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CROPS NURTURED BY MAN 



Man makes wheat grow where formerly buffalo grass thrived; but only by constant 

 care and management. Wheat never grew so luxuriantly by itself; yet how quickly 

 would it be replaced by other grasses should man cease his nurture! 



We saw that rabbits, introduced into Australia, became a pest (see page 

 564). They interfered not only with the native wild animals but with agri- 

 culture and sheep- raising. Bounties were paid to encourage the destruction 

 of the rabbits. The water-cress was similarly introduced into New Zealand, 

 and in a comparatively short time it choked all the rivers. Elodea and the 

 muskrat were brought to England and multiplied much more rapidly than 

 they had done in their older habitats. The English sparrow was brought to this 

 country to destroy the tent caterpillar, which was injuring shade and orchard 

 trees. The sparrows took to living in the cities too, feeding largely on the un- 

 digested seeds in the droppings of horses. By the end of the century they 

 had become a nuisance. They were not helping to fight the insects, and they 

 were interfering with other birds. They have been gradually disappearing 

 from our cities, however — but not because we have done anything to dis- 

 courage them. We replaced our horses with automobiles, which yield no by- 

 product that sparrows can use. 



Mining versus Cropping Man was intelligent enough to devise weap- 

 ons and tools which enabled him to kill and destroy out of all proportion to 

 his actual needs. Using his excess power, he changed the balance among living 

 species in the areas he occupied. In his hurry to get a quick profit from the 

 forest while the getting was good man not only destroyed the forest, but 

 exterminated game and fur animals and birds. He brought about far-reaching 

 changes in the soil and water relations of areas stretching across the states. 



589 



