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reduced to sea level, begin with March 12 in southern France and 
extend to April 21 in northern France. The dates of flowering begin 
with April 6 in southern France and extend to May 16 in northern 
France. 
The sums 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 
date of leafing, 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 pedunculata) has a 
retardation of four days per ascent of 100 meters, and the reduced 
epochs begin with the 6th 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 940° C., counting above 2° C. and 
from the date of the last heavy frost. 
The flowering of the elder (Sambucus 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 flowering of the common linden (77/ia europea) or the Tilia 
silvestris is retarded three days. per 100 meters’ ascent for the moun- 
taimnous countries, but four days is adopted for the whole of France, 
and the reduced dates of flowering begin with the Ist 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 
above 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. 
