The science of botany consists of many branches and, in most of them, the microscope is the scientist’s constant aid. The study of bacteria, really a branch of botany, we have dealt with in another chapter, so here we will omit these interesting though lowly plants. By far the number of botanical objects for the microscope consist of sections—exceedingly thin slices of whatever portion of the plant is being examined, cut either with a sharp razor or a special instrument called a microtome. Section cutting, though not a difficult accomplishment, requires a considerable amount of practice and cannot be learned from a book; all our descriptions, therefore, will be confined to objects from the plant world which may be studied without the assistance of razor or microtome.

One cannot help being struck with the fact that green is the prevailing colour among plants and the reason is not far to seek. If we take a cabbage leaf and carefully tear off the skin, we shall find green spongy matter below. A little of this green material may be examined under the microscope and will show us rounded green bodies composed of a substance called chlorophyll. Now chlorophyll is absolutely necessary to all plants, except the fungi and to one or two parasitic plants. It is necessary because, by its aid, plants can build up raw food material into food which will be useful to them. It is not formed in darkness; that is why a board, a roller or any similar object left on a lawn, causes the grass below to turn yellow; it is the reason also why certain parts of plants, not usually green, turn that colour when exposed to the light. Chlorophyll does not always occur in round globules, sometimes it is found in bands.

One of the most interesting botanical studies for the microscope is furnished by the leaf of the American water-weed. This plant, which was introduced into the country from North America some years ago, has now spread far and wide and is easily obtained. A leaf which is slightly yellowed with age is the best to take for the experiment. It should be cut from the plant, placed at once in a small bottle of water and kept warm for a few hours; this may be accomplished by keeping the bottle in one’s pocket. After a sufficient interval, put a drop of water in a clean slide, put the portion of leaf in the drop of water, cover with a coverslip and examine with a moderately high power. If the experiment has been properly carried out a wonderful sight will reward us. We shall see that the leaf is divided into a number of divisions called cells; this name has been handed down from the very early days of the microscope, because of a supposed resemblance to the cells in a bee’s honey comb. In each cell we shall see signs of activity, the little round grains of chlorophyll are there, but instead of being stationary, as in the cabbage leaf, they are slowly moving round the walls of each cell. In reality they are carried along in the stream of living matter within the cell. It is a wonderful sight and brings home to the observer very forcibly a fact which is liable to be forgotten, that the plant is just as much a living being as an animal. Perhaps our experiment will not succeed at the first attempt, then we must try again; maybe we have been too rough in detaching the leaf or we have not kept it sufficiently warm. Sometimes the movement may be started by slightly warming the slide over a flame; too much heat, of course, will kill the leaf.

We shall see this green colouring matter over and over again in our botanical studies, in fact it is found in all manner of situations, in leaf and stem. Very often its colour is hidden by sap of another colour, as for instance in copper beech leaves or in the brown seaweeds. Chlorophyll dissolves in alcohol, however, and this affords us a ready means of detecting its presence though we cannot see its green colour. If we boil any leaf, suspected of containing chlorophyll, in alcohol we shall obtain a solution with rather peculiar properties because, when held up to the light it appears green, but when light is reflected from it, it appears reddish.

From the under side of the cabbage leaf whence we obtained our first specimen of chlorophyll, we must now take another piece of skin. If we perform the operation properly the skin will be colourless, like a piece of thin parchment; any green colour will show that we have torn off more than the skin and we must make another attempt. Having secured our piece of skin we place it in a drop of water on a clean slide and examine it under the microscope. We first notice that the skin is divided up into a number of small areas called cells and dotted here and there amongst the cells are several oval bodies, containing chlorophyll. These oval bodies are the pores through which the leaf breathes, amongst other things. In the centre of each pore there is a hole, at least there is if the pore is open, for the two cells comprising the pore have the power of opening and closing.

