Preface 9 



upon tha more salient points. The avoidance of technical 

 terms is in many cases impossible, but I have endeavored 

 to reduce them to a minimum. 



It is of course impossible in such a story to avoid referring 

 to the work of biologists in other lands. Nor is it desirable. 

 Science is not bounded by political and racial lines, and the 

 work of American biologists can only be appreciated in the 

 light of what their colleagues in other lands have been doing. 

 The book is, however, a record of American biology, so that 

 reference to the work of other biologists will be only incidental 

 to the main trend of the story. 



A zoologist should perhaps apologize for the title, since 

 the main emphasis will naturally fall on that branch of 

 biology with which he is most familiar. The great principles 

 of life, however, apply equally to plants and animals, and 

 even though the examples which illustrate these principles 

 have been drawn mainly from the animal world, nevertheless 

 the title will be justified if the discoveries recorded are those 

 which in the main illustrate the laws which govern plants 

 and animals alike. 



