PLANT BIOLOGY CHAPTER I GENERAL INTRODUCTION 1. Lifeless Things and Living Things. As we look about us, we find that the world in which we live is wholly composed of two classes of things, which we commonly speak of as living things and lifeless things. Soil, air, and water, for example, we know to be lifeless. Water is probably the simplest of these three so far as its composition is concerned. Soil, on the other hand, is very complex in composition, being formed of nearly all the substances known to the scientist. Enveloping the earth is a mixture of gases called the atmosphere which extends outward in every direction for a distance of about fifty miles. Everybody knows, too, that over the surface of the earth, in the water, and even in the air are countless numbers of living things which we designate as either plants or animals. One might think that it would be an easy matter to set down the characteristics by which living things are distinguished from those that are lifeless. And such is the case when we compare a rock in a field with a horse that is feeding beside it. Unlike the animal, the lifeless rock is unable to move itself, it neither eats nor breathes, and it gives no evidence of feeling or of will power. But suppose we select for comparison a railroad locomotive and a horse. Both move; both need a plentiful supply of air; both develop heat and power to do work; and both give off certain waste matters. The horse, we may say, requires food, but so does the engine; for coal and water are as necessary for the development of heat and power in the engine, as food and water are for a similar purpose in the horse. When we try to state characteristics that will distinguish all plants from all lifeless objects, we find the task still more difficult; for most plants do not move about from place to place, it is difficult to realize that they give off heat, and they do not give evidence that they have conscious feelings as do the common animals. In spite, however, of these similarities, we are usually able to distinguish living from lifeless objects at least by the three following characteristics. 2. Growth of Living Things. In the first place living things use some of the food they eat for growth. No one ever heard of an engine or other lifeless object beginning as a small machine, and then slowly growing larger until it comes to have many times its former weight. pens to all plants and all animals. instance, at birth weighs seven to eight weight is over twenty times as great. And if we try to compare the weight of an oak tree with that of an acorn from which it started, the amount of increase we find to be enor mous. Yet this is what hapThe average child, for pounds; while a man's 3. Repair of Living Things. — In the second place, parts of a locomotive or of any other lifeless machine by continual use become worn or broken, and the engine must be sent to the machine-shop for repairs. Our bodies, too, are being constantly worn away; for every time we make a motion of 1 While it is true that icicles and other crystals apparently grow, this kind of growth is brought about wholly by the addition of material to the outer surface. any sort, some of our living muscle is used up; every time we think or exert our will power, some of the living brain substance is probably changed into dead waste material. But in contrast to lifeless machines, our bodies are self-repairing. The food we eat not only goes to increase the size of the body; it also furnishes material to make good the wear and tear of everyday life. This power of self-repair is likewise present in all animals and in plants as well. 4. Reproduction of Living Things. A third characteristic that distinguishes living things from those that are lifeless is the fact that they produce seeds (in the case of plants) or eggs (in the case of animals), which in turn come to form plants or animals like those by which these seeds or eggs were produced. No lifeless object can do this. We shall find in our laboratory study that, while there are a great many different methods of producing these new organisms, still in their essential features these various methods of reproduction are much the same from the lowest plants to the highest animals. 5. Summary. - -In brief, then, we may say that all living things have the power of growth from within, of self-repair, and of the reproduction of their kind; but that so far as we know lifeless objects possess none of these powers. 6. Science and its Subdivisions. - Ever since the dawn of history we find that mankind has been seeking to learn the secrets of living and lifeless matter. During the past century our knowledge has increased so rapidly that many sciences have been completely rewritten. The discoveries, for example, of the characteristics of radium and of X-rays have revolutionized much of what was formerly believed as to the properties of lifeless matter. In the same way our increased knowledge regarding germs and other microscopic plants and animals has made possible the scientific treatment of disease, and what is more important, the prevention of disease. As our knowledge of the living and lifeless world has increased, it has become necessary to divide this knowledge into a great many different branches, some of which are physics, chemistry, geology (a study of the earth), mathematics, psychology (a study of mind), and biology. = 7. Biology (from Greek, bi'os = life + lo'gos discourse) is the general name given to the study of all living things. Hence, this science treats of both animals and plants. If we confine our study to the structure and activities of plants alone, we call this part of the science plant biology, or botany. Animal biology, or zoology, on the other hand, treats of animals. So-called human physiology (better known as human biology) discusses man, the highest type of the animal kingdom; hence, it is a branch of the science of zoölogy, which in turn is one of the subdivisions of the study of biology. |