It is interesting to try the same experiment with a fern leaf and to notice that there are pores, very similar to those of the cabbage, but that the walls bounding the cells of the leaf are irregular and that they contain chlorophyll. We may try several other leaves and also the upper and lower surfaces of leaves, then we shall soon learn that, in leaves with distinct upper and lower surfaces, there are far more pores on the lower than the upper surface; leaves like those of the iris have almost the same number on each side, and floating leaves, like those of water lily have all their pores on the upper side. There is a reason for this; the pores are likely to become filled with dust, being on the lower side they are protected somewhat; flat leaves, by their shape, afford no protection and floating leaves must have their pores on the upper surface to obtain air.

There are many other interesting things we may learn about leaves, with the help of our microscope. The cabbage leaf is quite smooth, but if we are observant we shall have noticed that sometimes each leaf appears as though it had been powdered, it has a decided bloom. The bloom does not appear on the leaf for ornament but for a purpose. It is a waxy substance and it prevents the leaf from losing moisture too quickly in dry weather. This is very important for the plant; if the moisture taken up from the soil were lost in the air too quickly by the leaves, the plants would wither and eventually die. It is not all plants which can wear a protective covering when danger threatens, most plants have either no protection or are permanently protected. There is a large class of plants with folded or rolled leaves; heather and marram grass belong to this class. We must examine some of these leaves and we shall find that all the pores are on the inside of the leaf whether it be folded or rolled. The reason for this is that moisture also escapes through the pores and, when they are thus protected, it is not carried off too quickly by drying winds.

Many plants are protected, as far as their leaves are concerned, at anyrate, by hairs. They take the place of the bloom in such plants as the cabbage. There are thousands of plants with hairy leaves and they will provide as many interesting objects for our microscope. Let us examine as many as we can for the hairy covering of each plant will be a little different to the one we examined previously. There are simple hairs, quite ordinary affairs, forked hairs, branched hairs, T-shaped, star-shaped and club-shaped hairs. If we are clever with our microscope we shall notice that, however complex each hair may be it is really nothing but one cell of the skin of the leaf which has assumed a peculiar shape.

The leaves of the nettle are armed with ordinary and stinging hairs; the latter are worth examining and we shall notice that there is one great difference between all the other hairs we have examined and the stinging hairs of the nettle. The former are of one cell only, the latter of several cells. A high magnification will show that the stinging hair of the nettle is not quite so simple as it appears at first sight.

There are plants whose leaves are protected by very thick skins and others whose leaves become armed with hard flinty matter, so that they resemble stones rather than leaves.

If we can find some quite young seedlings we must manage to secure one or more for examination under our microscope. We must take one up very carefully and wash the earth from its roots—if we pull the earth away our specimen will be ruined. Near the tips of the root branches we shall see something which might be mistaken for mould. Our microscope will show us that they belong to the root; they are, in fact, root hairs. We shall very likely be able to make out that, like the leaf hairs, each root hair is made up of a single cell. The root hairs are interesting because it is through them that water is taken up by the plant from the soil.

In many plants a considerable space separates the root from the leaves. When we have learned how to cut sections, we can make slides for our microscope which will show us the whole course along which the water travels, from its point of entry at a root hair to its exit at a leaf pore. Although we have not yet reached that stage, it need not prevent us from seeing some of the minute tubes through which the water passes. Any fleshy stemmed plant will serve our purpose. We must tear it to pieces lengthways with a needle and we shall find many threads—this is not their correct name but it expresses our meaning—running the whole length of the stem. They run, in fact, from the tips of the root to the leaf, and may be seen as leaf veins. If we remove one of these threads and tease it with needles on a slide we shall reduce it to still finer threads. By the way, teasing in the sense we have used it here, means separating the various parts. Let us examine some of these fine threads, we shall see that some of them appear like coiled springs at first glance. A more careful examination will show us long tubes with spiral thickenings. We all know the garden hose-pipe with stout wire coiled round it as a protection; these tubes may clearly be compared with the familiar hose-pipe, where the rubber portion represents the cell wall and the stout wire the thickened parts of the wall. There is, however, this great difference, the wire is outside the hose-pipe, the thickened portion of the plant tube is inside the wall. These tubes are the ducts for water passing from root to leaf.

If the agricultural side of botany attracts us we shall not have much difficulty in finding many more objects from the fungus world than are mentioned in our chapter on Agriculture, whilst the study of bacteria may truthfully be termed never ending. Ponds and rivers teem with vegetation suitable for microscopic study. The testing of foods for impurities is largely botanical work. The botanist, of all men, need never allow his microscope to be idle.

