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 CLIMATIC RELATIONS 277 



annual sum total of heat required for maturity of a crop, 

 or completion of any stage of its growth, is, according to 

 Linsser, the same wherever the crop is acclimatized, and 

 was called by him the " physiological constant." 



Recently Merriam (1894) has studied this subject, and 

 does not think that the distribution southward of plants 

 and animals can be explained by any previously stated 

 law of temperature control. He proposes, therefore, 

 the following additional fundamental law : Animals and 

 plants are restricted in southward distribution by the 

 mean temperature of a brief period covering the hottest 

 part of the year. 



292. Retardation of the harvest. Angot studied the 

 retardation of the harvest in France as affected by alti- 

 tude, and found that the harvest of rye and spring barley 

 is retarded at the rate of about 4 days to 100 meters of 

 altitude. He also found that the date of harvest, reduced 

 to sea level, begins with June 5 in southern France and 

 ends with July 25 on the northern border. Incidentally, 

 Angot also determined, from observations at several 

 hundred stations, that in France rye requires less heat 

 than winter wheat for maturing the crop, but for the 

 fruiting period alone, rye requires more heat than winter 

 wheat. 



Abbe (1905) has brought together a large amount of 

 phenological information in one place, extracted from 

 writings of the above-mentioned investigators and many 

 others, and gives an extensive bibliography. 



