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approximations derived from the observation of the temperature of 
the air only. If when the grain has sprouted the soil continues very 
dry, the nourishment having all been drawn from the seed, the young 
plant may droop and die. If, again, the frost penetrates to the seed 
while it is germinating, many of the seeds will perish, and the field 
will appear as if sparsely sown, but this latter mishap is generally 
repaired by nature if the soil is good and the springtime favorable, 
for the sowing is generally in excess and the extra heading will 
supply the loss of the seeds that have perished, but in poor soil the 
harvest will be notably diminished, and often it will be profitable to 
plow the soil for a new sowing. 
In any case the chances for a successful crop vary very much with 
the date of the sowing, as we shall see by the study of the following 
table, which shows that in each year the season for sowing that is 
favorable to the crop of that year is very much restricted by the early 
arrival of the winter cold. Thus in 1871 the sowing was stopped on 
the 20th of October by the cold weather; in 1872 it continued through- 
out the autumn until the 29th of December; in 1880 it occurred on the 
3d of November. Sometimes heavy rains prevent the sowing, but in 
1881 neither cold nor rain prevented field work until the middle of 
December. [In order to save space I have omitted the elaborate 
tables of frosts, low temperatures, and rains given by Marié-Davy for 
each of these years and weeks.—C. A. | 
The grain now arrives at the epoch of heading, at which the orig- 
inal stalk becomes several branches, each of which bears an immature 
head on which the rudimentary seed can already be counted under 
the microscope; the number of such seeds will not increase in the 
further development of the plant, but many of them may not come to 
maturity; therefore a careful count of these rudimentary seeds over 
a small area of the field would give a first estimate of the maximum 
possible crop. 
According to Gasparin the length of time that elapses from the 
moment when the mean daily temperature of the air in the shade is 
5° C. up to the date of heading of the wheat is such that the sum 
total of the mean daily shade temperatures is 430° C., but as the 
initial date is difficult to determine we shall in our calculations adopt 
the rule of Hervé Mangon, according to whom the sum of the mean 
daily temperature in the shade, rejecting all that are below 6° C. 
(at which the wheat does not vegetate), is 640° C. if we count from 
the date of sowing, or 555° C.if we count from the date of germina- 
tion. The following table is computed by counting from the former 
date; a parallel computation from the latter date shows that on the 
a 
