normal series. How, then, can a copious supply of rich
food, such as is provided by cultivation, produce double flowers? To
this question, according to our theory, the reply would be that the
quantity of food is excessive, more than the plant can properly digest;
and hence vegetative action is stopped, at least partially--pretty much
as it would be if the plant were placed in the opposite condition of
starvation. The effect of supplying a plant (or an animal) with an
excessive supply of food, which it cannot assimilate, is in many
respects similar to that which results from partially cutting off the
supplies. And the same reasoning applies to sterility. If by high
culture, or the supply of an undue quantity of nourishment, the
constitution of the plant be impaired, or if the plant be pampered, it
is no wonderful thing that sterility should ensue. Hence, then, may it
not be asserted as a general principle that in the production of double
flowers a partial arrest of development, if not of growth, however
produced, is an essential preliminary? All the attendant phenomena, such
as the obliteration of the stamens, the augmentation in the number of
floral whorls, the occurrence of prolification, are consistent with the
supposition of a primary arrest of development, more or less complete,
as the case may be: at one time permanent, at another time relaxed and
intermittent, or in a third set of cases the vegetative activity or
power of growth may be restored, and from the centre of the flower may
spring a perfect branch with perfect leaves, the production of sheaths
only being superseded by the development of leaves, in which all the
parts--sheath, stalk, and blade--are present.

When once the disposition to form double flowers is established, that
tendency becomes hereditary: there are races of single Stocks in which,
out of hundreds of plants, scarcely one double-flowered form is met
with; but when the tendency to produce double blooms is set up, single
flowers become the exception: thus, in the Balsams, before mentioned,
not one in fifty now produces single flowers, and the seeds of these
double Balsams produce double-flowered seedlings, with scarcely a
"rogue" among them.

The following list of plants producing double flowers of any kind is
taken from that given in 'Seemann's Journal of Botany,' vol. ii, p. 177,
and to which some additions have been made. Miscalled double flowers,
such as those of the _Compositae_, _Viburn