218 GENETICS IN RELATION TO AGRICULTURE 



be conceived to result in the production of male intersexes, i.e., individuals 

 of the chromosome constitution ZZ which display female characters, 

 because the weaker potency simply means a more or less close approach 

 to the potency of the normal factor in the heterozygous condition and a 

 consequent approach of the individual to the characters of the male. 

 Goldschmidt's results are intensely interesting and promise much for 

 an elucidation of the problems connected with sex-determination. 



We cannot refrain from drawing a comparison between these re- 

 sults and some which have been secured in species crosses in Nicotiana. 

 Thus a definite factor for calycine flower in Nicotiana tabacum causes the 

 flowers to develop a petaloid calyx and a split corolla, a striking terato- 

 logical form. The character is a simple recessive to the normal form in 

 variety crosses but when crossed with N. sylvestris, a different species, 

 the normal flower factor in N. sylvestris appears to possess a lower 

 potency than that of normal flowered varieties of N. tabacum. Con- 

 sequently the hybrids are intermediate with respect to the flower char- 

 acter expression, all of the flowers on a given plant exhibiting some 

 development of the calycine flower character. We interpret this to 

 indicate that the normal flower factor of N. sylvestris does not interact 

 normally with the set of factors which interact to determine the floral 

 character expression in the hybrid, but that the calycine flower factor 

 is able to interact normally and to its full extent with these factors. As a 

 consequence the flowers of the F\ hybrid are strongly calycine. This 

 interpretation is further supported by the fact which we have previously 

 set forth in some detail that practically the entire set of characters are 

 determined by the TV. tabacum parent. It is conceivable that crosses 

 with other species would show the same character of variability in po- 

 tency as has been found for the sex-factors of Lymantria. At any rate 

 a close analogy here exists between the behavior of sex as a character 

 and the behavior of a character known to depend upon a simple factor 

 difference. 



The evidence which has been presented with reference to the determi- 

 nation of sex lends strong support throughout to the idea that sex-de- 

 termination depends on the genotypic constitution of the individual. 

 This does not, it must be clearly understood, mean that other external 

 factors may not act to disturb the usual relations just as they occasion- 

 ally do with other factors; but as in such cases these external factors 

 must act in conjunction with the genotypic sex-factors. To assume 

 that changes occur willy-nilly in the case of sex-factors is no more warrant- 

 able than to assume that other factors change frequently in response to 

 environmental conditions, an assumption that does violence to the high 

 degree of stability which has been observed to obtain for factors in general. 



