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PLANT BIOLOGY

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View in the Hemlock Forest, New York Botanical Garden. - (Courtesy

of New York Botanical Garden.)

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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;

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