EQUAL-STYLED VARIETIES.
The tendency of the dimorphic species of Primula to produce equal-styled varieties deserves notice. Cases of this kind have been observed, as shown in the last chapter, in no less than six species, namely, P. veris, vulgaris, Sinensis, auricula, farinosa, and elatior. In the case of P. veris, the stamens resemble in length, position and size of their pollen-grains the stamens of the short-styled form; whilst the pistil closely resembles that of the long-styled, but as it varies much in length, one proper to the short-styled form appears to have been elongated and to have assumed at the same time the functions of a long-styled pistil. Consequently the flowers are capable of spontaneous self- fertilisation of a legitimate nature and yield a full complement of seed, or even more than the number produced by ordinary flowers legitimately fertilised. With P. Sinensis, on the other hand, the stamens resemble in all respects the shorter ones proper to the long-styled form, whilst the pistil makes a near approach to that of the short-styled, but as it varies in length, it would appear as if a long-styled pistil had been reduced in length and modified in function. The flowers in this case as in the last are capable of spontaneous legitimate fertilisation, and are rather more productive than ordinary flowers legitimately fertilised. With P. auricula and farinosa the stamens resemble those of the short-styled form in length, but those of the long-styled in the size of their pollen-grains; the pistil also resembles that of the long-styled, so that although the stamens and pistil are of nearly equal length, and consequently pollen is spontaneously deposited on the stigma, yet the flowers are not legitimately fertilised and yield only a very moderate supply of seed. We thus see, firstly, that equal-styled varieties have originated in various ways, and, secondly, that the combination of the two forms in the same flower differs in completeness. With P. elatior some of the flowers on the same plant have become equal-styled, instead of all of them as in the other species.
Mr. Scott has suggested that the equal-styled varieties arise through reversion to the former homostyled condition of the genus. This view is supported by the remarkable fidelity with which the equal-styled variation is transmitted after it has once appeared. I have shown in Chapter 13 of my ‘Variation of Animals and Plants under Domestication,’ that any cause which disturbs the constitution tends to induce reversion, and it is chiefly the cultivated species of Primula which become equal-styled. Illegitimate fertilisation, which is an abnormal process, is likewise an exciting cause; and with illegitimately descended long- styled plants of P. Sinensis, I have observed the first appearance and subsequent stages of this variation. With some other plants of P. Sinensis of similar parentage the flowers appeared to have reverted to their original wild condition. Again, some hybrids between P. veris and vulgaris were strictly equal-styled, and others made a near approach to this structure. All these facts support the view that this variation results, at least in part, from reversion to the original state of the genus, before the species had become heterostyled. On the other hand, some considerations indicate, as previously remarked, that the aboriginal parent-form of Primula had a pistil which exceeded the stamens in length. The fertility of the equal-styled varieties has been somewhat modified, being sometimes greater and sometimes less than that of a legitimate union. Another view, however, may be taken with respect to the origin of the equal- styled varieties, and their appearance may be compared with that of hermaphrodites amongst animals which properly have their sexes separated; for the two sexes are combined in a monstrous hermaphrodite in a somewhat similar manner as the two sexual forms are combined in the same flower of an equal- styled variety of a heterostyled species.
FINAL REMARKS.
The existence of plants which have been rendered heterostyled is a highly remarkable phenomenon, as the two or three forms of the same undoubted species differ not only in important points of structure, but in the nature of their reproductive powers. As far as structure is concerned, the two sexes of many animals and of some plants differ to an extreme degree; and in both kingdoms the same species may consist of males, females, and hermaphrodites. Certain hermaphrodite cirripedes are aided in their reproduction by a whole cluster of what I have called complemental males, which differ wonderfully from the ordinary hermaphrodite form. With ants we have males and females, and two or three castes of sterile females or workers. With Termites there are, as Fritz Muller has shown, both winged and wingless males and females, besides the workers. But in none of these cases is there any reason to believe that the several males or several females of the same species differ in their sexual powers, except in the atrophied condition of the reproductive organs in the workers of social insects. Many hermaphrodite animals must unite for reproduction, but the necessity of such union apparently depends solely on their structure. On the other hand, with heterostyled dimorphic species there are two females and two sets of males, and with trimorphic species three females and three sets of males, which differ essentially in their sexual powers. We shall, perhaps, best perceive the complex and extraordinary nature of the marriage arrangements of a trimorphic plant by the following illustration. Let us suppose that the individuals of the same species of ant always lived in triple communities; and that in one of these, a large-sized female (differing also in other characters) lived with six middle-sized and six small-sized males; in the second community a middle-sized female lived with six large- and six small-sized males; and in the third, a small-sized female lived with six large- and six middle-sized males. Each of these three females, though enabled to unite with any male, would be nearly sterile with her own two sets of males, and likewise with two other sets of males of the same size with her own which lived in the other two communities; but she would be fully fertile when paired with a male of her own size. Hence the thirty-six males, distributed by half-dozens in the three communities, would be divided into three sets of a dozen each; and these sets, as well as the three females, would differ from one another in their reproductive powers in exactly the same manner as do the distinct species of the same genus. But it is a still more remarkable fact that young ants raised from any one of the three female ants, illegitimately fertilised by a male of a different size would resemble in a whole series of relations the hybrid offspring from a cross between two distinct species of ants. They would be dwarfed in stature, and more or less, or even utterly barren. Naturalists are so much accustomed to behold great diversities of structure associated with the two sexes, that they feel no surprise at almost any amount of difference; but differences in sexual nature have been thought to be the very touchstone of specific distinction. We now see that such sexual differences—the greater or less power of fertilising and being fertilised—may characterise the co-existing individuals of the same species, in the same manner as they characterise and have kept separate those groups of individuals, produced during the lapse of ages, which we rank and denominate as distinct species.
CHAPTER VII. POLYGAMOUS, DIOECIOUS, AND GYNO-DIOECIOUS PLANTS.
The conversion in various ways of hermaphrodite into dioecious plants.
Heterostyled plants rendered dioecious.
Rubiaceae.
Verbenaceae.
Polygamous and sub-dioecious plants.
Euonymus.
Fragaria.
The two sub-forms of both sexes of Rhamnus and Epigaea.
Ilex.
Gyno-dioecious plants.
Thymus, difference in fertility of the hermaphrodite and female individuals.
Satureia.
Manner in which the two forms probably originated.
Scabiosa and other gyno-dioecious plants.
Difference in the size of the corolla in the forms of polygamous, dioecious, and
gyno-dioecious plants.
There are several groups of plants in which all the species are dioecious, and these exhibit no rudiments in the one sex of the organs proper to the other. About the origin of such plants nothing is known. It is possible that they may be descended from ancient lowly organised forms, which had from the first their sexes separated; so that they have never existed as hermaphrodites. There are, however, many other groups of species and single ones, which from being allied on all sides to hermaphrodites, and from exhibiting in the female flowers plain rudiments of male organs, and conversely in the male flowers rudiments of female organs, we may feel sure are descended from plants which formerly had the two sexes combined in the same flower. It is a curious and obscure problem how and why such hermaphrodites have been rendered bisexual.