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; 0b, March 4; c, March 3; d, Feb- 
ruary 26.] 
Duration eect ane aie Duration of heading stage. 
Year. 
a. b. @ d. a. b. (o d. 
Days. | Days. | Days. | Days. | Days. | Days. | Days. | Days. 
83 Be err ae ae any eae ee 5 6 12 13 111 159 142 142 
TS Ce a eas Sea a ogee ere Eh 7 6 9 23 151 166 163 143 
Iii as ae eee UE as Co ee ae 6 7 9 40 151 165 148 118 
SiGe soe ree Cee Oe ee ee eee 5 7 13 12 59 87 93 113 
IS GF Pie, eae eR me a ee ee al, 9 10 8 ay 128 180 149 137 
STG Bea Se Leet: See ne aa BE 6 6 26 45 151 179 151 128 
S(O Meee ies Sete eek ee 5 ee i 9 11 94 155 156 152 57 
ICH) ple se Be et OE ae ge SORA Fe eed oe 6 9 16 23 86 133 125 87 
Average duration._-...__.... 6.4 7.5 13.0 33.4 124 147 140 116 
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. Marié-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 
Hervé 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 16° C. or 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. 
Marié-Davy, as before, adopts the views of Hervé Mangon as to 
