292 



LIVES OF PLANTS AND ANIMALS 





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E7. S. Fores* Service 

 In the tropics, where heat and rainfall are plentiful, vegetation is abundant. Why is this true? 



causing the death of the fish. Fish breeders know how sensitive 

 young fish are to changes of temperature, and any fisherman knows 

 that the trout will go into deep water or will lie in the cool spring 

 holes during hot weather. 



We know plants either die or become dormant in winter, while 

 many animals hibernate (become inactive) during the cold 

 weather. But we are not so apt to think of the effect of con- 

 tinuous cold or equally continuous warmth as seen in the arctic 

 regions or in the tropics. The wealth of tropical vegetation and 

 animal life is due in part to the higher temperature. Animals 

 develop faster and go more quickly through their life cycle. In 

 southern California the heat often transforms garden biennials 

 into annuals and the converse is seen in cold countries where 

 annuals may be changed for a time to biennials. High temperature 

 seems to increase the amount of certain pigment in birds and other 

 animals so that they are more highly colored in hot climates. 



On the other hand, some fish, as the trout and salmon, are 

 found only in cold water. Dr. H. B. Ward of the University of 

 Illinois says that when salmon ascend a stream to lay their eggs 

 they will invariably take the cooler branch of the river. In 

 ascending the side of a mountain we find different types of animals 



