protoplasm, dotted with minute green cells, each of which carry two fine threads or ‘‘cilia,”’ and it is by means of the rapid 28 MINUTE MARVELS OF NATURE vibrations of these that the plant rolls itself through the water. This little plant is often abundant in ponds, and in reality is a rounded colony of vegetable Fig. 17. Thread-like plants, composed of vegetable cells attached to each other (Spirogyra) cells; only a few of which take part in repro- duction. Other forms again show indications of the stem (see Fig. 19) by producing a row of supporting cells which take no part in reproduction, this being left to the rows of cells that they support. As our concluding example, a still more advanced type shows a differentiation in the structure of THE BEGINNINGS OF PLANT LIFE 29 its stem, possessing a central system of cells, with a protective outer layer of other cells, and so something akin to the bark or skin of the higher plant forms appears. Fig. 20 shows an alga possessing this first differentiation in stem Fig. 18 A many-celled globular plant (/’o/vov globatoy) which swims about in ponds. Actual size about 54, of an inch structure. Advancing structure may readily be traced, although all alge are still of lowly form, for even with our last example, each disc on its stem is but a cluster of simple thread-like cells all radiating from the one point. So we may trace a gradual rise from the lowest to the highest forms of life, and learn to recognise 30 MINUTE MARVELS OF NATURE that all life is akin. No isolated and unconnected instances occur, although it is not always perhaps possible to link up our chain and trace direct Fig. 19. A lowly aquatic alga, showing the early stages in the evolution of the plant stem (Draparnaldia) connection between the beginning and the end. Yet surely there is enough evidence to show that Nature is one harmonious whole. Breaks which are difficult to explain may occur here and there, THE BEGINNINGS OF PLANT LIFE 31 but time and advancing knowledge will reveal much. Fig. 20. Another aquatic alga that approaches nearer the higher plant forms by a differentiation in the cellular arrangement of its stem cells (Latracho- Sperm) CHAPTER I] GLIMPSES INTO PLANT STRUCTURE In the first chapter I mentioned that the common green stain which coloured the damp portions of my old wooden fence was made up of myriads of individual living plants, and that these probably reproduce to-day that simplest form of plant life from which by natural evolution all the complex and specialised trees and herbs around us have gradually risen. Some of the simplest forms I have already illustrated: but in view of the dignity of their relationship it may be worth while to con- sider more in detail these tiny plant-atoms which occupy almost every damp and vacant niche in Nature. Look at the old fence. A green film has en- crusted all the lower part, so far as the damp earth’s influence reaches, giving it a bright colour that you can see across the garden. I scrape it with my little finger-nail and the green stuff that comes off consists of many hundreds of one of the simplest of known plants. These are the one- GLIMPSES INTO PLANT STRUCTURE 33 celled alge, known to botanists as Protococcus viridis. Fig. 21 shows a magnified photograph of this green stuff off my finger-nail, under a medium magnifying power, and reveals a con- Fig. 21. The green stain on damp fences, &c., is composed ot myriads of microscopic plants glomeration of granules, each granule a plant. If we examine one of these green granules under very high magnifying powers, we find that it possesses considerable structural detail, simple, perhaps, compared with the structure of the higher plants; but then it must be remembered that these tiny living plant-atoms occupy only about one-thousandth of an inch of space. e 34 MINUTE MARVELS OF NATURE The envelope or cell-wall which surrounds each granule shows clearly a double outline and con- tains the life-matter known as protoplasm. Em- bedded in this can be detected the living life centre of each cell or plant, which botanists term the xaucleus. Each of these minute atoms of plant life quickly attains to independent ma- turity, and divides itself by means of a partition- wall which forms like a film of ice and cuts the cell into halves. Each half, when completely separated, very soon divides again; and so myriads of plants are quickly formed, which cover large areas in short spaces of time. In the Arctic regions early explorers were astounded to find large areas of red snow; but the phenomenon is now familiar to men of science, who know that red snow, like a green garden fence, is due to the presence of unicellular algz, the only difference being in the colouring-matter of the protoplasm. It is said that acres of snow are frequently covered in a single night by these tiny plants. Many vegetable cells are so small that over one hundred millions would barely occupy a cubic inch of space; and in each of these the work of life goes on. It is not necessary, however, to examine these exceedingly tiny plants in order to find single cells; nor do they, perhaps, throw GLIMPSES INTO PLANT STRUCTURE 35 the clearest light upon the ordinary function of the cell in plant-structure. Let us take, instead, from a ripe russet apple, a minute particle of tissue near the core. Fig. 22 shows some of the cells of Fig. 22. We consume myriads of vegetable cells like these when eating an apple which it consists. Although taken from the middle of a mass of pulp tissue, it exhibits a con- glomeration of single cells, very similar to the alge previously examined, but much larger. The cell- wall and contents can be well seen, but these cells are transparent and colourless. 