HOPKINS: BIOCUMATIC I^AW 39 



Thus the fundamental question to be answered is, what amount 

 of variation from the constant in terms of days, feet, or degrees 

 of distance, are we to expect for the varying local and regional 

 influences which contribute to earlier or later dates, or higher 

 or lower altitude. 



During recent years special efforts have been made to find 

 a reliable basis for answering this question. The first clue 

 towards the answer was obtained from a study of over 40,000 

 reported dates of the beginning of wheat harvest, within the range 

 of winter wheat culture in the United States. The results showed 

 that the variations from the date constants, for all of the geo- 

 graphical units involved,^ were in the same directions in certain 

 regions of the country. 



Throughout the Mississippi Basin from the Great Lakes south- 

 ward, the reported dates were universally -+- or later than the 

 computed constants; throughout the Great Plains, Rocky Moun- 

 tain Plateau and part of the Great Basin, the reported dates 

 were — , or earher; throughout the Pacific Slope they were later; 

 and so on. These results were strikingly significant of prevail- 

 ing influences towards the acceleration in some regions and re- 

 tardation in others of periodical phenomena as compared with 

 the time-constant of the law. 



Continued investigations along this line involved a detailed 

 study of the altitude limits of species and of biological associa- 

 tions of plants and animals as mapped by the federal and state 

 biological surv^eys and determined in a number of cases by per- 

 sonal investigations. The results of these later studies served 

 not only to verify the evidence furnished by the wheat harvest 

 records but to establish, as a general principle, the approximate 

 amount of variation we may expect to find in all regions, from 

 those in which there is no perceptible retarding or accelerating 

 influence to those where the intensity of the influences reaches 

 its maximum. As measured in time the variation from the con- 

 stants is found to range from one to forty, with a maximum of 

 fifty days at certain points along the Pacific Coast. As mea- 

 sured in altitude the variations are from 100 to 3000, with a 



^ Quadrangle V4 X i degree, and the average altitude. 



