194 Darling: Sex in dioecious plants 



the mother-cell stage in the anther. Kerner shows that all stages 

 may be found from those forms in which both functional stamens 

 and pistils are produced, to those where only stamens or pistils 

 develop. In fact all kinds of combinations and stages from strictly 

 hermaphrodite forms to strictly dioecious ones exist. All of these 

 facts might be interpreted as pointing to the conclusion that both 

 tendencies do exist in the sporophyte but that one may be more or 

 less dominant. If these tendencies should be of sufficient potency, 

 then a hermaphrodite sporophyte would result ; if the potency of 

 the two varied, then one or the other of the tendencies would 

 appear in proportion to their potency. 



Considering the case of dioecious Spermatophyta, the only evi- 

 dence at hand seems to indicate that there are two kinds of pollen 

 spores, and that the sporophyte resulting from one kind will be 

 staminate and from the other pistillate. As to the sex tendency of 

 the megaspore there is little evidence; Correns' work seems to in- 

 dicate that it contains the tendency to develop pistillate individ- 

 uals. However, the evidence at present is not sufficient to w^arrant 

 any conclusion as to whether there is a dominancy or a separa- 

 tion of the tendencies in the formation of the megaspore. 



In conclusion I may briefly state the current hypotheses 

 regarding the determination of sex. I use the term '^ tendency" 

 In the sense of ''power to develop," as I have in the preceding 

 discussions. 



Correns ('07) believes that the female organism contains only 

 the female tendency and that it is recessive to the male ; while the 

 male contains both tendencies, the male dominant and the female 

 latent. 



Punnett and Bateson's ('08) hypothesis is practically the reverse 

 of that of Correns. They believe that the male contains only the 

 male tendency and that it is recessive to the female ; while the 

 female contains both tendencies, the female dominant and the 

 male recessive or latent. 



Wilson ('09 d) accounts for the determination of sex on a cyto- 

 logical basis. He concludes that the female tendency is the result 

 of one or more X-elements which are not found in the male ; this 

 X-element may be represented by an idiochromosome. He 

 believes that the male contains the determining factors, and so in 

 a general way agrees with Correns. 



