IN MEMOI Richard M. ^IAM Holman Richard M. Holman >»•» "• 9 2 given out is about the same as the amount of oxygen absorbed. This action goes on wherever there is actively living substance, but only where it is living, as shown by the fact that there is no change in the tube C. It does not go on, for instance, in the centre of a large tree-trunk, for the wood there is not alive but dead. It is this dead heart-wood, often coloured red or brown, which alone is of any use as timber. But everywhere else in the plant where there is actual life, there respiration goes on. The COs which is formed makes its way along minute crevices and passages, not tubes, in the tissues, till it gets to the outer surface, either through special cracks in the bark of the smaller branches, or more generally through the stomas. From the roots it also passes out through the root- hairs, and, dissolved in the water of the soil, helps in the natural breaking up of the mineral substances. RESPIRATION 27 Put a clean fresh shell of a river mussel, or any shellfish — or if there is room, several shells — in a pot of soil, their inner sides facing upwards, and sow seeds in it. After a few weeks take the soil out and examine the shells. On the shining inside surface you will find very thin lines. These are made by the root-hairs, the CO2 secreted by them dissolving the calcium carbonate of which the shell is composed. 9. We have learnt that wood contains a very small quantity of mineral substances, which are incombustible and constitute the ash, and that these are taken up out of the ground by the roots. But what about the rest, the part that does burn ? The products of ordinary combustion are carbon dioxide and water-vapour. You may prove this quite easily by holding a burning match or splinter of wood in the mouth of a test-tube half full of lime-water (i.e. water with a little freshly roasted chunam in it) for a minute or so, then shaking the tube up. A cloudy ap- pearance, due to the formation of carbonate of lime or chunam, shows that carbon dioxide is produced in the burning. Now hold over a burning match a clean cold piece of glass or of brightly polished metal. The bright surface will be clouded for just an instant by a deposit of moisture showing that water-vapour is also formed and is condensed by the cold glass. The same cloudy appearance can be seen whenever a cold glass chimney is put on a newly lit paraffin lamp. It passes away at once as the glass becomes warm. Carbon dioxide and water-vapour therefore are pro- duced by the combustion of wood — that is, by the 28 GENERAL BOTANY solid matter of plants. These are both colourless gases, and smoke is black only because it contains solid particles of carbon that are carried away by the draught before they can be completely burnt. Now burning means oxidation, and the fact that carbon dioxide and water-vapour are produced when wood is burnt shows that it consists very largely of the two elements carbon and hydrogen. The solid framework of a plant is in fact formed entirely of a substance called cellulose, which is a compound or mixture of compounds of hydrogen, oxygen and carbon, in which there are always eight parts of weight of oxy- gen to one of hydrogen. Starch and sugar, which we obtain only from plants, are also compounds of these three elements (and of no others) and in them too the oxygen and hydrogen are in the proportion of eight to one, the difference being in the amount of carbon, and in the arrangement of the atoms in the molecule. Because the hydrogen and oxygen are in the same proportion as they are in water, these substances (and others of the same kind) are called by the general name of carbohydrates. Now where does the plant obtain these elements ? Hydrogen and oxygen it gets from the ground as water, but the carbon cannot come from the ground. We cannot burn earth, even that in which plants grow best, and we have only to look at the soil of a paddy or cornfield after the crop has been cut and carried away, to see that except for the roots left behind there is no carbonaceous matter in it at all. Many plants indeed will grow quite well on the sand by the seashore or in waste places where there CARBON IN PLANTS 29 is not even a vestige of combustible matter, i.e. of carbon. Strange as it may seem, the whole of the car- bon in an ordinary plant, making about one half of the weight of its dry substance, is obtained from the at- mosphere. Ordinary air contains, in addition to nitro- gen, oxygen, water-vapour and other gases, a very small quantity of carbon dioxide. In ten thousand parts of air there are only four of carbon dioxide, and by weight only three-elevenths of this gas is carbon, so that the amount of this element in the atmosphere is comparatively very small. Still it has been proved by careful experiments that it is from the air and only from it that green plants get their carbon. All green parts are capable of taking in this carbon, but it is the leaves that are chiefly concerned in this work. The carbon dioxide passes in with the air through the small holes — stomas — through which, as we have already learnt water passes out in the form of vapour, and, making its way through the spaces in the tissues, is absorbed by the living substance of the leaf. There it undergoes chemical change ; the carbon is separated from the oxygen, and made to combine with the elements of the water to form a carbo- hydrate. This process is termed assimilation, and the sub- stance first formed appears to be a kind of sugar. But in most plants this is condensed, so to speak, into starch, which, being insoluble in the water of the leaf, occurs 'as distinct grains, too small however to be seen except with the help of a microscope. That starch is formed you can prove in this way. Take any thin leaf, such as that of a Tobacco 30 GENERAL BOTANY plant which has been out in the sun. Dip it first into boiling water to kill it, then leave for a few hours in alcohol, which will dissolve out the green •colour. When nearly white put it into a strong solution of iodine, made by adding iodine to a solu- tion of potassium-iodide in water. The leaf will turn blue or black, because starch forms with iodine .a blue compound. Drop a little of the iodine solution on new white cotton cloth or paper (which usually •contains starch) and note the dark blue or black colour. Some plants, however, will not give this reaction with iodine, because starch is not formed in their leaves, the product of assimilation being sugar. But most ordinary quickly grown plants, which have been in the sunlight for a few hours, will give it. If you try this experiment with leaves from the same plant which have been plucked in the early morning, you will find that they do not turn such a dark colour, showing that assimilation does not go on during the night, and that the starch formed during the day is passed down into the branches. Being insoluble it has to be first converted into a sugar and is passed down in that form to all parts of the shoot and to the roots. It is only a certain part of the first formed pro- duct of assimilation which is converted into starch ..and sugar, and passed on as such to the rest of the plant. The rest is made to combine with the mineral substances taken up by the root to form with them peculiar chemical compounds known as proteids. Proteids are, as we know, absolutely necessary to animals as food, and they are just as necessary to PLANT FOOD 31 the living substance of a plant, only the plant makes them first for itself. Sow seeds of any quickly-growing herb, and when three or four leaves have appeared on each, cut them all off from some of the plants, leaving the others entire. In a few days the mutilated plants will prob- ably be dead ; or if they are still alive after a week, it will be very apparent that they have not grown as those which have still their leaves. This shows us that the leaves are essential to the life of the plant, that they in fact supply its food. Now grow in pots some more of the same or any other plant that naturally grows in the open, such as Cotton, Sunn-hemp, or Castor. When they have come up, put some of them out in the sun, giving them plenty of water, and keep the others in a dark room. In a few days' time those in the dark room will be very likely a little taller, especially if the plant be naturally a climber (the reason for this we shall come to later on), but they will be weak and sickly in appearance, and if left for some time will probably die, while the others will be sturdy and strong and have a healthy green colour. We learn by this that light is necessary for green plants, and that without light they cannot obtain their food, but starve and die. It is, therefore, only during the day that the making of carbohydrates can go on, and for that reason this process is also called photo- synthesis (photos = light, synthesis = combination). Since carbon is taken from the gas carbon dioxide in the process of assimilation, oxygen must be set 32 GENERAL BOTANY free, and this oxygen passes out into the atmo- sphere again through the stomas ; or, in the case of water plants that live always under water and have no stomas, through the whole surface. This can be shown very easily as follows. Get a clean glass jar nearly nil it with clean water, and add a little ordinary soda-water. Then put in some healthy water-weed such as you will find at the bottom of any clean tank or channel that is constantly full of water. Stand the jar in the sun ; very soon bubbles of gas will form on the leaves and rise up to the surface. This gas can be easily collected in a test- tube full of water inverted over the weed. Or better still by a glass funnel Avith a short piece of rub- ber tube fitting over the tube and closed by a clip. This is let down into the water, with the clip open, till quite submerged and the tube is full of water, then the clip is closed. If the bubbles stop rising add a little more soda-water (which contains carbon dioxide) and they will at once appear again. When sufficient gas has been collected (it may take an hour or so), take the test-tube out, or open the clip on the funnel, and introduce into the gas a smouldering piece of wood. It will at once burst into flame, showing that the gas is oxygen. The fact that soda-water contains carbon dioxide, and that instead of that gas we get bubbles of oxygen shows very clearly what the action of the plant is. Now cover the jar with something that will keep out all the light. The bubbles will at once cease and hardly any gas be collected in the tube. FUNCTIONS OF LEAVES 33 10. These simple experiments teach us the function of the leaves. In the first place it is through them almost entirely that the water taken up in such large quantities by the roots is sent out again into the air. This large quantity of water is necessary, as we saw, to supply the mineral substances which can only be taken up by the roots in a very dilute solution. The second and more important function is the making of the plant's food, that is to say, assimilation of carbon and perhaps also the formation of proteids. FIG. 4 These processes take place only in the green parts, and only in sunlight. And thirdly, through the stomas of the leaves also passes out some of the carbon dioxide produced by respiration of the living substance. 11. In order that leaves may do their work pro- perly they must have plenty of air and light. The more of these they get the more carbon can be assimilated from the air, and the more proteid food substance be made. We see therefore why it is that the branches of most trees and bushes spread so widely, and divide so repeatedly ; and why nearly all the leaves are on the smallest branches, and towards their ends, on the outside : so that a well-branched 3 34 GENERAL BOTANY tree, for instance a Rain-tree, seems like a hollow green dome of leaves supported by its branches. For if there were leaves in the middle of the tree, they would be shaded by the outer ones, and not get enough light, those that were there have in fact died. Nor are they ever so crowded together that air cannot pass easily between them ; it is only in very hot and dry places that we find leaves closely overlapping each other, and then it is because if spread out widely, they would lose more water than the roots could supply. For look at a branch of Banyan or RAUWOLFIA or any other plant whose leaves stand out horizontally, and notice that those which are near together do not overlap each other, but each is as fully exposed to the light as circumstances will allow. The functions of the stem and branches of the shoot are now easily made out. Their first and chief use is J.o bear the leaves, so that they may obtain as much light and air as possible. For this reason they must be strong to stand not only the weight of the leaves and of each other, but the pressure of the wind against them. It is on this account that there is in the branches far more cellulose, and that of a harder and stronger kind in the wood than in the leaves. Most branches are round in cross section, like the main trunk, but when a horizontal branch is rather long and has to be specially strong to support the weight of its leaves, it is often elliptical, thicker in the vertical direction, than in the horizontal. This can be seen in the long branches of Banyan trees, that stretch over a road, and in the Firs and Pines FUNCTIONS OF THE STEM 35 planted in our hill stations, and sometimes even a tree which has fallen or been forced slantwise away from the perpendicular grows in consequence more quickly in the vertical direction, becoming very much thicker across the vertical diameter. An equally important function is the conveyance of water and the contained mineral salts from the root to the leaves, and of made-up food materials — sugar and proteids — from the leaves down to all parts •of the shoot and the roots. To prevent loss of water by evaporation, and also for protection against damage by accident or by animals, the stem and branches are covered with a thick water- proof bark. The outer part of the bark consists of dead tissue, and its only use appears to be to protect the inner parts against injuries and loss of water ; for, not being strong and tough like wood, it does not con- tribute in the smallest degree to the strength of the part. We can now understand why leaves are flat and branches and stems cylindrical in shape. The work of a leaf is a surface-work, the greater the surface •exposed to the light and air, the greater (other things being equal) the amount of carbon assimilated and of water evaporated. The function of the stem and branches on the other hand is to support the leaves, and to conduct water to them and food from them ; so the less the surface exposed to risk of injury and loss of water the better. This is the reason why leaves are thin — thereby having the greatest surface, and branches cylindrical. A stem or a branch may be angular when young, but after a year or so, it always 36 GENERAL BOTANY becomes cylindrical, for that is the form which exposes the least possible surface. But the lower end of a tree-trunk, where it enters- the ground, is very often not round, but very ir- regular in form and very much expanded, so that a cross-section would be anything but circular. This is particularly the case in very high trees, and these expansions serve to make the stem much more rigid. The extra wastage in dead bark-tissue to cover the expansion is therefore compensated by the increased strength and thickness of the trunk at this part ; for it is just near the ground where it is fixed firmly by the roots that the trunk of a tall; tree might be broken in a high wind. It may be asked why, if this is the case, the upper part of the stem and branches have not expansions to make them more rigid. The answer is that it is no disadvantage,, rather it is an advantage, if the branches bend and yield to a strong wind. It is only at the base where: the trunk is fixed by roots firmly into the ground,, and therefore cannot give, that it needs extra strength to prevent its being broken. CHAPTER IV THE LEAF 1. In chapter ii we spoke of leaves as being either opposite or alternate, but in reality these terms cover a number of slightly differing arrangements. Opposite leaves. — When leaves are opposite, (i.e. in pairs), the stem is usually, though by no means always, four- sided, and each pair of leaves is then at right angles to the next pair above and below. This arrangement is called decussate. When how- ever the leaves stand out to right and left, with, usually, all the blades in one plane, as often happens with branches that are horizontal, they are said to be bifarious. Sometimes we find at a node not two but three leaves, when they are said to be ternate ; and if there are four or more we speak of them generally as being whorled, or ' in whorls ' of four or more. Alternate leaves. — In grasses and all plants of that kind (e.g. all the cereal crop plants) and in some others as HEDYCHIUM (wild Cardamom), and RAVENALA, the * Traveller's Palm ', the leaves are in two rows one on either side of the stem, and stand out to right and left, but not all round it. This arrangement is termed 38 GENERAL BOTANY distichous and corresponds to the bifarious arrange- ment in opposite leaves. In CYPERUS, CAREX, and all others of that family, the leaves are in three rows, and if one looks down on the top of a plant (e.g. of the common CYPERUS BULBOSUS, or the Papyrus) the leaves appear as in a spiral, one edge of each at the base being covered by, and the other edge covering, the leaf next above and below. And if starting with any leaf, we take them in ascending order, we find that the third leaf after the one we started with stands exactly over the latter, and the sixth again over both, and the ninth, twelfth, and so on. In passing round the axis, therefore, we pass through three leaves, or each is separated from the one next above or below by one-third of a circle. Now on every plant with alternate leaves, the leaves are arranged in some sort of spiral, and in the case of PAN DAN US, the screw-pine, they give a twisted appearance to the axis. On some plants it is a two-fifths spiral, that is, on going from a leaf to the one exactly above it, we should have to pass five leaves, and wind twice round the axis. Another common arrangement is the three-eighths spiral, in which we must pass three times round the axis, and take eight leaves on the way, before coming to one that is exactly above the first. This we find in LINUM USITATISSIMUM, the Flax plant. There are other spirals with higher numbers which can be easily determined by careful examination. 2. We learnt in chapter iii that the work of the leaves is chiefly to assimilate carbon from the air, and THE LEAF 39 to build up with it and the mineral substances brought up from the ground, those peculiar complex bodies, carbohydrates and proteids, which are the plant's real food. Since the action of the leaves, depending as it does on light, is a surface one, nearly all leaves are comparatively broad and thin, or at least a part of. the leaf is so, and this part is called the blade. Some leaves, like those of the Sunn-hemp and Poppy, consist of nothing else, the broad blade standing out from the shoot-axis without any intervening stalk ; such leaves are termed sessile. But -in most cases the blade is held out away from the axis by a cylindrical stalk, as in the Mango and Cotton, this stalk being called the petiole. In contradistinction to sessile leaves, these are said to be petioled. The end of the petiole where it is attached to the axis is often swollen or broadened out, and is called the leaf-base. In some plants the leaf-base is very conspicuous and wraps round the axis. This occurs for instance in the Canna and the Ginger plant. In all grasses and plants like them, e.g. the cereal crop plants and Bamboo, there is no petiole, but only a blade, and a sheathing leaf-base which may be as long as the blade ; and except for a slit down the further side completely encircles the stem like a tube. Notice that in these plants there is a fringe of hairs or of thin tissue passing across the leaf at the line where the blade and sheath join. In others again the base of the petiole is distinctly thickened, and is flexible so that the whole leaf may move up and down. It is then called a pulvinus. We shall refer to this again later. A similar swelling 40 GENERAL BOTANY occurs at the junction of blade and sheath in the leaves of MARANTA and PHRYNIUM. 3. In many plants, e.g. Cotton and HIBISCUS, there are on the axis, just at the junction between it and the leaf, two small greenish or brown scales, one on either side of the petiole. These are termed Stipules. They vary somewhat in shape, and are sometimes so small as to be hardly visible, and often they fall off very quickly, so that one can find them only on the youngest parts, towards the ends of the branches. In CASSIA AURICULATA (fig. 5) they are large and ear-shaped, from which the name AURICULATA (ear- like) is taken. They are larger still in the common Pea, and being green take the place of the leaf-blade which is changed into a tendril. But in most cases they are narrow and pointed, and less than quarter inch long. In the Coffee plant, in IXORA and others the leaves are opposite, and the stipules of the two leaves are joined together in pairs, to form what looks like one stipule, connecting the two leaves, on each side of the axis. In POLYGON UM FIG. 5 CASSIA AURICULATA STIPULES 41 the stipules form a complete sheath surrounding the axis (like the sheath of CYPERUS, but above the point of attachment, not below it). In the Banyan, Fig, Jak, and a number of other plants the stipules are also in the form of a tube which at first completely surrounds and covers the young bud above the leaf. As the internodes of the bud lengthen and each leaf opens out, the stipule splits into two and is then like the normal pair of stipules but soon falls off, and the only sign left is a scar running round the axis. The same happens with MICHELIA, a plant in every other respect very differ- ent from the Banyan. In a few other plants too the stipules are so large that they completely sur- round the axis, and leave a scar not unlike that of FIG. 6 the Banyan or Fig, or of HIBISCUS TILIACEUS MICHELIA, though not like these, tabular in shape, e.g. in HIBISCUS TILIACEUS {fig. 6). 4. If the blade of a leaf be single and undivided, as, for instance, the Mango, Banyan, Fig, Cotton, Tobacco and Hibiscus, it is said to be simple. But if it is 42 GENERAL BOTANY FIG. 7 PHYLLANTHUS NIRURI THE LEAFLET 45 divided into a number of small blades connected with the main petiole by their own little stalks, (fig. 5), the leaf is compound, and each separate blade is a leaflet. FIG. 8 CLEOME VISCOSA It may in some cases be at first sight difficult to- determine whether one is dealing with a compound leaf or a number of small leaves, but the question can 44 GENERAL BOTANY nearly always be settled without any real difficulty T}y noting the presence or absence of axillary buds. For while, as we have already learnt, every leaf should have in its axil at least the rudiments of a bud, there is never one in that of a leaflet. For instance PHYLLANTHUS NIRURI (fig. 7), which is such a common weed among grass in gardens, may appear at first sight, to have alter- nate compound leaves. But closer examination shows that in the axils of some at any rate of the apparent leaflets arise small stalked flowers, and on the axis, just below each apparent leaf-stalk, there is a slight ridge, a leaf-scar. So that the ap- parent leaf -stalks are branches, and the small blades, true leaves. Com- pare CASSIA AURICULATA (fig. 5) and INDIGOFERA ENNEAPHYLLA (fig. 9). The main stalk (petiole) of a compound leaf is generally called the rachis, and a compound leaf is said to be pinnate or pinnately-compound if the leaf- lets are borne on either side of the rachis. If they radiate out from the end of the rachis, as in BOM- BAX MALABARICUM and HEPTAPLEURUM, they are called palmate or palmately compound (fig. 10). Very often the pinnate leaf is still further divided as if it were itself made up of pinnate leaves. We find this, for instance, in CAESALPINIA PULCHERRIMA and in POINCIANA REGIA, the Gold-Mohur. The leaf is then said to be bipinnate, and the groups of FIG. 9 INDIGOFERA ENNEAPHYLLA COMPOUND LEAVES 45 leaflets — which look like compound leaves — are termed pinnas. These pinnas again may be themselves bi- pinnate, or still further divided, so that the leaf is FIG. 10 CRATAEVA RELIGIOSA trebly or more pinnate, as in MORINGA PTERYGOSPERMA the Horse-radish tree, when it is usually said to be decompound. In any case the ultimate undivided seg- ments are called leaflets. Pinnas and leaflets may have small stipules, or stipels as they are often called, and they very often have a pulvinus, like the 46 GENERAL BOTANY leaves : but are always distinguished by the absence of axillary buds. In pinnate leaves or pinnas the leaflets may be alternate or in pairs (opposite) and in the latter case, if there is a terminal one, so that the number of leaflets is odd, as in MURRAYA EXOTICA or in fig. 9, the leaf is said to be odd-pinnate or impari-pinnate. If there is no terminal leaflet, so that the number of the opposite leaflets is even, as in the Tamarind and ADENANTHERA, the leaf is pari-pinnate, or abruptly pinnate. When there are only three leaflets the leaf is generally spoken of as trifoliate, and we distinguish as palmately trifoliate those in which the three leaflets are attached together at the end of the rachis as in CR'ATAEVA RELiGiosA (fig. 10) from the pinnately trifoliate, in which the rachis is continued a little beyond the first pair of leaflets, as, for instance, in ERYTHRINA INDICA (fig. 9). FIG. 11. YOUNG LEAVES OF ERYTHRINA INDICA CHAPTER V THE SEED AND ITS GERMINATION 1. So far we have been studying the outlines of the vegetative life and work of plants, but, as we have learnt, there is another work, that of REPRODUC- TION, which is just as important, if not more so. All flowering plants reproduce, in a normal way, by seeds formed inside a special organ which may even- tually become a hollow pod, or a soft and juicy fruit. This organ is called the ovary, and is a part, the innermost or central organ, of the flower. Now take a nearly ripe pod of the common Lablab or of the Pea. In general shape it is a narrow oblong, pointed at each end, and curved at one side. Along the outer edge, the convex side, there runs a narrow ridge, and along the inner or concave side another, but thicker raised ridge which is double. These ridges are called the sutures. That on the convex side being the dorsal, that on the concave side the ventral suture. At one end there is a short round stalk which was the stalk of the flower by the development of one part of which the pod has been formed. At the junc- tion of the pod and its stalk is a raised ring which represents the base of the flower, all the rest of which 48 GENERAL BOTANY has fallen off. At the other end the pod narrows into a thin long point which curves in the opposite direc- tion. This is the style of the ovary and is no larger than it was in the flower ; at the very tip the style is