62 



BOTANY 



are thus actually exterminated. Many of our common weeds 

 have been introduced from other countries and have, through 

 their numerous adaptations, driven out other plants which 

 stood in their way. It is evident that the plants which are best 

 adapted to changes in their surroundings, those plants which 

 have allowed themselves to be molded to fit into new conditions, 

 are the successful ones. Such is the Russian thistle. First in- 

 troduced from Russia in 1873, it spread so rapidly that in twenty 

 years it had appeared as a common weed over an area of some 

 twenty-five thousand square miles. It is now one of the greatest 

 pests in our Northwest. 



Economic Value of Fruits. — Our grains are the cultivated progeny of 

 wild grasses. Domestication of plants and animals mark epochs in the 



^ — ^_ 



CORN "^ 





640 to 3200 bushels per sauare mile \ 



\oyer3ZOO 



10 



H 



ie_ 



Indian Corn Production— Percentage 



^A 



40 



i^ 



60 



JL 



80 



1 



iL 



-A 



m^ 



I 



Illinois 



Lowa 



Neb. Mo. Kan. Ohio Ind. Tex. Rest of United States 



advance of civilization. The man of the stone age hunted wild beasts for 

 food, and lived like one of them in a cave or wherever he happened to be ; 

 he was a nomad, a wanderer, with no fixed home. The tribes which first 

 cultivated the soil made a great step in advance, for they had as a result a 