36 MINUTE MARVELS OF NATURE Cells, then, are the bricks which build up the plant edifice. The simplest plant is built of one brick, as we have seen; and next in simplicity come plants composed of a few simple cells united together in a chain as previously considered. Complexity begins when a plant exhibits cells of different kinds, each kind fulfilling specific functions in the life of the plant. The apple-pulp cells are very simple in structure, but much more compli- cated tissues are found in other parts of the parent tree. To show the differentiation of cells for various purposes in plant economy, we may take almost at random any insignificant fragments of any plant. Every one has observed, for instance, that plants are frequently hairy on leaves, flowers or stems, &c., and Fig. 23 shows a few hairs from the throat, as we call it, of the common yellow pansy. These hairs are in reality single cells, which, instead of remaining as flat skin-cells of the petal, have poked themselves out into elon- gated shapes with irregular knotted swellings. To the naked eye they look like minute hairs, but under the microscope more closely resemble rugged glass tubes, being quite transparent and filled with granular matter like the cells in their more simple forms. Hundreds of these uni- cellular hairs, with others of entirely different GLIMPSES INTO PLANT STRUCTURE ey; forms, are hidden away in the interior of every pansy ; and all serve a purpose in the economy Fig. 23. Hairs from the throat or interior of the common yellow pansy of the plant. Otherwise they would not exist, for Nature makes nothing that is useless. No 38 MINUTE MARVELS OF NATURE ornament even exists in Nature without serving some other definite purpose. And while speaking of ornaments we may look at the surface of a common scarlet geranium’s Fig. 24. The fetal of a geranium has a surface of cells hike this petal. How is its invitingly soft and velvety appearance produced ? we ask of the microscope ; and Fig. 24 shows the skin-cells in this instance, not elongated and hair-like as in the hairs of the pansy, but with central elevations or papille, which reflect the light; and so the velvety gloss of the petals of many flowers is effected. We will take one other simple skin tissue, and GLIMPSES INTO PLANT STRUCTURE 39 this time a scale from a fern. These broad scale-like appendages correspond to the hairs be. Fig. 25. Scales from the frond of a fern, showing their structure on flowering plants and (Fig. 25) are built up of quite a number of regular cells. We might multiply illustrations to show how cells collectively compose the various structures of plants, though some become so much altered 40 MINUTE MARVELS OF NATURE that it is difficult to recognise any trace of the original cell-shape in them. By making a longi- NY AA RRR RES Fig. 26. A longitudinal section through part of the creeping stem of the bracken fern, showing the vascular tubes embedded in the frond tissue. tudinal section, with a sharp razor, through the growing-point of a plant stem, for instance, we GLIMPSES INTO PLANT STRUCTURE 41 find that at some little distance behind the grow- ing-point the cells have lost their globular and oval shapes, and are long and thin. This elonga- tion goes on with time, and the connections or division walls which separate adjoining cells dis- appear, until at last, instead of a network of ordinary cells, we have a series of bundles of long tubes, or “vessels,” as botanists call them. Part of such a band of tissue is shown in section at Fig. 26. These tubes, uniting with each other, form the tough fibres that permeate all the prin- cipal tissues of higher plants, and in a section of the Sarsaparilla plant-stem (Fig. 27), these ‘ fibro- vascular” bundles—once more borrowing the weird phraseology of the botanist—may be seen scattered in amongst the pith or cellular structure. These scatfered bundles characterise the struc- ture of plant-stems in one of the great divisions of the vegetable kingdom, known as the ‘ mono- cotyledons,” which means that seeds, when sprout- ing, send up a single blade, like a grain of corn, a date stone, or a lily seed. Such plants generally bear leaves with parallel veins, and have their flowers arranged in whorls of three. These features are in contradistinction to the structure and arrangement of the ‘ dicotyledons,” to which belong almost all our common field plants, except grasses, and nearly all our native 42 MINUTE MARVELS OF NATURE shrubs and trees. In Fig. 28 and Frontispiece sections of the stems of sycamore and beech show Fig. 27. A thin slice of the stem of the sarsaparilla plant, showing its structure that