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.