curved abruptly still more backwards. If now the pod be opened along the dorsal suture, five or six seeds will be seen attached along the inside of the opposite or ventral suture. Each has a short stalk called the funicle, attached to the pod and to a large white growth on the seed called the hilum. In many plants the hilum is not so large as in the Lablab, but is hardly visible at all, its position being then marked by the scar left by the funicle on the seed when the latter falls out of the pod. At one end of the hilum, the end which was towards the stalk of the Bean-pod, there is a small hole, which can sometimes be seen more clearly after the seed has been soaked in water, for if it be then wiped and squeezed, water will ooze out of this hole. This is called the micropyle, and occurs in every seed. The position of the micropyle in relation to the funicle and to the pod is the same in all the seeds of the pod, and of all plants which are akin to the Bean. On the side opposite to the hilum the skin of the seed appears to be drawn together. This is the chalaza, and marks what is really the base of the seed. Between the hilum and the. chalaza is a raised ridge barely visible, which is called the raphe. Examine also the seeds of other Beans — the Broad- bean, Brown-bean and Gram, and make out the same parts in them. On the Brown-bean at one end of the hilum, furthest from the micropyle, there is a small THE SEED 49 dark triangular area ; on the Broad-bean two brown spots in the same place. This is termed an aril. It is much larger in some seeds, as the Nutmeg where it extends almost all over the seed in red finger-like processes. In the Korukapuli it extends half over the surface as a yellowish-white body. But it is not a necessary part of any seed, and is altogether absent from those of most plants. Now take a Castor-seed. It is oval in outline ; with a slight ridge down the middle of one side. This ridge is the raphe, and where it ends is the chalaza. At the other end of the seed is a yellowish-white outgrowth called the caruncle ; this occurs in very few seeds, being peculiar to the Castor and plants allied to it. It surrounds the micropyle, which can be seen as a minute hole at its end. The hilum is almost too small to be visible, but on breaking open a pod that is not quite ripe, we may see that the seeds are attached, one in each chamber of the pod, by short stalks just under the caruncle, so that the raphe. runs down from the hilum, as it does in the Bean seeds, and is clearly seen as a slight ridge. Sow seeds of the Broad-bean, Brown-bean, Gram, Melon or Cucumber, Castor, Date, Onion, Maize, and any other kinds you like, in pots of soft sandy soil and keep them moist, covering them with a plate of glass or wood. All these seeds, except the Maize, have a hilum and micropyle, though these are some- times very difficult to make out. In the Melon-seed they are close together at one end, and it may not be easy to make out which is which. The Date-seed 4 50 GENERAL BOTANY has a groove down one side while in the opposite is the hilum. The micropyle is next to it, but hard to see. The Maize-grain — as also all cereal grains, Wheat, Paddy, Cholam — has no micropyle, for the seed is in reality enclosed in its own pod, but too tightly to be separated from it, and the micropyle is hidden inside. After about a week, sow another lot of seeds. When the first lot has begun to germinate and show above the soil, we may examine them in turn. 2. We will first take the melon-seedlings. The first sign of the young plant is an arched axis which pushes up the soil, and in a day or two comes clear out above it. Pull one of them up. One arm of the arch is short and is connected with something inside the seed; the other is much larger and has branches going obliquely downwards through the soil — these are the roots. Now notice that the seed-coat gapes open, and that the lower side is held down by a swelling on the other arm of the arch, just above the topmost root-branch. This swelling is quite peculiar, and is found only in plants of the Melon and Cucumber kind. In the course of the next day or two the arched axis bends backwards, and literally pulls out of the seed-coat two thick flat oval bodies which very soon turn green. The axis then straightens and becomes upright, in a line with the root, and the two flat green things stand out sideways. Their resemblance to leaves is obvious, they must be leaves. Between them is a tiny bud, and in a few days this grows out as a shoot axis, and bears leaves. When the plant has THE FIRST ORGANS 51 grown a bit, we see that the first two leaves are utterly unlike the others. They are, for instance, opposite, while the later and ordinary leaves are alternate. Then again they are attached close to the axis, and have a smooth surface and an even outline, whereas the ordinary leaves have long stalks, and are of quite a different shape, and may be rough to the feel and have a jagged outline. Because these two first leaves are so very different from the ordinary leaves of the plant, they have been given a special name, cotyledon, and the part of the axis which is below the coty- ledons, and between them and the root proper (which begins at the level of the peculiar swelling referred to), is called the hypocotyl. Now examine seeds that have been a shorter time in water, or in the moist earth. They are larger than when dry, and the seed-coat is burst open at the narrow end (where the micropyle and hilum are). Through the opening there protrudes first a smooth white pointed body. This develops after- wards into the first root, and is called the radicle, and you should notice that it always points down- wards. In whatever position the seed may be put, whether sideways or flat, or with the micropyle upwards or downwards, the radicle, as soon as it has emerged, turns downwards through the soil. Now if we split the seed right open, we shall find inside only two white flat bodies, which obviously are what afterwards become the green cotyledons. We may take seeds which have hardly begun to germinate, and still find these two flat white coty- ledons, so that the cotyledons and the short bit of 52 GENERAL BOTANY axis that connects them and ends in the radicle are already formed in the seed. Germination only means the greater development of the different parts — coty- ledons, radicle, hypocotyl and bud. . This miniature plant that is in the seed is termed an embryo. We must not suppose that the whole FIG. 12 THE BROWN-BEAN AND ITS GERMINATION. § NATURAL SIZE m. micropyle h. hilum str. strophiole or aril cot. cotyledon plant is present in the embryo, it is only the coty- ledons, and the short piece of axis which connects them and terminates in one direction in the radicle, and in the other in the bud of the shoot. This by the way constitutes another of the differences which DICOTYLEDONS— MELON AND BEAN 53 separate plants from animals. The embryo, of at any rate one of the higher animals, expands after birth* while that of a flowering plant remains practically the same size, becoming the mature plant only by the_ addition of new organs. 3. Now look at the pot containing the Gram or the Brown-bean seeds. Here again, the first sign of the new plant is an arched axis which pushes up the soil, and breaking its way through, at length emerges, and as it straightens, pulls up out of the seed two thick flat bodies. Between them is a bud, which soon develops as a shoot axis with two green leaves at the top, each folded along its middle line, and one inside the fold of the other. These being exactly like the later ones are the first normal leaves and correspond to the first rough leaves of the Melon. So that the two thick white bodies correspond to the cotyledons* Indeed, while still in the seed, they are in no essen- tial point different. But those of the Melon turn green, and are thus able to make food for the young plant soon after they have emerged from the ground, while the cotyledons of the Bean are thicker and contain so much ready-made food- material given to them by the mother-plant, that they can, without turning green, supply food at once to the seedling. It is perhaps because of this that the shoot-bud of the Bean is larger and develops more quickly than does that of the Melon. It would seem indeed, as if there were no necessity for the cotyledons of the Brown- bean or Gram to leave the seed at all, because, being colourless, they can gain nothing from the light and air, and might as well stay underground. 54 GENERAL BOTANY 4. With this in our mind let us turn to the seed- lings of the Broad-bean and Pea. At first sight the germination appears to be utterly different. There is no arched hypocotyl drawing up two broad or thick cotyledons out of the seed. Instead, the earth is pushed up by a leafy shoot whose first leaves are at once of the ordinary kind, a little simpler perhaps, but not really different from those which come after. More- over they are not opposite as cotyledons are, but alternate. If we pull a seedling up we shall find it still attached to its seed, or rather to two thick white bodies which completely fill the seed and which we at once recog- nize as corresponding to the cotyledons of the Brown- bean or Gram. They are indeed no way different from them, except that they remain inside the seed, and are not drawn up above the ground. In a very short time after the beginning of germi- nation they become soft and watery and eventually disappear, not because they decay, but because their whole substance is absorbed by the young plant. And here we see the principle of providing for the seedling by packing food in the cotyledons, followed to perfection. The waste of material and energy in the drawing out of the cotyledons by the hypocotyl as we see it in the Gram and Broad-bean is done away with, and the shoot can begin its life just a little earlier. Now examine seeds that have been soaked in water a day or two, and become soft. As in the Melon, so in the Brown-bean, Gram, Broad-bean and Pea, there is an embryo consisting of two large cotyledons, which fill practically the whole seed, and are connected with DICOTYLEDONS— PEA AND CASTOR 55 a short axis, smooth and pointed at one end which is to become the radicle and having at the other end a bud. The seed coat is folded in between the radicle and the cotyledons, so that there is as it were a separate pocket for it. The bud of the Broad-bean or Pea is easily made out, having two or more leaves which, though small, are clearly visible. Those of the Brown- bean and Gram are not so obvious, for the leaves are not so far developed; and that of the Melon is still more difficult to distinguish. These differences seem to be connected with the amount of food the cotyledons can supply, and the consequent rapidity with which the young plant can develop. 5. Now look at the Castor seedlings. The first sign of the young plant just as it was in the case of the Brown-bean, Gram and Melon, is an arched hypocotyl which draws after it through the soil two flat cotyledons ; these spread out to the light and turn green. Between them is the bud of the shoot, and as the other leaves appear, notice again how different they are in every way, except colour, from the cotyledons. If the seeds have not been buried deeply you will often find on the coty- ledons, and at first closing over their ends a slimy yel- lowish substance, which if left on gradually dries up till scarcely thicker than a piece of paper, and then falls off. As the cotyledons have come out of the seed, this slimy . substance must have done so also, and to find out what it is, we must examine the seed. Unlike the Bean, Gram and Melon, the Castor-seed swells very little in water, the coat being very hard. 56 GENERAL BOTANY But this splits open at the caruncle end, and we can easily remove it. Then we find not an embryo with two white cotyledons as in the Beans, but a white body with a thin papery covering, from one end of which — the micropyle end — there breaks out through it the tip of the radicle. The radicle, we must note, is not a part of the white body, but breaks through it from inside. Splitting this body open carefully we shall find the embryo inside. Its cotyledons are very thin, thinner at first than the thinnest paper, but as germination proceeds they become thicker and larger until they may each be four times as long and broad as the seed from which they came out. Their leaf -nature is indicated from the very first, by the lines with which they are marked — exactly as leaves are. In the seed, therefore, there is something else besides the embryo, — enclosing it. This substance is called the endosperm, and it is packed tight with oil and substances of a mineral and proteid nature. In the process of germination the endosperm absorbs water, swells and becomes soft, and the oil and other food substances in it are absorbed by the cotyledons. Thus it is that these, though at first as thin as paper and only quarter inch long, become eventually over an inch in length and comparatively thick, while the endosperm itself becomes soft and slimy and is gradually absorbed till there is left only a skin which finally falls off. Comparing the Bean and the Castor-seed we see that in both there is food-material stored up for the young plants; but in the Bean it is in the cotyledons MONOCOTYLEDONS— ONION 5.7 — part of the embryo itself — while in the Castor-seed it is outside the embryo, and must be absorbed by the cotyledons. 6. Now examine the Onion seedling. Here again is a green arch which pushes up through the soil, and coming up above the surface gradually pulls one end out of the seed (to which however it remains attached for some time), while the other end fixes itself in the ground by roots. Then it stands upright — a thin cylindrical green organ, without petiole or blade, but. with quite low down on it, a tiny white scale. This scale turns out to be the beginning of a leaf, and other leaves follow, narrow and with- out difference of stalk and blade, and thereby quite unlike the broad stalked leaves of the other seedlings we have studied, but still in every sense of the word — leaves. They all arise from about the same place, the stem, so far as there is one, appears to begin and end at this spot. It is indeed very short almost entirely absent. What then is the green curved body that came first out of the seed ? Its likeness to the ordinary leaves of the mature Onion plant points to its being of a leaf -nature, and just as in the Castor, the two cotyledons, obvi- ously the first leaves, remain for some time with at least their tips inside the seed coat, and in intimate contact with the endosperm which they gradually absorb, so here in the Onion the first leaf is con- nected by its tip with the seed and absorbs nourish- ment from it, and must in the same way be called a cotyledon. But there is this difference, the Onion has only one cotyledon, not two, nor is there in it 58 GENERAL BOTANY any trace of a division, for it is not formed as one might possibly suppose by the coalescence of two leaves, but is just a single one. 7. The Date-seed will take much longer to germi- nate and when it has done so, the first thing to appear above ground is a thin upright leaf — there is no curved organ like that of the Onion. But look again. This leaf will be found to spring from quite deep down in the soil, and the short stem from which it and the later leaves arise are connected with the seed by a long organ whose tip is in the seed, and can be seen as a wrinkled swollen head inside the endosperm. The latter which at first is very hard has become softer, and just round this head its clear blue colour is changed to an opaque white, which means it is being changed somehow by the action of the head. If the long green organ that connects the Onion plant to its seed is the cotyledon, that of the Date must be a cotyledon too, and in the same way, morphologically speaking, a leaf. The stem and radicle are at first very short and are pushed into the ground by the long growing cotyledon, and from the very short axis, the next few leaves arise. Before germination has begun it is very difficult to make out any parts in this embryo for the simple reason that the radicle and cotyledon are in one line and the shoot bud is hardly developed at all. But in seeds that have been some time in the earth, the hard bluish-white colour of the endosperm will have changed to a dull white soft substance just near the embryo, and as germination goes on this area of dull white spreads through the endosperm. MONOCOTYLEDONS— PALMS 59 Here we see the digestion of the hard endosperm by the cotyledon going on, for this hard white sub- stance is mostly solid cellulose, but from the tip of the cotyledon is secreted a substance which changes it into another kind of carbohydrate — sugar — which being soluble can be absorbed by the plant. Canna seedlings can more quickly be raised, and in them the structure is very much the same only that the cotyledon is very short, consisting in fact only of a round head inside the seed (absorbing the endosperm exactly as does that of the Date) and a very short stalk outside it. Looking at it by itself one would never call it a leaf — nor even a coty- ledon— but the case is after all, not so very different from that of the Pea — only that in the Pea there are two cotyledons and they have already, before the seed was ripe, absorbed the endosperm, a work which in the Canna seed is begun only with the germination. 8. Procure a cov- Palmyra nut that has been planted and has begun to germinate. There is no micropyle visible, for the seed is really enclosed inside the hard outer shell, so the FIG 13 micropyle cannot be GERMINATING FRUIT OF THE PALMYRA S66n. The germi- PALM BORASSUS FLABELLiFER nation is apparently cot. 60 GENERAL BOTANY much the same, but the young plant is very much lai^r from the first. A thick club-shaped organ comes out and grows -downwards. The tip of this is the radicle, the rest is the cotyledon which lengthens and pushes the radicle deep into the soil. The other end of the cotyledon remains in the seed and bulges out like a ball and here again one may easily see the change in the endosperm as it is digested by the coty- ledon. The hard bluish-white changes to dull white as the cellulose is digested and transformed into sugar. After a while the base of the cotyledon splits open, and allows the next young leaf to grow out. This pierces the soil straight, like the leaves of the Onion and the Date ; there is no drawing out of the leaf backwards and spreading it out horizontally as with the Pea and the Broad-bean. The germination of all Palms follows on much the same lines. The first few ordinary leaves arise towards t'>e lower end of an, often very long, thick organ, one end of which remains in the seed absorbing the endo- sperm, while the other grows down into the ground, pushing before it, at first, the minute radicle and stein, till the right depth for these is reached. In some palms this cotyledon grows down to a depth of six feet and more, before the ordinary leaves and roots .arise from the short axis at its lower end. Get a Coco-nut which has germinated and has four or five leaves. It appears to be very different from the Date or Palmyra for the leaves come out at the top, .and the roots grow out through the fibrous husk. But MONOCOTYLEDONS— MAIZE 61 cut through the fibre with a saw, and remove it, the roots will then be seen to spring from the same bulbous shoot,. outside the seed, as the leaves do ; and if the shell be broken open there will be found inside a yellow very soft and spongy globular body which almost completely fills the seed, and is connected to the young plant through a small hole in the hard shell. This is the cotyledon. It is not much like the other cotyledons we have studied, still less is it like a leaf. But by tracing in this way the various forms the cotyledon takes in monocotyledons, we see that this certainly corresponds with the leaf-like cotyledon- of the onion, and is therefore morphologically a leaf. 9. Now look at the Maize seedlings. There is first a short tube or sheath which may be only half an inch long. From inside it comes one a little longer, then a narrow green leaf, at first tightly rolled up inside. Pulling a plant up we find it still attached to the grain and closely to it, very much as the Pea plant is at- tached to its seed. From just above the grain, two, afterwards more, roots shoot out and unlike the first one and the single strongly growing vertical root of such a plant as the Pea, spread out more or less horizontally, and if the grains have not been buried deep enough, and the pot has been kept damp, may even lie exposed on the surface of the soil, and show very clearly the thick covering of root-hairs. Break open the grain ; the greater part of it is- now watery and rotten, but there is a firm white swollen body directly connected with the plant. This body has been called the scutellum and in grains, 62 GENERAL BOTANY that have been softened by lying in water this scutellum can be seen lying on one side of the endo- sperm, and can easily be removed from it. If we cut it open right down the middle, we shall find inside a bud of tightly-packed leaves at the upper end, that is the broader rounded end of the grain, and at the lower the pointed tip of the radicle. The axis between the two is attached to the scutellum itself, so that the embryo is enclosed inside the scutellum, and the latter appears to be part of it. In grains that have begun to germinate, that part of the endosperm next the scutellum is not hard and yellow as everywhere else, but is soft and white. It is the same sort of change as we found in the Castor, Date-seed and Palmyra-nut and is due to the digestion of the endosperm by some substance secreted from the scutellum. The change in this case is from starch (with which the endo- sperm is packed tight, and which being insoluble in water cannot be absorbed by the plant) into soluble sugar. This is, of course, why the grain be- comes watery and rotten — its substance is absorbed by the young plant, just as is the endosperm of the Castor, Date and Palmyra by their cotyledons. In the last case the lower part of the cotyledon sur- rounds the young bud for some time after germi- nation, while the upper part is expanded inside the seed. In the Coco-nut it nearly all remains inside the seed, just as do those of the Pea, and we have something not very different except only in shape from the scutellum of the Maize. We may infer, therefore, that the scutellum is indeed a cotyledon, HOMOLOGY OF ORGANS 63 quite different in shape from other cotyledons certainly, but like them, the first leaf organ of the embryo. The cotyledon, we learnt at the beginning of this chapter, is the first leaf of the young plant, and is already formed in the seed. No one would call the scutellum a leaf, but then neither would one at first sight call the two cotyledons of the Broad-bean and the Pea leaves. We argue that they are really leaves, though changed out of all recognition on account of the very different work that they have to perform, because they are situated exactly as are those of the Brown-bean which come out of the seed, and these again exactly as those of the Melon or Castor which are obviously of a leaf nature. 10. We learn from this that the same kind of organ, e.g. a leaf, may be quite different in shape and character in different plants and in different parts of the same plant, because of the different functions it may have to fulfil. So that the shape and struc- ture of an organ depends very largely if not altogether On its functions ; and it is only by comparison with similarly situated organs in other plants that we can tell what it really corresponds to. If it were not for the steps connecting the scutellum of the Maize with ordinary cotyledons and leaves, we might well conclude that it was a special organ produced, be- cause it was wanted to obtain nourishment. i We have had one instance of such a specially produced organ, in the curious swelling which arises on the hypocotyl of the seedling Melon and keeps the seed-coat open. But there is nothing connecting 64 GENERAL BOTANY this with any kind of organ, no plant has a leaf in this position, and it does not arise as far as one can see like a root or a branch of the shoot. We may conclude that it is an organ sui generis — i.e. of its own kind — specially developed on Melons and similar plants for the purpose of keeping the seed-coat open, though it might be an undeveloped root. This is a very important principle which is of universal application, and which we shall have continually to use in the study of botany. When an organ differs in character from the usual type, because put to a different use, we say that it is homologous with the type but a modified form. Thus the cotyledons of the Castor and Melon are slightly modified leaves, those of the Brown-bean are more modified, those of the Pea and Broad-bean are still . more modified. So also the curved connecting cotyledon of the Onion and Date is a modified leaf or leaf-stalk ; and the scutellum of the Maize, Cholam, Paddy, Wheat, Barley, etc., is also homologous with a leaf but a very much modified form. 1 1 . Looking back on what we have studied we learn what germination means — that it is a very interesting and complicated process whereby the embryo in the seed emerges and develops into the young plant. First water makes its way in through the micropyle and causes the kernel inside to swell so that it splits open the seed-coat. Then the embryo begins to grow, the radicle, being nearest the micropyle grows out first, and it is interesting to see that it shows its root-nature from the very beginning by always turning downwards deeper into the ground. FOOD MATERIALS IN SEEDS 65 Then the cotyledon or cotyledons swell and, if there is endosperm, absorb it, dissolving it with a special digestive substance secreted by them. What follows after this depends on the nature of the plant. In some, as the Broad-bean, Pea and Maize, the cotyledon remains in the seed, and is said to be hypogeal. In others, Palms and Onions, it comes partly out and pushes the radicle further into the earth ; in others again it is drawn up out of the seed by the arched hypocotyl and brought up above the ground, and then it is said to be epigeal. If there is endosperm the coty- ledons are thin, but if there is not, they are nearly always rather thick — because they contain food mate- rial— and then as the young plant grows become thin and wasted. In every case the young plant begins its life on the food stored in the seed by the mother plant. This stored food consists always of large quan- tities of carbonaceous matter and some nitrogenous and proteid substances. The carbonaceous matter differs in different plants ; in some it is a carbohydrate — starch — and seeds with starchy endosperms or coty- ledons form valuable articles of food, such as all cereal grains and pulses. In others it is a different kind of carbohydrate, cellulose, as in the Date and Palms generally, and is useless as a food for man, but can be eaten by many animals. In others again it is oily in nature, as Castor, Sunflower, Cotton. In a few it is sugar, as in the Sugar-corn, a special variety of Maize. 