the structural arrangement of these plants is more symmetrical and that their vascular bundles GLIMPSES INTO PLANT STRUCTURE 43 are not scattered about, but arranged around a cen- tral pith, each bundle separated from its neighbour Fig. 28. Slice or section of a twig from the sycamore-tree. Actual diameter ,%; of an inch by a ray from the central pith portion. These fea- tures of the stem are generally associated with 44 MINUTE MARVELS OF NATURE the net-veined leaves of most of our English plants and with fowers arranged in whorls of four or five. Thus, as a zoologist can build up an animal from a single tooth, the botanist can, from a thin slice or section of the stem of a plant, at once gain considerable knowledge of the class of plant from which it was taken. And now just a word regarding these string- like bundles of tissue which we find in the stems and leaves. Each bundle, as I have already shown, originates near the growing-point by the gradual alteration of some cells into long tubes, and on examining these at a later stage, each bundle is seen to consist mainly of two distinct kinds of tissue separated by a layer of delicate cells. The tubular vessels nearest the central pith, when mature, generally lose their proto- plasm or living matter, and usually contain air only, although sometimes liquids are conducted through them. Outside these come the wood fibres which give strength to the bundle, and following these the delicate cells which separates one class of tissue from the other. Those vessels on the outer side nearest the bark are similar to the fibrous wood-cells, but more delicate and filled with mucilaginous matter. Now the layer of delicate cells that separates these tissues is a very important factor to the GLIMPSES INTO PLANT STRUCTURE as plant or tree, and in the growing season is con- stantly forming new cells by division. By this means new vessels and wood-cells are formed. And as the new cells keep multiplying they exert pressure upon their surroundings, so that the tree gradually expands and increases in girth during the growing season. In the autumn a strong outer coat of bark is formed to enclose and protect the living cells. Dormant, yet full of life, these remain throughout the cold and wintry weather; but in the spring active life begins again. The cells commence once more to divide and multiply, and the outer coat of bark, which was firm and strong when it enclosed its living successors—for it origi- nates from these soft, active cells—is burst asunder as the sap rushes through the cells and distends them. Thus the rough broken bark, with which we are all familiar, is formed upon the trunks of trees. During the spring and summer seasons the erowth and multiplication of the cells goes on, but pauses again in winter; and in due course, when the woodman comes along, he can approxi- mately estimate the age of the tree by its annual rings of growth. The successive zones of growth are usually quite distinct, owing to the wood 5 formed in the spring being less dense or having 46 MINUTE MARVELS OF NATURE wider cells than the compacter layer formed later in the year. Fig. 29 shows a section of a stem with longi- Fig. 29. Clematis bas longitudinal furrows on its stem which show in this section tudinal furrows, one of the numerous variations which the stems of plants assume. Some are flattened, others triangular; and a square stem ious its cur stem of date-palm, showing Fig. 30. Section or ells scattered bundles of fibrous c form and the 48 MINUTE MARVELS OF NATURE is not uncommon. Those of the red and white dead-nettle must be familiar to every one who notices wild plants at all. The stem of the date- Fig. 31. A section through the stem of a water-plaut, showing air cavities palm presents another curious form in section and is illustrated at Fig. 30. This again shows the scattered vascular bundles of the monocotyledons. In Fig. 31 is shown the section of the creeping stem of a tiny water-plant, which grows on the edges of moorlands ponds, and is called the ‘ pill- Fig. 32. Section of common marestail, showing beautiful arrangement of cells and air-cavities fo MINUTE MARVELS OF NATURE wort.” Here we see a ring of comparatively large, open gaps in the tissue of cells ; and most aquatic plants possess these air cavities among their tissues, serving as buoys to the plant-stem. ape: as se LOE Mes Sel ot Pn 6 Fig. 33. The structure of a club-moss stem The common water-lilies are familiar examples ; while another beautiful example from the stem of a familiar pond and ditch plant called ‘‘ marestail”’ is shown in Fig. 32. Perhaps lady readers m‘ght profitably use this as a pattern for fancy work, and so obtain a new design ‘direct from Nature.” Another curious form of stem structure is shown GLIMPSES INTO PLANT STRUCTURE 51 in Fig. 33, taken from a plant commonly found on moorland hills and known as ‘‘club-moss.” This is a tiny moss-like plant only a few inches in height at the present day ; but many geological Fig. 34. The structure of a rush stem ages ago the ancestors of our club-mosses were amongst the most prominent forms of the vege- table kingdom, bourgeoning as large trees with stems or trunks sometimes