440 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



phyte in reference to what may be called the critical point in the 

 growth of the pollen tube. It is highly possible that the style 

 and stigma get their differential ciualities by diffusion of secretions 

 (hormones) from the gametophytes after reduction has occurred. 



Types of sterility in dimorphic and trimorphic species. — Thus far 

 we have considered the phenomena of sterility (chiefly physio- 

 logical incompatibility) that appears in such non-dimorphic species 

 as Eschscholtzia californica, Cardamine pratensis, and Cichorium 

 Intybus/m which, as has been emphasized, there is no anatomical 

 incompatibility in the relative differentiation of sex organs of the 

 different plants. The evidence at hand, however, indicates that 

 quite similar if not identical types of incompatibility also exist 

 in various dimorphic and trimorphic species. Here, as Darwin 

 ('62, '64, '65, '69) and Scott ('65) have especially pointed out, 

 various morphological differences and similarities indicate in a 

 general way the combinations that Darwin proposes to call 

 legitimate and illegitimate, which are terms highly useful in a 

 careful analysis of the relations in dimorphic and trimorphic 

 species. 



The real bearing of sex heteromorphism will become clearer if 

 we summarize the general facts of sex differentiation. \\'e evi- 

 dently need, in a consideration of all these conditions, a more 

 accurate classification of the grades and types of differentiation 

 that are in evidence. In respect to differentiations of sex that are 

 either morphological or physiological, or correlations of both, we 

 may quite readily distinguish in flowering plants such grades as 

 the following: 



I. Differentiation of organs within an individual plant. 



1. General sex differentiation as ordinarily recognized, giving 



male and female sex organs with both exhibiting a 

 certain degree of morphological and functional difference, 

 but maintaining essential constitutional organization. 

 Differences in time of development, giving grades of 

 proterandry and proterogyny, especially when seen in 

 perfect flowers, may be included here. 



2. Differentiation between different flowers, giving grades of 



maleness and femaleness to a flower as a unit (pistillate, 

 staminate, perfect, or neutral as in monoecious, or 

 polygamous, forms) or in \arious composite combina- 

 tions. 



