BRIDGES 



a single-sexed plant but is a protan- 

 drous hermaphrodite. Furthermore, 

 the 4N gametophvte that combines 2 

 male chromosome groups with 2 fe- 

 male groups (FFA4M) is a hermaphro- 

 dite like the ¥M hemiaphrodite. But 

 a triploid form in which two groups 

 are female and one is male is a her- 

 maphrodite that is strongly protogynic 

 instead of protandrous. On the other 

 hand, in working with monoecious 

 mosses where the haploid group is a 

 hermaphrodite, then all haploid, dip- 

 loid, triploid and tetraploid plants 

 were hermaphrodite without distinc- 

 tion, as they should be from their pos- 

 session of the same ratio of female to 

 male determiners. 



A series of sex-indices, similar to 

 those for Drosophila, can be fitted to 

 the dioecious mosses, as shown in 

 Table II. Here it is assumed that there 

 is a pair of chromosomes, X and X', 

 whose difference accounts for the dif- 

 ference between the female and male 

 types. It is assumed that in both these 

 sexes the net effect of the other chro- 

 mosomes, that may be represented by 

 A, is male-determining. Then, since 

 the X,A type is a female, the value for 

 A must be less than that of X, e.g., 

 X=100 and A = 80. Likewise, since 

 X',A is a male, the value X' must be 

 less than that of A, e.g., X'=50. Also, 

 since the FM plant is a hermaphrodite 

 that resembles the normal male more 

 than the normal female, X-l-X' < 2 A. 

 And, since the FFA4 plant is a her- 

 maphrodite that resembles the normal 

 female more closely, X-l-X+X' > 

 3A. We have thus five limiting equa- 

 tions for the three values, X, X', and 

 A. As the table shows, the assigned 

 values of 100, 50 and 80 are possible, 



123 



although there may be other slightly 

 different values that would give a set 

 of indices whose intervals would cor- 

 respond even more closely to the 

 observed differences than to those 

 given. 



The same conformity to the ratio 

 rule seems to be true in the haploid, 

 diploid, triploid and tetraploid daturas, 

 as far as I can gather. But on the genie 

 balance view each of the twelve kinds 

 of chromosomes of Datura might have 

 a distinctive internal unbalance of the 

 sex-controlling genes, similar to the 

 unbalance in the fourth chromosome 

 of Drosophila. In Datura there is a 

 full series of forms that differ from the 

 2N by the addition of a particular 

 extra chromosome. If any of these 

 twelve kinds of chromosomes contain 

 more effective male tendency genes 

 than female tendency genes, or vice 

 versa, then one may well expect to 

 discover that some of Blakeslee's 

 "Apostles" and "Acolytes" have atyp- 

 ical sex-relations. 



LITERATURE 



Blakeslee, A. F. 1922 Variations in Datura, 

 due to changes in chromosome number. 

 Avi. Nat., vol. 56, pp. 16-31. 



Bridges, C. B. 1922 The origin of variations 

 in sexual and sex-limited characters. A7n. 

 Nat., vol. 56, pp. 51-63. 



Goldschmidt, R. 1920 Untersuchungen iiber 

 Intersexualitat. Zeit. f. bid. Abst. u. Verer., 

 vol. 23, pp. 1-197. 



Morgan, L. V. 1922 Non-criss-cross inherit- 

 ance in Drosophila melanogaster. Biol. 

 Bull, vol. 42, pp. 267-274. 



Schweitzer, J. 1923 Polyploidie und Ge- 

 schlechterverteilung bei Splachnum spheri- 

 cum Schwartz. Flora, vol. 116, pp. 1-72. 



Wettstein, F. v. 1924 Morphologie und 

 Physiologie des Formwechsels der Moose 

 auf genetischer Grundlage. 2.eit. f. ind. 

 Abst. 11. Verer., vol. 33, pp. 1-236. 



1^ 



