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Show 406 CONCLUSION AND SUMMARY CIIAP. XI. incapacity of union rather than on reversion, for the flowers or f]:uit which are first produced display by segments the characters of both parents. In the Gytisus adami and the Bizzarria orange, whatever their origin may have been, tho two parent species occur blended together under the form of a sterile hybrid, or reappear with their characters per£ ct and their reproductive organs effective; and those trees, retaining the same sportive character, can bo propagated by buds. These various facts ought to be well consirlered 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 modifie<l 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 Jist 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 origjn of Gytisus adami, several cases were given of partial or complete reversion, both CHAP. XI. OF TilE CITAPTER. 407 with hybrid and mon~rel plants; hence we may suspect that tho strong tendency m tho Chrysanthemum, for instance, to produce by bud-variation differently-coloured :flowers, results from tho varieties formerly having been intentionally or accid~ ntally 01:ossed; and that their de,·cendants at the present day st1ll occasiOnally revert by buds to the colours of the more p~rsistent. par~nt-va~ieties. This is almost certainly the case w1th Rolhsson.s Umque Pelargonium; and so it may be to a large extent with the bud-varieties of the Dahlia and with the " broken colours" of Tulips. l\iany cases of bud-variation, however, cannot be attributed to reversio~, but t? spontaneous variability, such as so commonly occ~rs wtth cultivated plants when raised from seed. As a single var~et! of the Chrysanthemum has produced by buds six other vanetl~s, and as one variety of the gooseberry has borne at the same t~me 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 mauy peaches which have yielded nectarinebuds 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. vVe must attnbute all such cases to actual variability in the buds. The varieties which have thus arisen cannot be distinguished by any. external c~ar~cter from seedlings; this is notoriously the case w1th the vaneties of the Rose, Azalea, and many other plants .. I~ deserves ~otic~ that all the plants which have yielded bud-vanatwns have likewise varied greatly by seed. rrhese plants belong to so many orders that we may infer that almost every plant would be liable to bud-variation if placed under the proper exciting conditions. These conditions, as far as ~e ~an judge, mainly depend on long-continued and high cultiva~wn; for almo1:;t all the plants in the foregoing lists are perenmals, and have been largely propagated in many soils and under different climates, by cuttings, offsets, bulbs, tubers, and especially by budding or grafting. The instances of annuals varying by buds, or producing on the same plant differ- |