12. All these substances are highly concentrated food-stuffs, packed in the seed by the mother-plant for the benefit of the next generation. And if we consider the hundreds of thousands of seeds that most plants 5 66 GENERAL BOTANY produce each season, we shall easily understand that the providing of all this food-stuff must be a great FIG. 14 AGAVE IN FLOWER strain on a plant's resources, and that the reproductive work of a plant calls for really great efforts. Many plants indeed die under the strain, all those small ones, SEED BEARING AN EFFORT 67 for instance, which spring up, flower, and wither away in the course of one or two seasons (annuals and biennials, pp. 71, 74). And it happens even with quite large plants — such as the AGAVE (fig. 14) which is planted so much as fencing along railway lines : and with even the giant Talipot Palm, one of the largest of all Palms, which may grow on for thirty, fifty, or even a hundred years, and attain a height of a hundred feet, with a stem a couple of feet thick. For when at last a branched flowering axis is shot up and has ripened its hundreds and thousands of seeds, the whole gigantic palm dies, and rapidly decays (multiennials, p. 74). That with the common AGAVE death is due to the effort of providing for the next generation is recognized in the common practice of cutting down the flowering shoots, whose truncated and bent stems are a familiar sight along our Indian railway lines. It is for a similar reason that grass cut -for hay is much more nutritious just before or * at the time of flowering than after the seed has ripened. For the flowering stems are then full of sugar and other food- material passing up from the underground parts to the seed. Later on they are little more than woody stalks, and the seeds which contain the food-material soon drop off and are lost. For the same reason the worst time for moving bulbs and tubers is just at flowering time, or after, for they are then at their weakest, having given up their sugar or other food substance to feed the seeds. 13. Reviewing all these plants whose germination we have been studying, we see that they fall naturally 68 GENERAL BOTANY into two groups, those which have one cotyledon and those which have two. And the plants of these two groups differ in many other respects too, for, when full-grown, Beans, Melons and Castors have a well-branched shoot and broad flat leaves with veins that branch in all directions, and leaf-stalks which stand out more or less at right angles to the axis, so that the blades face the light. The stems of Paddy and Wheat or Maize on the other hand are not branched, except quite close to the ground, and their leaves are long and narrow, with parallel veins and no petioles. The Onion has no stem at all above ground, except for the flowers, all the leaves springing directly from the short bulbous stem. The Coco-nut and Palmyra and palms in general certainly have a stem, but this practically never branches, and their large flat leaves are not a bit like those of our ordinary trees. We see then that the difference in the cotyledons accompanies differences of the shoot and leaves and in fact in the general character of the mature plants ; and for this reason all ordinary flowering plants have been divided into two great classes distinguished as monocotyledons and dicotyledons. I. The DICOTYLEDONS have two cotyledons, and include all our trees (other than Palms), ordinary shrubs (but not Bamboos) and nearly all broad-leaved flowering plants, except Caladiums, Arums, and Yams (DIOSCOREA). II. The MONOCOTYLEDONS have but one coty- ledon, and include all our cereal plants (Maize, Paddy, Wheat, Cholam and Grasses), in all of which, the cotyledon is specially modified as the scutellum, Lilies, MONOCOTS AND DICOTS 69 FIG. 15 A FIR MONOPODIAL GROWTH AND VERY REGULAR BRANCHING CRINUM, Onion and nearly all bulbous and narrow- leaved plants together with the Palms, and a few with broad leaves, as the Yams and Arums. There is, as a matter of fact, a third group of quasi -flowering plants, with which however we are not concerned in this book. Their seeds are borne on the out- side of special scales, not inside a pod, and for this reason they are known as GYMNOSPERMS. On the plains of India there are very few examples of this group, the common Cycad (CYCAS ClRCiNALis) being about the only one ; on the hills there are a few others, but for the most part planted by Europeans, and not wild, such as the Pines and Firs (fig. 15). In colder, climates this group is of much greater impor- tance than it is with us. CHAPTER VI THE DIFFERENT TYPES OF PLANTS THE functions which we studied in chapter iii are concerned directly with the life of the plant it- self, and are termed vegetative functions. But we learnt that there is another work that a plant — together with every kind of living thing — must do, and that is to reproduce its own kind. The ordi- nary mode of reproduction is by seeds, and these are produced only in the flowers. So that while the roots and leaves are concerned with the vege- tative functions, the reproductive functions belong properly to the flowers. The proper performance of the vegetative functions benefits the individual plant itself : the more water and mineral salts the roots can absorb, the more light and air the leaves can obtain, the more food-material will be made and the larger and stronger will the plant become, so that it will be the less likely to be damaged by grazing animals or hurt by the hot, dry winds of summer. The production and scattering of the seeds are of no benefit whatever to the plant itself — they are on the contrary a tax, for the more seeds are ANNUALS 71 produced the more of its substance is scattered and lost to the individual. It is on the other hand the race as a whole which is benefited, for obviously the larger the number of seeds, and the stronger the young plants produced each year, the more rapidly will the race increase in numbers and spread over new land. We must think, therefore, of every plant as being engaged in two great kinds of work. One, to make itself as strong as possible, and protect itself from any injury, and the other to produce as many and as healthy new plants as possible, to carry on the next generation. These two functions are to a great extent antagonistic ; for instance, it requires time for a tree to grow large, so that its leaves are well out of reach of every grazing animal and its roots deep enough down to get water even in hot weather. And while it is merely growing, a smaller plant may have matured and shed thousands of seeds, which growing up quickly multiply again in their turn, and thus • that race of plants may become far more numerous and more widely spread than that of the tree. Every plant then in striving to carry on these two works to the best of its power under the peculiar circumstances in which it is placed, has to make some sort of compromise between them — and thus it is that we get so many different kinds and sizes of plants. Some take only a few weeks or a month to grow up from seed, produce flowers and scatter their seeds. Plants which do this between one growing season and the next are termed annuals. Naturally they have 72 GENERAL BOTANY no time to make strong woody shoots and are almost always small plants, such as the ordinary food grains, Paddy, Cholam, Wheat, and Barley, Tobacco and the many ^flowering annuals, that are sown every cold season in our gardens. Others live on for many years and produce seeds every year, though usually not in their first season* These are termed perennials. There are several kinds of perennial plants. First are. those which have a thick main axis (stem) and a crown of large leaves. This is the Palm type — too well known in the tropics to need description. Not only Palms but Cycads and Tree-ferns are of this character. Then there are what we ordinarily call trees — woody plants with a thick stem that divides or branches at a certain height above the ground, and bear a very great number of much smaller leaves — such as the Mango, Banyan, and Teak. Those which have no main stem, but several woody stems springing from the ground, like the Bamboo, Ixora, Pomegranate, Rose are termed shrubs. In some of these the stems are weak, and support themselves by straggling over other plants, as ZIZYPHUS, LANTANA, RUBUS. These pass gradually into the fourth group of plants, which like the Vine, BOUGAINVILLAEA BAUHINIA, THUNBERGIA, the Pea and others climb up the trunks of trees, or the surface of rocks, supporting themselves by thorns, clinging roots or special clasping organs called tendrils. This we may call the vine or liane or climbing group. A fifth group of perennial plants consists of those which have no woody parts, but are on the contrary PERENNIALS 73 very soft and juicy, like the Prickly-pear. These are termed succulents, and usually have green stems and no leaves, like OPUNTIA the Prickly-pear, or if there are leaves they are very thick and fleshy, as in BRYOPHYLLUM and KALANCHOE. Then there is a sixth group, which have a soft green leafy part above ground, that dies down like an annual each year, while the part below in the ground lives on. Common instances of this are the Ginger plant, Canna and Lily. These are perennial herbs. Of these six groups, all except the last live on practically unchanged through the year, being able to stand the heat and dryness of summer in the tropics, or the cold of winter in the cooler parts of the world, either because all the parts above ground except the leaves are hard and woody (as in the Palms, Trees and Shrubs), or because they contain quantities of water stored up in their tissues (as the succulents), this water being used up gradually during the hot months, or because they drop their leaves in the dry season. Look at a Prickly-pear, and see how soft and watery it is at the end of the wet season ; and look at it again after the dry months and see how thin and shrunken it looks. The difference in appearance is entirely due to the loss of the stored up water which has taken place during the dry months. The sixth group has no woody or succulent parts, but the perennial part, being underground, is not likely to become too dry. This usually contains a good deal of food material with which to build the new shoot at the beginning of each year, and for this reason is 74 GENERAL BOTANY often a very useful article of food, as the COLOCASIA and ONION. In colder countries where there is much more differ- ence between the seasons, and where during one part of the year active life ceases, not because of dryness but because of the cold which prevents roots taking up water, there are plants which live only two years,, and spend the first season in purely vegetative work, making large quantities of food and storing it for use during the second season, which is devoted to the pro- duction of flower-seeds, that is, to reproductive work. These are termed biennials, and most of them have rather thick underground parts in which food- material made during the first season is stored for making the seeds the second year. For this reason many of them, like the sixth group of perennials,, are valuable food plants, and some, as the Carrot, Radish, Turnip, are grown in this country. Then again there are those referred to in the last chapter (section 12) which live for many years, but flower only once and die soon after the seeds have fallen. These may be called multiennials. They have mostly stems of a palm nature, as the Talipot-palm (CORYPHA), or the so-called Aloe (AGAVE). Looking at plants from the point of view of the length of their lives, we class them as annuals, biennials,, multiennials and perennials ; looking at them from the point of view of their nature and substance, we may classify them as : — (l) herbaceous, when they are soft and not woody, for example, the ordinary field and garden annuals and some perennials. BIENNIALS AND MULTIENNIALS 75 (2) succulent, when they contain much water, and (3) woody, when hard like shrubs and trees, Palms, and most vines. It must not, however, be supposed that these classes are divided sharply one from another. It is some- times difficult to know whether to call a plant a small tree or a shrub; and in hot countries like India, herbs will often become woody towards the beginning of the hot weather. But generally speaking herbs are small plants, less than the height of a man. MUSA, the common Plantain or Banana, is larger, but it is by far the largest of all herbs. Shrubs seldom run up above twenty feet, only some very large Bamboos attaining the height of an ordinary tree. CHAPTER VII GROWTH 1. The study of the mode of growth of plants is so closely dependent on that of their internal structure (another branch of Botany called HISTO- LOGY with which this book does not deal), that we cannot go fully into it ; but there are a few main facts that can be made out without much difficulty. If you watch from day to day the ends of the branches of any tree or bush that is putting out new leaves, you will see that they increase in length by the growth of the internodes of the bud, new pieces being literally added on in this way one after the other. To prove that this is the only way in which a branch increases in length and that the other parts do not themselves become longer, we have only to take any quickly growing branch or stem and mark on it thin black lines with India ink at equal distances, say one-eighth inch apart. In a day or two those on the youngest internode will be much further apart, showing that it has really lengthened as a whole. The next internode may also show slight signs of growth, but after two or three days the marks remain exactly the GROWTH IN LENGTH 77 same distance apart, and will do so however long the observations are continued. There are some trees (see section 3) on the surface of which the leaf-scars persist for many years, and we may, by direct comparison of the old stems and young branches, see that the leaf- scars are on the whole the same distance apart, and therefore that there has been no longitudinal growth. This is an observation which you should not fail to make for it is quite easy, and it is a clear proof of a very important principle that a tree does not grow, as is sometimes supposed, by a general lengthening of the trunk and branches, nor by being pushed up out of the ground from the roots, but only by the addition of new pieces to the ends of the stem and branches above. So that if a branch meets the stem at a height, say of ten feet from the ground one year, it will be at the same level the next year, and the next, and for a hundred years if it lasts so long. It is only the height of a tree as a whole that increases each year, and it does so as a rule till death or accident puts a stop to further growth. This mode of growth constitutes an important point of difference between animals and plants, for animals grow by enlargement of every part and organ, not by addition to the ends of the trunk and limbs. 2. Again, the branch or stem of an ordinary tree consists of a hard woody core surrounded by a tough bark, which is soft or hard and stringy on its inside, and often rough and broken towards the exterior. These two parts, the woody core and the surrounding bark are entirely different in nature. Wood never turns into bark, rior does bark turn into wood ; and 78 GENERAL BOTANY they can be readily separated when in active growth because between them is a very thin layer of delicate tissue which is easily ruptured. This layer is called the cambium, an'd by its growth and development woody tissue is added to the core, and soft or stringy fibrous- tissue to the bark. So that the core grows centrifugally by the addition of new layers of wood to the outside, and the bark centripetally by new layers on its inner side. Now it is only through small tubes in the young- est parts of the wood and the bark that sap passes up from the roots and down from the leaves, the middle of the core being useless for this purpose. At the beginning of the hot weather, when the buds are opening out and growth is rapid, the new tubes of wood that are formed are larger than later on in the year when growth is slower ; and by the regular alternation of the wet and dry seasons year after year, there are formed alternating zones of more and of less compact and hard tissue. This is why, when the trunk or branch of a tree is cut across, a number of concentric rings can generally be seen. In countries where the difference between the seasons is more marked thari in the tropics, these rings are always very distinct and show by their number the exact age of the part ; for each ring corresponds to a winter or a summer, and indicates one year's growth. This is also the cause of the * grain ' of timber — those lines and markings which can be seen on nearly all wood. By feeling with a knife one can at once tell which are the hard winter or dry weather and late GROWTH IN THICKNESS 79 summer layers, and which the softer spring or wet weather growths. This growth in thickness by means of the cambium layer takes place only in dicotyledons. Monocotyledons do not increase at all (except in one or two genera and then by a different method) for they have no cambium, and in consequence also no bark. Com- pare, for instance, a Palm with a Rain-tree (PITHECOLOBIUM SAM AN), or Indian Cork (MILLING- TONIA), or any ordi- nary tree. The latter have a bark that can be easily stripped off the younger branches, but there is none on the Palm, its substance is of the same nature right through, though harder towards the circum- To show how such a tree grows in ference being merely thickness at or near the surface, not by j ,1 , . , . , y covered on the outside expansion from the middle. _, . , by the bases of the The wire has not bitten into the tree, but the tree has grown round the wire. leaves that have fallen. FIG. 16 TRUNK OF A TREE, ACACIA MELANOXYLON, WHICH HAS BEEN USED AS A POST FOR TYING THE WIRE OF A RAILING 80 GENERAL BOTANY Now one may often see a plant twining round the stem of a tree, and looking as if it had cut into the bark. This is because the tree has gone on growing in thickness except where actually prevented by the coils. But you never see this on a Palm. For in- stance one sometimes sees a FICUS or Banyan growing on a Palmyra and sending its roots round the stem, having started from seed left by some bird in he axil of an old leaf-base. But it never has the appearance of cutting into the palm, simply because the latter has not increased at all in thickness. It is probably because of their inability to grow in thickness that, with the exception of Palms, all mono- cotyledons are comparatively small plants, and do not have branches except near the ground. Even Palms, tall as they may be, have comparatively thin stems, and are very rarely branched. Formerly it was supposed that Palms and other monocotyledons did grow a little in thickness by the addition of new woody matter inside the old, and they were therefore called Endogens (or inside growers) while dicotyledons were called Exogens (outside growers). These names, though still used by some people, and in old botany books, have now no scientific value. Dicotyledons on the other hand may attain almost any thickness. There used to be a Chestnut-tree on Mount Etna, 180 feet in circumference ; and BOMBAX MALABARICUM, the silk-cotton tree, has been known to attain an even greater thickness, and another very thick tree the Baobab (ADANSONIA DIGITATA) is often found in gardens, with trunks ten feet or more thick. PHELLOGEN AND CORK 81 All these started life as seedling plants, thinner than a lead-pencil. 3. Now consider bark more closely. On some trees, as species of FICUS (Banyan, Peepul, etc.), the bark is smooth, and being thin, quite a small cut will reach the cambium and young wood layers. But in most trees the bark is thick, and cracked on the outside, and if one cuts it with a knife there is no water or sap : it is quite dry and dead. The drying up of the outer parts is due to the formation of a special waterproof substance called cork. This is formed by a layer called the phellogen which grows like the cambium but produces cork on its outside. Cork, being almost impervious to air and water, prevents loss of sap by evaporation from the surface, and it also cuts off the outer tissues from the sap, so that they dry up and die. If the phellogen occurs only just underneath the epidermis and forms but little cork on its outer side, the bark may remain smooth, as in FICUS. But when, as more usually happens the phellogen occurs deeper in, nearer the wood, there is much more bark tissue outside it. And since this bark, being dead, cannot grow or expand as the tree increases in thickness, the pressure of the growing wood from within causes it to split open in longitudinal cracks. This is the cause of the familiar rough appearance of bark ; and different kinds of trees differ in the roughness of their bark according to the difference in the depth of the phellogen below the surface and the amount of bark which is formed. In some trees, e.g. MILLINGTONIA (the Indian cork-tree) and in the ordinary Spanish Cork-Oak, the 6 82 GENERAL BOTANY cork, in the course of a few years, may become two or three inches thick, or even more, and it can then .be cut off, and made into corks for bottles, etc. Just as layers of hard and of softer wood are formed in different seasons of the year, so, too, layers of hard and soft tissue are formed in the cork. These can nearly always be seen in any bottle-cork — the softer broader part is formed in the spring months, March, April, May, and the other later on in the year. It is the waterproof and yielding, yet firm nature of cork, that renders it so useful for keeping liquids in bottles, etc. ; and it is precisely those same charac- teristics that make it so useful to the tree. For it prevents loss of sap by evaporation from the surface of the tree, and the dead tissue outside offers no attraction to animals to nibble at the trunks. In FICUS (Banyan, Peepul, etc.) and some other trees the cork and bark are very thin and can easily be bitten through ; but the sticky and poisonous milky juice contained in these trees prevents animals to a certain extent from doing much damage. Again in many trees a second layer of phellogen is formed deeper in the wood, and by forming cork cuts off the sap from the original phellogen, which therefore dies. When this happens the outer part, from the first layer of phellogen outwards, generally comes off, it may be in flakes as in STEPHIGYNE, PINUS (Pine) and PLATANUS, the Plane-tree, or in long pieces as in the EUCALYPTUS, or in almost complete cylinders as in the Cherry-tree and Birch. On the young branches of very many shrubs and trees there are often to be seen little brown or BARK 83 yellowish pustules or openings in the outer skin. These are called lenticels and consist of very loosely arranged tissue, through which air and water-vapour can pass in or out. They are formed underneath the stomas when, owing to the formation of cork the latter are cut off, and die along with the epidermis ; and to a certain extent they take their place, allow- ing the carbon-dioxide respired by the living tissues close by to escape. But they differ from stomas in that they do not open and shut, and therefore do not in any way control the amount of air and water- vapour passing through. Later on, when the bark is more fully formed and its outer layers become dry and peel off, the lenticels of course are destroyed too, and there appear to be then no regular passages for the interchange of air. In a few trees the epidermis persists for a long time and when the bark is formed it is thin and does not fall away. In consequence the leaf-scars remain visible even when the branch or trunk is a foot thick. This occurs in FICUS RELIGIOSA, the Peepul, ACACIA MELANOXYLON, the Black wattle, PLUMERIA ACUTIFOLIA, the Pagoda tree, INGA DULCE, the Koru- kapuli, and others. We can see the leaf -scars on quite old trunks or branches, extending,' it may be, six inches or even a couple of feet in length across the surface. This is because the outer layers have not died but have lived and grown with the growth of the part, and so the scar has extended with them. It is instructive to note that while leaf-scars and bud-scars are pulled out side- ways by the natural stretching of the bark as the trunk or branch grows in thickness, as stated above, 84 GENERAL BOTANY no change takes place in their vertical distance one from another on any of these trees. 4. Cork is formed not only in the bark of trees and shrubs, but also across the stalks of the leaves, at the base where they join on to the branch. When it has formed completely across, the leaf necessarily dies and falls, breaking off at the corky layer. So that the wound or scar so made is covered at once by the cork, and loss of water from the exposed surface is prevented. This is why leaves fall off so cleanly with their stalks, and do not leave a ragged broken stem. Palms, on the other hand, do not form cork (just as they do not increase in thickness) and so when the leaf dies it breaks and leaves a ragged, untidy leaf -base still on the stem. It is only later on that the leaf-base becomes detached and leaves the stem clean. Cork is also formed wherever soft living tissue is exposed by a wound. If a leaf be cut a thin brown layer forms and prevents loss of water from the cut surface. The same happens with fruits and tubers. If a potato is cut, cork forms over the cut surface ; and if it be pricked with a needle a cylindrical layer forms round the wound and prevents loss of water. The great difference that even a vrery thin layer of cork makes can be seen very easily in this way. Take two young potatoes, the smaller the better, as nearly as possible the same size. Weigh them, and weigh again in a day or two. Provided that the skin is unbroken very little difference will be found in their weights. But remove the skin from one ; weigh it, and VALUE OF CORK 85 weigh both again the next day, and the next. The peeled potato loses weight at once, and will shrink very much in size. In an experiment made in this way the two potatoes each weighed f tola. One was peeled, and in two days (in a cool place) it had lost \ tola ; and in another two days had decreased by yet another J tola ; while the difference in the other was hardly visible. Three days later the peeled potato weighed scarcely an eighth of a tola and had shrunk to less than a quar- ter of its original size, while the other was hardly, if at all, different. 5. By the formation of cork and bark from the cambium, plants are able to heal over wounds caused by the breaking of branches by wind or animals. Thus it is that neat rounded lumps grow where branches have been cut off close to the stem. But if a portion of the branch is left, so that the exposed sur- face is not close enough to the main axis to be well supplied with sap, the phellogen gets dry and dies, and very soon the core of the branch, exposed as it is to rain and attacks of insects and fungi, be- comes rotten and hollow. In time the rot may extend into the trunk of the tree till at last the whole is destroyed, or the weakened trunk breaks across in a high wind. Many a tree has died for no other reason than that a branch had been broken off carelessly, so that the phellogen could not form and cover the wound, instead of being cut off as close as possible to the stem to allow the natural healing to take place. 