300 
PHYSIOLOGY. 
BOOK II. 
enabling it to "preserve the unalterability" to which its pre- 
servation is owing. This superfluous carbon renders it 
scarcely soluble in water. To enable the parts to be suffi- 
ciently moistened, it is consequently necessary that the seed 
should be decarbonized by the oxygen of the air. This ex- 
plains why Peas scarcely ripe will germinate much more 
rapidly than those which are fully matured ; the former con- 
tain more pure water and less carbon. In fact, the effect of the 
abstraction by oxygen of the fixed carbon is to bring back the 
seed to the state in which it was before it was provided with the 
means of remaining unchanged in a torpid state. The sweet 
taste of germinating barley is, in reality, what the seeds pos- 
sessed before they were finally hardened. The destruction of 
the oxygen of the air by the carbon of the seed produces a 
sensible heat in germination, just as a similar cause produces 
a similar effect in flowers when the foecula of their disk is 
converted into sugar (see p. 276.). Hence the heat of masses 
of Barley which are made to germinate in darkness in order 
to become malt. And it can scarcely be doubted, that the 
change of the starch of that grain into sugar is chemically 
owing to the abstraction of a proportion of its carbon and the 
addition of some other proportion of oxygen. 
In the opinion of some persons, oxygen also acts as a stimu- 
lant of the vital actions of the embryo. Humboldt remarked 
that seeds plunged in chlorine, and taken out before 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 succeeded, by this 
process, in bringing about germination in old seeds which ap- 
peared 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 chlo- 
rine was explained is now abandoned, one cannot avoid en- 
tertaining doubts as to the accuracy of the alleged facts. 
Heat it is 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 
