84 Original Articles. [Jan. 
process of germination is by no means a simple one. The nutriment 
stored up in the seed is in great part in the condition of insoluble 
starch ; and this must be brought into a soluble form before it can be 
appropriated by the embryo. The metamorphosis is effected by the 
agency of a ferment termed diastase ; which is laid up in the imme- 
diate neighbourhood of the embryo, and which, when brought to act 
on starch, converts it in the first instance into soluble dextrine, and 
then (if its action be continued) into sugar. The dextrine and sugar, 
combined with the albuminous and oily compounds also stored up in 
the seed, form the “ protoplasm” which is the substance immediately 
supplied to the young plant as the material of its tissues; and the 
conversion of this protoplasm into various forms of organized tissue, 
which become more and more differentiated as development advances, 
is obviously referable to the vital activity of the germ. Now it can 
be very easily shown experimentally that the rate of growth in the 
germinating embryo is so closely related (within certain limits) to the 
amount of Heat supplied, as to place its dependence on that agency 
beyond reasonable question ; so that we seem fully entitled to say that 
Heat, acting through the germ, supplies the constructive force or power 
by which the Vegetable fabric is built up.* But there appears to be 
another source of that power in the seed itself. In the conversion of 
the insoluble starch of the seed into sugar, and probably also in a 
further metamorphosis of a part of that sugar, a large quantity of carbon 
is eliminated from the seed by combining with the oxygen of the air 
so as to form carbonic acid; this combination is necessarily attended 
with a disengagement of heat, which becomes very sensible when (as in 
malting) a large number of germinating seeds are aggregated together ; 
and it cannot but be regarded as probable that the heat thus evolved 
within the seed concurs with that derived from without, in supplying 
to the germ the force that promotes its evolution. 
The condition of the Plant which has attained a more advanced 
stage of its development differs from that of the germinating embryo 
essentially in this particular, that the organic compounds which it re- 
quires as the materials of the extension of the fabric are formed by 
itself, instead of being supplied to it from without. The tissues of 
the coloured surfaces of the leaves and stems, when acted on by light, 
have the peculiar power of generating—at the expense of carbonic acid, 
water, and ammonia—various ternary and quaternary organic com- 
pounds, such as chlorophyll, starch, oil, and albumen ; and of the 
compounds thus generated, some are appropriated by the constructive 
force of the Plant (derived from the heat with which it is supplied) to 
the formation of new tissues ; whilst others are stored up in the cavities 
of those tissues, where they ultimately serve either for the evolution 
* The effect of Heat is doubtless manifested very differently by different seeds ; 
such variations being partly specific, partly individual. But these are no greater 
than we see in the inorganic world; the increment of temperature and the 
augmentation of bulk exhibited by different substances when subjected to the 
same absolute measure of heat, being as diverse as the substances themselves. 
The whole process of “malting,” it may be remarked, is based on the regularity 
with which the seeds of a particular species may be at any time forced to a definite 
rate of germination by a definite increment of temperature. 
