But man’s use of plants, in fact his absolute reliance upon them, is not the only reason for attempting to find out more about them, what they are, where they came from, how they live and produce their young. A knowledge of even a small part of such a science opens up a rich field of inquiry involving a concept of plant life of greater interest than mere bread and butter. For those with an eye to see and knowledge to interpret, a landscape with its trees or flowers or marshes may contain a host of hidden secrets of dramatic import. Unfolded before one may be found a spectacle of struggle and strife, quiet tragedies of the forest, the inexorable pressure of plants upon their neighbors, the woods upon the prairies or an apparently forlorn hope of some plant living in a hot desert or upon some icy mountain peak. And while these rather obvious things are happening how much more is hidden of the adjustments that leaves or flowers or roots or other organs of the plant are constantly making to the conditions about them. Upon the perfection of such adjustments to light, heat, or water, for instance, depends their very existence. Mistakes are fatal, the forces of nature seem peculiarly relentless, and it is literally a case where many are called but few chosen. Of the untold millions of seeds produced each year few ever grow, yet out of this enormous wastage springs all that makes the earth not only habitable but the beautiful panorama of vegetation to which we are so accustomed that it is nearly taken for granted.
The study of botany attempts to answer some of the questions raised above and many others. Subsequent parts of the book will deal with what plants are, the behavior of them, with the life histories of some of the better known ones, with the grouping of plants in families and their relationships one to another, with their uses to man, with the history of their development from the earliest times, and finally with their distribution over the earth. The latter will be discussed last because it is the most important of all the phases of plant life. How plants are distributed, whether as forest or prairie or thickets or what not, depends upon the response of individual plants and their organs to the conditions about them. The type of vegetation in different parts of the world has been dictated by the success of the survivors in meeting existing conditions and of having met them in the past. Upon this fact rests our civilization to-day. Upon this fact there has been reared a study the cultural, esthetic, and practical value of which may well outweigh any other.
While the study of botany is necessarily a technical one with a language all its own, its terms, though generally unfamiliar, are unexcelled for their purpose. They will be avoided here as much as a clear understanding of the subject will permit. The few that must be used will be explained where they first occur and it is assumed that the reader will understand their subsequent use.
CHAPTER I
WHAT PLANTS ARE
WHAT we commonly call plants, such as corn or buttercups or an oak tree, are so familiar that a definition of what plants are may seem needless. It would be quite so if these generally recognized examples comprised all the plant kingdom. Actually what are ordinarily thought of as plants make up only a fraction of the great plant world. The fact that our familiar roadside and garden plants produce blossoms followed by a fruit and seed, such as peas and beans and all the ordinary flora of any region, separates them at once from that other large group of plants that do not. Common examples of the latter class are the green scum on the ponds, moss, seaweed, the rust on wheat, yeast, disease-causing bacteria, the smallest of all known plants, and many others. Most of these organisms are so small that they can be distinguished only under the higher powers of the microscope. Some of them in their habits and growth are like the minute animals described in the volume of this series devoted to that subject. In fact there are organisms about which scientists are still in doubt as to their animal or vegetable character.
One or two characteristics common to most plants, however, separate them from animals and these are their method of getting food and their practically immovable mode of life. Animals, however simple, do eat and digest their food, plants take various mineral substances from the earth or air or water in the form of inorganic matter such as oxygen, carbon, nitrogen, and all the food materials found in the soil, and transform them, with the aid of sunshine, into the structure that characterizes each particular form. Plants, then, may be defined as any living organism that, with minor exceptions, has the power to assimilate inorganic substances and transform them into organic matter. Nothing else in all the realm of nature has this power. It is a possession beyond all price, this ability to take from the soil and air and water simple chemical substances and under the magic of sunlight transform them into the wonderful plant life of the world. But this faculty has its handicaps, for it is usually, though not always, associated with inability to move from place to place, which, in some measure, even the simplest animals can accomplish.
It will be readily understood that this definition of plants includes many other things that are commonly attributed to the plant kingdom. For our purpose the discussion of these relatively unfamiliar forms of plant life will be left until later. A rough and ready distinction between those plants that everyone recognizes as such and those others like yeast and microbes, which are plants to most of us only by virtue of the definition given above, is that the first group produce flowers and seeds and the second do not. It should not be forgotten, and it will be shown later, that this is not a true distinction, but for practical purposes of dividing the plant kingdom it suffices.
1. Flowering Plants
The fact of outstanding importance to everyone who really looks at most plants is that part of them are above ground and part below. This simple observation carries with it the recognition of a fundamental difference of plant structure, namely roots and stem. Most plants bear obvious leaves, and at some time in their life flowers, inevitably followed by fruits and seeds. The ideally perfect plant would consist, then, of root, stem, leaves, flowers, fruit, and seed. These are subject to many changes of form, sometimes they are put to strange uses, and occasionally one or two may be lacking, as the stem is apparently from many violets, and leaves from some cactus and from the Tjemoro tree of Malaya. In fact, so varied are the different forms of these common attributes of most plants, so important are these differences of structure that no right understanding of plant life can be had without examining each in some detail.