Our British insectivorous plants are of great interest and they will supply us with some objects for our microscope. We only possess three different kinds of these curious plants in this country, the Bladderworts which live in water and the Sundews and Butterwort, which frequent moist, peaty land.

The pond-dwelling Bladderworts are not rare, indeed they occur in plenty in certain localities, but they are not very evenly distributed over the country and in some districts one may search for them in vain. It is worth while making a special effort to obtain a specimen. Each plant bears a number of hollow structures, the bladders. There is an entrance to each bladder, edged with stiff hairs and closed by a trap door, which opens inwards but will not open outwards. All these parts may be seen under the microscope as may the interior of a bladder; its walls are studded with short hairs. When small water animals enter a bladder, it is said that they do so to escape from their enemies; they are entrapped forever, they die and eventually decay. The juices which arise from their decaying bodies are absorbed by the hairs lining the bladder.

The Sundews are pretty plants, with rosettes of reddish leaves and minute white flowers. With the naked eye we can usually see many drops of clear liquid on the leaves, a number of substantial-looking hairs and a few insects adhering thereto. If we examine one of these hairs under the microscope, we shall see that it is club-shaped; it is, in fact, a hair which gives off a sticky liquid with the power of holding any luckless insect that settles thereon and absorbing its softer parts for the nourishment of the Sundew. An examination of a complete leaf with our pocket lens will show that where an insect has settled, several of these hairs have curled over so that they touch their victim. Because the hairs possess this power of movement they are often wrongly called tentacles.

Butterwort, like Sundew has a rosette of leaves but they are greasy looking and pale green. Their flowers are a pretty blue. Most probably we shall notice that the edges of the leaves are curled inwards, and if we look below the curled portion we shall surely find some captured insects undergoing digestion. The leaf of this plant makes an interesting object for the microscope. There are two kinds of hairs on its surface, short stout ones and longer knobbed ones; the former give off a sticky liquid which holds any small insects that touch it, the latter give off digestive juices. While the hairs are used in digestion, after the manner of those of Sundew, the leaf itself curls so that more of the hairs are brought into contact with the victim and thereby its digestion is hastened.

Many small flowers may be examined with low magnifications. When we examine them thus, we shall probably realise for the first time how beautiful are many of these seemingly inconspicuous blossoms. Grass flowers are always interesting; they are not ornamental it is true, but that does not detract from their interest. There is one part of each flower known as the stigma; it is the part on which the pollen grain must be placed in order that seeds may be formed. The pollen grains are taken to the stigmas in many ways, but the most usual agencies are insects and wind. In the case of grasses, wind is the agency and for that reason the stigmas of grass flowers are feathery, so that they can easily hold the pollen grains carried to them by the lightest breeze. We shall probably see many pollen grains entangled in the feathery stigma of the flower we are examining. In the flowers of other plants we shall find, when we magnify them, that there are all manner of contrivances on the stigmas, all designed for holding the pollen grains; hairs, knobs, hooks and the like.

An interesting collection could be made of various pollen grains, which are easily obtained by merely dusting the anthers of flowers on to a clean, dry slide. They are varied in shape, colour and size; some are smooth, some studded with spines, others again, those of the Mallow for example, have little lids which open when the pollen grain germinates. The germination of pollen grains is easily observed under the microscope, by putting a few of the grains in an exceedingly weak solution of sugar and water. The vigil may be a long one, but if the pollen grains are ripe and fresh, and the sugary solution sufficiently weak, the patience of the microscopist will be rewarded by the observance of the bursting of the pollen grain’s coat and the outgrowth of the pollen tube.

Other pollen grains worthy of examination, are those of various lilies, of Eschscholtzia and of Scotch Fir; the last named have curious little air-bladders, for the purpose of rendering them more buoyant.

