PART II 



FACTORS INFLUENCING CROP DISTRIBUTION 

 IN THE UNITED STATES.^ 



That the crop plants are bound by the same laws of physiology 

 as other plants is an obvious truism. They respond in the same way 

 to changes in the environment. They become adjusted to the condi- 

 tions which they encounter. From the point of view of the crop 

 grower, this response is indicated by an increased yield. There are 

 well known physiological strains and races of cultivated plants just 

 as clearly distinct as morphological races. Examples are: Sixty 

 Day Oats, rust-proof asparagus and anthracnose resistant varieties 

 of beans. 



It is important to determine how far the analysis of the rela- 

 tionship of the plant to its environment can be carried in the crop 

 plants. Are the methods of study used in ecology useful here? 

 Can a relationship be established between plants under cultural 

 conditions and the natural vegetation? The study of the indicator 

 significance of the natural vegetation is just beginning, and offers 

 to lead the way to possible future crop production. It has been 

 applied to cropping in the Great Plains by Shantz (1911), Kearney 

 (1914) , and to locating forest sites by Korstian (1917) , and others. 

 The results indicate how much can be done by the intelligent appli- 

 cation of the methods for studying plant associations to problems 

 of culture. It also seems possible that very slowly a scheme of eco- 

 logical equivalents might be worked out. For example the state- 

 ment is generally accepted that where sassafrass grows peaches 

 can be successfully produced. This statement is misleading. For 

 sassafras can be found growing under a great diversity of condi- 

 tions, and there are many varieties of peaches. It is useless to 

 spend much time in looking for individual ecological equivalents, 

 unless they can be grown under controlled or at least measurable 

 conditions. 



In the present discussion an attempt is made to indicate some 

 of the relationships between great plant formations and certain crop 

 centers. The studies are, entirely, generalizations. Only the broad- 



1 Presented at the Pittsburgh meeting of the Ecological Society of America, Jan., 1918. 



33 



