Feb., 1918] Sexual Dimorphism 109 



of the same texture, but somewhat different in shape and size. 

 (Figs. 4 and 5). Here the dimorphic state has spread far 

 beyond the spores, and sporangia, until it affects the differ- 

 entiation over a considerable area. The microsporangiate 

 and megasporangiate states are set up in the incepts of the 

 sporophylls. In the one case we have male determination, 

 in the other female. Again, how is this determination brought 

 about? By the activity and latency, whether only partial or 

 complete, of hereditary factors. The sexual differentiation 

 takes place before and outside of the phenomena of the reduction 

 division and fertilization. It has absolutely nothing to do with 

 segregation or association of chromosomes or allosomes. 



In the gymnosperms generally the dimorphism is expressed 

 not only in a difference in shape, size and structure of the 

 sporophylls, but usually also in a difference in color; and since 

 the cones are usually monosporangiate in the living species, the 

 dimorphism extends to the floral axis or even beyond. But 

 as all of these advancing evolutionary stages are also repre- 

 sented in the Anthophyta, no special consideration will be 

 given here to the sexual dimorphisms of the gymnosperms. 



When we come to the lowest Anthophyta, as in various 

 genera of the Ranales, there is a considerable advance over the 

 condition in Selaginella and related plants. Figures 6 and 7 

 represent a stamen and a carpel of Aquilegia canadensis L. 

 The dimorphism appears in the shape, size and color of the 

 sporophylls and in addition the megasporophyll shows that 

 remarkable secondary sexual character, the stigma, which 

 becomes necessary here because of the closed condition of the 

 carpellate blade. The ovulary is also covered with prominent 

 hairs while the stamen is smooth, a sex-limited character. In 

 this case the sexual dimorphism expressed in parts of the 

 sporophyte is about as great in character and degree as is usual 

 for secondary sexual differentiations either of plants or animals. 

 But the difference is confined to the sporophylls. The spor- 

 ophyte as an individual shows but one form and nature and the 

 dimorphism is developed in closely associated organs arising 

 from a common tissue. The condition as represented by the 

 flowers of Aquilegia canadensis L. is the normal state for the 

 flowering plants. Indeed, if defined in general terms, the 

 Anthophyta are plants with bisporangiate flowers with here 

 and there groups or individual species which have advanced in 