Many lowly plants thrive in weak sugar solutions, after the manner of pollen grains. The yeast plant is one of them. A very small portion of yeast, in a drop of sugar solution, will show us one of the simplest methods of vegetable reproduction. Yeast is a fungus and it is also a plant composed of only one cell. Under the microscope, it appears as a colourless oval body. The sugar solution causes it to multiply and, after the lapse of a little time, most of the yeast plants will be seen to bear outgrowths, called buds, which grow larger and larger till, at length, they break away from the parent plants and start a separate existence. Sometimes, when these plants are increasing very rapidly, the buds will bear smaller buds and these again still smaller ones till a fairly long chain of yeast plants is formed.

It is always interesting and also instructive to make comparisons as we progress with our work. To illustrate our meaning let us compare the budding of the yeast plant with the budding of the hydra, which is described in our chapter on pond life. In the same chapter we described the division of a proteus animalcule into two separate organisms, a process which is also undergone by bacteria when circumstances are favourable to their increase. We shall find many points of similarity if we make careful comparisons, and several important differences.

Objects for the microscope we can find in plenty, without going far afield. The white mould which we can probably find in the larder, on a pot of jam or other food that has been allowed to stand for some time, will provide a good subject to start upon. A little of this plant, for such it is, carefully lifted on to a dry slide will show the threads of the mould, terminated by round black knobs. Breathe on the specimen and the moisture of your breath will cause these little balls to break and set free a quantity of fine dust-like bodies called spores. The spores will be carried about in the air, they are so light, and if they settle on a suitable medium they will germinate and start another growth of mould. The blue-green mould of cheese is constructed quite differently; its spores are not contained in any hollow structures like those of our first object, but grow in chains radiating from a central point, like the outstretched fingers of the hand. It is this fungus, by the way, which imparts the colour and flavour to gorgonzola cheese.

For some reason living organisms, possessing the power of movement, be it ever so slight, are always more attractive than those which are apparently motionless. Let us study two common objects from the plant world which may easily be obtained by any nature student, objects which owe their power of movement—not to be confused with locomotion, by the way—to the presence or absence of moisture in the air. On the under side of the fronds of many ferns there will be found more or less rounded reddish-brown spots. These outgrowths, for such they are, vary in position and shape according to the species of fern. An examination, with a pocket lens, will show that these brownish spots consist of minute tufts of knobbed structures, growing from the tissues of the frond. Sometimes the structures are naked, sometimes covered with a membrane. In either case, one or more of the knobbed structures is worth examining under the microscope; we shall then see that it consists of a stalk terminated by a thin walled portion, shaped like a bi-convex lens. Round the edge of the greater part of this lens-shaped portion there is a much more substantial-looking rim. Within the lens-shaped part we can easily see brown spores. If we have chosen our object at an opportune moment, any excessive moisture in the air will cause the thick-walled rim to straighten itself out, tearing away the thin-walled, lens-shaped part in so doing and setting free the spores.

Closely related to the ferns, the horsetails provide another interesting object for the microscope. The fertile shoots of these plants, somewhat resembling asparagus, though in reality belonging to an entirely different family, will, when gently tapped on a clean dry microscope slide, leave behind a pale yellow powder. The powder consists of spores, and most interesting they are. When dry, each spore will be seen to have four somewhat thread-like outgrowths, flattened at the end; breathe on the spores and each of the outgrowths will coil up so as to form a complete covering for the body of the spore. As drying takes place, these outgrowths gradually uncoil again.

We have mentioned spores several times in this and other chapters. Strictly speaking a spore cannot be compared with a seed, but for our purpose it is sufficient to know that spores are more or less seedlike in appearance and that they give rise to new plants when they germinate. They are found in all ferns, on horsetails, these odd plants with their creeping stems and rings of scale-like leaves, on club mosses, mosses proper and fungi but not on flowering plants.

Should the student of plant life not yet be satiated with following the suggestions we have made, he can turn his attention to fruits and seeds and the contrivances designed for their distribution. The fruits of goosegrass, popularly known as cleavers, are studded with little hooks so that they may adhere to any passing animal. The fruits of Burdock are similarly armed and if we make a study of fruits and seeds we shall find that this is a very common method of ensuring distribution. There are also a number of seeds covered with hairs which render them buoyant; those of the willow herb are easily found, so too are the fruits of dandelion, thistle and groundsel. These and many more will give us many an interesting hour, towards autumn.