452 Genetics of Sex Determination 



shows, as do the facts in Mckindriiim, that hermaphroditism (monoe- 

 cism) is based also on the sex-determining mechanism of F/M balance 

 with F = M. However, there must be an additional genetic system 

 which causes the spatially separate anlagen, that is, a definite primary 

 developmental pattern. Needless to say, such a genetic system also 

 permits shifts by genetic or environmental means, which then could 

 be called intersexuality, just as in frogs or in Melandriiim. Actually, 

 Buttner (1950) found that in a host containing only male Schisio- 

 sotnum mansoni their testes may degenerate and rudimentary ovaries 

 appear. 



We spoke of a primary determinative pattern controlling the 

 spatial arrangement of the female and male parts in a hermaphrodite. 

 In animals this patterning part of the determinative process can show 

 many variations: separate gonads or a single gonad with separation of 

 sex cells, consecutive functioning of the female and male parts of the 

 gonad with and without much modifiability. (See all the variants in 

 mollusks, especially studied by Coe.) In plants it is probably the 

 specific aspect of differentiation at a vegetative point which causes the 

 always more or less identical spatial relationships. 



b. Shift of sex expression in maize 



This situation, and simultaneously the correctness of the inter- 

 pretation used, comes out best in the well-known work of Emerson 

 and especially Jones (1934) in maize. Maize is monoecious, with the 

 additional feature — based on a genetic condition, which is inde- 

 pendent of sex determination itself — that the apical flowers (the 

 tassel) have normal anthers and a rudimentary gynoecium, thus being 

 male functionally. This means that something suppresses female dif- 

 ferentiation, though all flowers are genetically monoecious, in the 

 language of balance, F/M, F = M. The lateral flowers (where the cob 

 develops) are functionally female, while the anthers are rudimentary, 

 the interpretation being the opposite from that of the tassel flowers. 

 Emerson and Jones found and analyzed modifying mutants which 

 specifically counteract the local suppressor action upon the anlagen of 

 one sex in the genetically monoecious flower and enhance the other 

 sex. (I present only the interpretation of the facts which I favor and 

 which fits into the entire genetic picture of sex determination in 

 monoecists.) One recessive locus, tassel seed, affects the terminal 

 flowers in which anther development is suppressed and gynoecium 

 development enhanced so that real seed can be formed. Such a tS2 tS2 



