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.