6. In section 2 we learnt that one great difference between monocotyledons and dicotyledons is that the 86 GENERAL BOTANY stem (and the roots too) of the former do not increase in thickness, and have no true bark as in the latter. But we can easily learn more than this. If we examine the stem of any small monocotyledon, e.g. Cholam, Wheat, Paddy or a Lily, more closely, we find that it is composed of numerous strands of fairly tough material imbedded in a much softer ground-tissue, which can easily be torn apart with the fingers to separate the strands. This is quite different from the stem of a dicotyledon, where (except in a very few cases) there is a solid cylinder of wood. These strands run into the leaves and there form the veins. Those nearer the surface are closer together, and form a hard casing, but not a true bark. These strands are called vascular bundles and are composed of six main kinds of elements : — (1) Continuous tubes with fairly thick walls, in which there are thinner places (pits, not holes). These are called vessels, and it is through them mainly that water passes up from the roots to the leaves. (2) Shorter closed tubes with pointed ends and much the same kind of walls. These are called tracheids, and share in the conduction of water up the plant. (3) Long thin elements, like tracheids, but with excessively thick walls so that there is little or no space inside ; these are fibres, and their function is to add strength to the vascular bundle, and the plant generally., They usually form a sheath round the bundle and in old decaying stems of Palms one can see the black fibrous, sheaths, often after the insides have decayed away. Individually the fibres are really short (seldom more than one-eighth inch) but they often form strong strands VASCULAR BUNDLES 87 which are of great use, e.g. those in the leaves of the AGAVE make * Aloe-fibre '. (4) Long soft tubes, not continuous, but connected end to end through small holes in the terminal walls, which look like the holes in the rose of a watering can or a sieve. For this reason these are called sieve-tubes, and it is along them that the food-stuffs manufactured in the leaves, pass to the other parts of the shoot and roots. (5) Narrower closed tubes of the same length, with pointed ends. They accompany the sieve-tubes and are therefore called companion-cells. (6) Short elements, more or less cubical in shape, like the material of the ground-tissue between the bundles, and called parenchyma. The vessels, tracheids, fibres, and some of the parenchyma are made of the specially hardened kind of cellulose, we call wood ; the sieve-tubes, companion- cells and most of the parenchyma, of unaltered cellulose. These six main classes of elements, individually too- small as a rule to be seen except through a microscope* make up the vascular bundle, the sieve-tubes and com- panion-cells, collectively called the phloem, being always on the side nearer the outer surface of the stem, or the lower of the leaf, the vessels and tracheids on the inner, or the upper side in tne case of a leaf. Separate bundles can also be seen in a very few dicotyledons, e.g. the Pepper, and ARISTOLOCHIA (in the latter the vessels are so large that they can be easily made out with the naked eye), and as a matter of fact in all when quite young. But not in older stems and roots, for in a very short time, generally before 88 GENERAL BOTANY the plant is a month old, the vessels and tracheids are separated from the sieve-tubes and companion- cells (phloem) by the cambium, which forming as we have learnt, fresh wood (vessels, tracheids, fibres and some parenchyma), on its inside, and fresh phloem (sieve-tubes and companion-cells), with some fibre and parenchyma, on its outer, makes the hard central cylinder of wood, and the outer covering of bark. Thus we see that there is a fundamental difference in structure between the stem or root of a monocotyledon and that of a dicotyledon. The former is composed mainly of vascular bundles which have run down from the leaves, those from the higher ones joining others lower down, the latter of a secondary tissue, the cambium-formed woody cylinder and bark, to which the leaf bundles are attached, the wood to the wood, the phloem to the phloem. CHAPTER VIII BRANCHING 1. We learnt in chapter ii that branches of the shoot arise by development of buds, which are as a rule in the a^ils of leaves, so that their arrangement depends in the first instance on that of the leaves. But even in a young seedling plant only a few of the buds grow out into branches, there would indeed hardly be room for them all to develop. As the plant grows older and taller, the lower leaves and branches are shaded by the upper, and being as we learnt in chapter iii dependent on light to enable them to get food from the air, are starved and very soon die and drop off. If the plant grows to become a tree, hundreds of little twigs and leaves are thus killed off from the lower parts and hundreds of buds never develop at all, and so it comes about that the stem is not branched close to the ground, and neither it nor the larger branches have leaves. Only towards the outside where there is plenty of light and air, do we find small twigs and leaves. This is well seen in PITHECOLOBIUM SAMAN, the Rain tree, which is so frequently planted by the 90 GENERAL BOTANY roadside. A young tree has branches and leaves close to the ground. The branches of an old tree are entirely destitute of leaves except at their ends,, and there is thus formed a hollow crown of foliage supported by the branches, like an umbrella by its frame. The same is true of the Banyan, Mango and indeed all trees, though in some the outer leaves make so little shade that a few others can grow on the inner branches as well (see fig. 20, p. 102). But, besides all this, many kinds of trees have their own peculiar shape by which they can be recognized even at a distance. This is due to, among other things, the angle at which the branches leave the main axis. In PITHECOLOBIUM, the Rain tree, they slope steeply upwards, at an angle of about 50° to the vertical. The secondary branches leave them again on the lower side at a similar angle, and there is thus formed a regular hemispherical crown. The large branches of CASUARINA again are much more upright, while the small ones bring their bend down again, giving to the tree its peculiar drooping graceful appearance. Those of the Banyan grow almost horizontally, and when supported by their pillar- roots, spread very widely. But the shape depends also very much on the tree's immediate surroundings. If it is in the open, and not shaded by other trees or by buildings, it grows freely and to its natural shape. But when it is with other trees, the shape may be quite different. Branches that are shaded and cannot get sufficient light, are on that ac- count robbed of their due supply of sap by the more favoured shoots and therefore wither and fall off, while SHAPES OF TREES 91 the main stem grows taller and thinner. For this reason when trees are planted for the sake of their timber, they are put fairly close together. The stem then grows very straight upwards, and there being no large branches the ' grain ' of the wood is straight and free of knots. But if the tree is grown for the sake of its fruit, it must have plenty of room to branch side- ways, and not be made to suffer from overcrowding. A tree that is on the edge of a wood, with one side shaded by other trees and the other in the open air, grows outward all the more widely, because on the side towards the other tree its branches die off, and there is then more sap for the others. It becomes therefore very much one-sided. It is for this reason that trees grown for shade by a roadside should be fairly close together. They then do not grow much towards each other, and more water and sap is available for the branches that grow across the road, and these therefore grow the more quickly. 2. When we come to look at the branching more closely and in detail, we find there considerable dif- ferences in the way in which the smaller branches arise. When the leaves are alternate, the branches are naturally alternate too, and when they are opposite, one would expect to find the branches also opposite. Modifications of these two fundamental arrangements are however caused by the development of some and suppression of other buds. The simplest arrangement is when the main axis continues to grow more strongly than any of the side branches, these latter arising occasionally, and being 92 GENERAL BOTANY alternate, opposite, or whorled, as are the leaves. Growth of this kind is termed monopodial, or a monopodium and is the usual arrangement in herbs and young trees. In Pines and Firs the branching is always of this type, the terminal bud, unless destroyed by accident, continuing to grow strongly throughout the life of the tree. The branches are whorled and arise from leaf- axils near the growing end, and so are progressively older and longer from the top to the ground. The whole tree is in consequence very regular in shape, and has the appearance of a cone (fig. 15, p. 69). But in most of our ordinary trees the terminal bud of the main stem or branch dies at the end of the growing reason, or gives rise to flowers, so that the lengthening of the axis in that direction is stopped. Growth is then continued by a lateral branch stretching out on one side, or, if the leaves are opposite, by two branches, so that the original axis appears to be divided into two. In either case the direction of growth is now no longer the same, and it is for this reason that our ordinary trees spread out horizontally and have a more or less rounded appearance so very different from the sharp conical shape of the Fir. The third type of branching is a further develop- ment of the second. The terminal bud dies regularly after one or two leaves have been formed, and its place is taken by the lateral bud standing nearest to it. This becomes a branch, which, pushing aside the now dead terminal bud, continues growing in the original direction. SYSTEMS OF BRANCHING 93 terminal bud of this season's growth, now dead bud for the commg seasor in axil of a leaf -scar. scars of bud of present season, terminal bud of last season — dead. terminal bud of last season butane dead — scars of bud of last seasc FIG. 17 TWIG OF AN ORDINARY TREE OR SHRUB Showing leaf and bud scars, and annual sympodial growth. The whole then appears exactly like one straight axis, but the presence of a leaf-scar on one side with- out its axillary bud, and of a dead bud on the other side without any subtending leaf, show what it is» This method of growth is called sympodial, and the resulting axis a sympodium. It is very common in 94 GENERAL BOTANY underground root-stocks, e.g. of grasses, and plants of the Ginger and Canna kind, the horizontal stems of many orchids, and the Vine. Examine a piece of Vine stem or of CISSUS. The leaves are alternate and some of them, but not all, have tendrils opposite to them. There are generally two leaves with tendrils opposite them, then one with- out, two again with tendrils and one without ; though this is not invariably the arrangement. Those leaves which have a tendril opposite them have no buds in their axils, or if there be a bud it is very small and has arisen as an extra one. If we apply the rule that branches arise only in the axils of leaves, and that every leaf has its axil- lary bud, it follows that the tendril is really the continuation of the axis immediately below it, and has been pushed to one side by the branch which arises in the axil of the leaf opposite, and then grows straight on as if it were a continuation of the original axis. If there is a second leaf, that leaf has of course its axillary bud. At the next node, the shoot again becomes a tendril, and is in its turn pushed to one side by an axillary branch. This is a typical sym- podial arrangement. 3. It often happens that a bud which, because it is shaded or for some other reason, does not get its due supply of sap and does not grow out into a branch, yet remains alive, and may develop after many years if stimulated to do so by the destruc- tion of other branches. It grows slowly, so as • to remain at the surface of the axis as it increases in thickness. BUDS 95 FIG. 18 CAPPARIS HORRIDA To such dormant buds are due the branches which often spring from the sides of a tree when the upper branches have been cut. Again totally new branches will often arise from the exposed end of a tree-stump that has been cut down. They are formed de novo from the growing tissue, and are termed adventitious buds. The Neem and Divi-divi trees sprout out very readily in this way, so does the EUCALYPTUS as can be seen in any 96 GENERAL BOTANY plantation on the hills. In some plants adventitious buds also occur on the roots, and develop into new stems. The suckers of the Wattle are of this character. This occurs very frequently in the case of the ordinary coffee tree. When the terminal bud has been broken off, to prevent the tree growing too high, n£w branches developing from buds just below the next branches, grow vertically up to take its place. But we may often find more than one bud in the axil of a leaf. This is very frequently the case with plants that climb by means of tendrils. One bud grows out as a tendril, the other may develop into an ordinary branch, as in the common ANTIGONON LEPTOPUS that is grown so much in South Indian gardens. In the axils of the leaves of CAPPARIS HORRIDA again (fig. 18), there are generally three or four flowers on separate pedicels, each from a separate bud. Here the buds are superposed one above the other, in other cases they are lateral, side by side. Ordinarily only one develops into a branch or flower as in BERBERIS the Barberry, where there are three buds, while in ZANTHOXYLUM there may be as many as eight or nine buds in each leaf axil. These extra or accessory buds may at first sight appear to be superfluous, but their use is that when a normal branch is destroyed by accident or by being eaten by animals, there may be another branch developing from one of the other buds to take its place. CHAPTER IX FACTORS INFLUENCING GROWTH 1. The stems of all trees and of most shrubs grow vertically, straight up out of the ground, while the main root grows in exactly the opposite direction, downwards. This upward tendency of stems and downward tendency of roots is apparent at the very beginning of the plant's life when it emerges from the seed. For, put seeds of Bean or Marrow in all positions in soft earth, and examine them when the first signs of germination appear. The radicle, you will find, is in every case bent downward, and the shoot, though it may be curved at first while passing through the earth, stands straight upright when it is free. And again take seeds which have begun to germinate and have half an inch or so of radicle exposed, and put them in various positions, covering them with light soil or moss or sawdust ; then look at them again after a couple of days. You will find that in every case the end of the radicle is bent downwards, and the shoot upwards. We may see the same thing in older plants of all kinds. The Palmyra- Date and Coco-nut palms are 7 98 GENERAL BOTANY FIG. 19 PHOTOGRAPHED AFTER 12 HOURS Growing end of a COLEUS after it has been fixed horizontally and marked to show the region of growth. constantly to be met with, curving at the base for some reason or other, but growing straight up afterwards. Branches of trees and shrubs that have been forcibly bent down or half broken often bend up at their ends. Observe that it is only the ends which turn up ; and actual proof of this fact can be shown quite easily. Take a quickly-growing annual plant, almost any one will do, so long as it is one which naturally grows up- wards ; cut the leaves off, and with India ink mark, on the internodes at the tip of the shoot, fine lines at equal distances apart, say i in. or J in., according to the size of the plant. Then place it horizontally against a piece of board, on which you may mark its position^ either keeping it in its pot, or with its end in a corked tube of water to keep it alive. Cover it with something to keep off any light, and prevent REGIONS OF GROWTH 99 its being touched, and leave for the night; By morning the end will have turned upwards, and you will find by looking at the marks that it is only the youngest parts, those internodes which are still in the process of lengthening, that bend ; the older parts that have finished growth do not move. If you have another plant treated in the same way but standing vertically, you will find that the lines on the lower side of the curved end of the horizontal plant are further apart than those in a similar position on the upright plant ; which shows that the lower side of the horizontal plant is somehow stimulated to grow a little faster than it would otherwise have done. This experiment is a very easy one and should be made without fail. You may do the same with the root. The best way is to take a large seed, such as the Broad-bean, and, after it has begun to germinate, and the radicle is about 1 inch long, to mark it in the same way with very thin lines at equal distances of TF inch and then fix the seed by a strong pin with the root horizontal, on the under side of the cork of a wide-mouthed bottle. Put a little water in the bottle to keep the air moist, and cover all over to keep out the light. In a few hours the tip will have begun to bend downwards and will go on growing downwards. You may turn the bottle round, so that the tip of the root is again horizontal, and it will again bend downwards. No matter how often you repeat the experiment you will find that it is only that part which, as shown by the marks, is growing longer that bends down — the older parts which have ceased to grow are incapable of bending. 100 GENERAL BOTANY These experiments with stem and root show that there is in these organs a power of discerning the direction of the vertical. It is not its weight that makes the root bend downwards, for it will do so even in mercury, on which it would easily float, but there is a sense of direction in these organs akin to that by which we ourselves are able to stand upright even on a steeply-sloping hillside and is not anything of the nature of instinct but is due to the action of gravity on something inside the plant. In the case of roots, this sense is in the extreme tip only, for if the experiment described above be repeated, but with the last yV of the root cut off there will be no bending. The downward tendency of roots is termed geo- tropism, and the upward tendency of stems apo- geotropism. These tendencies are usually only noticeable in the main portion of the stem or root, being suppressed and apparently absent in the side branches. The branches from the main root are, in fact, fairly hori- zontal, as you will see if you grow a Broad-bean with its roots in water (and covered up from the light) ; and in them the tendency is rather to lie across the vertical. This is called dia-geotropism. In many trees the branches slope upwards, but in some they are almost horizontal, being, like the secondary roots, diageotropic. 2. Light has also a great influence on the position of the shoot-axis. Take any small actively growing plant that has a fairly straight vertical stem, and put it in a box open on one side but covered in above, so GRAVITY AND LIGHT .10.1 that light can get to it only from one direction. In a day or so the shoot will have bent round towards the light, and again as in the experiment with the stem laid horizontally, it is only the young growing part that bends. This curving is called heliotropism, and an organ which bends towards the light is said to be heliotropic. The stalks of the leaves also bend till the blades face the light, at right angles to its direction, and with the upper side towards it. The blades of leaves may in the same way be said to be dia-heliotropic. These two actions take place very commonly in nature. We may see examples of it in any garden, in any clump of trees, wherever in fact a plant is shaded on one side. Most roots, on the other hand, bend away from the light, as can be seen quite easily by repeating the experiment with the germinated bean fixed to a cork, but with black paper pasted more than half way round the bottle, so that light enters only from one side. Roots are therefore said to be ap-heliotropic. This apheliotropism of roots is less commonly seen in nature than the heliotropism or the apogeotropism of stems, because, of course, roots are mostly under- ground. But it can often be seen in the hanging roots of the Banyan, which curve a little towards a less lighted side, generally that on which is the trunk. But as in the other case, so in this, there are a few exceptions, to which we shall have to refer later on. 3. Roots are affected also by moisture, towards which they will always make their way, growing into the dampest places in the soil. So that, if, when a plant is watered, the water is only poured just near 102 GENERAL BOTANY FIG. 20 AN ACACIA MELANOXYLON Showing how the smaller branches run outwards at right angles to the general surface, i.e. towards the light. This tree had another one growing in front of it, and too close to allow of branching in this direction, and by its removal the arrangement of the branches has been well exposed. MOISTURE 103 the stem, as is so often done in gardens, instead of over a wide area, the roots will • concentrate them- selves there, and in consequence have but a small volume of soil from which to draw both their mineral food-material and water; and if the latter fails, the plant will suffer. Whereas, if the water is poured in a wide circle round the plant, the roots are induced to spread out widely, thus having a much larger volume of soil from which to draw their food and water, and are in consequence less liable to be killed by drought. In nature this is provided for by the outward sloping of most leaves, so that rain drips off them some little distance from the main stem. With a shady tree, whose almost rain-proof crown of foliage is highest in the middle and slopes towards the sides, this is even more the case, for the water drips from leaf to leaf till it drops to the ground in a wide circle. This is why though near the trunk there is shelter, towards the sides the drops are heavier than in the open and the ground underneath wetter. It is here that the youngest roots are in consequence concentrated, and, since they alone possess root-hairs, it is here that the chief absorption takes place. As the branches grow and extend the crown wider, the circle of wetness is widened too, and with it the rootlets invade new ground. Exactly the opposite is how- ever the case with some plants, especially certain monocotyledons, such as ALOCASSIA, CANNA and the Traveller's palm (p. 398), whose leaves slope to- wards the centre and are channelled so that rain water is directed inwards. This hydrotropism of roots is responsible also for the invasion of well watered 104 GENERAL BOTANY pots and beds by the roots of neighbouring trees (see p. 124.) 4. We learnt in chapter iii that, like every other living part, roots respire and give out carbon-dioxide. This gas must be got rid of because too much of it is injurious to living tissues, and it has been proved that a root will grow away from a region rich in carbon-dioxide, and towards one rich in oxygen. This reaction is however much less powerful than the others mentioned. The necessity of comparatively free interchange of air so as to prevent an injurious accumulation of carbon-dioxide is partly, though not wholly, the reason why plants grow as a rule much better in soil which is kept constantly stirred and loose than in one al- lowed to get stiff, and why a stiff clay is often sterile. Another reason is the greater quantity of water which, it has been proved by experiment, is lost by evapora- tion from a hard smooth surface than from loose soil. See p. 345 on the peculiar upright roots of certain mangroves. CHAPTER X STEMS 1. In chapter vi we saw that plants could be divid- ed into trees, shrubs, succulents and herbs, by their size and nature — -whether woody or not, or succulent ; and that they could also be divided into annuals, biennials, multiennials and perennials. They differ from each other also in habit, i.e. in their mode of life. All trees and most shrubs grow straight upright, but many shrubs and herbs spread flat on the ground (p. 112), or support themselves by straggling or climbing over other plants, or twining round them. 2. TWINERS. Common examples are PHASEOLUS the Bean, IPOM^A, BONA-NOX the Moon-flower, D^EMIA (fig. 58, p. 257) and CEROPEGIA (fig. 79, p. 352). They are all small plants and found for the most part only on thin-stemmed trees and shrubs. Some twiners coil in the direction of the hands of • a watch, when looked at from above, others in the opposite direction ; and various explanations have been propounded to account for this twining. But if we look at a twining plant, such as the common IPOM^EA QUAMOCLIT, L., which has been allowed to coil round 106 GENERAL BOTANY a stick, we shall see that the lower coils slope steeply upwards while the last few are flatter and the tip itself stands almost, if not quite, horizontal. And if we take a plant growing in a small pot and fix it horizontally to a clock-work mechanism so that it may be rotated at a uniform speed, the last few coils will untwist and the growing end become free and no longer twine. And, if a plant is put upside down, the last few coils will again untwist and twine upwards in the same direction, clockwise or anti- clockwise as the case may be. 3. Now all that the rotation on a horizontal axis does is to neutralize the influence of gravity by con- stantly changing the direction of its action on any part of the plant. No other condition need be altered, for it is the same if the light be from above or from one side. We must conclude, therefore, that the twin- ing is due neither to light, nor to any independent tendency of the plant, nor to a sensitiveness to contact as in the case of tendrils (see p. Ill), but to a pe- culiar reaction to gravity whereby the growing end is kept horizontal like a dia-geotropic organ, and also made to bend sideways, unlike any other part. A little behind the growing point the shoot is weakly apo-geotropic, like an ordinary stem, and under the stimulus of gravity bends upwards so that the coil- ing is made steeper and at Jrtie same time, as may easily be seen by coiling a narrow strip of paper round a pencil and pulling it out, much tighter. When a part of the stem has finished growing in length, it becomes thicker and woody, so that the coils are not easily unwound. STRAGGLERS 107 We see, therefore, that the twining of a shoot round its support and its firmness is not such a simple process, as it may at first appear. A peculiarity of the top internodes causes it to bend sideways instead of growing upright; the irregularity of its growth and the influence of gravity cause it to nutate or revolve slowly round; and the upward tendency of all shoots makes the spiral longer and narrower so as to clasp more tightly still ; and then with the hardening of its substance, so that the coils do not come loose, the process is complete. 