Increased number of ovules or seeds.—This appears not to be of very frequent occurrence, at least in those plants where the number of these organs is normally small; where, as in Primula, the ovules and seeds are produced in large quantities, it is not practicable to ascertain whether the number be augmented or not in any particular case. Very probably, the attachment or source of origin of the ovules determines, in some measure, their number. Thus, in the case of marginal placentation the number must be limited by the narrow space from which they proceed, whereas in parietal and free central placentation the ovules are generally numerous. In the latter case, however, it will be remembered that solitary ovules are not rare. An increased number of ovules is generally remarked in conjunction with some other change, such as a foliaceous condition of the carpel, in which the margins are disunited. In such cases the ovules may occupy the margin or may be placed a short distance within it, as in the case of some open carpels of Ranunculus Ficaria,[417] and in which two ovules were borne in shallow depressions on the upper or inner surface of the open carpel and supplied with vascular cords from the central bundle or midrib. The outer coating of the ovule here contained barred or spiral fusiform vessels derived from the source just indicated.

In the very common cases where the pistil of Trifolium repens becomes foliaceous (see Frondescence), the outer ovules are generally two or more instead of being solitary. So, also, in the Rose with polliniferous ovules ([see p. 274]). Among Umbelliferæ affected with frondescence of the pistil a similar increase in the number of ovules takes place. It will be borne in mind that in most, if not all, these cases the structure of the ovule is itself imperfect.[418]

What are called in popular parlance double almonds or double nuts (Corylus) are cases where two seeds are developed in place of one.

In the 'Revue Horticole,' 1867, p. 382, mention is made of a bush which produces these double nuts each year—in fact, it never produces any single-seeded fruit. The plant was a chance seedling, perhaps itself the offspring of a double-seeded parent. It would be interesting to observe if the character be retained by the original plant, and whether it can be perpetuated by seed or by grafting.

It is necessary to distinguish in the case of the nut between additional seeds or ovules, as just described, and the double, triple, or fourfold nuts that are occasionally met with, and which are the result either of actual multiplication of the carpels or of the continued development of some of the carpels which, under ordinary circumstances cease to grow ([see ante, p. 364]). In the case of a ripe nut with two seeds it might be impossible to tell whether the adventitious seed were the product of multiplication, or whether it belonged, in the first instance, to the same carpel as that producing the fellow-seed, or to a different and now obliterated ovary. In all probability, however, the second seed would be accounted for by the development of two seeds in one carpellary cavity.

There is still another condition occasionally met with in the almond, and which must be discriminated from the more common multiplication of the seed, and which is the multiplication of the embryos within the seed, and which furnishes the subject of the succeeding paragraph.

Increased number of embryos.—A ripe seed usually contains but a single embryo, although in the ovular state preparation is commonly made for more; and, indeed, in certain natural orders plurality of embryos in the same seed does occur, as in Cycadeæ and Coniferæ. In the seeds of the orange (Citrus), in those of some Euphorbiaceæ, &c., there are frequently two or more additional embryos. A similar occurrence has been recorded in the mango, for a specimen of which I am indebted to the Rev. Mr. Parish, of Moulmein.[419]

Plurality of embryos has also been observed in—