=Abortion of the pistil, fruit, &c.=--Traces of the carpels occur in
many male flowers of unisexual plants, _e.g._ _Sterculiaceae_,
_Euphorbiaceae_, _Restiaceae_, &c. &c., and in some natural orders there
appears to be a tendency towards a dioecious condition, _e.g._
_Caryophylleae_, as in _Lychnis dioica_, _Silene otites_, _Arenaria
tetraquetra_, &c. The last-named plant is stated to have, in some cases,
imperfect pistils; in others, rudimentary stamens; while a third set of
flowers are hermaphrodite.[536] The ovary of aconites, according to
Moquin, is very subject to atrophy.

[Illustration: FIG. 218.--Bladder plum.]

During the maturation of the pistil, and its passage to the fruit, great
changes of consistence frequently take place, owing to the development
of cellular tissue, or of woody matter, according as the fruit is
succulent or woody. It sometimes happens that, owing to some disturbing
causes, the changes that usually occur fail to do so; thus, the stone of
plums is occasionally deficient, as in what are termed bladder-plums
(fig. 218); some of these, consisting merely of a thin bladder, are
curiously like the pods of _Colutea_.[537]

MM. Fournier and Bonnet[538] describe a fruit of a _Rubus_, with
perfectly dry fruits, like those of a _Geum_, and this form was
considered by Steudel to form a distinct species. It is, however, merely
a variety in which the fruits have not become succulent.[539]

Schlechtendal describes[540] the ordinarily baccate fruit of a vine as
becoming dry, and even dehiscing by valves like a capsule.

In maize it occasionally happens that one or two of the longitudinal
series of fruits become abortive, leaving a smooth furrow, at first of a
greenish colour, but ultimately of a reddish yellow. Often a second row
of fruits, opposite to the first, is also atrophied, so that the whole
spike changes its cylindrical form for a flattened one.[541] See also
under Heterogamy, Meiophylly, &c.

=Abortion of the ovules.=--In the case of a pluri-ovulate ovary it
rarely happens that all the ovules attain to maturity, some never get
fertilised, others, pressed on by their neighbours on either side,
become impeded in their development, and finally disappear, or remain as
rudiments.[542] This is the case, under ordinary circumstances, and
still more so in the case of hybrid plants, or of monsters. Where the
outer coats of the ovule become more or less leafy in appearance (see p.
262), the inner in