Ryder.] [May 16> 



have been built up, that alone would be a sufficient reason for a renewed 

 discussion of the subject. If, moreover, the evolution of sexuality, 

 through natural causes, has not only been one of the most important 

 agents in evolution of all the multicellular types past and present, but 

 also the means through which the first possibilities of individual varia- 

 bility, fertility and morphological capability were greatly augmented, it is 

 exceedingly desirable that the evidence upon which such claims are 

 based, should be presented. Finally, if sexuality has led to consequences 

 as far-reaching as these, it is also obvious that its claim to consideration, 

 as a factor in biological evolution, is, perhaps, quite as great as that of the 

 principle of natural selection, to the elucidation and demonstration of 

 which Darwin devoted the best years of his life with a singleness of pur- 

 pose which has been rarely equaled. 



That so strongly expressed a characteristic as sexuality, in both the 

 animal and vegetable kingdoms, should have been developed for mere 

 reproduction, is completely disproved by the data of sexuality themselves. 

 It is clear that sexuality becomes more specialized with the progress of the 

 structural complication of organisms, yet external influences may lead to 

 the suppression of fully developed sexuality. It has been most conclu- 

 sively proved, that if a species is artificially cared for, in a word, culti- 

 vated, as in the case of plants, it may. be indefinitely reproduced by 

 means other than those of sexuality. It is even probable that partial or 

 complete sterility has been so induced in not a few plants cultivated for 

 their fruits. The only remaining effect, if effect it can be called, is the 

 impotent fructification of the ovules, whereby the fleshy esculent meso- 

 carp of the ovary or fruit is stimulated to growth and development, for 

 which alone the plant is valued by its cultivator, man. But, so far as I 

 am aware, it has not yet been even proved that such fertilization is 

 necessary. 



If parthenogenesis can and does occur in C&lobogyne and in Saprolegnia, 

 there is no reason why, even in highly developed monocotyledons, such 

 as the astonishingly productive Banana, in spite of its sterility, should pro- 

 duce indefinitely, through a kind of abortive parthenogenesis and as a 

 result of its great vigor, its succulent but seedless fruits. 



If the progressive differentiation or the gradually more intensified expres- 

 sion of sexuality means anything at all, in both plants and animals, 

 beyond providing for mere reproduction, it must mean something of far 

 more utility to species than to provide for variability alone. If the grad- 

 ual acquirement of viviparity in both animals and plants has any signifi- 

 cance, it includes not only a provision for variability, but also achieves the 

 far more important end of providing greatly increased chances for the 

 survival of the thus protected germs or viviparously produced young. 



That the young of such forms are more susceptible to the altering influ- 

 ences of outer conditions than the adult is conspicuously established by 

 the evidence drawn from comparatively complex forms. It is well known 

 that the normal alga-like, filiform protonema of Sphagnum may, in some 



