180 Darling: Sex in dioecious plants 



in the dioeciousness of the Bryophyta and Pteridophyta would 

 seem to be merely one of time as to the separation or dominancy 



I 



of one tendency, In the former appearing with the production of 

 the spores, in the latter before spore formation. 



Owing to the parasitism of the female gametophyte, the 

 Spermatophyta do not lend themselves so readily to experimenta- 

 tion. However, the unique and careful work of Correns ('07) on 

 Bryonia indicates that two kinds of microspores are formed in 

 dioecious flowering plants ; one through fertilization causes a stami- 

 nate sporophyte to develop, the other a pistillate. 



In this work Correns pollinated the pistillate flowers of the 

 dioecious Bryonia dioica with pollen from the monoecious Bryonia 

 alba ; the offspring were in the main dioecious, a few staminate 

 flowers appearing on the same plant with the pistillate but soon 

 dying. This showed that dioeciousness dominated monoecious- 

 ness, though not completely. Furthermore, the offspring were 

 pistillate, no staminate plant^ being developed; this showed that 

 the pistillate character of the dioecious plant dominated the stami- 

 nate character of the monoecious plant, Correns concludes, there- 

 fore, that all ^^^ cells of Bryonia dioica bear the same tendency, 

 and that this tendency Is to develop pistillate plants. 



He next pollinated the pistillate flowers of Bryoiua dioica with 

 pollen from the staminate flowers of the same species, and obtained 

 in the offspring twenty-one staminate and twenty-one pistillate. 

 Since he used flowers from the same pistillate plant as in his first 

 crossing, the staminate character must have been introduced by 

 the pollen spores ; and since half of the offspring were staminate, 

 and the Qgg contained the pistillate tendency, it would follow that 

 there is a difference in the pollen spores. 



In the third place he pollinated the pistillate flowers of Bryonia 

 alba with pollen from Bryonia dioica and obtained all dioecious off- 

 spring, thirty- eight staminate and thirty-eight pistillate ; this further 

 showed that dioeciousness was dominant. He concludes from 

 this and the preceding experiment that the pollen spores of Bry- 

 onia dioica are of two kinds or otherwise all plants would have 

 been pistillate as in his first experiment. These results were so 

 unexpected, he says, that he tried them over and over with differ- 

 ent individual plants but always with the same results. These 