4. CLIMBERS. — Climbers support themselves on trees and rocks in various ways. In many cases the plant is thorny and its thorns catch on the branches of the larger tree, and prevent it sliding down. This is the means, for instance, where- by the common BOUGAINVILLEA grows up trees or straggles over some support. Some species of ZIZYPHUS straggle by the same means over small trees. So to a certain extent does the common LANTANA, and CAPPARIS HORRIDA (fig. 18). In the moist forests (e.g. of the slopes of the ghauts) are many plants of this kind, among these several species of a climbing Palm, CALAMUS (fig. 21), l which have very thin stems, in some cases no thicker than an ordinary lead-pencil, profusely supplied with long straight thorns by which they are supported in the thick vegetation, and grow to im- mense heights, attaining several hundred feet in length. 1 The steins of these climbing Palms — Rotangs — are commonly known as 'canes', and used for making the ordinary split-cane floor-mat of Indian houses, the seats of chairs, walking sticks •(Rattan-cane), etc. 108 GENERAL BOTANY On the high, more open parts of the hills the wild Rose, and various species of RUB us (Bramble) straggle by the aid of prickles in a similar way, but with the exception of the climbing Palms, none of these thorn-stragglers, as we may call them, grow to any great height. Turning now to plants which may really be said to climb, and not merely straggle over the others, we find that they attach themselves to their supports by roots, petioles or tendrils. Examples of root-climbers are those thick-stemmed climbers so common on large trees, in Indian gardens, PHILODENDRON and POTHOS. These plants develop on the side next to the supporting tree, numerous, short roots, which are, of course, adventitious. That they are roots and not a specialized form of some other organ, is shown by the fact that they grow out from inside the stem, breaking through the epidermis, for this we learnt in chapter ii is a characteristic of roots as distinguished from leaves or branches.. FIG. 21 A CALAMUS Part of the stem and of a leaf of a climbing palm showing spines. ROOT CLIMBERS 109 The cracks in the outer tissues, by which the roots break through, can be easily seen with the naked eye. These roots grow as they do, because they are insensi- tive to gravity, but like normal roots very sensitive to light. This causes them to grow out from the darker side of the stem, that next the tree, and turn into crevices in the bark. Other common garden plants which climb by roots are Ficus SCANDENS, a small creeper, and HOYA CARNOSA, the wax-flower. The English Ivy is also a root climber. Many orchids and a few ferns, though FIG. 22 GLORIOSA SUPERBA 110 GENERAL BOTANY they can hardly be said to climb, attach themselves firmly to trees by similar roots. (Epiphytes.) The common garden Potato-creeper — SOLANUM SEAFORTHIANUM will cling on any thin support, such as a wire, by curving the petiole round it. So also does the garden ' Nasturtium ' (TROP^OLUM) and the Pitcher plant (NEPENTHES), a native of America. In GLORIOSA SUPERBA, common enough in hedges all over South India, the leaves have long extensions which coil round any available object (fig. 22). It has been proved that in such cases the coiling is due to the outer side growing more rapidly than the inner, because stimulated to do so by the friction of the object touched. In other plants occur special holding organs, called tendrils, which, whatever their morphological nature, are merely thin threads very sensitive to contact with any rough surface, and readily twine round any object. If we examine the tendrils of the Vine, ANTIGONON, PASSIFLORA the Passion-flower, Pea, CLEMATIS or any other tendril-climber, we shall find that in every case the fully-formed mature tendril is coiled up like a spring, acting just as a spring in allowing itself to be stretched and contracting again. The direction of the twist of this spiral, it will be noticed, changes one, three or some odd number of times, which shows that the spiral is made after the end has fastened to the support. We have only to tie a piece of string or tape between two points, and twist it up in the middle to see that the direction of the spiral must be different at either end. TENDRIL CLIMBERS 111 The tendril is carried round by a revolving move- ment similar to that of a twining stem, and if thus, FIG. 23 BIGNONIA GRACILIS Showing tendrils or by the wind, it is brought into contact with some thin stem that is not too smooth, coils round it, because the stimulus of contact with a rough surface (it won't round a smooth glass rod) causes the outer side to grow more quickly than the inner. Most ten- drils are branched at the top with three curved prongs, which easily catch on any rough objects. When several coils have been formed, the tissues become woody and tough, so that the coils are made fast and 112 GENERAL BOTANY cannot become uncoiled with any ordinary pull. The rest of the tendril then twists round its axis so as to form a spiral which brings the branch it belongs to, nearer the support, and as the tissues harden becomes a strong and elastic spring that yields when a branch is swayed by the wind, and does not snap as a straight connecting link would hardly fail to do. We will refer again, more fully, to tendrils in chapter xiv. 5. There are still other plants, which are not erect and do not- climb, but grow more or less horizontally along the surface of the ground. These for descriptive purposes have been given special names. They are -described as :— decumbent when a short bit of the lower part of the stem lies along the ground, while the greater part rises upwards ; prostrate when the whole lies flat on the surface, as in TRIBULUS TERRESTRIS (Nerinjee) and many other small plants, and creeping when roots arise from the prostrate stems and branches as in LIPPIA NODIFLORA (fig. 24). In sandy places, especially near the sea, creeping plants are very common, and one of these — IPOMCEA BILOBA is characteristic of tropical seashores. Its leaves are borne on stalks at intervals of six inches or more along thin shoots which grow forward on the surface, but are soon covered by the sand which is driven by the wind along the beach. In this way they become under-ground branches, and if they are all pulled up, roots will be found growing down from the under side of the nodes, and running deeply into the sand, while the leaf-stalks may be short or long, but always CREEPING PLANTS 113- FIG. 24, LIPPIA NODIFLORA A creeping plant FIG. 25. LAUNEA PINNATIFIDA 114 GENERAL BOTANY just long enough to bring the leaves above the surface. This is because the leaf-stalks of this plant are capable of continual growth, and keep on lengthening when darkened, i.e. in correspondence with the depth of the sand that accumulates over them. Another plant very commonly found on sandy places is LAUNEA PINNATIFIDA. It can be recognized at once on the seashore by the rosettes (fig. 25) of grayish green leaves dotted about on the sand. If one be pulled up, there will be found below the leaves a thick axis which runs vertically down into the sand and ends in roots. On it are the scars of old leaves, showing that it is of the nature of a shoot (stem) not a root. 6. A shoot axis (stem) which, like this, is under ground, is termed a root-Stock. In LAUNEA nearly every plant is attached to some other one by a thin leafless branch which runs along the surface. This is a branch with very long internodes and but few leaves, from the nodes of which roots are developed. An axillary bud then grows out and becomes a short vertical axis with many leaves crowded into a rosette, i.e. with very short internodes. This axis thickens, and as the sand drifts over it, grows slowly upwards, and so becomes a new plant, connected by the long inter- node of the horizontal branch to the original plant. A horizontal branch of this kind, which starts a new plant some distance off from the parent, is termed a stolon. Other plants have branches which run horizontally, but always under ground. New plants rise as axillary buds on them, or by the end turning upwards. Such branches are also termed runners. UNDER-GROUND SHOOTS 115 If we examine an ordinary potato, we shall find on the surface a number of depressions (a few or many •according to its size) and by each depression and on the same side of it, a curved line. If the potato, or any part of it that has one of these depressions, be put into the earth, a branch will grow up out of the hollow, and pushing its way up to the surface of the ground, develop into an ordinary leaf-bearing stem (shoot). This must have arisen from a bud, which shows us that the depression is the axil of a leaf and the curved line, next it, a leaf-scar. And this is why the line is always on the same side of the depression. The potato is formed under ground, but the leaf- scars and buds (in the depressions) show that it is of a shoot-nature, not a root. It is in fact a specially thickened portion of an under-ground shoot or runner, and if the whole potato plant be carefully taken up the shoot-nature of the runners on which the potatoes are formed will be shown still more clearly by the small scale-leaves on them. A thickened part, whether of a shoot or of a root, is termed a tuber. The Sweet-potato is on the other hand a root, not a stem-tuber, being formed by the enlargement of a true root, and having in consequence no leaf-scar or bud on it. The under-ground part of a CANNA, ACORUS CALAMUS the Sweet flag, or of a Ginger-plant, consists of a thick whitish or brown horizontal axis from which roots arise and spread out into the soil. On this under- ground horizontal axis are thin brown scales, which are larger towards the end where the axis turns up 116 GENERAL BOTANY and becomes the leafy stem, and appear to pass gradually into the ordinary leaves. We conclude,, therefore, that these scales are leaves reduced to mere scales, because, being underground, they cannot do the ordinary work of leaves, and that therefore the axis is part of the shoot, and not a root — just as is the under-ground branch of the potato plant, only here the axis is much thicker and the internodes very short. An under-ground stem of this kind is termed a rhizome (which means root-like), or sometimes root- Stock, and is of the same nature as the root-stock of LAUNEA, except that it is horizontal instead of vertical. In a few cases the part which comes up above ground is not the end of the horizontal rhizome itself, but a side branch developed from a bud in the axil of one of the scale-leaves. But in most cases (e. g. in CANNA and ACORUS CALAMUS) the end of the rhizome itself turns up, and becomes the leafy shoot, and its horizontal growth is continued by a lateral branchr so that the whole horizontal under-ground part is a sympodium (chapter viii, section 2). In some plants again, e.g. CROCUS and COLOCASSIA,. there is a very thick and short root stock, of the shape of a ball and covered with thin papery scales, which like those of the Canna rhizome, are reduced leaves. This is termed a corm. At the beginning of each growing sea- son, a terminal bud shoots up from the apex of the corm, and becomes a leafy shoot bearing leaves and flowers, and dies down again at the end of the season. New corms are formed at the side of the old by devel- opment of the axis of axillary buds. UNDER-GROUND BUDS 117 The bulb of which common examples are those of the so-called garden ' Lilies ' — EUCHARis, CRINUM, and PANCRATIUM, is another form of under-ground shoot, but this unlike all the others has a very short axis on which are many thick leaves closely crowded together. It is in fact a bud, the leaves of which .are very thick and large. In some bulbs (e.g. the onion), the outer leaves completely overlap and enclose the inner, and the outermost of all are very •thin, like paper, and brown. In others (as in LILIUM) all the scales are alike thick, and the outer are shorter ;so that the surface of the bulb is rough or scaley, not smooth as in the onion. Some of the scales are not -merely reduced leaves, but are the bases of the green leaves which were formed during the proceeding vegetative season, and whose tops have died down and withered away. 7. Now if we ask what are the reasons for all ihese different kinds of shoots, why some plants climb .and others creep, why some have stolons or bulbs or rhizomes, we shall find the answer by keeping in mind the work that a plant has to do, and the kind of soil and situation in which each grows. 8. It is in places where the soil is too thin and shallow to allow trees and shrubs to grow, that we find the annual type at its best. On the slopes of hills and in valleys, where the rainfall is good so that there is plenty of moisture and the soil is rich and deep, grow, unless destroyed by man or other animals, the finest specimens of the opposite type — tall well branched trees under whose shade there is generally a •thick undergrowth of such shrubs and perennial herbs, 118 GENERAL BOTANY as can do without much light, and luxuriate in the cool damp air. It is in such places too that we find most climbing plants ; so numerous, indeed, are they in most tropical forests, that one rarely sees a tree without some climbing plant hanging from its branches or twined round its stem. By supporting themselves on the sturdier trees these can, with very little expenditure of constructive material, and therefore also of time, reach to considerable heights, and so obtain the neces- sary light and air. Their flowers too can be exposed to the sunshine and to the visits of insects (which as we shall see later, is of great advantage to the race), while their seeds can be scattered from the great height more widely, by wind or birds. But in loose sandy soil, where trees cannot grow SO' Avell, and where there is little shade, and too little mois- ture to support a large number of plants, are found those of exactly the opposite kind — prostrate and creeping plants. These spread their weak branches along the surface of the ground, and thus save in part the material that would be required to make stiff upright stems. Their leaves are developed not all round the axis, but mostly to right and left, in one plane, and so face upward to the light, at the same time shading the soil and keeping it a little cooler and less dry than it would be if fully exposed to the sun, whereby a little more moisture is available for the plant. Creeping plants, whose branches send down roots on their own account, can spread more widely that those which are merely prostrate, for they increase their supply of water by drawing on a larger area. ENVIRONMENT AND HABIT 119 Again in countries which have two well marked seasons to the year, a warm moist period when plants can grow actively — (as after the rains in India, and during the early summer months in temperate climates),, followed by a very hot and dry, or a very cold season, when all tender herbaceous vegetation is killed off,, it is of advantage to a plant if it possesses some part that will live on through this latter period, and from which new shoots can spring up as soon as ever the climate allows, thus taking an early advantage of the favourable season. The need of this perennial part is supplied by the bulb, corm, tuber or root-stock as the case may be. It always contains a large quantity of water to enable it to live on during the season, when the roots cannot supply moisture because of the dryness or the cold, and also a certain amount of carbonaceous food- material, packed away generally in the form of starch as in the potato and other stem- or root-tubers, but sometimes partly as sugar, e.g. in the onion-bulb. These carbohydrates are used up at the beginning of the growing season to make the new shoot, and if a young potato plant be dug up, the tuber from which it grew will be found an empty and shrivelled skin, or a mere slimy mass much less than its. original size. During the vegetative season the first work of the plant, after making its stem and leaves, is to provide for the seeds. In them nitrogenous and car- bonaceous food-material is packed away in even more concentrated form and with scarcely any water, and it is only after the year's seeds have been provided 120 GENERAL BOTANY for, that a new bulb or continuation of the root-stock is formed to carry on the plant to the next season, and to provide for its new shoot. We can see from this that, if we wish to move a bulb or root- stock from one place to another, we should do . it at the end of the growing season, and after all the leaves have withered and fallen. To move a bulb while it is in flower, as people, who, finding a pretty flower growing wild, and desiring to have it in their garden, so often do, must nearly always prove a failure, because the bulb is then at its weakest, and as the roots are destroyed in the moving, the plant suffers severely. We can see too, that the larger the bulb or tuber, and the more the water and food material packed in it, the stronger and larger will be the new shoot and leaves that spring from it, and therefore the more food will the new plant be able to make, and the stronger and more numerous the seeds that it can distribute. A horizontal rhizome has this advantage o\7er a vertical root-stock, a corm or a bulb, that the whole plant moves on just a little each year to a fresh piece of ground. Runners and stolons are more useful still, for they start new plants growing well away from the parent, providing them with food and water from the mother- plant, till they are sufficiently rooted to take care of themselves, and reproduction thus takes place more quickly and more certainly than by seeds. Gardeners make use of this habit to propagate many useful or ornamental plants, as the Strawberry, Raspberry, REPRODUCTION WITHOUT SEEDS 121 VERBENA and London pride. But runners cannot make their way through very hard earth, and we find them mostly on plants that, like the Potato, naturally grow in loose soil. CHAPTER XI ROOTS 1. The first root arises as we saw in our germinated seeds as an extension of the radicle. In nearly all trees and shrubs and in many herbs, this grows on as a strong main root, pushing its way downwards, and giving off branches which at first grow nearly horizontally (showing that they are dia-geo-tropic) and themselves branch again in all directions. These smaller branches grow out in any direction, without reference to gravity, but only towards dampness. The root branches start always from the youngest parts, so that those nearer the ends are younger and shorter than those further back, as may be seen very well on the seedling of a Broad-bean grown in a glass bottle. When the first root grows on strongly like this, it is often termed a tap-root. But in many plants (for instance with the com- mon Bean) the end of the main root soon dies and its place is taken by a large number of smaller roots which arise at the base of the hypocotyl, and branch- ing out in all directions, are of much the same size and importance. These are termed fibrous. Most ROOT-SYSTEMS MONOCOTYLEDONS and nearly all plants that grow in the mud at the bottom of tanks or in very wet places, have roots of this kind and not tap-roots. The difference between tap-roots and fibrous roots is not only one of size. A tap-root strikes down deep into the ground, fibrous roots remain nearer the surface, and if we examine plants carefully, we find that the root -system is not a mere chance result depending on the tap-root being injured or not, but that, except when forced by the nature of the ground, some kinds of plants have always deep roots others always shallow, and a knowledge of this is invaluable in agriculture or gardening. Trees are mostly deep rooted — those whose roots are shallow are much less firmly held on the ground and much more easily upset in a storm of wind. But of shrubs and herbs, many have roots which keep close to the surface of the soil, and are therefore easily injured if the soil is disturbed, soon suffer if it becomes too dry, and as quickly revive after a shower of rain. Fruit-trees are often of this type — the Coffee-bush for instance is a shallow rooting tree, which must have the surface soil kept constantly moist and undisturbed, and readily responds to a surface dressing of manure. A deeply-rooted tree does not impoverish the soil, for it draws its food- materials from deep down in the ground. Rather, it slowly enriches it by the decay of the leaves and branches it sheds. But when a number of shallow- rooted shrubs are growing, the surface soil is soon impoverished and must be constantly manured, and a little consideration will show that if we want our 124 GENERAL BOTANY shrubs and herbs to grow well, we must not put them near shallow-rooted trees. In a garden or coffee estate deeply-rooted trees do no harm, but are rather good as explained above, shallow-rooted trees like species of FICUS, the Banyan, Fig, etc., and PITHECOLOBIUM, the Rain-tree, are fatal. Every gardener knows that pots left under a Banyan tree soon get infested with the Banyan's roots, which are attracted thereto by the water poured into the pots and the rich manure they -contain. A Rain-tree has in the same way a depress- ing effect on any beds of flowering plants, that may be within the range of its roots. So has the ACACIA MELANOXYLON. 2. In Cholam, Wheat, and other cereal plants, the roots are all fibrous, and some come from the stem above the scutellum — that is above the hypocotyl. Of these the lowest are the eldest, the uppermost the youngest, exactly the opposite of what we find in the ordinary branches of a tap-root. Roots which arise like these, not from another root, but from the stem or branches, are termed adventitious. At the base of nearly every Coco-nut palm (a MONOCOTYLEDON) can be seen a number of these fibrous adventitious roots, radiating out into the ground. Perhaps, however, the most familiar and most easily recognized of adventitious roots, are those which hang •down from the branches of the Banyan tree, and will, if left undisturbed, grow into the ground, becoming after a while, thick stem-like pillars. But that they are roots and not a peculiar kind of branch, is shown by the entire absence of leaves or scales, and by the little brown root-cap which occurs at the end of each. ROOTS FROM SHOOTS 125 Moreover, if the tip be eaten by animals or otherwise damaged, branches soon arise and these can be easily seen to come out from the inside by narrow cracks, and not from the surface as, we have learnt, do the branches of the shoot. . That they ultimately come to look so like stems, is due to the fact that though quite different in struc- ture when very young, roots increase in thickness, exactly as do stems, and form cork and bark in the same way. These adventitious roots of the Banyan serve of course to support the branches, and so enable one tree to grow enormously and cover a great space- of* ground. There is one very famous tree in Cal- cutta whose stem-Hke supports number about 500, and bear a crown of branches of over 900 feet in circumference, and other trees famous for their size are found in Madura and other places. The adven- titious roots of cereals and palms, also act as extra holdfasts and supports to keep the stem upright. Such supporting roots are better developed in the Screw- pine, PANDANUS, where they are sometimes a couple of inches thick, and have very large scaley root-caps (fig. 2). Several trees which habitually live in the mud- flats of tropical seashores, also have adventitious supporting roots which, like those of Pandanus, grow down obliquely into the mud and form a much better and firmer support for the plant than a single thick stem, which might be washed away by a strong tide, could do. These trees are called MANGROVES, and they grow very commonly in the tropics by the mouths of rivers and wherever the seashore is soft and muddy. 126 GENERAL BOTANY The roots which arise from the under side of creep- ing plants like LIPPIA, and those by which, as we have already learnt in chapter x, some climbers as like PHILODENDRON and PIPER, cling to their supports, are also adventitious. In the latter the geotropic tendency is altogether absent while the apheliotropic is very strong, so that they arise only on the darkened side of the climbing stem, and make their way into the cracks of the bark of the supporting tree. The hanging roots of the Banyan, on the other hand, are so much more sensitive to gravity than to light, that they grow straight downwards, and can only very occasionally be seen curving towards the main trunk — i.e. to the shadier side. Adventitious roots will arise on almost any piece of a shoot axis, that is buried in the ground, or even merely darkened, and on this account many plants can be easily propagated. If pieces of the common Sugar- cane or Prickly-pear, for instance, be stuck into or even laid flat on the ground, roots soon grow out from the nodes (where the spines are) and make their \vay into the soil. The ordinary way of propagating the common potato, sweet potato, hariyali-grass, and many other plants depends on this property. In the case of the common potato, a tuber (which we have learnt is part of the shoot) or any part of it that contains an * eye ' (or bud), may be used. In the case of the Sweet potato, the tuber is part of the root- system, but from any portion of the stem, as long as it contains a node, roots and buds will grow out. Gardeners make use of this same habit — of roots growing out of buried or darkened portions of a shoot — ROOTS FROM LEAVES 127 to propagate many of our flowering or ornamental shrubs, which either (like the HIBISCUS) do not pro- duce fertile seeds, or would not come up exactly the same from seed — as in the case of the CROTON and PANAX. In some cases a branch is bent down to the ground, and a part of it kept covered with damp earth till roots have formed. In others, earth is put round the stem or branch, bound on with a piece of cloth and kept moist. When the roots have grown, as they soon do, the branch can be cut off, and planted separately. Adventitious roots and buds will even arise in some cases from a leaf, e.g. from the notches in the edge of the leaf of BRYOPHYLLUM without being put into the ground, or even darkened, as every one knows who has had one hung up in his house. If a leaf of a BEGONIA is cut off and the base stuck into moist earth or sand, roots will soon grow out, and after them a bud, also adventitiously, and so a new plant be produced. This is a common way of propagating these plants. There is one family of plants, the GESNERACE^E, in many of which this happens in the natural state. In DIDYMOCARPUS (one of this family) after the seed has germinated, one of the cotyledons dies, as also do the stem-bud and the radicle. The remaining cotyledon grows till it becomes a very large leaf, lying flat on the ground. At its base adventitious roots strike down into the soil, and an adventitious bud becomes the flowering stem. 3. In chapter iii we learnt that one of the chief functions of roots was to fix the plant firmly in the soil, and that the great combined length of its many 128 GENERAL BOTANY branches, and the combined effect of their countless root hairs made roots stick very tight in the ground. Some roots, however, not only keep the shoot firm, but actually drag it deeper into the soil. This is especially the case with some monocots that have horizontal rhizomes, e.g. CANNA. If the soil from above the rhizome be scraped away, so that the latter is not so deeply buried, the roots contract and drag it further downwards. There are some plants too, whose roots have no root hairs. They are mostly water plants, whose roots being always in water do not require hairs — and many land plants which normally have root hairs, do not if grown in water. 