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Show 402 ON TilE DIRECT AC1'ION OF TilE CHAP. X the fruit thus affected, though he has crossed thousands of a~plo and other fruit-trees. There is not the least reason to .believe that a branch which has borne seed or fruit directly mochfied by foreign pollen is itself affected, so as subsequently to produce modified buds: such an occurrence, from the temporary ?onnection of the flower with the stem, would be hardly possible. Hence but very few, if any, of the cases of sudden m~difieations in the fruit of trees, given in the early part of this chapter, can be accounted for by the action of foreign pollen; for such modified fruits have commonly been afterwards propagated by budding or grafting. It is also obvious that changes. o~ colour in the flower which necessarily supervene long before It IS ready for fertilisation, and changes in the shape or colour of the leaves, can have no relation to the action of foreign pollen: all such cases must be attributed to simple bud-variation. The proofs of the action of foreign P?llen on the. mot~erplant have been given in considerabl~ deta,Il, be?ause this act~ on, as we shall see in a future chapter, IS of the highest theoretical importance, ancl because it is in itself a remarkable and apparent!! anomalous circumstance. That it is remarkable under a physiological point of view is clear, for tl~e m~lo element not only affects in accordance with its proper functwn, the germ, but the smTou~ding tissues of the mother-plant. That ~he ac~ion is anomalous in appearance is true, but hardly so m reality, for apparently it plays the same part in the ordinary ferti~isatio~ of many flowers. Gartner has shown, 135 by gradu~lly m?1:c~smg the number of pollen-grains until he succeeded m fertllismg a Malva that many grains are expended in the development, or, as he ~xpresses it, in the satiation, of the. pistil. a~d ovari~m. Again, when one plant is fertilised by a widely distmct species, it often happens that the ovarium is fully and quickly developed without any seeds being formed, or the coats of the seeds are developed without an embryo being formed within. Dr. HildeLrand also has lately shown in a valuable paper 136 that, with several Orchidere, the action of the plant's own 135 'Beitrngo zur Kcnntniss der Befruchtung,' 1844, s. 317-351. 136 'Die Fruchtbildung dor Orchideen, ein Beweis fUr die doppelte Wir-kung des Pollen,' Botanische Zeitung, No. 44 et seq., Oct. 30, 1863; and 1865, s. 219. CHAP. XI. MALE ELEMENT ON THE MOTHER FORM. 403 pollen is necessary for the development of the ovarium, and that this development takes place not only long before the pollen-tubes have reached the ovules, but even before the placentre and ovules have been formed· so that with these orchids tho pollen apparently acts dire~tly on the ovarium. On the other hand, we must not overrate the efficacy of pollen in this respect; for in the case of hybridised plants it might be argued that an embryo had been formed and had affected the surrounding tissues of th0 mother-plant before it perished at a very early age. Again, it is well known that with many plants tho ovarium may be fully developed, though pollen be wholly excluded. And lastly, Mr. Smith, the late Curator at Kew (as I hear through Dr. Hooker), observed the singular fact with an orchid, the Bonatea speciosa, the development of the ovarium could be effected by mechanical irritation of the stigma. Neverthelcss, from the number of the pollen-grains expended "in the satiation of the ovarium and pistil,"-·from the generality of the formation of the ovarium and seed-coats in sterile hybridisecl plants,-and from Dr. HilJ.ebrand's observations on orchids, we may admit that in most cases the swelling of the ovarium, and the formation of the seed-coats, are at least aided, if not wholly caused, by the direct action of the pollen, independently of the intervention of the fertilised germ. Therefore, in the previously- given cases we have only to adll to our belief in the power of the plant's own pollen on the development of the ovarium and seed-coats, its further power, when applied to a distinct species or variety, of influencing the shape, size, colour, textme, &c., of these same parts. Turning now to the animal kingdom. If we could imagine the same flower to yield seeds during successive years, then it would not be very surprising that a flower of which the ovarium had been modified by foreign pollen should next year produce, when self-fertilised, offspring modified by the previous male influence. Closely analogous cases have actually occurred with animals. In the case often quoted from Lord Morton, 137 a nearly purely-bren, Arabian, chesnut mare bore a hybrid to a quagga; she was subsequently sent to Sir Gore Ouseley, and produced 137 'Philos. Trnnsnct.,' 1821, p. 20. 2 D 2 |