Different Genetic Possibilities within the Balance Theory 445 



some. We might well describe it as a modifier acting in the opposite 

 direction from that in Melandriwn, namely, enhancing femaleness, 

 with the result of producing a very labile, almost monoecious condition 

 in the IX males. The many races of frogs, in regard to more or less 

 labile sex determination, extending to complete dioecism, represent 

 different valencies of the F and M factors, just as in Lymantria, and, 

 in addition, different conditions of the Y-chromosome modifier. It is 

 remarkable that P. and G. Hertwig (1922) were led to adopt Witschi's 

 formulation in their study of crosses involving natural subandroecious- 

 ness (male intersexes) in Melandrium. They used different valencies 

 of the F factors in the X-chromosomes and the Y-chromosomal factor 

 ( or modifier in my terminology, a weak F in Witschi's = f if i ) to 

 explain all the individual results. The decisive point is that they needed 

 the F/M balance, different F valencies in different strains, and a 

 special modifier in the Y-chromosome. Another problem enters all 

 these discussions: the relation between andro- or gynodioecism and 

 intersexuality, terms which were used indiscriminately in the discus- 

 sion of Melandrium. This is actually a problem of great theoretical 

 significance when it comes to finding a general solution of the problem 

 of sex determination which fits all the different cases already analyzed 

 and still to be analyzed. (A separate chapter will be devoted to these 

 questions. ) 



We discussed the more complicated developments in Melandrium 

 without much reference to the simpler genetic facts, because 

 Westergaard has used the results to cast doubt upon the basic 

 tenets of genetics of sex in animals, which made it imperative to 

 show that the facts actually fall in line with others. We should now 

 add a few words on simpler cases, for they show the relations of 

 monoecism and dioecism at a less complicated level. As is well known, 

 Correns (1907) made the first crosses between monoecious and 

 dioecious species, which led to the formulation FF = $ , FM = $ , 

 plus something additional for an explanation of monoecism; he could 

 not analyze the latter because of Fi sterility. Galan (1946; see 1951) 

 has since finished this analysis in another form, Ecballium elaterium, 

 which occurs in monoecious and dioecious races that cross freely. The 

 crosses in Fi and Fo (together with interesting changes occurring in 

 the same plants flowering the second year) lead to a simple genetic 

 interpretation which is borne out by all experiments. Decisive are 

 three "genes" of a multiple allelomorphic series, a, a^, a'', and the 

 effect of their combination is tabulated (see overleaf). 



