2 THE STUDY OF PLANTS 
upon plants or upon plant-eating animals, it follows that if 
it were not for plants the whole animal kingdom, ourselves 
included, would soon starve. So too in the matter of clothing 
we depend partly upon the plants which yield cotton, flax, 
and similar materials, and partly upon those plant-fed ani- 
mals which give us silk, wool, and leather. Forests yield the 
chief materials for ships and other means of transportation, 
for houses, furniture, and innumerable utensils. The fuel 
which cooks our food, heats our dwellings, and drives the 
machinery of factories, ships, and locomotives, comes either 
from plants recently alive or from coal-plants which died 
long ages ago and were buried in the earth. In sickness, too, 
the drugs which allay our suffering and help to cure us, are 
almost entirely of vegetable origin. So whichever way we 
turn we find plants serving us in most important ways— 
feeding us, clothing us, sheltering us, warming us, working 
for us, and making us well—indeed, our dependence upon 
them is so constant that we seldom realize how intimately 
our lives are bound up with theirs. 
4. Human needs and the needs of plants. We must not 
. forget that plants as well as animals are living things growing 
from infancy to old age, needing food and protection, and 
bearing offspring. Their various parts may be useful to us, 
but primarily are of use to the plants themselves. The plant- 
food which we take for our use, the plant had accumulated — 
for its own purposes. The thorns which make a hedge effect- 
ive against intruders, serve similarly as a defense to the 
shrub which bears them. Not only then as contributors to — 
our welfare, but as sharers in the mysterious gift of life, 
should plants have a profound interest for mankind. How 
plants obtain their food, how they avoid injury, in what re- 
spects they are like animals, and how they differ from them— 
such questions soon press for an answer, and then it is seen 
that all plants, even the most humble, may have secrets 
of value to tell us. 
5. How plants are named. Whenever many objects are 
to be studied and compared, it is necessary to have some 
convenient system of naming them and some method of 
expressing the various degrees of resemblance and difference 