4. SPECIAL FORM OF ROOTS. — We ha\e already referred to the Sweet-potato as being a root-tuber. The garden DAHLIA is another plant whose roots become swollen and tuberous. In the common country Radish, it is the tap-root that becomes swollen, and the branch roots, which arise in two vertical lines, on either side of it, are quite thin and small. (In the English radish the tuber is formed from part of the hypocotyl). These tuberous roots, have the same importance as rhizomes, stem-tubers and corms — car- bonaceous food-material, mostly in the form of starch, is stored in them for the use of the next year's shoot and its seeds. Very peculiar roots occur on some plants which grow not in the ground but on trees. These epiphytes, as they are called, cling to trees by small roots which like those of root-climbers are strongly aphelio- tropic, and making their way into the crevices of ROOTS OF EPIPHYTES 129 the bark, absorb some of the water that runs down the branches and trunk of the tree after every shower, and also any mineral matter that may be blown up from the ground as dust, and be dissolved in it. But being entirely unconnected with the ground, this, and the little rain that actually falls on them is all these plants get, and therefore as one might ex- pect, they grow only where the air is moist and rain falls frequently. On the roads of Singapore which has a very damp climate, almost every tree has on it some — often very many — epiphytic ferns. In addition to these clinging roots, some epiphytes (not ferns) have others which are about the thickness of an ordinary lead pencil, and hang down freely, being apparently quite insensitive to light, or if any thing, attracted not repelled by it. The orchid, VANDA ROXBURGHII, is a fairly common Indian epiphyte which has these roots well developed. When dry, the root looks quite white, but if moistened, greenish. Breaking it with the fingers, one can easily separate the soft outer white part from a firmer central part. This soft outer portion, is composed of very loose spongy tissue, with lots of little spaces empty of everything except air, and looks white for the same reason as the foam of the sea, or the froth on fermenting toddy, looks white, that is, because the light is reflected in all directions from numbers of tiny bubbles of air. When this tissue is wetted, the air is replaced by water, and it becomes more or less transparent so that the green colour of the central part shows through. This aerial root then differs from all ordinary roots, in having a green layer overlaid by a spongy one. 9 130 GENERAL BOTANY This porous spongy layer, readily absorbs any water, that, like rain, may fall on it, and also allows air to reach the green layer underneath, and thus these roots act both as true roots in absorbing moisture, and also like leaves in assimilating carbon from the air. It seems very likely too, that nitrogen in the form of ammonia, produced by the decay of vege- table and animal matter, may be absorbed in the damp spongy tissue and ultimately made use of by the plant. 5. All the types we have been considering have been normal green plants, absorbing their food-ma- terials from soil and air by their own roots and leaves. There are, however, plants which depend wholly or in part on others for their water and food. These are called parasites or semi-parasites, as the case may be, and the plants they feed on are called their hosts. SXRIGA is a very common semi-parasite on the plains, growing on the roots of SORGHUM and other grasses, to which it attaches itself by little round tubercles, called haustoriums. The Sandalwood tree, SANTALUM ALBUM, is another, for it attaches itself to the roots of shrubs, such as LANTANA, by similar haustoriums, and LORANTHUS is a very common semi-parasite on the branches of trees, into which it sends special sucking organs to draw the sap. These semi-parasites have all chlorophyl in their leaves, and are, therefore, able to assimilate car- bon and manufacture a certain amount of food- materials for themselves, but they seldom have the full green colour of a normal plant. FORM AND FUNCTION 131 The true parasites are quite devoid of chlorophyl and are entirely dependent on their hosts. Some which grow on roots have, like the common CHRIS- TISONIA of our hills, a short stem and colourless scale- like leaves, or like BALANOPHORA, practically no stem at all, but only a few scales and a mass of flowers forming a large warty lump on the roots of trees. Others like the common CASSYTHA, and CUS- CUTA the Dodder, grow on the branches of soft barked shrubs and herbs, looking like strands of yellow string, but attached to the host by numerous haustoriums, and with no leaves. All these parasites and semi -parasites have perfectly normal flowers however much the rest of the shoot may be reduced. 6. In all these types, in the stout trunk of a tree with perhaps its buttressed base, or the thin flexible stem of a twiner, in the weak bifarious branches of a creeping herb, the bulb or tuber of a perennial, and the peculiarities of a parasite or an epiphyte, we see examples of the intimate connexion between form and function which we came across in our study of cotyledons. And this is emphasized by the fact that the flowers whose function of reproduction is, of course, the same whatever be a plant's vegetative habit, are not affected by these differences. A tall tree and a creeping herb, a root-parasite and a shrub, an epiphyte and a climber, may have flowers of the same size and form. CHAPTER XII SPECIES AND GENUS COMMON experience shows us that all the leaves of a plant are very much alike and arranged in the same way on all the branches, though they may differ in size, and though sometimes those which grow on the younger branches are more or are less regular in shape, than those on the older, and in a few plants which grow in water, the submerged leaves are different from those above water. With these excep- tions all the leaves of a plant resemble each other in shape, thickness and feel. Every one recognizes too that there are different kinds of plants — jus,t as there are of animals — and that all the members of any one kind however much they may differ from one another in size — that depending so much on external conditions, such as the state of the soil and the amount of water and light available — yet resemble each other very closely in regard to their flowers, general habit and leaves, and differ, especially, in their leaves from those of all other kinds. We conclude, therefore, that the nature and ap- pearance of its leaves are characteristic not only of the MEANING OF SPECIES 133 individual plant, but of the kind, and are thus able to distinguish the different kinds of plants. Thus we can distinguish easily and at a glance, the Palmyra-palm with its dark-coloured unbranched stem and crown of broad fan-like leaves with ribs and cuts radiating from the base where the stalk is attached, from the Coco-nut whose stem is also unbranched, and marked also with rings across it, but whose leaves are much larger and made up of a number of segments (leaflets) attached to a central stalk, and each folded down- wards along its middle. The common Date-palm again, we distinguish easily from the Coco-nut, because of its smaller leaves, and their leaflets, arranged as in the Coco-nut-palm, but folded along their middle line upwards instead of downwards. The Peepul again, has a much branched stem covered with a fairly smooth grey bark (marked at intervals of a few inches by lines running round the axis) and small undivided leaves which have a long acuminate point, a shiny surface, and long flexible stalks. The Banyan, on the other hand, while resembling the Peepul in being branched, though more widely so, and in its grey -coloured bark, is different in having roots that hang down from the branches and leaves with rather thick stalks, thick blades, blunt ends and a smooth not shiny surface. Every kind of plant has its own kind of leaf- however much the general shape of the plants may differ. And if we put a Palmyra fruit in the ground and water it, we know that we may get from it eventually a Palmyra-palm, never anything else. If we sow 134 GENERAL BOTANY seeds of Flax or Wheat or Cotton or Paddy, only Flax, Wheat, Cotton or Paddy, as the case may be, will come up. No one has ever raised Cholam from Paddy seed, nor Barley from Wheat, nor even Jowari cotton plants from Karunganni cotton seed. Since every plant has sprung (by seed or directly) from another more or less like it, all those of any one kind must be related to each other, and have descended, through perhaps a long past, from one common, or several very similar, ancestors. Such a group (or kind) of plants, all the members of which resemble each other in the more important respects of flowers, general habit and leaves, looking therefore as if all had come from a common ancestor, is termed a species. Coco-nut-palms, for instance, all belong to one species — the Coco-nut species — known botanically as COCOS NUCIFERA. (We shall see shortly why the name is a double one — the second half is the species' own special name). Palmyra-palms belong to another species known as BORASSUS FLABELLIFER. The common Indian Date-palms to another, PHOENIX SYLVESTRIS. All Banyan trees belong to one species called FICUS BENGALENSIS. All Peepul trees to another, FICUS RELIGIOSA. Now we do not find any species of plant growing wild all over the world. Some grow only in the eastern hemisphere, others only in the western, some are found in the tropics, others only in temperate climates. Coco-nut-palms, for instance, grow quite commonly on the shores of the tropical parts of America, Africa, and Asia, and on all the islands of Malay Archipelago, and the Coral islands of the Pacific, THE GROUPING OF SPECIES 135 but even in the tropics not far inland, not, for instance, on the plains of central and northern India, and are quite absent from temperate regions. The common Indian Date-palm, PHOENIX SYLVESTRIS, grows only in India and Burma, being entirely unknown (at least wild) in Europe and America. It differs from the Coco-nut in that it thrives on the plains, far away from the sea. Paddy again requires a great deal of water and a high temperature and cannot be grown (except per- haps in a small way with artificial heat) in the cooler parts of the world. On the other hand, Wheat (another cereal crop plant) grows splendidly in Europe without being irrigated, and will even live for weeks in ground, the surface of which is frozen hard like ice by the cold. Thus a species is a group of plants with common wants and common habits, as well as a common appear- ance ; and just as we think of a plant as doing its best to grow strong and reproduce itself, as much as it can, under the conditions in which it finds itself, so must we also think of the whole species, as trying to adapt itself to the districts in which it lives, and to spread as widely as possible over them. But consider now the three well-known species — the Banyan, the Peepul, and the country Fig. These three species are all trees, they all have alternate leaves, and large cap-like stipules which cover the next leaf (and all above it) in bud, and as the internodes develop, fall off and leave a scar extending like a ring right round the branch. They have this also in common that if a leaf be torn or a branch broken a white sticky juice exudes — 136 GENERAL BOTANY and this does not happen with very many species. Lastly, their flowers are very minute and imperfect, and are massed together inside a hollow structure which eventually becomes a fruit, of a bright red colour and more or less ' fleshy ', so as to be edible by animals and men. Consider again the two common species — the Vayai marum or Neem tree, and the Malaivayai marum. These are both trees, they have alternate compound leaves — in the one case pinnate, in the other bipinnate. The flowers in both cases are not very large and are borne in large branched inflorescences termed panicles, and consist of five sepals, five petals and a staminal tube bearing ten anthers sessile at the top. The fruit in both is a ' drupe ' containing one hard stone. It is only in the leaves and perhaps the colour of the flowers that these two species differ. In all other respects they are very much alike. Take again the three fruiting trees — the Custard-apple (Seetah), the Bullock's heart (Ramseetah), and the Sour-sop (Mooklooseetah). These three species are shrubs or small trees, with alternate rather leathery bifarious leaves and short petioles. Their flowers are borne in much the same way, solitary or in close bunches (fascicles). In each too, there are three sepals and either three or six petals (three inner and three outer). That is, the sepals and petals are in sets of three, a very unusual number in dicotyledonous plants. They have this too in common that the stamens are very numerous and rather peculiar, having very short filaments and large anthers, each surmounted by a sort of crest — MEANING OF GENUS 137 the continuation of the connective. There are in each of these species also, many carpels which, at first separate, become fused in fruit so as to form one fleshy mass with several black seeds. If one of these be cut open, the endosperm will be seen to be marked by irregular lines running in from the seed coat (technically known as being ruminate). These three species are thus very much alike in all the important respects of (i) the arrangement of the leaves, (ii) the arrangement of the flowers, (iii) the nature of the flowers themselves even to the minute detail of the stamens, (iv) the fruit, and (v) the seed. Only in the shape of the leaves, and in the ap- pearance and taste of the fruit do they really differ. In the same way we find in the cooler parts of India (and on the hills of South India and Ceylon) several kinds of ground Orchid which differ in the size of the stem, leaves and flower, in the length of the spur, in the erect or spreading position of the sepals, in their white or purple colour, and in the shape of the lip, but all are very much alike in the arrangement of the flowers on the stem (a spike), in the inferior, twisted ovary, in the large front petal (lip), in the presence of five other smaller petals or sepals, and in the other parts of the flower. All the common Strobi- lanths of our hills, again have opposite leaves, swol- len nodes, and flowers of the same pattern, but differ in habit and in the shape and size of the leaves. The two common garden Cosmeas, COSMOS, the yellow C. KLONDYKE and the pink or white (or purple) C. BIPINNATA, which differ in the much more divided leaves, are in their flowers exactly alike (except in 138 GENERAL BOTANY colour). Many other instances of the same sort of simi- larity between different species will occur to the reader. We thus see that just as plants can be grouped into species, species can also be grouped. A group of species possessing in common certain character- istics of flower and fruit, though differing in habit perhaps and in their leaves (characters which we have already learnt are of minor importance) is called a genus. Thus the Banyan, the Peepul and the country Fig, belong to a genus known scientifically as FICUS. It is a very large genus, comprising a large number of species, most of them trees, and all with a sticky milk-white juice, large hood-like stipules, and minute imperfect flowers aggregated inside a hollow receptacle, but differing among themselves in their general habit (the Banyan for instance has roots hanging down from the branches, the Peepul and Fig have not), in the appearance of the leaves and fruit and other characters of lesser importance. In the same way the Bullock's heart, Custard-apple and Sour-sop are three species belonging to another genus named ANONA, because similar to each other in the chief characters of flowers, fruits and seeds, but differing in their leaves, and in the outward appearance of the fruit. It has been found convenient therefore to give to every species, two names, one of its genus the other its own special name, and it is usually necessary and sufficient in describing a plant to give these two names, the genus always first, the species second. But to add clearness and preciseness to the name, and MEANING OF VARIETY 139 to avoid any confusion due to a species being named more than once by different botanists, it is usual to add the name of the man who first gave to the species its name. Thus the Banyan is called FICUS BENGALENSIS, Linn. : because it was first described and named by Linnaeus, over a hundred years ago. He too, first described the Peepul naming it RELIGIOSA — and it is therefore FICUS RELIGIOSA, Linn. In the same way FICUS GLOMERATA, Roxb. means the species which Roxburgh first described and named glomerata. This is the edible Fig tree of South India. So too, the Custard-apple is ANONA SQUAMOSA, Linn. : because Linnaeus first named it squamosa on account of its luscious fruit. The Bullock's heart (Ramseetah) is ANONA RETICULATA, Linn. : named such by Linnaeus, because of the net-like markings on the fruit, and the Sour-sop is ANONA MURICATA, Linn. — from the projections on the outside of the fruit. In a few cases, but only in a few, it is necessary to add another name to describe the peculiar variety of the species meant. This is the case mostly with cultivated plants, which, in process of cultivation have given rise to several varieties like, for instance, the different kinds of plantain fruit. The species is then the wild plant from which these varieties are considered to have been derived, thus the Citron, Sweet-lime and Lemon, are considered to be varieties of one species CITRUS MEDICA, Linn. — the Citron being CITRUS MEDICA, Linn, (proper) the Sweet-lime CITRUS MEDICA, Linn., var. LIMETTA and the Lemon CITRUS MEDICA, Linn., var. ACIDA. Of most cultivated plants there 140 GENERAL BOTANY are numerous varieties — which are considered to belong to one natural species, because their differences have arisen only in cultivation. All the many kinds of Paddy for instance belong to one species ORYZA SATIVA, Linn., all our garden Crotons to CODI^UM VARIE- GATUM, Blume. Well-defined varieties occur also wild in a few species. When we have collected and examined a large number of genera, we shall easily see that just as species can be grouped into genera, so genera fall naturally into more or less well-defined families. We shall understand the characteristics by which families are distinguished from each other when we have studied more plants in detail, but for the present it may be said that for this purpose we judge by characteristics which are not likely to have been much modified by external conditions, namely, the position of the leaves (whether opposite or alternate), the presence or absence of stipules, and, chiefly, the general nature of the flower. FIG. 26 PLUMERIA ACUTIFOLIA, Poiret GROUPING OF GENERA 141 i FIG. 27 PLUMERIA ALBA, L. The Frangipanni The Pagoda-tree (fig. 26) and the Frangipanni are two species very much alike in almost every respect, except their leaves, and therefore placed in one genus. CHAPTER XIII LEAVES 1. Of all the organs of a plant, the green leaves are at once the most important, and the most delicate. More than roots or branches or flowers, are the leaves susceptible to the conditions of the plant's life, and so it is in the leaves of plants that we find the greatest variety, and the greatest difference between the several species of a genus, because of their different wants and different aims. To distinguish therefore, one species from another, it is important to be able to discern accurately the nature of the leaves, and that others may know from our description of a plant, what particular species we are referring to, we must have some commonly recog- nized terms for the different forms. 2. A leaf — or any organ if flat is described as linear — if many times as long as broad, like grass, or ZEPHYRANTHES the ' Crocus ' of Indian gardens. oblong — if two or three times only as long as broad and with more or less parallel sides, as in some leaves Of IXORA PARVIFLORA and IMPATIENS CHINENSIS (fig. 28), PLUMERIA ALBA (fig. 27). SHAPES OF LEAVES 143 a. wing petcul. FIG. 28 IMPATIENS CHINENSIS, L. elliptic — if tapering off at each end and broadest at the middle like an ellipse. As in VINCA ROSEA, and IXORA PARVIFLORA, PLUMERIA ACUTIFOLIA (fig. 26), FICUS NITIDA, Roxb. (fig. 29). 144 GENERAL BOTANY lanceolate— if several times as long as broad, tapering off at each end, with the broadest part on the stalk side of the middle, as in N E R I U M 0 D o R u M and G L O R I O S A SUPERBA (fig. 22). Noblanceolate— if of a similar shape to the last but the broadest part on the other side of the middle, nearer the point. (Cf. 1 e a fl e t s of CALAMUS, fig. 21). ovate — if like lanceolate, but hardly twice as long as broad, like an egg, as in FICUS BENGALENSIS (the Banyan), CROTALARIA RUBIGINOSA (fig. 30), ABUTILON INDICUM (fig. 31) and figs. 34, 35. obovate — if of the same shape, but with the broadest part nearer the tip, as in TECTONA GRANDIS (the Teak tree), in CAREYA ARBOREA, LIPPIA (fig. 24) and CAPPARIS (fig. 18). FIG. 29 FICUS NITIDA, Roxb. SHAPES OF LEAVES 145 rotund or orbicular — if nearly circular, as those of the Sacred- lotus (NELUMBIUM SPECIOSUM) ; cuneate — if broadest beyond the middle and tapering with nearly straight sides towards the base, like a wedge, as SIDA CARPINIFOLIA (fig. 32); deltoid — similar to cu- neate but broader, as the leaflets of ERYTHRINA INDICA (fig. 11) ; falcate — if not sym- metrical, but curved side- ways, as the ordinary leaves of EUCALYPTUS. The apex, or point, of a leaf is described as acuminate — if long and pointed as in Ficus RELI- GIOSA, the Peepul or Bo-tree (fig. 33), and in figs. 10 and 22 ; cuspidate — if broad and suddenly pointed in the shape of a cusp, as in HIBISCUS TILIACEUS (fig. 6, p. 41) ; acute — if sharp but not prolonged, as in PLUMERIA ACUTIFOLIA (fig. 26) ; obtuse — if blunt, as in the Banyan (FICUS BENGAL* ENSis) ; retuse — if obtuse and slightly indented (fig. 34) ; emarginate — if with a decided notch at the tin; 10 FIG. 30 CROTALARIA RUBIGINOSA, Willd. 146 GENERAL BOTANY FIG. 31 ABUTILON INDICUM, G. Don. mucronate — if the mid-rib is prolonged as a short hair beyond the end, as the leaflets of many CASSIAS (fig. 5) and C^ESALPINIAS and CROTALARIA RUBI- GINOSA (fig. 30). The base of the leaf-blade is, when necessary, described as rounded, acute or narrowed as the case may be ; cordate — if indented at the junction of the petiole, in the shape of the conventional heart, as in the LEAF-APEX 147 Peepul (FICUS RELI- GIOSA), and most of -— X\ \ Y' the CONVOLVULACE^E ^dTT^AMl / ^T^. ^ and MENISPER- M A C E ^E, and in ANTIGONON (and figs 31, 35); renifor m — if the blade is broader than long, with a broad shallow indentation in the shape of a kidney, as in HYDROCOTYLE ASIATIC A and the common garden plant, PASSIFLORA LUNATA J auricled or eared — if prolonged backwards a little on each side, in two lobes ; sagittate — if these prolongations or lobes are straight and sharp ; hastate — if they diverge sideways as in TYPHONIUM TRILOBATUM. According to the nature of the edge or margin a leaf is described as entire — if it is quite even, with no indentations; dentate — if with triangular indentations or teeth, as in HIBISCUS ROSA-CHINENSIS (the common Shoe- flower) ; serrate — if the teeth point forwards as in LIPPIA (fig. 24) and IMPATIENS CHINENSIS, L. (fig. 28) ; crenate — if they are rounded, as in HYDROCOTYLE ASIATICA and fig. 35 lowest leaf ; FIG. 32 SIDA CARPINIFOLIA, L. 148 GENERAL BOTANY FIG. 33 F, RELIGIOSA, L. F. ELASTICA, Roxb. The Peepul or Bo-tree FIG. 34 CROTALARIA VERRUCOSA, L, F. BENGALENSIS, L- The Banyan undulate or sinuate if wavy, as in POLYAL- THIA L O N G I - FOLIA ; lobed — if the undulations ex- tend inwards but not half-way to- the centre (fig. 36); Cleft or fid— if indented more than half-way as the leaflets of CARD IOSPER- MUM (fig. 37) ; LEAF-EDGE 149 FIG. 35. SIDA HUMILIS, Willd. partite — if divided almost to the mid-rib. The last two are used in compound words as pinnati-fid, palmately-partite. A leaf divided quite to the mid-rib or petiole would be pinnately compound or palmately compound as the case might be, or if divided into three sections, trifoliate or ternately compound, ERYTHRINA INDICA (fig. ll) and CRAT^VA RELIGIOSA (fig. 10, p. 45). According to the thickness and composition of the blade a leaf is described as, fleshy or succulent if thick and soft on account, of the water contained in it, as in BRYOPHYLLUM 150 GENERAL BOTANY FIG. 36 HELIOTROPIUM INDICUM, L. CALOTROPIS, PORTULACCA, VANILLA, HOYA, AGAVE, SEDUM the Wall-pepper, etc. coriaceous — if less thick, but firm and tough like leather, as the Banyan, and many trees and shrubs; -crustaceous — if stiff and brittle as PETR.EA VOLUBILIS, and KIGELIA PINNATA the sausage tree ; membranous or herbaceous — if thin and flexible, as in most herbs ; scarious — when very thin and more or less trans- parent, not green — and applicable rather to scales and stipules, as the scales (glumes and paleae) which enclose the flower of grasses. Some leaves are quite smooth, others have hair- like outgrowths, which give the surface a peculiar LEAF-TEXTURE 151 soft or rough feel. A leaf is therefore described according to its surface as glabrous — if quite smooth, as in FICUS RELIGIOSA (Peepul), FICUS BENGALENSIS (Banyan), VINCA RO SE A, HIBISCUS ROSA SINENSIS (common Shoe- flower) ; pubescen t — if there are a few short soft hairs; villous — if the hairs are long and weak ; hispid — if they are rather stiff; scabrid — if the hairs are very short and stiff, making the surface feel rough to the touch, as in LANTANA, TRICHODESMA INDICA, CLEOME FELINA (very scabrid like a cat's tongue), LEUCAS ASPERA, NYCTANTHES ARBOR-TRISTIS, POUZOLZIA SCABRA ; tomentose — if the hairs are branched and matted close together, covering the whole surface with a soft, often brown, coating, as in the young parts and buds of many trees STERCULIA, GUAZUMA, ZIZYPHUS (fig. 39) and CAPPARIS HORRIDA ; FIG. 37 CARDIOSPERMUM HALICACABUM, L. 152 GENERAL BOTANY lanate or woolly if they are long and cover the leaf thickly like wool ; silky if long and fine and shining like silk ; glandular if they make the leaf sticky; ciliate if the edge has fine short hairs like cilia. Compound words are often used and will be easily understood, as glandular-pubescent, meaning that the hairs are glandular and short, silkily-pubescent, and so on. Ordinary common words are also used as velvety (meaning a soft but shining surface like that of fine velvet). Some leaves when held up against the light show numerous white dots, due to globules of transparent oil. Such leaves are gland-dotted. The oil is nearly always scented, and gives a strong smell to the leaf if it be crushed, as the Orange, Eucalyptus and Myrtle. The leaf-blade is traversed by veins (vascular bundles) which carry the sap backwards and forwards to every part of the blade, and also serve to stiffen it, for being thin it could not remain flat without this stiffening. The way in which the veins run is often very characteristic, serving to distinguish plants and even whole families of plants, and is termed the venation. There are three main types of venation. Parallel venation — in the leaves of grasses, Bam- boo, Wheat, Paddy and other similar plants, a number of veins enter the blade from the leaf-base, and run more or less parallel to the tip. They are connected by numerous much thinner cross veins which are in comparison quite inconspicuous. This is termed parallel venation. LEAF-SURFACE 153 When the leaves are broader, as in the MELAS- TOMACE^E, and ARACE^E, the veins curve outwards like bows and come together again at the tip. This is really of the same parallel type, adapted to the greater breadth of the leaf, but to distinguish it from the truly parallel type is termed basal. Pinnate venation. — In most leaves there is one central vein termed the mid-rib which bears side veins to right and left, these side veins again branching in all directions. This is termed pinnate or feather veining. In some leaves, e.g. in the common Plantain (MUSA), the side veins run straight from the mid-rib to the edge of the leaf, and are connected together by very much smaller cross veins. This is the most typical form of pinnate venation being very like a feather, and is easily torn by a slight wind. In some leaves the side veins are fewer and comparatively strong and run straight to the margin where they end in teeth, but in most cases they curve for- wards towards the margin of the leaf and join each other in a more or less regular marginal vein, as in Ficus RELIGIOSA (the Peepul, fig. 33), and PLUMERIA (figs. 26 and 27). The side veins are joined by secondary veins and these branch again, forming a net-work of veins, described often as reticulate venation, as distinguished from the parallel cross venation of grasses and the parallel secondary venation of the Plantain leaf. Palmate venation. — In some leaves, e.g. in Cotton, STERCULIA, ZIZYPHUS, three, five or more veins start from the petiole and radiate like the bones in the palm of a hand straight through the blade, ending 154 GENERAL BOTANY generally at the tips of teeth or lobes. This is termed palmate venation. These main veins are generally branched again pinnately, so that the term palmate refers only to the main veins. In NELUMBIUM (Sacred-lotus) and TROP^OLUM (Garden-nasturtium) the petiole meets the blade not at the edge but inside it, and the veins radiate out in all directions. This is the most perfect form of palmate venation, and a leaf of this kind (i.e. with the petiole attached inside the margin of the blade) is termed peltate. The venation of ZIZYPHUS is very charac- teristic, veins enter the blade palmately, the two lateral veins branch pinnately, with strong secondary veins towards the outside, much weaker ones on the inside. The middle vein also branches pinnately, but the side veins are here rather weak. Leaves with parallel venation are always entire, those with palmate venation are either roundish — as in NELUMBIUM and TROP^OLUM or lobed, the side veins ending in the lobes, as in ordinary Cotton plant, STERCULIA, and many others. 