2S2 SANSOME 



when crossed with one hermaphrodite give similar sex ratios and 

 different females give different sex ratios. Also it is similar to 

 results obtained when two intersexual forms of such a species as 

 Mercurialis annua are used in crossing. Here the grade of 

 intersexuality of the progeny depends on the grade of inter- 

 sexuality of both the parents. This leads one to examine the 

 behaviour of hermaphrodites in sub-dioecious species. The be- 

 haviour of hermaphrodites in Silena Otites and 5". Rczmeri is 

 different in type from that of hermaphrodites in true dioecious 

 species, either of plants or higher animals. The hermaphrodites 

 of sub-dicecious species behave as genetic males when crossed 

 with a female, that is, they produce males and females in equal 

 proportions and only a small proportion of intersexes. When 

 selfed or intercrossed, or crossed with a male, these herma- 

 phrodites give no females according to Correns, or extremely 

 few females according to Newton's results. 



Further, if hermaphrodites of different grades of inter- 

 sexuality — strong male-like and strong female-like — are inter- 

 crossed, the progeny will have a range in grade between the 

 grades of the parents, that is, a much greater range than the 

 progeny of either parent selfed. It should be noticed that there 

 is no difference in result in reciprocal crosses. These herma- 

 phrodites, therefore, behave similarly to the normal plant of 

 polycecious species such as Mercurialis annua, Plantago 

 lanceolata, Cirsium oleraceum, C. palustre, C. acaule, Silene 

 infiata and 5". dichotoma, and differ from the usual behaviour 

 of hermaphrodites in true dioecious species. Correns suggests 

 that the male of Silene Rcemeri or S. Otites is heterogametic, 

 but that many more factors are present which, if they enter into 

 the male, cause a greater or less degree of intersexuality. 



The arbitrary but useful division of species into dioecious, 

 sub-dioecious, polycecious, monoecious and hermaphrodite 

 species in plants corresponds with the fundamental gradation 

 in stability of sexuality. The behaviour of sub-dicecious plants 

 forms a bridge between that of true dioecious species and those 

 forms where the diploid phase is not highly differentiated for 

 sex, that is, hermaphrodite species. 



The genetic basis for sex determination in species which 

 have more than two main sex types and which are considerably 

 influenced by external environment is thus more clearly seen. 



