for an unlimited period; but so soon as they
are exposed to the air, germination immediately commences. Illustrations
of this fact are frequently observed where earth from a considerable
depth has been thrown up to the surface, when it often becomes covered
with plants not usually seen in the neighbourhood, which have sprung
from buried seeds. When all the necessary conditions for germination are
fulfilled, the seed absorbs moisture, swells up, and sends out a shoot
which rises to the surface, and a radicle which descends--the one
destined to develop the leaves, the other the roots, by which the plant
is afterwards to derive its nutriment from the air and the soil. But
until these organs are properly developed, the plant is dependent on the
matters contained in the seed itself. These substances are mostly
insoluble, but are brought into solution by the atmospheric oxygen
acting upon the gluten, and converting it into a soluble substance
called diastase, which in its turn reacts upon the starch, converting it
first into dextrine, and then into cellulose, and the latter is finally
deposited in the form of organised cells, and produces the first little
shoot of the plant. At the first moment of germination, the oxygen
absorbed appears simply to oxidize the constituents of the seed, but
this condition exists only for a very limited period, and is soon
followed by the evolution of carbonic acid, water being at the same time
formed from the organic constituents of the seed, which gradually
diminishes in weight. The amount of this diminution is different with
different plants, but always considerable. Boussingault found that the
loss of dry substance in the pea amounted in 26 days to 52 per cent, and
in wheat to 57 per cent in 51 days. Against this, of course, is to be
put the weight of the young plant produced; but this is never sufficient
to counterbalance the diminished weight of the seed, for Saussure found
that a horse bean and the plant produced from it weighed, after 16 days,
less by 29 per cent than the seed before germination. The same
phenomenon is observed in the process of malting, which is in fact the
artificial germination of barley, the malt produced always weighing
considerably less than the grain from which it was obtained. It was
believed by Saussure, and the older investigators, that the carbonic
acid evolved was entirely produced from starch and sugar; and as these
substances may be viewed as compounds of ca