3. In describing leaves, it is usual to begin with its position and nature (simple or compound) and the presence or absence of a stalk ; then to give the general shape of the blade (or perhaps of the whole leaf if it is compound) using the terms given in section 2 simply or in combination as may be required ; the shape of the base or apex, if it is distinctive enough, follows ; then the nature of the edge ; of the surface and of the texture; and finally the venation, if characteristic. Thus the leaves of PLUMERIA ALBA (fig. 27) ' are alternate, simple, shortly petioled, oblong, VENATION OF LEAVES 155 obtuse or retuse, base acute, entire, glabrous, cori- aceous, with prominent pinnate venation.' That of PLUMERIA ACU- TIFOLIA (fig. 26) is the same ex- cept that it is 'elliptic acute at both ends ' in- stead of 'oblong', etc. The leaves of ERYTHRINA INDICA (fig. 11) are 'alternate, pinnately trifo- liate ; 1 e a fl e t s with pulvinus and two large glands at the base, broadly ovate-deltoid en- tire, glabrous'. Combinations are used to de- scribe inter- mediate types, thus a broad lanceolate leaf would be called ovate - lanceolate ', and a narrow lanceolate might be linear- lanceolate ' (fig. 38). It is not usual to mention any character which is not prominent. Thus if the point is not specially acute or obtuse it might not be mentioned at all. But it is always necessary to name the position, nature, FIG. 38 CROTALARIA JUNCEA, L. 156 GENERAL BOTANY shape and margin. In Part II will be found descrip- tions of common plants, and these should be carefully gone through, with the specimens themselves. It must always be remembered that variations occur in all leaves. We must, therefore, try always to get hold of the most usual or distinctive type and describe that, and avoid abnormal cases. CHAPTER XIV BUDS 1. We have already learnt that water is a very important constituent of a plant, and especially so of the young tender growing parts, and that to prevent loss of water the leaves and smaller branches are provided with a thin but" waterproof skin, through which are holes (stomas) that can be opened or shut as required, while older parts of the shoot and the roots have a corky covering. These protective skins do not allow of much ex- pansion and are not therefore suitable for the young- est actively growing ends of the branches, which are, therefore, protected in various other ways. In some the delicate growing parts are covered by a coat of thickly matted branched hairs (tomentum generally of a brown colour. This we find in ZIZYPHUS (fig. 39), DESMODIUM RUFESCENS, STERCULIA and many tropical trees. But in most herbs and shrubs and in most trees of colder climates the end of the branch is covered with young leaves or with specially formed scales, consti- tuting a bud. 158 GENERAL BOTANY In some the leaves of the bud are not at all different from ordinary leaves, and the younger and smaller are protected by the bases of the older and larger. This we may see in nearly all an- nual plants and grasses, and in some tropical shrubs and trees as in BARING- TONIA, where the young leaves stand out red and straight at the end of the branch. The outer and FIG. 39 Young leaves of ZIZYPHUS JUJUBA, Lam. first leaves are smaller and obviously scales. In others the outer scales of the bud are brown or whitish, and as the bud opens are thrown off, never becoming ordinary leaves. But if we take a bud of this kind, e.g. of GORDONIA, or the Tea plant, we shall find that inside th'e thin brown outer scales are others thicker and whiter, while the innermost of all are evidently immature leaves. We can find indeed every gradation between bud-scales and leaves, so that the former must be a special form of leaf. Taking the scales and young leaves off one by one, we find them getting smaller and smaller, the smallest nearest the tip of the branch. In the centre of the bud is the conical tip which with a magnifying BUD-SCALES 159 glass we can see is studded by little humps arranged spirally round. The extreme tip is naked, lower down the humps begin and becoming bigger merge with the young leaves. Leaves, therefore, arise as humps on the ends of the branches, and the younger are always nearer the tip. Just above each of the lower larger humps, we may see another smaller one the beginning of the axillary bud. *w-- Examine an opening leaf-bud of BROWNEA COC- CINEA. There are a few scales, the outer are small and tough, and hardly grow at all, but the inner grow slightly and eventually protrude beyond them, Inside these are a number of pinnate leaves, the normal leaves of the plant, mixed up with long hair- like things, which spring from near the bases of the leaves and must therefore be modified stipules. The leaves when they emerge hang down for several days colourless and limp, and these leaflets are at first inrolled from either edge to the centre. It is only after some days that the leaflets having opened out turn green and strong, and then the leaves rise up and stand horizontal. The outer scales soon drop off, their purpose being only to cover the young leaves, and being over with the opening of the bud. In some plants especially those that grow in colder climates, the outer scales are not only tough but sticky with resin or some other secretion, which makes them more impervious to water-vapour. Now examine a bud of the Banyan. The end of the branch is encased on a thin yellowish organ 160 GENERAL BOTANY which is split and thrown off as the bud expands. It rises on the branch just at the level of each leaf, and is formed of the stipules. The same thing occurs in ARTO- CARPUS (the Jak fruit tree) and in other kinds of Figs. Also in SARACA INDICA and a number of other plants. Here, therefore, the bud is pro- tected by the stipule of the pre- FIG. 40 FICUS BENGALENSIS, L. the same kind throughout the year. But besides the terminal bud of a branch there are buds in the axils of the leaves, though the rule that every leaf has in its axil a bud" is not universally followed. Among monocotyledons there are many species which seldom or never branch and though this might be on account of the buds not developing, in many cases it is because there are no buds at all. There are, for instance, none in the axils of most of the leaves of the common Dracaenas of our gardens, nor again in there of most Palms. Extra buds occur in the ordinary cultivated Coffee tree, where when the terminal bud has been destroyed viously opened leaf, and is of VARIATION IN BUDS 161 to prevent the tree growing too high, a new branch, from just below an ordinary branch, grows up to take its place. The axillary buds are generally small editions of the main and terminal bud of the branch, but are often also protected by the stipules or by the leaf itself, being sunk in a small pit in the base of the leaf stalk, and so quite invisible from outside. This is the case, for instance, with SCHOTIA LATI- FOLIA a tree belonging to the family LEGUMINOSE^, ADANSONIA DIGITATA, and BIGNONIA MEGAPOTAMICA. In BRASSAIA ACTINOPHYLLA there are stipule-like upward extensions of the leaf base which completely cover the axillary bud. In IXORA, Coffee and other plants belonging to the family RUBIACE.E, the axillary buds are covered by the large stipules, which are jointed together and form a tube round the axis. The same in the case in RUMEX the Dock, and POLYGONUM and others of that family, where there is also a tube surrounding the axis just above each leaf. We see, therefore, that there is considerable variation in buds. There are what we may call naked buds — where the end of the branch is without leaves, these only developing later, and is covered only by hairs ; secondly open buds — where the end is protected by ordinary foliage leaves; and thirdly specialized or closed buds — in which some or all the scales are of a special nature, and must be considered as modified leaves or stipules. There are no hard and fast lines of distinction between these three classes, they merge one into another. Naked buds are found generally in dry 11 162 GENERAL BOTANY countries, open buds where the air is generally damp and shrubs can be leafy and grow all the year round, and the closed buds in colder climates where they need special protection against the cold of winter, and also in hot countries where vegetation is checked by a hot dry season. 2. Buds also differ in the way the leaves are packed inside them. In MUSA (the Plantain) and CANNA, the whole leaf is rolled up from one edge to the other. In MARANTA one-half of the blade is smaller than the other, and wraps round it. In QUISQUALIS (the Rangoon-creeper), ARTOCARPUS (the Jak), FICUS (Banyan, Fig, Bo, etc.), and NELUM- BIUM (Sacred-lotus), the leaf is rolled inwards from both edges towards the mid-rib, the under surface of the leaf being outside (see also fig. 39 ZlZYPHUs). In NERIUM, POLYGONUM, and some palms the leaf is also rolled inward from each edge, but the upper side is outermost. One of the commonest arrangements is for the two halves of the leaf, or leaflet, to be folded together along the mid-rib, e.g. HIBISCUS TILIACEUS (fig. 6, p. 41). In the grass family the leaves are arranged in two ranks, one on either side of the axis (not spirally) and fit closely over each other. The fronds of ferns and the leaflets of CYCAS (fig. 41) are peculiar in that they are coiled up along their length, with the tip inside and gradually unroll. In some plants the leaf (or leaflet) is folded along the main veins, and when just emerging from the bud, shows only these veins towards the outside, COLOUR OF YOUNG LEAVES 163 FIG. 41 YOUNG LEAF OF CYCAS CIRCINALIS, L. the delicate green parts being tucked away inside. This can be well seen in FLEMINGIA (fig. 42). There is an interesting feature in connexion with the opening of buds of tropical plants, which every one must have noticed. It is that the young leaves are very often of a red or purple colour, and that they generally hang down quite limp, and become 164 GENERAL BOTANY stiff and flat only after a few days. This is very obvious in the Mango, and in BROWNEA COC- CINEA, and is really a very common occur- rence. The red or purple colour appears in some mysterious way to protect the delicate tissues of the young leaves from the injurious effect of intense light and heat, probably by absorbing the rays which com- pose the yellow- green part of the spectrum, and we do not find this colouring nearly so common, in plants of the temperate climates where the sun is less powerful. The vertical position of the hanging blade (figs. 6, 11 and 42) also protects the leaf from the rays of the sun, for during the middle part of the day where the sun is vertically over head and his rays are most FIG. 42 FLEMINGIA GRAHAMIANA, W. & A. SHEDDING OF LEAVES 165 powerful, they hardly strike such leaves at all. In some cases the young leaves are stiff and stand vertically upright, this position having of course the same advantage as regards the sun as the hanging one. This is very clear in FICUS (the Banyan and other species, fig. 40) in BARRINGTONIA, and many other plants. 3. A great number of trees and shrubs drop all their leaves together, at one time of the year. In Europe and other countries which enjoy a temperate climate and cold winters, this happens during the autumn months, October and November, just before the winter. In India it is often in February, March or April before the hot weather. Such trees and shrubs are called deciduous, to distinguish them from evergreens, which are green all the year round, because some leaves fall and new ones are formed continuously. In temperate climates most of the trees are deci- duous, few except those of the Pine family, Gym- nosperms, being evergreen, so that there is a very great difference between the appearance of the country- side in summer when all the trees are in leaf, and in winter when they show only the bare leafless branches. On the other hand, in those tropical districts where there is always plenty of rain, most of the trees are evergreen, and vegetation has much the same appear- ance all the year round. But where there is a season of dry hot weather every year, some at least of the trees are usually deciduous, and bare of leaves during these months, or at least for a few weeks. Common examples of such deciduous trees are ERIODENDRON 166 GENERAL BOTANY ANFRACTUOSUM, whose bare branches sticking out at right angles to the trunk are so familiar a sight in South India. Other common deciduous trees are : — BOMBAX MALABARICUM (the Silk-cotton tree), POIN- CIANA REGIA (the Gold-mohur), ALBIZZIA LEBBEK, SLEICHERIA TRIJUGA, PLUMERIA (the Pagoda-tree), ODINA WODIER and Teak. In some of these the young leaves are formed within a few days of the fall of the old ones, and in some POINCIANA, PLUMERIA and BOMBAX, the flowers appear before the young leaves; this indeed is very commonly the case. The fall of a leaf does not mean a mere tearing away from the branch. In many palms, indeed, the leaf-stalk breaks, and leaves for a while a ragged untidy part on the stem, but with ordinary trees and shrubs, the leaf and stalk fall cleanly away from the branch, and there remains only a perfectly clean scar, the leaf -scar. If one be examined directly after the leaf has fallen, it will be seen to have its own perfect skin, a thin layer of bark. This layer is formed across the petiole before the leaf falls, and gradually cuts the leaf blade off from the sap in the axis. The vessels which conduct the sap are the last to be cut by this layer, and when they are the leaf withers and falls off. So that when the leaf has fallen all the sap which would have gone to the blade, and have evaporated from it into the air, is saved for the plant, while the protective covering of cork which is formed over the scar prevents any further loss. It seems indeed as if this were partly at least, the purpose of the annual shedding of the leaves — SLEEP OF LEAVES 167 to cut off all sources of loss of water, during the months when on account of the extreme coldness of the soil, or the great heat and dryness of the air, the roots would be unable to obtain from the ground sufficient water for the leaves. 4. If one goes out on any moonlit night, one cannot fail to be struck with the different appear- ance of a great many of our common plants — whether herbs, shrubs or trees — owing to a change in the position of the leaves or leaflets. The Tamarind and the Rain-tree (piTHECOLO- BIUM SAM AN) so commonly planted along roads, are good instances of this. Though by day their shade is dense, at night the moon shines easily through. In the Tamarind this is due to the leaflets closing up along the rachides of the pinnae, and turning so that each faces sideways, and the edge, not the flat side, turns upwards. In the Rain-tree, the leaflets fall downwards, so that they also face sideways, not up and down. The rachis of each pinna falls a little also. In ARACHIS HYPOG^EA (the Ground-nut) the leaflets turn up a little so as to face sideways rather than upwards. A very large number of plants with compound leaves behave in a similar manner, the leaflets moving so as to assume a position in which they are ver- tical instead of being horizontal. If we examine the leaves of these plants we shall nearly always find that the short stalk of each leaflet and of each pinna or leaf, is swollen at the base, and that this swollen pulvinus is the motile 168 GENERAL BOTANY organ. By a contraction of the lower, and expan- sion of the upper side of the pulvinus, the blade is made to turn down, and by the reverse action, the blade would be brought up. Many plants with simple leaves, and with leaves or leaflets that have no pulvinus, act in much the same way. Thus, the leaves of SIDA CARPINI- FOLIA (fig. 32) rise at sunset, to an angle of about 50° to the horizontal, i.e. more than half way to the vertical position. Those of PHYLLAN- THUS NIRURI, which is very common among grass (fig. 7), fold along the axis and face sideways. Those of EUPHORBIA ROSEA, another common little herb,, move towards the stem and the edges roll back a little. In INDIGOFERA ENNEAPHYLLA (fig. 9), another very common herb which has pinnate leaves, the leaflets rise slightly and each folds up along its mid- rib. In OXALIS, each leaflet folds up along its mid- rib, and these fall down so as to face sideways. A large number of similar cases can be seen without difficulty on any night after sunset, among trees, shrubs, our garden flowering herbs, and the smaller herbs that make up the ordinary Indian ' grass '. The movements are very regular, the sleep position being taken up each evening, and the day position on each morning at definite hours. These curious movements must be of some use to the plant, and that they are of a protective nature is known, because it has been found that leaves or leaflets which are artificially prevented from assuming their natural 'sleep position', suffer. It is certain that a horizontal blade loses far more heat bv radiation SLEEP OF LEAVES 169 to the sky than a vertical one, and that the latter is therefore less likely to be unduly chilled on a clear night, and less likely, too, to be wetted with cold dew. To avoid the leaves being chilled, appears there- fore to be the purpose of these movements. CHAPTER XV EXAMPLES OF HOMOLOGY IN chapter ii we learnt that the three principal vege- tative organs of a plant are its stem, its roots and its leaves, and while studying the germination of seeds, we saw that leaves are capable of considerable modification, and may indeed be so altered in general appearance, that their leaf nature is at first quite unrecognizable. The modification in the form of the embryo's leaf is connected, we saw, with the particular work it had to perform, and the particular circum- stances in which it was placed. The cotyledons for instance, even when as with RICINUS, the Castor plant, they come out of the seed and turning green behave thereafter like true leaves, are simple leaves with entire margin, however lobed or toothed the normal leaves may be, and this, we saw, is because they thus fit best into the seed, with least waste of room. We learnt too, that some cotyledons are still more unlike leaves, because they are used as stores of food for the seedling plant, the culmination of such modification being reached in the scutellum of the Maize, which is utterly different in every way from the ordinary MODIFICATION OF ORGANS 171 leaf, and performs utterly different functions, for which indeed it is admirably adapted, but yet from analogy must be % considered as homologous with a leaf. Then in chapters x and xi we learnt that stems and roots are also capable of modification, so that dif- ferent forms of these organs occur, and that their different forms depend on the particular work each has to perform. All this shows that we may, and indeed to understand plants properly must, study their organs from at least two different points of view. We must try to find out first what any organ really is, that is to say what it corresponds to in the normal plant, whether to root, or shoot-portion (axis, stipule, leaf, or leaflet), and secondly, why it has that particular form, and what end the modification serves. The first of these studies is comprised in a special branch of Botany termed morphology (the science of form), the second is another branch termed physiology (the science of nature and vital processes). Though distinct branches of study, these must be taken to a certain extent together, for they mutually assist each other, and any inquiry into the modifi- cation in shape of an organ would be barren without a knowledge of the physiological conditions. In the following pages of this chapter, a few com- mon plants that can be found almost everywhere in south India, are described with special reference to some organ that is modified in some respect, and the student is advised to examine actual living speci- mens of as many as he can procure, and to follow carefully the description given in each case. It can- not be too consistently borne in mind that mere reading 172 GENERAL BOTANY of these (or any) descriptions is almost useless. Each point mentioned must be made out in the actual speci- men, and since those described here are all common plants, there should be no difficulty in this. Homology of thorns ZIZYPHUS JUJUBA, Lamk, the Jujube Or on the hills any other species of ZIZYPHUS. This very common and cultivated tree, grows chiefly in dry places. The young branches and flowers are covered with a thick reddish brown tomentum or layer of short branched hairs set closely together, which protects them from drying in a hot day. It is thickest on the youngest parts and buds, where the protection is most needed (fig. 37). At the base of each leaf are sometimes one, some- times two thorns. Their position — for they occur nowhere else — points to their being modified stipules, and towards the end of the youngest branches, they may be found still quite soft like ordinary stipules. These thorns prevent animals grazing on the branches, and so afford the plant the same sort of protection. We must not, however, from this, jump to the conclusion that the stipules have developed as thorns in order to keep animals off. The change has probably been due to the dryness of the air of the places where ZIZYPHUS usually grows, the keeping off of grazing animals being probably only an accidental result. 