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Show 364 PROVISIONAL HYPOTHESIS CnAP. XXVII. stigma, a few seeds of small size were formed. The pollengrains of Mirabilis are extraordinarily large, and the ovarium contains only a single ovule; and these circumstances led N audin 11 to make the following interesting experiments : a flower was fertilised by three grains and succeeded perfectly; twelve flowers were fertilised by two grains, and seventeen flowers by a single grain, and of these one flower alone in each lot perfected its seed; and it deserves especial notice that the plants produced by these two seeds never attained their proper dimensions, and bore flowers of remarkably small size. From these facts we clearly see that the quantity of tho peculiar formative matter which is contained within the spermatozoa and pollen-grains is an all-important element in the act of fertilisation, not only in the full development of the seed, but in the vigour of the plant produced from such seed. VVe see something of the same kind in certain cases of partheuogonesis, that is, when the male element is wholly excluded; for l\1. J om·dan 12 found that, out of about 58,000 eggs laid by unimpregnated silk-moths, many passed through their early embryonic stages, showing that they were capable of selfdevelopment, but only twenty-nine out of the whole number prorluced caterpillars. Therefore it is not an improbable view that deficient bulk or quantity in the formative matter, contained within the sexual elements, is the main cause of their not having the capacity of prolonged separate existence and development. The belief that it is the fun ction of the spermatozoa to communicate life to the ovule seems a strange one, seeing that the unimpregnated ovule is already alive and continues for a considerable time alive. We shall hereafter see that it .is probable that the sexual elements, or possibly only the female element, include certain primordial cells, that is, such as have undergone no differentiation, and which are not present in an active state in buds. Graft-hybrids.-When discussing in the eleventh chapter the cm·ious case of the Cytisus adami, facts were given which render it to a certain degree probable, in accordance with the belief of some distinguished botanists, that, when the tissues of two plants 11 'Nouvelles Archives du Museum,' tom. i. p. 27. 12 As quoted by Sir J. Lubbock in' Nat. Hist. Review,' 18G2, p. 345. CuAP. XXVII. OF PANGENESIS. 365 belonging to distinct species or varieties are intimately united, buds are afterwards occasionally produced which, like hybrids, combine the characters of the two united forms. It is certain that when trees with variegated leaves are grafted or budded on a common stock, the latter sometimes produces buds bearing variegated leaves; but this may perhaps be looked at as a case of inoculated disease. Should it ever be proved that hybridised buds can be formed by the union of two distinct vegetative tissues, the essential identity of sexual and asexual reproduction would be 8hown in the most interesting manner; for the power of combining in the offspring the characters of both parents, is the most striking of all the functions of sexual generation. Direct Action of the Male Element on the Female.-In the chapter just referred to, I have given abundant proofs that foreign pollen occasionally affects the mother-plant in a direct manner. Thus, when Gallesio fertilised an orange-flower with pollen from the lemon, the fruit bore stripes of perfectly characterised lemon-peel: with peas, several observers have seen the colour of the seed-coats and even of the pod directly affected by the pollen of a distinct variety; so it has been with the fruit of the apple, which consists of the modified calyx and upper part of the flower-stalk. These parts in ordinary cases are wholly formed by the mother-plant. We here see the male element affecting and hybridising not that part which it is properly adapted to affect, namely the ovule, but the partially developed tissues of a distinct individual. We are thus brought half-way towards a graft-hybrid, in which the cellular tissue of one form, instead of its pollen, is believed to hybridise the tissues of a distinct form. I formerly assigned reasons for rejecting the belief that the mother-plant is affected through the intervention of the hybridised embryo; but even if this view were admitted, the case would become one of graft-hybridism, for the fertilised embryo and the mother-plant must be looked at as distinct individuals. With animals which do not breed until nearly mature, and of which all the parts are then fully developed, it is hardly possible that the male elem~nt should directly affect the female. But we have the analogous and perfectly well-ascertained case of the male element of a distinct form, as with the |