Chap. XXVII. OF PANGENESIS. 387 



why unnatural conditions of life, though compatible with health, 

 should cause sterility; or why continued close interbreeding, or the 

 illegitimate unions of dimorphic and trimorphic plants, induce 

 the same result The conclusion that the reproductive organs 

 alone are affected, and not the whole organisation, agrees per- 

 fectly with the unimpaired or even increased capacity in hybrid 

 plants for propagation by buds; for this implies, according 

 to our hypothesis, that the cells of the hybrids throw off 

 hybridised cell-gemmules, which become aggregated into buds, 

 but fail to become aggregated within the reproductive organs' 

 so as to form the sexual elements. In a similar manner many 

 plants, when placed under unnatural conditions, fail to produce 

 seed, but can readily be propagated by buds. We shall 

 presently see that pangenesis agrees well with the strong ten- 

 dency to reversion exhibited by all crossed animals and plants. 



As by our hypothesis budding or fission differs from seminal 

 generation only in the manner in which the gemmules are first 

 aggregated, we can understand the possibility of the formation of 

 graft-hybrids; and these graft-hybrids, which combine the 

 characters of the two forms of which the tissues have become 

 united, connect in the closest and most interesting manner gem- 

 mation and sexual reproduction. 



Abundant evidence has been advanced proving that pollen 

 taken from one species or variety and applied to the stigma of 

 another sometimes directly affects the tissues of the mother- 

 plant. It is probable that this occurs with many plants during 

 fertilisation, but can only be detected when distinct forms are 

 crossed. On any ordinary theory of reproduction this is a most 

 anomalous circumstance, for the pollen-grains are manifestly 

 adapted to act on the ovule, but in these cases they act on the 

 colour, texture, and form of the coats of the seeds, on the 

 ovarium lt self, which is a modified leaf, and even on the calyx 

 and upper part of the flower-peduncle. In accordance with the 

 hypothesis of pangenesis pollen includes gemmules, derived from 

 every part of the organisation, which diffuse themselves and 

 multiply _by self-division : hence it is not surprising that gem- 

 mules .within the pollen, which are derived from the parts near the 

 reproductive organs, should sometimes be able to affect the same 

 parts, whilst still undergoing development, in the mother plant. 



2 c 2 



