Introduction 7 



again two lines of inquiry : (1) Is the crop suited to the 

 general conditions of the region? (2) Are the conditions 

 of environment and the cultural practices afforded the 

 crop such as to result in maximum yield? It is not ex- 

 pected that any considerable number of facts enabling one 

 better to answer the first question shall be presented in 

 this book; such facts, at any rate, may be only incidentally 

 touched upon. The fundamental facts developed should, 

 however, enable one to observe, test, and answer for himself 

 more completely any question which would fall in the sec- 

 ond group of inquiry. 



6. Crop ecology. - - Since ecological data may be in- 

 cluded only incidentally, a few words may be said here 

 concerning the general relations of plants as distributed 

 over the surface of the earth or as cultivated under special 

 conditions. In the steppes of northern Africa and portions 

 of Australia, in the dry prairies of the western United States 

 and southern Russia, or in the equivalent regions of west- 

 ern Brazil, the vegetation is similar in physiognomy. Here 

 tough and drought-resistant grasses thrive, and for the 

 most part these regions are treeless tracts where rains fall 

 infrequently or precipitation is poorly distributed, and 

 here, too, winds often exert their highest force. The great 

 permanent grass lands, such as these areas are, may be 

 considered as being ecologically most closely related to true 

 desert. 



On the other hand, in tropical or temperate regions of 

 abundant, or at least sufficient, rainfall forests of one type 

 or another find a natural home. It is clear that upon the 

 discovery of North America, the region now included in the 

 United States was, practically speaking, a continuous forest 



