45 



nourished female prothallia will predomiuute, while with poor iiourish- 

 meut the vast majority of spores will give rise to male gametophytes. Au 

 examination of cultures grown under favorable conditions for hiboratory 

 use, in which the spores were sown thickly, showed that certain spores 

 produced strictly male plants, others female, and still others bisexual 

 prothallia. A small number of spores were isolated and grown under 

 similar and very favorable conditions, with sinular results. The pure males 

 were almost equal in number to those bearing the female organs, while the 

 bisexual plants were few, being about four per cent, of the whole number. 

 The foregoing results seem to lend encouragement to the view that environ- 

 mental conditions may have much less to do with the development of male 

 and female prothallia than had hitherto been supposed. The very brief 

 study showed clearly that in the fern in question there is a great mortality 

 among the spores, which, as can be readily seen vary greatly in size. 

 Among the first things to establish in this and similar cases is whether 

 mortality is greatest among the smaller or larger spores, and whether 

 the prothallia springing from the small spores tend to remain small and 

 produce only autheridia, while the larger female plants arise only from 

 the larger spores, an so on. I have no notion what sort of results a careful 

 and extended study will bring forth. 



Of all efforts to ascertain the influence of the environment upon the 

 determination of sex, doubtless the studies carried on upon dioecious plants 

 by Strasburger and many others are the most noteworthy. Especially 

 interesting and instructive in this connection is a I'epresentative of the pink 

 family, the Red Campion, Lychnis dioica, which is attacked by a smut, 

 Ustilago violaceae, whose spores are produced in the anthers instead of 

 pollen. This red campion is dioecious, certain individuals bearing only 

 staminate and others pistillate flowers. The structure of the staminate and 

 pistillate flowers are shown in the following figure. 



If a plant, bearing staminate flowers, be infected by the smut, the 

 anthers when mature will be filled with smut spores instead of pollen. 

 Apart from the color of the anthers the form of the staminate flower is 

 unchanged by the presence of the parasite. On the other hand, if a plant, 

 bearing pistillate flowers, is befallen by the snuit, the blossoms on the 

 branches affected by the smut, will develop normally appearing stamens, 

 whose anthers are filled with smut spores instead of pollen, while the pistil 

 remains in a rudimentary condition. The only apparent difference between 

 a pistillate flower thus affected by the parasite and the normal staminate 



