An abortive condition of the stamens and of the pollen, is of very common occurrence among hybridised plants. Gaertner and other writers have spoken of this defective condition as contabescence.[535] It forms one reason for the sterility so frequently observed in the case of true hybrids. In some hybrid passion-flowers, while all other parts of the flower were apparently perfect, even to the ovules, the stamens were atrophied, and distorted, and contained little or no pollen; the few grains of the latter being smaller than usual. (See under Heterogamy, pp. 193–196, and p. 398.)
Abortion of the pistil, fruit, &c.—Traces of the carpels occur in many male flowers of unisexual plants, e.g. Sterculiaceæ, Euphorbiaceæ, Restiaceæ, &c. &c., and in some natural orders there appears to be a tendency towards a diœcious condition, e.g. Caryophylleæ, 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.
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 investments become more or less atrophied, or are even more frequently entirely suppressed, as is also the nucleus.