THE RELATION OF CLIMATE TO POMOLOGY 235 



4. Other conditions being equal, the variation in the time 

 of occurrence of a given periocUcal event in hfe activity in 

 temperate North America is at the general average rate of 

 4 days to each 1 degree of latitude, 5 degrees of longitude, 

 and 400 feet of altitude, later northward, eastward and up- 

 ward ill the spring and early summer, and the reverse in 

 late suimiier and autumn. 



5. Owing to the fact that all conditions are never exactly 

 equal in two or more biological or climatic regions of the 

 continent, and rarely alike in two or more places within the 

 same region or locality, there are always departures from 

 the theoretical time constant. 



6. The departures, in number of days from a theoretical 

 time constant, are in direct relation to the intensity of the 

 controlling influences. Therefore, the constant, as expressed 

 in the time coordinates of the law, is a measure of the inten- 

 sity of the influences. 



Fig. 32 shows the working of this law as adapted to North 

 America. "Taking base maps of North America and of 

 the major and minor political divisions, parallel lines (des- 

 ignated as isophanes ^) are drawn on them to define, accord- 

 ing to the bioclimatic law, theoretical lines and zones of 

 equal phenomena as to time of occurrence and equal biocli- 

 matic conditions, at the same level."- 



"The isophanes, instead of following the parallels of 

 north latitude in North America, proceed from the Atlan- 

 tic to the Pacific in a northwestward curve at the rate of 1 

 degree of latitude to 5 degrees of longitude (Fig. 32), so 



* Isophane. In phenology, an isochrone of the first blossoming of 

 a specified plant. 



Isochrone. Phenological isochrone is a line drawn between points 

 at which plants of the same species attain the same degree of de- 

 velopment simultaneously. (Standard Dictionary.) 



^ For full explanation, see original text. 



