332 rrocccciiiKjs of the Ohio State .Icadcniy of Science 



here a])])arently by the fact tliat tlie androspores are very small 

 spores when compared with those which produce the egg-bearing 

 plant. Indeed tlie an(h'ospore appears t(j be a modified sperm- 

 atozoid which developing parthenogenetically produces a stunted 

 individual with male sexuality. 



When one goes into the higher groups where unisexual in- 

 dividuals appear in species whose close relatives are hermaphro- 

 dite, one occasionally has a most striking sexual (lim()r])hism be- 

 tween normal males and females. Thus in species of the com- 

 mon mosses belong to the genus Polytrichum the sexual branches 

 are not only distinguished by having terminal scales of a dif- 

 ferent shape and size, but the female is entirely green while the 

 tip of the male plant in which the antheridia are hidden is red. 

 In the Liverwort, Marchantia, the difiference in shape of the 

 branches which bear the sexual organs is also very great but 

 there is no difference in color. 



The Heterosporous Pteridophytes show an extraordinary 

 difference in the size of the sexual individuals and the same con- 

 dition exists in most of the Gymnosperms. Finally, in the 

 Angiosperms, when one meets with a dimorphism of the sporo- 

 phytes, there is often a decided difference in the color of the 

 flower-clusters ; as in the common cottonwood where the carpel- 

 late catkins are green and the staminate ones red. At the time 

 of blooming, therefore, there is a great contrast in the appearance 

 of the two individuals. Examples like this could be multiplied 

 indefinitely. It is sufficient to repeat again that similar develop- 

 ments and dimorphisms appear whether the sexual organs or 

 branches are borne on unisexual or hermaphrodite individuals. 

 It has commonly been assumed that the sexual dimorphism of 

 the higher animals arose through sexual selection, either through 

 a preference shown by the male or the female or both for some 

 pattern or color. Evidently such an explanation to the similar 

 phenomena observerl in many plants would be the extreme of 

 absurdity whatever one may think of its fitness as an explanation 

 of sexual dimorphism in the intelligent animals. 



T believe that sexual dimorphism or polymorphism \vhether 

 of the sexual organs themselves or of sexual individuals is fun- 



