CONSISTENCE OF ORGANS.

In the animal kingdom the entire adult organism, as well as each of its
separate parts, has certain dimensions, beyond which, under ordinary
circumstances, it does not pass, either in the one direction or the
other. It may not be easy or possible to state what the limits are, but,
practically, this inability to frame a precise limitation is productive
of no inconvenience. It is universally admitted that a certain animal
attains such and such dimensions, and that one organ has a certain
proportionate size as contrasted with another. The same rules hold good
in the case of plants, though in them it is vastly more difficult to
ascertain what may be called the normal dimensions or proportions.
Nevertheless observation and experience soon show what may be termed the
average size of each plant, and any disproportion between the several
organs is speedily detected.

When there is a general reduction in size throughout all the organs of a
plant, or throughout all the nutritive organs, stem, leaves, &c., and
the several portions participate in this diminished size, we have what
are generally termed "dwarf varieties," dwarf in comparison, that is,
with the ordinary condition of the plants; on the other hand, if the
entire plant, or, at least, if the whole of one set of organs be
increased in size beyond the recognised average, we have large
varieties, often qualified by such terms as _macrophylla_, _longifolia_,
_macrantha_, &c. &c. In all these cases either the entire plant or whole
series of organs are alike increased or diminished beyond average
limits; and such variations are often very constant, and are transmitted
by hereditary transmission. It may be supposed that such deviations may
have originated, in the first instance, either from excessive use, or
from disuse, or from the agency of certain conditions promoting or
checking growth, as the case may be; but whether or no, it is certain
that these variations often persist under different conditions, and that
they often retain their distinctive characters side by side with plants
presenting the normal average dimensions. In other cases the variations
in size are of a less general character, and affect certain organs of a
whorl in a relative manner, as, for instance, in the case of didynamous
or tetradynamous stamens, where two or four stamens are longer than
their fellows, the long or short stamens and styles of di- and
tri-morphic flowers, &c. Th