302 INDUSTRIAL PLANTS 
of to-day and of bog-plants that lived perhaps hundreds of 
years ago, but in imagination one is led back to strange 
forests. which disappeared from the earth many thousands of 
years ago and became turned to stone. Therefore, if we ask 
ourselves, Whence comes this material that men burn to get 
heat and power? the answer is, From the bodies of plants, 
some of which lived ages before the coming of mankind. 
And if we further ask, Whence comes the energy which all 
these plants have stored in their bodies, and left for us to 
set free? students of nature tell us, From the sun. That is 
to say, plants with foliage are the sunbeam-traps of our 
planet, and except for their marvelous ability to lock the 
energy of sunshine into the material of food and fuel, the 
life of the world as we know it would be impossible. How 
plants are able thus to store up sunshine, and why they do it, 
are questions to be answered only by the study of their 
processes of life. 
81. Useful and harmful plants in general. From our 
study of some of the more important groups of economic 
plants we have learned not only that the very existence of 
the human race depends upon the vegetable kingdom but 
also that the progress of humanity at every stage has been 
profoundly influenced by the properties of plants and by 
man’s knowledge of them. The needs of primitive man must 
have been met largely by wild plants. Through the cultiva- 
tion of plants, as we have seen, civilizations were developed 
in those regions where the most useful plants grew most 
abundantly. The desire for spices and similar luxuries led 
to the discovery of America. The vegetable products of the 
New World are now revolutionizing human life to the re- 
motest ends of the earth. 
Our brief study of vegetable foods, food-adjuncts, medi- 
cines, and raw products has shown that what we take from 
plants for our own use has often a similar use for the plants 
themselves, though sometimes the use is quite different; and 
in some cases, so far as we can see, the product is of no use 
whatever in the plant’s economy. In other cases it has been 
found that substances poisonous to us are also poisonous 
- to the plants which produce them, just as the venom of cer- 