four and five feet in diameter. Fossilised trunks of these great club- mosses are often found amongst the coal measures; 52 MINUTE MARVELS OF NATURE and forty or more different species grew in the British Isles during the Carboniferous period ; but Fig. 35. Stem section of ivy, showing rootlets to-day we have only half aj;dozen or so of their diminutive representatives, whose stems measure scarcely one-tenth of an inch in width. Rushes, as every one who has gathered them GLIMPSES INTO PLANT STRUCTURE 353 knows, have a pithy stem; and Fig. 34 shows a magnified section of a rush stem. The centre of the stem is not, however, hollow as it appears, but is filled with very unsubstantial star-shaped cells, which are too delicate for reproduction in section, Fig. 35 represents a stem section, which seems curiously irregular in form; but when I explain that it is taken from the stem of the common ivy—which, the reader will remember, has tiny tentacles or rootlets along its stem, by means of which it adheres to walls and trees—the shape will readily explain itself. As a concluding example of stem structure, Fig. 36 illustrates the central portion only of the stem of a liana, or tropical climbing plant, which, in some of the Brazilian forests, forms vast festoons, passing from one tree to another, and so binding together all kinds of vegetation in a maze of living network. This stem will be seen to be light in structure, probably owing to the plant’s exceed- ingly rapid growth in the humid atmosphere of tropical forests, thus reproducing in an exaggerated form the peculiarity of the tissue formed in English trees in spring, when growth is quicker than at other seasons. Rightly viewed, however, the stems of plants are merely enlarged and permanent developments Fig. 36. Central portion of the stem structure of a Braziliav climbing plant GLIMPSES INTO PLANT STRUCTURE o% of a leaf stalk—there are many plants which pro- duce only a single leaf—and the leaf stalk in turn bears the same relation to the mid-rib of the leaf. Se, in Fig. 37, | show the internal structure of Fig. 37. The structure of the mid-rib, or central vein of a rhododendron leaf the mid-rib of the leaf of a rhododendron. There are some leaves, moreover, which apparently have no mid-rib, or are all mid-rib. It would be diff- cult, for instance, to say how much of the needle of a pine-tree was ‘‘ blade” and how much ‘ mid- rib” and “nerves” when viewed externally, but the microscope reveals, when the leaf is seen in section, that the vascular strands of the mid-rib 56 MINUTE MARVELS OF NATURE are not wholly lost but still continue their course through the central portion of these curious leaves. In Fig. 38 is shown the wonderful combination of cells which compose the pine-needle; and % ‘4 vt Fig. 38. The wonderful structure of the needle-like leaf of the pine. Actual diameter from corners, ;'; of an inch. between this and the great pine-trunk, with girth greater than a man can clasp, rising sheer to the height of a church steeple, there is only the natural gradation of development. Thus, from the simple Pvotococcus viridis, which you can scrape by tens of thousands off my old garden GLIMPSES INTO PLANT STRUCTURE 57 fence with your finger-nail, to the towering trunks of the pine-woods which furnish masts for the navy that rules the seas, there is only this differ- ence of cells forced by compression to take some shapes and expanding with vitality into others, according to the function which Nature’s necessity has decreed that they must perform. It is not easy to make so very dry a subject as structural botany interesting. It is too full of terrifying technical terms. I am endeavouring, however, so far as possible, to avoid all “ nomen- clature,” and I hope that this and the other chapters dealing with structural botany in this volume may not appear altogether uninteresting and unintelligible even to non-scientific readers. To the well-balanced mind, any portion of any plant, when microscopically examined, reveals the ordered pencilling of its Creator, no matter in what human terms its wonders may be expressed. BiArw. ERLE! A GREEN LEAF THERE are really no “marvels” in Nature, because everything which is has its proper place in a sequence of simple cause and effect. Yet we are so accustomed to judge things by what we can see of them with our unaided eyes that it is hard to hold back the exclamation of surprise and wonder when the microscope reveals to us un- suspected complexities in structures which we have previously regarded as simple and _ insignifi- cant. Take a green leaf for example. Nine out of ten of us are satisfied to know that it is the habit of plants to be covered with green leaves, which usually fall off when the cold of winter nips them but grow again in spring. To ask why plants have leaves seems as idle a question as why birds have feathers, or fishes scales: so when, under the microscope the elaborate struc- ture and important functions of leaves are made plain—when we see that, not only the life of plants, but the life of all things that live depends A GREEN LEAF 59 upon the activity of a certain green-coloured sub- stance which fills one layer of tiny