MINUTE STRUCTURE OP PLANT HYBRIDS. 281 



spite of arguments advanced by Weismann and his school, we adhere to Darwin's widely 

 collected facts and reasonings on them as entirely favouring this), and gathers up the 

 features of that individual in its development and maturation owing to the constant 

 action and reaction between its chromatic substance and that of co-organismal cells, 

 it follows that for the accomplishment of this there must be a certain co-ordination or 

 rhythmic harmony in the motion of the molecules, and an appropriate attraction — 

 chemical or otherwise — in the combining molecules. If otherwise, then instead of 

 integration of molecule to molecule, disintegration or at least an incapacity for union will 

 hold. 



But it should here be emphasized that reproductive cells are greatly more concentrated 

 in their history than ordinary vegetative cells, and only attain their full maturity after 

 the active stage has been passed in the last, or, as Professor Ryder has well put it in 

 his suggestive paper on the subject, "Sexuality begins when growth ends."* This 

 does not, however, interfere with the fact that sex-cells are often cut off at a very early 

 period from the vegetative ones, for the former may then undergo, as we know them in 

 many cases to do, a slow maturing process, and be greatly acted on or modified by the 

 latter. Now we know that the most impressionable time in the history both of plants and 

 animals is that of growth — not of maturity — and therefore the experiments which may 

 have been instituted on animals, and such arguments as those bearing on exercierknochen, 

 &c, are practically worthless, because the individuals practised on have not in most cases 

 been treated from the earliest impressionable period, when the substance of the sexual cells 

 is in process of formation. It should be noted also that in the human subject and other 

 mammals the eggs are observable in the Graffian follicles at birth, and yet are not 

 matured and shed till years of slow upbuilding and moulding action have affected them. 



If we return now to hybrid production of the more extreme types, though in virtue 

 of the attraction which exists between sexual elements, the original male and female 

 cells from parents of different species — in the absence of cells from the same species — 

 may be capable of uniting, and, in the process, of overcoming the repulsion due to 

 dissimilar co-relative molecules in each, when the attempt is made by all the hermaphrodite 

 cells of the resulting hybrid organism to concentrate representative hermaphrodite groups 

 of molecules, many cases will occur in which these will blend imperfectly, owing to 

 differences in the composition and amount of chemical substances present, or interference 

 and cancelling effects due to unequal propagation of waves of motion between the 

 molecules. Thus many groups of molecules will break down or fail to reach their 

 destination, so that gaps or vacancies will occur in the organic completeness of the pollen 

 or egg cell. It will then have the shrivelled half-empty look so characteristic of 

 hybrid sex-cells that are sterile. In hybrids from more nearly related species the 

 interfering or cancelling effects will be reduced in proportion, and a larger number of 

 sex-cells will have a chance to mature. 



(h) Value of Microscopic Characters in the Future Verification of 'Doubtful Hybrids. — 



* " The Origin of Sex," Proc. Amer. Phil. Soc, vol. xxviii. 



