252 



assumption that the sum of the mean daily temperatures in the shade 

 must be 84° C. 



[Date of sowing: a, October 1; b, October 15; c, November 1; d, November 15. Aver- 

 age date of germination: a, October 7; b, October 22; c, November 14; d, December. 

 18. Average date of heading : a, February 8 ; b, March 4 ; c, March 3 ; d, Feb- 

 ruary 26.] 



Counting from the date when the mean daily temperature is 5° C. 

 and the wheat begins to sprout to the date when the wheat begins to 

 head, Gasparin adopts 430° C. as the sum of the mean daily shade 

 temperatures. Marie-Davy finds from the date of actual sowing of 

 the seed to the date of heading out a sum of 555° C. after rejecting all 

 daily mean temperatures that are below 6° C. according to the rule of 

 Herve Mangon. He also finds 639° C. for the sum total of tempera- 

 tures between the dates of germination and heading out after reject- 

 ing all days below 6° C. On this last hypothesis are calculated the 

 duration of the heading stage and the mean dates of heading for the 

 respective years as given in the columns 6 to 9 of this table. These 

 computed dates of heading out show that the sowing of wheat on 

 October 15 or November 1 or 15 brings it to a head at the end of 

 February or beginning of March, but when the sowing occurs on 

 October 1 it is brought to a head so much earlier in February as to 

 expose it to great chance of injury by the frost; for although the 

 grasses and the green wheat plant resist the action of frost, yet the 

 embryo seed in the ear or head does not do so, and if once destroyed 

 by frost will not be replaced unless the soil is very fertile. 



The third epoch, or the flowering of the wheat, takes place in 

 France, according to Gasparin, when the mean temperature has 

 risen to 1G° C. oi* when the sum total of daily shade temperatures 

 has amounted to 813° C, counting from the beginning of vegetation 

 in the spring or from the date when the mean daily temperatures 

 is 5° C. in the shade. This figure relates, of course, to an average 

 of many years, and the individual years may vary very considerably. 

 Marie-Davy, as before, adopts the views of Herve Mangon as to 



