COMPOSITION IN SUCCESSIVE STAGES. 205 
in Germany, at the same time, but independently of each 
other, resumed the subject, and to their labors the sub- 
joined figures and conclusions are due. 
Here follows a statement of the Periods at which the 
plants were taken for analysis. 
Peri June 18, Arendt—Three lower leaves unfolded, two upper still closed, 
ist Period } ‘* 19, Bretschneider—Four to five leaves developed. 
June 30, (12 days,) At.—Shortly before the plants were fully headed, 
“29, (10 days,) Br.—The plants were headed. 
- .) duly 10, (10 days,) At.—Immediately after bloom. 
-aialaaees ai 8, (9 days,) Br.—Full bloom. 
. July 21, (11 days.) At.—Beginning to ripen. 
4th Period ginning 
¢ 28, (20 days,) Br.— - se 
th Period ied 31, (10 days,) At.—Fully ripe. 
Aug. 6, (9 days,) Br— “ bg 
8d Period \ 
It will be seen that the periods, though differing some- 
what as to time, correspond almost perfectly in regard to 
the development of the plants. It must be mentioned 
that Arendt carefully selected luxuriant plants of equal 
size, so as to analyze a uniform material, (see p. 210,) and 
took no account of the yield of a given surface of soil. 
Bretschneider, on the other hand, examined the entire 
produce of a square rod. The former procedure is best 
adapted to study the composition of the well-nourished 
individual plant ; the latter gives a truer view of the crop. 
The unlike character of the material as just indicated is 
but one of the various causes which might render the two 
series of observations discrepant. Thus, differences in 
soil, weather, and seeding, would necessarily influence the 
velative as well as the absolute development of the two 
crops. The results are, notwithstanding, strikingly accord- 
ant in many particulars. In all cases the roots were not 
and could not be included in the investigation, as it is im- 
possible to free them from adhering soil. 
The Total Weight of Crop per English acre, at the 
end of each period, was as follows: 
