281 



reduced to sea level, begin with March 12 in southern France and 

 extend to April '21 in northern France. The dates of fiowerinij; begin 

 with April G in southern France and extend to May 10 in northern 

 France. 



The smns of temperatures are counted from the last severe frost, 

 and the most accordant results are obtained when the sums of daily 

 maxima are taken, counting from 2° C. The sum total is 715° to 

 (late of leahng, and from leafing to flowering 1,070". 



The leafing of the birch is found by Angot to have the same rate 

 of retardation — very little less than four days per 100 meters — and 

 the reduced epochs of leafing begin the 9th of March at the southeast 

 corner of France and extend to the 16th of April at the northern 

 border. The sums of temperatures up to the time of leafing are 

 best computed by taking the sums of daily maxima above 2° C, but 

 are very uncertain. 



The leafing of the common oak {Quercus peduncidata) has ^ 

 retardation of four days per ascent of 100 meters, and the reduced 

 epochs begin with the (Jth of April in southern France and end with 

 the 6th of May in northern France. We can .provisionally admit 

 that the leafing of the oak occurs when the sum of the maximum 

 daily temperatures has attained 910° C, counting above 2° C. and 

 from the date of the last heavy frost. 



The flowering of the elder {Samhucus nigra) has an approximate 

 retardation of four days per 100 meters. The reduced dates begin on 

 the 6th of April in southern France and end on the 10th of June in 

 northern France. The flowering of the elder occurs when the sum 

 of the mean daily temperatures since the date of the last frost has 

 attained 840° C. if we count from 2°, or 630° if we count from 4° C. 



The flow^ering of the common linden {Tilia euroj)oea) or the Tilia 

 silvestris is retarded three days per 100 meters' ascent for the moun- 

 tainous countries, but four days is adopted for the whole of France, 

 and the reduced dates of flowering begin with the 1st of May in 

 southeastern France and extend to the 20th of June in northern 

 France. The flowering of the linden occurs when the sum of the 

 mean daily temperatures, counting from the last heavy frost and 

 r.bove 2° C., has attained 1,090° C. 



It would seem to result from all this that the leafing of the trees 

 and shrubs occurs when the sum total of the maximum daily tem- 

 peratures, counting above a certain limiting value and from the date 

 of the last heavy frost, has attained a certain value characteristic of 

 each plant. But for a certain number of plants the flowering seems 

 rather to depend on the sum of the mean daily temperatures. 



