; flowers have similarly changed in
shape, colour, and doubleness, and greatly in the character of the calyx;
young branches or shoots have changed in colour, in bearing spines, and in
habit of growth, as in climbing and weeping; leaves have changed in colour,
variegation, shape, period of unfolding, and in their arrangement on the
axis. Buds of all kinds, whether produced on ordinary branches or on
subterranean stems, whether simple or, as in tubers and bulbs, much
modified and supplied with a stock of nutriment, are all liable to sudden
variations of the same general nature.

In the list, many of the cases are certainly due to reversion to characters
not acquired from a cross, but which were formerly present, and have been
lost for a longer or shorter period of time;--as when a bud on a variegated
plant produces plain leaves, or when variously-coloured flowers on the
Chrysanthemum revert to the aboriginal yellow tint. Many other cases
included in the list are probably due to the plants being of crossed
parentage, and to the buds reverting to one of the two parent-forms. In
illustration of the origin of _Cytisus adami_, several cases were given of
partial or complete reversion, both {407} with hybrid and mongrel plants;
hence we may suspect that the strong tendency in the Chrysanthemum, for
instance, to produce by bud-variation differently-coloured flowers, results
from the varieties formerly having been intentionally or accidentally
crossed; and that their descendants at the present day still occasionally
revert by buds to the colours of the more persistent parent-varieties. This
is almost certainly the case with Rollisson's Unique Pelargonium; and so it
may be to a large extent with the bud-varieties of the Dahlia and with the
"broken colours" of Tulips.

Many cases of bud-variation, however, cannot be attributed to reversion,
but to spontaneous variability, such as so commonly occurs with cultivated
plants when raised from seed. As a single variety of the Chrysanthemum has
produced by buds six other varieties, and as one variety of the gooseberry
has borne at the same time four distinct varieties of fruit, it is scarcely
possible to believe that all these variations are reversions to former
parents. We can hardly believe, as remarked in a previous chapter, that all
the many peaches which have yielded nectarine-buds are of crossed
parentage. Lastly, in such cases as that of the moss-rose with its peculiar
calyx, and