267 



heading occur (lurin*)- the very cold season likely to be injurious to 

 vegetation. 



We pass no-w to the period from the heading of the wheat to the 

 flowering. Acconling to the determination of Herve Mangon, the 

 sum total of the mean daily air temperatures in the shade necessary 

 to flowering is 1,500° C, counting from the date of sowing, or 8G0° 

 if counted from the date of heading. If we consider the date thus 

 fixed for the flowering we shall find that it corresponds to a mean 

 daily temperature at that epoch of 1().5° C. on the average of many 

 years; but if we consider the individual years we shall find the actual 

 mean temperatures of that date to vary from 8° to 22° C., and also 

 that for temperatures below 13° the flowering becomes uncertain, 

 prolonged, and detrimental to the crop; but as to the upper limit, 

 22° C, there is no evidence that even higher temperatures wnll be 

 injurious. The following table gives the calculated number of days 

 that elapse from the sowing to the flowering, together with the aver- 

 age duration and the corresponding average date. The correspond- 

 ing tables of mean temj^eratures and lowest temperatures at the date 

 and the quantity of rainfall are omitted for want of space. 



Duration hi dans from the soiriii!/ to the ffoireriuf/ of irhiter irhcat at Mont- 

 sour is, France. 



235 



229 



224 



219 ! 



214 



211 



205 



199 



195 



191 



186 



181 



Average for 

 1872-1881. 



Dura 



tion. 



Date. 



May 16 

 May 23 

 May 29 

 June 3 

 June 8 

 June 12 

 June 14 

 June 17 

 June 19 

 June 21 

 June 22 

 June 23 

 June 24 

 June 24 

 June 26 



The ripening of wheat is perfected when the ])lant has received a 

 suni total of Tnean daily air temperatures in the shade of 815° C. since 

 the date of flowering. This result happens on the average of Paris 

 forty-four days after flowering, and the individual irregularities 

 scarcely ever exceed four or five days. Therefore the date of flower- 



