THE PROBLEM OF SEX IN PLANTS 361 



have identified in the cell-nuclei of the male gametophytes 

 one ^-element, distinguished by its much smaller size 

 (Fig. 265, a). As would be anticipated, the cell-nuclei of 

 the sphorophyte generation contain both the x- and the 

 ^-elements. On the basis of these discoveries Prof. Allen 

 predicts that further investigation is likely to reveal the 

 presence of similar bodies or elements in other plants. 



326. The Meaning of Sex. Just what is accomplished 

 for plants by the occurrence of two sexes is not entirely 

 understood. Among the lower plants the primitive expres- 

 sions of sex seem in some cases, to have met a need for better 

 nutrition, or to have resulted in rejuvenating the protoplasts 

 of the gametes; but these explanations are not satisfactory, 

 especially for the higher plants. We do know that fertili- 

 zation always results in increasing variation. When 

 plants are propagated vegetatively, as by cuttings or by 

 grafting, the characters remain constant in the new 

 plants, 1 but when reproduction is by seeds (resulting from 

 fertilization) we always observe great variation. This 

 is, of course, an advantage, for it is only by variation that 

 new characters may appear, and without the appearance 

 of new characters there would be no opportunity for the 

 improvement of plants either by nature or by man. 



The results of all studies and discussions of the question 

 of sex lead us to recognize the fact that it is still largely an 

 unsolved mystery. We must make further and more 

 accurate observations, and be careful and logical in our 

 reasoning, before we can hope to solve this difficult 

 problem. 



1 Except in the special case of bud-sporting (p. 532, and Fig. 400). 



