302 INDUSTRIAL PLANTS 



of to-day and of bog-plants that lived p6rhaps 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 fohage 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 sul^stances poisonous to us are also poisonous 

 to the plants which produce them, just as the venom of cer- 



