stout: pollinations in cichorium intybus 343 



tilization of one of the higher plants depends, in the first place, 

 on the mutual action of the pollen-grains and the stigmatic 

 secretion or tissues, and afterwards on the mutual action of the 

 contents of the pollen-grains and ovules. Both actions, judging 

 from the increased fertility of the parent plants and from the 

 increased powers of growth in the offspring, are favored by some 

 degree of differentiation in the elements that unite so as to form a 

 new being" ('77, p. 456). As to the conditions operating in self- 

 sterility, Darwin states that "their sexual elements and organs 

 are so acted on as to be rendered too uniform for such inter- 

 action, like those of a self-fertilized plant long cultivated under 

 the same conditions" ('77, p. 345). Darwin here considers that 

 it is lack of differentiation that leads to self-sterility. 



Darwin, however, expressed no opinion of the exact nature of 

 this assumed differentiation, such, for example, as Sachs' con- 

 ception of formative stuffs, Weismann's theory of idioplasmic 

 differentiation due to assumed qualitative cell divisions, or de 

 Vries' theory of intracellular pangenesis. While the determina- 

 tion of the nature of differentiation is essential to the knowledge 

 of sex phenomena, we are not at the present time able to give a 

 precise and exact account of the basal facts involved. 



It is clear, however, that Darwin does not mean merely visible 

 differences such as shape, size, and color of sexual and other organs, 

 and that in speaking specifically of constitutional differentiation 

 he is mainly concerned with egg and sperm cells. He notes, how- 

 ever, that an attempt to compare sex relations with chemical 

 afffnity or attraction is in harmony only with certain phases of 

 fertilization. The difficulty of relating pure chemical affinities 

 to the phenomena of so-called sex affinity is well illustrated by 

 Darwin's discussion. This has become more apparent as the cyto- 

 logical facts are revealed, so that it is now very evident that the 

 chemist knows of no purely chemical relations comparable to the 

 cellular reactions of fertilization, 



Darwin quite fully subscribed to the doctrine of functional inde- 

 pendence of the elements or units of the body as a general doctrine 

 of differentiation of organs, and of the modification of such organs 

 by environmental conditions. This was in fact the basis of his 

 doctrine of pangenesis. That this sort of differentiation is different 

 in degree at least from that of the sexual elements was apparently 

 a view held by Darwin. 



