INBREEDING, PARTHENOGENESIS, ASEXUAL REPRODUCTION 253 



even become in others the exclusive method of fertilization without 

 visible evil results? 



It seems to me that in these facts, established by observation, the 

 results of two quite different processes have been confused, and that 

 we can only gain clearness by studying them apart from one another ; 

 I mean the processes involved in the mechanism of fertilization and 

 those involved in the mingling of the germ-plasms. 



In many cases self-fertilization is said to yield less seed and 

 weaker seedlings. Let us for the present take tliis statement as the 

 basis of our consideration ; it does not seem to me conceivable, though 

 here I am not in agreement with views that have been expressed 

 by others, that both effects should depend upon the same causes, for 

 the smaller number of seeds cannot possibly depend upon the mingling 

 of the two parental germ-plasms, and thus not upon the process 

 of amphimixis itself, since the effect of the mingling does not 

 make itself felt until the organism of the offspring is being built up. 

 Of course the plant seed is the embryo of the young plant, but it will 

 hardly be thought probable that its development could be absolutely 

 prevented by the too close relationship of the two germ-cells, and thus 

 the number of the developing seeds cannot depend on the quality 

 of the ids co-operating in the segmentation-nucleus, but presumably 

 on the number of ova awaiting fertilization in the ovary, which are 

 reached by a pollen-tube and then by a paternal sex-nucleus. This 

 again will depend upon the impelling and attracting forces of the 

 pollen-grain on the one hand, and of the stigma and ' embryo-sac ' 

 of the flower on the other. In other words, the fertility of a flower 

 with its own pollen will depend upon whether the two products of the 

 flower are adapted for mutual co-operation, and in what degree they are 

 so. We are here dealing not with tlie primary reactions of the germ- 

 plasms, which are as they are and cannot be varied, but with secondary 

 relations, which may be thus or thus — in short, with adaptations. 



By what adaptations the pollen of a flower can be made ineflective 

 for that flower is a question which we must leave the botanists to 

 answer ; in any case it must have been possible, and we see clearly 

 that it depends upon adaptation when we consider the numerous 

 stages which occur — from the rare case of the actually poisonous 

 influence of self-pollination already noticed, to complete sterility, 

 and from lessened fertility to greater or even perfect fertility. It is 

 possible that chemical products, secretions of the stigma or the pollen- 

 grain, or the so-called synergid-cells, have to do with this, or that the 

 size and therewith the penetrating power of the pollen-cell in self- 

 fertilization stand in inverse ratio to the length of the pistil, as has 



