two colts by a black Arabian horse. These colts were partially dun-coloured, and were striped on the legs more plainly than the real hybrid, or even than the quagga. One of the two colts had its neck and some other parts of its body plainly marked with stripes. Stripes on the body, not to mention those on the legs, and the dun-colour, are extremely rare,—I speak after having long attended to the subject,—with horses of all kinds in Europe, and are unknown in the case of Arabians. But what makes the case still more striking is that the hair of the mane in these colts resembled that of the quagga, being short, stiff, and upright. Hence there can be no doubt that the quagga affected the character of the offspring subsequently begot by the black Arabian horse. With respect to the varieties of our domesticated animals, many similar and well-authenticated facts have been published,[[950]] and others have been communicated to me, plainly showing the influence of the first male on the progeny subsequently borne by the mother to other males. It will suffice to give a single instance, recorded in the 'Philosophical Transactions,' in a paper following that by Lord Morton: Mr. Giles put a sow of Lord Western's black and white Essex breed to a wild boar of a deep chesnut colour; and the "pigs produced partook in appearance of both boar and sow, but in some the chesnut colour of the boar strongly prevailed." After the boar had long been dead, the sow was put to a boar of her own black and white breed,—a kind which is well known to breed very true and never to show any chesnut colour,—yet from this union the sow produced some young pigs which were plainly marked with the same chesnut tint as in the first litter. Similar cases have so frequently occurred, that careful breeders avoid putting a choice female to an inferior male on account of the injury to her subsequent progeny which may be expected to follow.
Some physiologists have attempted to account for these remarkable results from a first impregnation by the close attachment and freely intercommunicating blood-vessels between the modified embryo and the mother. But it is a most improbable hypothesis that the mere blood of one individual should affect the reproductive organs of another individual in such a manner as to modify the subsequent offspring. The analogy from the direct action of foreign pollen on the ovarium and seed-coats of the mother-plant strongly supports the belief that the male element acts directly on the reproductive organs of the female, wonderful as is this action, and not through the intervention of the crossed embryo. With birds there is no such close connection between the embryo and mother as in the case of mammals: yet a careful observer, Dr. Chapuis, states[[951]] that with pigeons the influence of a first male sometimes makes itself perceived in the succeeding broods; but this statement, before it can be fully trusted, requires confirmation.
Conclusion and Summary of the Chapter.—The facts given in the latter half of this chapter are well worthy of consideration, as they show us in how many extraordinary modes one organic form may lead to the modification of another, and often without the intervention of seminal reproduction. There is ample evidence, as we have just seen, that the male element may either directly affect the structure of the female, or in the case of animals lead to the modification of her offspring. There is a considerable but insufficient body of evidence showing that the tissues of two plants may unite and form a bud having a blended character; or again, that buds inserted into a stock may affect all the buds subsequently produced by this stock. Two embryos, differing from each other and contained in the same seed, may cohere and form a single plant. Offspring from a cross between two species or varieties may in the first or in a succeeding generation revert in various degrees by bud-variation to their parent-forms; and this reversion or segregation of character may affect the whole flower, fruit, or leaf-bud, or only the half or smaller segment, or a single organ. In some cases this segregation of character apparently depends on some
incapacity of union rather than on reversion, for the flowers or fruit which are first produced display by segments the characters of both parents. In the Cytisus adami and the Bizzarria orange, whatever their origin may have been, the two parent species occur blended together under the form of a sterile hybrid, or reappear with their characters perfect and their reproductive organs effective; and these trees, retaining the same sportive character, can be propagated by buds. These various facts ought to be well considered by any one who wishes to embrace under a single point of view the various modes of reproduction by gemmation, division, and sexual union, the reparation of lost parts, variation, inheritance, reversion, and other such phenomena. In a chapter towards the close of the following volume I shall attempt to connect these facts together by a provisional hypothesis.
In the early half of this chapter I have given a long list of plants in which through bud-variation, that is, independently of reproduction by seed, the fruit has suddenly become modified in size, colour, flavour, hairiness, shape, and time of maturity; flowers have similarly changed in shape, colour, and doubleness, and greatly in the character of the calyx; young branches or shoots have changed in colour, in bearing spines, and in habit of growth, as in climbing and weeping; leaves have changed in colour, variegation, shape, period of unfolding, and in their arrangement on the axis. Buds of all kinds, whether produced on ordinary branches or on subterranean stems, whether simple or, as in tubers and bulbs, much modified and supplied with a stock of nutriment, are all liable to sudden variations of the same general nature.
In the list, many of the cases are certainly due to reversion to characters not acquired from a cross, but which were formerly present, and have been lost for a longer or shorter period of time;—as when a bud on a variegated plant produces plain leaves, or when variously-coloured flowers on the Chrysanthemum revert to the aboriginal yellow tint. Many other cases included in the list are probably due to the plants being of crossed parentage, and to the buds reverting to one of the two parent-forms. In illustration of the origin of Cytisus adami, several cases were given of partial or complete reversion, both
with hybrid and mongrel plants; hence we may suspect that the strong tendency in the Chrysanthemum, for instance, to produce by bud-variation differently-coloured flowers, results from the varieties formerly having been intentionally or accidentally crossed; and that their descendants at the present day still occasionally revert by buds to the colours of the more persistent parent-varieties. This is almost certainly the case with Rollisson's Unique Pelargonium; and so it may be to a large extent with the bud-varieties of the Dahlia and with the "broken colours" of Tulips.
Many cases of bud-variation, however, cannot be attributed to reversion, but to spontaneous variability, such as so commonly occurs with cultivated plants when raised from seed. As a single variety of the Chrysanthemum has produced by buds six other varieties, and as one variety of the gooseberry has borne at the same time four distinct varieties of fruit, it is scarcely possible to believe that all these variations are reversions to former parents. We can hardly believe, as remarked in a previous chapter, that all the many peaches which have yielded nectarine-buds are of crossed parentage. Lastly, in such cases as that of the moss-rose with its peculiar calyx, and of the rose which bears opposite leaves, in that of the Imatophyllum, &c., there is no known natural species or seedling variety, from which the characters in question could have been derived by crossing. We must attribute all such cases to actual variability in the buds. The varieties which have thus arisen cannot be distinguished by any external character from seedlings; this is notoriously the case with the varieties of the Rose, Azalea, and many other plants. It deserves notice that all the plants which have yielded bud-variations have likewise varied greatly by seed.