Monoecism and Intersexuality 455 



flower form which acts in exactly this way; and, further, that the 

 second group of facts ( W X P, etc. ) fits into such a scheme, assuming 

 a lower action of this modifier. Thus, while the AG explanation is 

 unworkable, a single Mendehan modifier, comparable to those found 

 in Drosophila (e.g., Sturtevant's repleta crosses), could account in a 

 general way for the results, together with a plasmonic difference and 

 an action within the system of independently determined monoecism, 

 that is, a pattern of development of the flower primordia. This modifier 

 would, then, act upon sexual differentiation, independently of the 

 primordia, shifting any development toward femaleness. We could 

 describe this as a case of intersexuality superimposed upon monoecism. 

 In view of the great confusion found in the discussions of sex deter- 

 mination, monoecism, and intersexuality in plants, I consider the 

 present discussion to be of major importance. 



Monoecism, then, would be here, as everywhere, a genetic condi- 

 tion of equal F/M balance, F = M, in the absence of an X-Y mecha- 

 nism. All individuals are FF MM, and the FF chromosomes have not 

 yet reached the status of X-chromosomes which they accomplish only 

 when one F drops out (XO or XY) or changes into a weaker F, as 

 discussed before for Melandrium, Ecballium, and frogs. The com- 

 pletely independent genetic condition which controls the pattern 

 formation of the flower primordia supplies in different places pri- 

 mordia for androecia and gynoecia, which, with the balance F = M, 

 differentiate independently. The estabhshment of an X-chromosome 

 mechanism could make the flowers andromonoecious and gyno- 

 monoecious by enhancer-suppressor action, and the estabhshment of 

 modifying Y material could affect the balance effect in a still more 

 extreme way. But the flowers would still be morphologically potential 

 monoecists with more or less extreme suppression of one t>'pe of organ. 

 Monoecism is thus a floral developmental pattern in the presence of 

 F/M equally balanced and dioecism developed from it as the result 

 of a shift in only one of the two components, the F/M balance via 

 production of a sex chromosome mechanism and (or) a change in the 

 potency of F or F and M. 



Intersexuahty, in which an androecium transforms into a gynoe- 

 cium (male intersexuality) or vice versa (female intersexuality), 

 could be superimposed upon monoecism-dioecism either by intro- 

 duction of a modifier which enhances F or M in both types of 

 primordia, which means intersexual transformation for one and 

 reduction for the other, and vice versa; or by the development of a 

 plasmon condition which has the same modifying effect; or by a 



