CHAP. X. 
SEED. 
361 
to be a fact of the first importance. {Comptes rendus, 
vii. 922.) 
It also appears that the carbon of seeds is lost, not only by 
the formation of carbonic acid, but by the production of 
acetic acid, during germination, a phenomenon which Messrs. 
Becquerel and Boussingault consider constant. {Comptes 
rendus,^ vi. 109.) 
In the opinion of some persons, oxygen also acts as a 
stimulant of the vital actions of the embryo. Humboldt 
remarked that seeds plunged in chlorine, and taken out be- 
fore the radicle appears externally, germinate more rapidly 
than ordinary ; Cress, for instance, may thus be made to 
germinate in 6 hours instead of 24 or 30. He even suc- 
ceeded, by this process, in bringing about germination in 
old seeds which appeared destitute of the power. These 
experiments have not, however, succeeded in all hands : 
in many cases it is possible that the success that is said 
to have attended them has been imaginary; and, as the 
theory upon which the action of chlorine was explained is 
now abandoned, one cannot avoid entertaining doubts as to 
the accuracy of the alleged facts. 
Heat is that in which the stimulus necessary to call the 
vitality of seeds into action seems really to reside. No seed 
can germinate at a temperature so low as that of freezing ; 
and each seems to have some one temperature more proper 
for it than any other, at the first dawn of its life. If, says 
De Candolle, the temperature is too high, germination pro- 
ceeds too rapidly, and the result is weak and languishing 
plants, in which we cannot avoid recognising beings too 
much excited and badly nourished. If the temperature is 
too low, the excitement is not sufficient ; and it often happens 
that the seed cannot resist the decay induced by the water 
it has absorbed, but not assimilated. It is between these 
limits that a suitable temperature for every species is to be 
sought. 
Edwards and Colin have instituted some experiments to 
determine what temperature seeds can bear. They found 
that Wheat, Barley, and Rye could germinate at 7° centig. 
(44*6° Fahr.) ; and that grain of the same description did not 
