es, having an envelope, insoluble in water, formed of a
kind of organized membrane, and containing within it a substance which
is soluble in water, termed amidin. This soluble material is the
nutritive element on which the young shoot, proceeding from every eye
or bud of the potatoes, is to subsist, till it has developed roots,
and unfolded its leaves to prepare additional alimentary substance.
But if this soluble material be enclosed in an insoluble membrane, how
are the contents to be made available for the growth of the plant? It
is true, indeed, that water of the temperature of 160 deg. Fahr. can
rupture this tegument, as occurs in the process of boiling potatoes;
but the water diffused through the earth in the neighbourhood of the
growing tuber, never reaches such a height. How then is the difficulty
obviated? This is effected by a secretion called _diastase_ which is
found in the tubers in the immediate vicinity of the eyes or buds. "It
is stored up in that situation for the purpose of being conveyed, by
the vessels connected with the bud, into the substance of the tuber,
when the demand for nutrition is occasioned by the development of the
shoot. It is probable that the secretion of _diastase_ takes place in
every instance in which starch previously deposited is to be
re-absorbed[M]." It is not to be found before grains or tubers begin
to sprout, yet, "such is its energy, that one part of it is sufficient
to render soluble the interior portion of two thousand parts of
starch, and to convert it into sugar[N]." Strong as is the analogy
between starch and gum, yet _diastase_ does not convert gum into
sugar; the one being as completely soluble as the other, its
intervention is clearly unnecessary. Neither does it act on sugar. It
is found, and exerts its powers, only where it is required. Nor does
it come into play one moment before the necessity for it occurs. While
the potatoe is in its state of winter repose, and no vegetative
process going on, the elements of which the _diastase_ is formed, are
equally quiescent, but no sooner does the season recur when an
augmented temperature rouses the slumbering energy of the tuber, than
this potent principle exhibits its efficacy, and changes the insoluble
starch into the nutritious sugar. Who, that can read, or reading
reflect and ponder on these things, but must conclude that the laws
which regulate the whole actions were impressed upon their subjects by
a Creator infinite