8'BK°' 10 CAPPARIS HORRIDA, Linn. A small tree which also grows in dry places. It is protected from hot winds and from grazing LEAVES AS SPINES 173 animals in very much the same way as is ZIZYPHUS. But the curved thorns also assist in climbing, for by them, the branches catch in the back of other trees and are prevented from slipping back. We should notice too that in this plant, there are three or four flower buds in the axils of some of the leaves, and that these buds are one above the other, in a vertical line, the oldest (the first flower to open) being at the top (fig. 18, p. 95). BERBERIS ARISTATA, D.C. The common Barberry of the hills. This is a very common plant growing wild on the hills. The branches are armed with sharp slender spines, which are generally three-pronged. Just above each three-pronged spine is a very short branch covered with small scales, and ending in a tuft of leaves, or perhaps a bunch of flowers. The three-pronged spine may represent one of two things — it may be a branch or a leaf. If it is a branch there must be below it a subtending leaf (or the scar of one), and the total absence of any sign of one shows that the spine is homologous with a leaf. The short branch above it is its axillary branch, the first few leaves of this are modified as small scales, and are followed by the normal leaves. Even if it bears flowers, this axillary branch is a short one of limited growth for the flowers termi- nate it. One effect of the spines is clearly to prevent ani- mals eating the plant and the three-prongs are, for this of course, better than one. The leaves are all 174 GENERAL BOTANY the better protected for being on very short shoots, just above and very close to each spine. PITHECOLOBIUM DULCE, Benth. The Korukapuli. This is a very well-known shrub, being frequently grown in hedges. It is rather thorny, and the thorns are in pairs, with a slight round swelling between them. On the younger branches there is between the two thorns of a pair, one (or some- times more than one), stalk which ends in a small point, and has two branches, each of which again ends in a small point, and bears two blades (leaf- lets). That these last are leaflets and not leaves is shown by the fact that there are no buds in their axils. There 'are, we should notice, small glands (not buds) on the main stalk just where it has the two branches, and also at the base of each leaflet. Now, if there are leaflets the whole must be a leaf, and there being no buds where the main stalk bears the two branches, these latter, with each their pair of leaflets, are two pinnae (not leaves), and the main stalk is the rachis of a pinnately bicompound leaf, which has only two pinnae, each with only two leaflets. The thorns at the base of this leaf must then be modified stipules. When there is more than one of these reduced com- pound leaves, between and behind the thorns, the others are the leaves of the shoot which is axillary to the main leaf, and which sometimes does not in STIPULES AS THORNS 175 itself develop further. This axillary branch can then be just seen, as a small point, but in other cases it grows out and becomes an ordinary branch. Here again, as in BERBERIS and ZIZYPHUS, protection from grazing animals is afforded to the leaves, by the conversion (or modification) of what are usually soft organs (the stipules and sometimes also the end of the rachis) into hard sharp thorns. And the value of this protection is increased as in BERBERIS by the shortness of some of the axillary shoots, so that the leaves they bear are quite close down among the thorns. At the same time the direct cause of this and other spinous modifications of stipules, leaves or branches is probably the dryness of the air or soil, for when cultivated under very damp conditions these spines often become ordinary soft leaves, etc. There are other species of the genus PITHE- COLOBIUM, some 3 have spines, some have not. One species PITHECOLOBIUM SAMAN, though also not a native of India is very common, being often planted along roads as a shade tree. Among Europeans it is known as the * Rain-tree '. There are no thorns on this tree, and each leaf has several pairs of pinnae, and each pinna several pairs of leaflets. Being a tree, it carries its leaves high up, and well out of the way of grazing animals, so that thorns are not necessary. You should notice that at the base of each leaflet and each pinna, is a pulvinus, and that at about five o'clock every evening the leaf- lets move downwards, and the pinnae also. The blades of the leaflets, instead of being more or less horizontal, thus come to be nearly vertical, so that while during 176 GENERAL BOTANY the day, they catch the sun's rays and let very little of the light and heat pass between to the ground below, at night the heat from the earth and the hot air can easily rise up and pass away. It is for this reason that the plant makes such an excellent roadside tree. Reduction in leaves and leaflets CASUARINA EQUISETIFOLIA, Forst. 01 Examine the smaller branches of CASUARINA, a tree, which, though not a native of India, grows very well here, and is planted very commonly in waste sandy places near the sea, for the sake of fire-wood, and also in peoples' gardens in the plains or the hills. The branches are brown and rough with sharp scales which occur in whorls or circles. On these branches arise slender cylindrical green organs, which, being green, do the work of leaves. But these green organs are not leaves. If you examine one, you will see that it is marked at intervals of about one- sixth inch with a whorl of very small triangular scales. There are shallow grooves too running longi- tudinally down from one whorl of scales to the next, and alternating with the next set of grooves. Now, no leaf structure bears whorls of scales, or anything else but hairs or glands. These green organs are in fact branches, and the small triangular scales which they bear represent leaves, though very much reduced and as leaves quite useless. As we find in nearly all cases of opposite or whorled leaves, those of one node stand not just above, but in lines between those of the next, so here, REDUCTION OF BLADE 177 the teeth of one whorl alternate with those of the next, and the grooves which run down from between each pair of teeth, alternate therefore with those from the next node (above or below). There is a small herbaceous plant, RUSSELA JUNCEA, Zucc. the Coral plant, very often grown in gardens in India, which shows something of the same habit. The stem and its branches are green and bear whorls of leaves, which sometimes are reduced to mere scales, at others are green and, though small, undoubtedly leaves, while quite large leaves often occur at the nodes. In this plant the change from the ordinary form of leaves to scales is not complete ; in CASUARINA it is. FERONIA ELEPHANTUM, Correa. The Wood-apple tree. This tree has a rough bark and many spines on the branches. These spines occur with the leaves, either in the axil of a leaf, or often below a bunch of leaves. But on looking carefully we find that in the latter case there is always the scar of a leaf below the spine, and that the spine is on one side of a bud of which it is really the modified first leaf (see p. 178). When leaves occur above a spine, they arise on an irregular lump, formed of abortive branches which do not develop further, but remain quite short and have only two or three leaves. The leaves are pinnate and often the rachis is broadened or winged. The leaflets are tough, very smooth, and if crushed smell strongly of aniseed. The 12 178 GENERAL BOTANY broadening of the rachis increases the area of green tissue which can do the work of assimilation, and being thick and tough this part would not suffer so much in a drought as would thin leaflets. The spines of course prevent animals eating the leaves and small branches, for some animals are very fond of aniseed oil, and here again as before the protection is all the better because of the shortness — amounting almost to total absence — of the axillary branch, so that the leaves are massed together close to the spines. CITRUS MEDICA, L. The Orange tree. The branches are green and angular, the leaves are spirally placed, i.e. are alternate, and at the base of each is a thorn, placed somewhat to one side of the minute axillary bud. On the upper branches of older trees these thorns are sometimes replaced by leaves, from which we must conclude that the thorn is not a modified branch, as it looks at first sight, but represents the first leaf of the axillary branch, which does not ordinarily develop further than the bud stage. This too in FERONIA. The leaf itself consists of two parts, a broad winged stalk and a blade, and at the junction of these two there is a sort of joint, a thing we never find in ordinary simple leaves. Compare this now with the leaf of FERONIA, which has several leaflets attached to the winged rachis, by joints very much like this in appearance. If there were on FERONIA only one leaflet, it would be exactly like the leaf of the Orange. We conclude, therefore,. REDUCTION OF LEAFLETS 179 that the Orange leaf is not simple, but is really a com- pound leaf having only one leaflet. The reason for this curious structure is a little diffi- cult, but we can see that by the rachis being broadened and by the branches being green, the area of green tissue exposed to the light is increased so that more assimilation can be done, while being thicker and tougher in nature, the broad petiole is less likely to suffer in an extra day or hot wind, than would ordinary leaflets. If the leaflet is held up against the light, a number of light spots will be seen. These are globular drops of oil (enclosed in special glands) which, being trans- parent, show white against the dark green tissue. The smell and bitter taste of this oil prevents animals eating the leaves, and the latter are also protected by thorns. But the axillary shoots here are not short, perhaps because the oil renders that unnecessary. PARKINSONIA ACULEATA, L. The branches are green, and have short stiff thorns, half an inch long. From the sides of these thorns spring (generally four) pinnate leaf -like organs. These have each a well marked pulvinus, a broad rachis, and numerous small elliptic leaflets. At the base of the thorn are two small marks or scars, and if we examine the youngest portion of the branch, we shall see that these are the scars of small pointed stipule- like scales. Just above the thorn is a small bud. Since there is no leaf-scar just below the thorn^ it cannot be of a branch nature, while the stipules on the sides and the minute bud in the axil, point to its 180 GENERAL BOTANY being a leaf. If it is a leaf, then the leaf -like organs which arise on it are pinnae and not leaves, and this is confirmed by the fact that there are no buds in their axils, as there would be if the thorn were a branch, and they were really leaves. Compare PITHECO- LOBIUM DULCE (p. 174). If we examine this plant when new growth is taking place at the beginning of the hot weather, we shall find the spines, and the stipules also, soft and green. Sometimes the stipules do not fall off, but harden and become thorns like the main rachis. The very young pinnae curve upwards at first with the minute leaflets folded flat along the upper side of the rachis. The conversion of the main rachis of the leaf into' a thorn, and the reduction in the size of the leaflets, is an adaptation to zerophytic, or dry land and air, conditions. Corresponding with the reduction in the size of the leaflets the rachises of the pinnae have become broad, and being much harder and tougher than the leaflets, are not so liable to be dried up and withered by a hot wind. Notice too, that when a branch has been picked for some time, or while it is on the plant if the day be hot, the leaflets fold flat along the upper surface, their upper sides downwards. A similar folding of the leaflets occurs in a num- ber of plants with compound leaves, and further reference to it was made in chapter xiii. We cannot doubt that it is of a protective nature, serving to prevent the leaflets being scorched by the hot mid- day sun when the air is dry, or suffering when for any reason, the supply of water is diminished. A FLATTENED SHOOT 181 similar movement at night appears to have for its object the protection of the green tissue against chill. OPUNTIA DILLENII, Haw. The Prickly-pear. At first sight, this plant seems to be made on an utterly different plan from the ordinary. It has normal roots but the shoot instead of consisting of cylindrical stems and branches, with flat green leaves, seems to be made up of a number of very thick flat oval seg- ments fixed end to end. These segments are studded with little areas, from which project numerous short barbed hairs (the fact that they remain so firmly stuck in the human skin shows that they are barbed) and one or two long yellow thorns. Occasionally on the uppermost segments, especially during rains, there are to be seen short thick green leaves, and, above each, one of these little thorny areas, which therefore are axillary to the leaves. These leaves soon fall off, so that most of the plant, and indeed the whole of the plant for much of the year, has no leaves at all. And this is why the stem is green — to make up for the absence of the leaves, and it is flattened for the same reason that leaves are flat, to expose the greater surface to the air and light. Each segment of the shoot represents a portion of the axis, for the shoot does not grow straight in monopodial growth, but after a few weeks, the direct growth ceases, and is continued by a lateral branch. This is the reason for the segmentation of the shoot, and for the irregular way in which the segments are attached to each other. 182 GENERAL BOTANY The thorns may represent axillary branches, as they are in many other cases. But the barbed hairs ap- pear to be a special structure peculiar to the family to which the Prickly-pear and Cactus belong. The spines, undoubtedly (as in the other cases cited) keep animals from eating the plant, for were it not for them, this luscious watery plant would .soon be eaten by animals, during the hot dry months. But we cannot say that they have been developed with the purpose of keep- ing cattle from eating the shoot. Indeed all these spines and thorns that we have examined, are probably the direct result of the dryness of the air, as was said in the case of ZIZYPHUS and the Barberry. ACACIA MELANOXYLON, R. Br. The Black-wattle which is planted on hill stations and also occasionally on the plains. This tree has alternate lanceolate or elliptic, slightly falcate leaves which stand stiffly upright. There are three things about these leaves which at . once strike a careful observer. In the first place, they are utterly different from those of all other Acacias. In the White-wattle, ACACIA DEALBATA, for instance, the leaves are bipinnate with numerous small leaflets, and the same is true of all Indian Acacias — for example ACACIA ARABICA (fig. 43). In the second place, these leaves have no marked midrib, but several veins which start from the base and curving out come together again at the tip — a basal venation which is rare among dicotyledons. In the third place, one sees at once that if the stalk be not twisted, the plane of the leaf is not at right angles to- PETIOLE AS BLADE 183 the twig on which it is borne, as it is with all leaves, but passes through it. The explanation of these anomalies will be found on some of the shoots which spring from low down on the trunk in the deep shade of the upper foliage,, or from the stump of a tree that has been cut down. There we find bipinnate leaves with small .leaf- lets, and a broad petiole that shows exactly how the upper * leaves * have been formed. We may find at every stage, leaves with several pairs of pinnae and a slightly broadened petiole, to leaves with broad petiole and only two small pinnae, and finally the broad red petiole alone without leaflets (fig. 44). This broad petiole standing stiffly upright with its plane vertical, thereby catches less of the sun when FIG. 43 ACACIA ARABICA, Willd. 184 GENERAL BOTANY directly overhead (its hottest time) than if horizon- tal like an ordinary leaf. Morning and evening the leaf faces the sun more, but its rays are then less intense. The object of the plant in doing without leaflets and having instead a broad vertical green petiole appears, then, to be to escape the sun's rays when they are strongest (cf. on buds pp. 96 & 163). FIG. 44 ACACIA MELANOXYLON, R. Br. Young plant showing the change in the form of the leaves. HOMOLOGY OF TENDRILS 185 When seed of this Acacia is sown, the young plant always has after its cotyledons, small but normal bipinnate leaves. Gradually as the seedling grows the leaves that arise have in succession, smaller pinnae and broader petioles, till the usual flat ' leaf ' appears, after that no more pinnate leaves are formed. The seeds germinate so readily that some should be sown and this change noted. It is an instance of a pheno- menon common enough among animals, of an indivi- dual going through in its own life the same sort of changes as have occurred in the evolution of the species. Homology of tendrils In chapter x, section 4, we learnt that many plants climb, fastening on to other sturdier trees and shrubs by means of thin sensitive organs called tendrils, and it was said that these tendrils are usually to be considered as modified forms of ordinary organs such as branches or leaves. Now examine the tendrils and flowering parts of the •ordinary ANTIGONON. The tendril is three-pronged at the top. On the lower parts of the plant it arises like a branch in the axil of a leaf, in the upper parts, it is obviously a continuation of the axis of an inflorescence (i.e. of an ordinary branch), and is homologous, there- fore, with the end of a branch, or inflorescence-axis. In the case of the PASSIFLORA, the Passion-flower, .and many other plants, the whole of the axillary branch is modified as a tendril. In VITIS the Vine, etc., some of the tendrils stand opposite to the leaves, and in the axil of those leaves there is no bud. Hence the tendril 186 GENERAL BOTANY is really the continuation of the main axis, the apparent continuation being the axillary branch of that leaf — a case of sympodial growth. In most cases the tendril is to be considered a modified leaf or part of a leaf, or leaflet. In various species of BIGNONIA (fig. 23), this is easily seen to be the case, the leaf consisting obviously of two leaflets and a tendril. Occasionally, one may find one or more of the branches of the tendril expanded into blades, that is, reverted into leaflets. In PISUM, the common Pea, the whole of the leaf is modified into a branched tendril, the branches corre- sponding to leaflets, and the functions of the leaf are undertaken by the very large stipules. In GLORIA SUPERBA (fig. 22] the tip of the leaf is prolonged as a tendril. In SMILAX outgrowths from the base of the leaf act as tendrils. These are sometimes said to be modified stipules, but as no others of the plants of that family possess stipules, it is better to consider them as special tendrilar outgrowths of the leaf-base. In CUCUMis, the Melon, Cucumber, etc. and other CUCURBlTACE^i, the tendril is partly a branch partly a leaf structure. Emergencies So far we have been studying plants with thorns,, spines or other structure which by observation of their position and surroundings we must consider to be modi- fied branches, stipules or parts of leaves. But there are many plants with structures to which we cannot assign in the same way the same morphological importance. EMERGENCIES 187 Thus examine branches of Rose, or TODDALIA ACULEATA, or LANTANA, or RUBUS. There are curved prickles on the branches and leaf stalks, but unlike those that we have studied, they seem to be in no particular arrangement, and are scattered without reference to the position of any other organ. We cannot therefore consider them as modified branches, stipules or anything else, but only as emergencies, that is, merely raised and hardened portions of the outer tissues. It is quite easy to remove one with a small piece of the cortex, for they have no connexion with the central part of the shoot, as have thorns that are modified branches. The same is the case with the strong hard thorns that occur on the branches and stem of ERYTHRINA INDICA, and of BOMBAX MALABARICUM, the Silk-cotton tree. They of course, serve the same function as other thorns — from the physiological point of view they have the same value, in homology they are utterly different, being, like hairs, outgrowths of the surface. CHAPTER XVI THE INFLORESCENCE 1. In some plants, as for instance, NELUMBIUM the Sacred-lotus, and NYMPHAEA the Water-lily, the flowers are borne singly on long leafless stalks which rise straight up out of the ground from the root-stock ; in others again, there is a bunch or a head of flowers at the end of such a stalk, as in CRINUM, EUCHARIS the Eucharis lily, TARAXUM the Dandelion, and several other COMPOSITE, and in KRIOCAULON. Such a leaf- less flower stalk is termed a scape. It occurs as a rule only on plants which have no leafy stem, but merely an underground root stock or bulb from which the leaves and the scape spring. Most plants, however, have leafy shoots above ground, and their flowers are borne on short stalks in the axils of the ordinary leaves, or on special branches, or at the ends of branches. The stalk of each in- dividual flower is termed its pedicel, and if there is a main stalk to the pedicels of several flowers it is termed the peduncle. The peduncle and the pedicel are to be considered as specialized branches, for they nearly always arise RACEMOSE TYPE 189 in the axils of leaves, or of small thin scales called bracts, and these may be regarded as reduced leaves, since we may find every stage between real normal leaves and very small scale-like bracts even on the same plant, for example in GYNANDROPSis and CLEOME (fig. 8, p. 43). Just as there are two systems of branching in the vegetative parts, the monopodial and the sympodial systems, so also are there two main systems in the flowering parts, called respectively the racemose and the cymose. 2. In CLEOME, ERYTHRINA, CLESALPINIA, POIN- CIANA the Gold-mohur, BRASSAIA NIGRA the common Mustard, and many other plants, the flowers are arranged on short pedicels, one after another along a main peduncle, which may continue to elongate in definitely giving off branches (pedicels), as in the mono- podial system of. branching. This kind of inflorescence is termed a raceme, and in it we see that the oldest flowers are at the base, the younger nearer the top. Of this racemose arrangement there are several different types, termed respectively :— (i) The corymb, when the pedicels of the younger flowers are shorter than those of the older, so that the flowers themselves stand at about one level, and the bunch is more or less flat, as occurs in JATROPHA, GYNANDROPSIS (at least in the younger stages), and many other plants. (ii) The spike, when there are no pedicels but the flowers are sessile on the main axis (peduncle), as in ACHYRANTHES (fig. 45) CELOSIA (Cock's comb), TRITICUM (Wheat), SORGHUM (Cholam) and others. 190 GENERAL BOTANY (iii) The Spa- dix, when the main axis is en- larged and fleshy, and the flowers are sunk in it, as in plants of the Arum family, ACORUS (Sweet- flag) CALLADIUM, etc. There is generally a large leaf-like organ called the spathe, which encircles and encloses the spadix at least before the flowers are matured. A spathe occurs on many plants which have not a spadix — in EUCHARIS, and CRINUM it is a thin brown papery thing which covers the flower buds •at first, and hangs down untidily afterwards. In some palms it is extremely large being two or three feet long and quite thick, and in the Arum family it is often very gaily coloured. For instance, in CALLA CETHIOPICA (the so-called Arum-lily, which however, is not a Lily .at all), it is large and white, and is the principal FIG. 45 ACHYRANTHES ASPEKA, L. UMBEL 191 ornament of the plant. In ARIS.EMA (the Cobra- plant) it is marked with brown lines and bends over the spadix, in ANTHURIUM it is often a bright red colour. (iv) The umbel when as in CRINUM, EUCHARIS, D^MIA EXTENSA (fig. 58). HER ACLEUM the Hemlock, PASTI- NACIA the Parsnip, CORIANDRUM the Coriander, and others, the pedicels spring from the same level, as if the internodes between them, i.e. of the peduncle were re- duced to nothing (fig. 46). In CRI- NUM, EUCHARIS, AGAPANTHUS and other monocoty- ledons, the umbel is borne on a scape and is at first enclosed in a large spathe ; in D^EMIA (fig. 58) and others of the ASCLEPIAD family, umbels occur short peduncles in the axils of the leaves of the shoot without any enclosing bract. In HERACLEUM, PASTINACEA and a number of other plants like them, there is a whorl of bracts at the point where the Fruit FIG. 46 HERACLEUM SPRENGELIANUM. W. & A 192 GENERAL BOTANY pedicels spring, and the umbels are themselves col- lected into larger umbels. This type of inflorescence is so distinctive that the name UMBELLIFER^E (umbel- bearing) has been given to the family to which these last belong. Some of the other umbels are really cymose in origin, see below. (v) The capitulum or head, when the flowers are sessile on a flat or slightly convex receptacle, as in the Sunflower, Zinnia, and all plants of that kind. This may be considered as formed from an umbel by reduction of the pedicels, so that the flowers become sessile at the end of the common peduncle ; or as a condensed spike, the axis of which is shortened almost to nothingness, and expanded laterally. In the raceme the lower flowers open first, the upper and younger later, and so of course, it is in the spike. In correspondence with this, in the true head the outermost flowers open first, the innermost last, as can be seen in any Sunflower. This type of inflorescence is again so distinctive as to have given the name COMPOSITE to a very large and important family of plants (almost the largest of all families), which include EUPATORIUM the Hemp-agrimony, HELIANTHUS the Sunflower, COSMEA, GAILLARDIA, CHRYSANTHEMUM, GNAPHALIUM the Everlasting, CNICUS the Thistle, TARAXUM the Dandelion, SONCHUS the Sow-thistle, COREOPSIS and all plants like them. Condensed inflorescences very similar in appearance to the capitulums of the COMPOSITE, occur in other families. The head of ERIOCAULON the Hat-pin plant of the hills, is composed like that of the COMPOSITE, of small flowers massed together with a common involucre CONDENSED TYPES 193 of green bracts below, but dif- fers from the latter in that the individual flowers are per- fect having well developed sepals. The Teazel, DIP- SAC us, has also a head of flowers, with bracts be- low, just like that of the COMPO- SITE, but the flowers open first in a ring about the middle of the spike, about half way between the centre of the head or summit of the spike, and the circumference or base, and it is FIG- 47 therefore prob- A SINGLE CYME FROM A BUNCH OF IXORA ably of a CVniOSe FLOWERS nature really. The common Below diagram snowing the arrangement ~ , . of the flowers. Numbers denote the order of bcablus> 3CABI- development. OSA, belongs to A typical DICHASIAL cyme. the same family. 13 194 GENERAL BOTANY In other cases the condensation is less complete, and not only are the flowers all perfect, but the bracts occur between them, and not all at the bottom in the form of an involucre, for example in GOMPHRENA one of the family AMARANTACEJ3. 3. But examine now a bunch of flowers of IXORA, or CINCHONA, or the common pink SILENE the Catch-fly of gardens on the hills1. Some may be fully expanded, others still folded in bud; and they are mixed up to- gether in, at first sight, no such obvious arrangement, as in the corymb or head, where those at the edge open first, the middle ones last. But the bunch can be easily divided into three lesser bunches, and these again into three, and we may go on dividing by three, till we come at last to a little group of three flowers only, of which the middle one always opens or unfolds earlier than the side ones (fig. 47). This is a typical cymose arrangement, each little group of three flowers being termed a cyme. In it the peduncle (of the cyme) ends in a flower, and has two little scales (bracteoles) on it, from the axils of which arise the pedicels of the side flowers. The order of the flowers is, therefore, the exact opposite to that in the raceme, for in the latter the terminal flower is the last to be formed and to open, the lateral flowers are earlier, while in the cyme the central flower opens first, the lateral after it. Of cymose inflorescences there are also several types, termed respectively :— (i) The dichasial, when the branches (pedicels) are in pairs as in IXORA, and CARISSA CARUN- DAS, HYPERICUM JAPONICUM, etc. and each pair CYMOSE TYPE 195 is at right angles to the one from which it arose. This happens only in plants with opposite leaves