In many Umbelliferæ, e.g. Torilis Anthriscus, Cicuta virosa, the central flowers are often male, owing to the suppression of the pistil. In many double flowers, owing to the excessive multiplication of petaloid stamens, the pistil is suppressed, in which cases it often happens that the flower is depressed in the centre, as in some garden varieties of Ranunculus. Schlechtendal, in describing a flower of Colchicum autumnale, in which the perianth was virescent, says that, although the stamens were present, the pistil was absent.
In proliferous flowers the pistil is often completely defective, its place being occupied by the adventitious bud or axis.
As in other cases of like nature, suppression of the pistil is very frequently consequent on fusion of flowers or other changes. Thus Morren relates an instance of synanthy in the flowers of Torenia scabra, accompanied by resorption or disappearance of some parts and spiral torsion of others. The pistil was entirely absent in this instance.[484]
M. Gaetano Licopoli places on record an instance where the petals and carpels of Melianthus major were suppressed.[485]
On the whole, the pistil seems less subject to changes of this character than the andrœcium.
Suppression of the pistil has been most frequently recorded in flowers (normally bisexual) of—
- Ranunculus!
- Aconitium!
- Delphinium!
- Pæonia.
- Caryophylleæ!
- Umbelliferæ.
- Trifolium repens.
- hybridum.
- Compositæ, sp. pl.
- Datura.
- Torenia asiatica.
- Colchicum autumnale.
Suppression of ovules,—abortion of seeds.—The two cases are taken together, as the effects are similar, though it must be remembered that in the one case the ovules at any rate have been formed, but their development has been arrested, while in the other they have never existed. The precise cause that has determined the absence of seed cannot in all cases be ascertained in the adult condition, hence it is convenient to treat the two phenomena under one head.
Many plants in other than their native climates either produce no fruit at all, or the fruits that are produced are destitute of seed, e.g. Musa, Artocarpus, &c. Some of the cultivated varieties of the grape and of the berberry produce no seeds.
Suppression or abortion of the seed is frequently associated with the excessive development either in size or number of other portions of the plant, or with an altered condition, as when carpels become foliaceous and their margins detached. Hybridisation and cross fertilisation are also well-known agents in diminishing the number and size of seeds.