cells in the leaves of plants, the temptation to exclaim ‘* Mar- vellous !” is great. It is not enough, of course, merely to gaze upon the magnifed structure; we must at the same time endeavour mentally to analyse a leaf and learn of what chemical elements it is chiefly composed. Having thus gained a knowledge of its structure, and of the matter of which it is principally built up, we are in a position to trace the connection of the two and the consequences of that connection. In Fig. 39 is shown part of a magnified section of the blade of a laurel leaf, made to exhibit its internal structure. As the laurel is an evergreen, the upper surface of its leaf has a protective layer of a varnish-like substance, probably to protect the leaves from injury by the frost of winter. Immediately below this varnish layer is situated another layer of large cells, which botanists call the ‘‘ epidermal tissue.” These cells usually are transparent and colourless, and full of water, and serve to protect the internal tissues of the leaf from excessive evaporation and external injuries. Boys are fond of tearing a laurel leaf crookedly so that this layer of colourless cells extends like a fringe beyond the green part ; then, placing the torn fragment between their two thumbs and 60 MINUTE MARVELS OF NATURE blowing hard, they produce horrid, squeaky noises. This, however, does not amount to scientific investigation of the structure of plants; and, resisting the temptation to make squeaky Fig, 39. Part of a section of the blade of a laurel leaf to show its internal structure noises with the skin of the leaf, we find below it a series of regular, closely packed green cells. These give the green colour to the leaf, being seen through the transparent layer above. They are called the ‘palisade cells,” and their green A GREEN LEAF * 61 colour is due to the presence of numerous micro- scopic green granules embedded in their other- wise colourless protoplasm, in the same way that our blood, which is really colourless, appears red Fig. go. The mid-rib or central vein of the laurel leaf, showing its structure owing to the minute red corpuscles with which it is crowded. These green ‘ chlorophyll-corpuscles ” may be said to perform the most important func- tion of any organism in the history of life, as we shall see later. Below these palisade cells comes a kind of 62 MINUTE MARVELS OF NATURE spongy cellular arrangement, which serves to evaporate superfluous water, and so keeps up /—_ Miran, boy VFL. te RI, Fig. 41. Part of a section through the blade of the sunflower leaf, showing many-celled hairs the circulation. Finally, the under-surface of the leaf, consisting of another epidermal layer of Fig. 42. The mid-rib or central vein of a sunflower lear 64 MINUTE MARVELS OF NATURE transparent cells, completes the structure, as shown in the illustration—excepting only the few darker rings of cells intermixed with the palisade and spongy cells, which represent the cut ends of the nerves or leaf veins. Fig. 40 gives the central vein or mid-rib from the same section of this leaf, showing that the mid-rib gradually assumes a_ structure more identical with that of the stem (a description of which was given in the previous chapter) rather than the leaf-blade. Figs. 41 and 42 illustrate sections from the blade and mid-rib of the sun- flower leaf for comparison; but you will notice that the rough leaf of the sunflower differs from the smooth one of the laurel in having minute many-celled hairs arising from the epidermal tissue. It is the continuation of the leaf-stalk or “petiole,” as botanists term it, which consti- tutes the mid-rib, and the same structure becomes similar to the young stem as it nears it; but towards the apex of the leaf the various vascular tissues often disappear by degrees, merging their original character in the more simple cellular structure of the leaf. If we examine the growing-point of a stem where new leaves are being formed, to trace their origin, we find at the apex (see Fig. 43) a conical A GREEN LEAF 65 mass of small-celled tissue or ‘ meristem,” as botanists term it, the cells of which are continu- Fig. 43. The growing point ot a stem, where new leaves are being formed ally dividing and subdividing to form new tissue, forming lateral protrusions in regular succession. Each protrusion is the basis of a leaf, and as these E 66 MINUTE MARVELS OF NATURE increase in size, spaces form between them, until we get the stem with leaves arranged symmetri- cally round it at regular distances, as we see it in the branch of any familiar tree. Of course there are many variations in leaf Fig. 44. Section of lcaf of the deadly nightshade, showing large palisade cells structure. For instance, Fig. 44 represents a section through the leaf of the deadly nightshade, the structure of which, on comparison with the laurel leaf section, will be seen to differ by the omission of the outer varnish layer and more con- spicuously by the palisade cells occupying at least A GREEN LEAF 67 one half of the leaf-tissue as a single layer of large cells instead of several layers, as in the case Fig. 45. The fleshy leaf of a stonecrop S45 a of the laurel and sunflower leaves.