CHROMOSOMES OF CONOCEPHALUM CONICUM 
Amos M. SHOWALTER 
(WITH PLATES IV, V) 
The discovery of visible chromosome differences between the 
sexes in many animals has led to a very wide acceptance of the 
hypothesis that sex in animals is determined by the presence or 
absence of certain chromosomes. This discovery has stimulated 
botanists also to search for sex determinants, and experimental 
work has apparently demonstrated that in Sphaerocarpos and 
Thallocarpus two of the four spores formed by the division of a 
spore mother cell produce male plants and the other two female 
plants. In several dioecious mosses also experimental results 
indicate that the sex potentialities are probably separated in the 
reduction divisions. As yet, however, a visible chromosome differ- 
ence between the sexes has been found in only two species of plants, 
Sphaerocarpos Donnellii reported by ALLEN,’ and S. texanus 
reported by Miss SCHACKE. 
The present study of the chromosomes of Conocephalum coni- 
cum (L.) Dum. was begun primarily for the purpose of determi- 
ning whether or not there exists a visible difference between the 
chromosomes of the two sexes in this species. The results in 
regard to this question are totally negative, but the chromosome 
number is found to be nine instead of eight, as reported by previous 
workers for the gametophytes of this species. 
The material used in the greater part of the study was grown 
in the greenhouse in two separate cultures of male and female 
plants respectively. These cultures were started with thalli bear- 
ing old gametophores of the previous season’s growth, collected 
* Arren, C. E., A cl diff lated with sex difference in S phaero- 
carpos. Science, N. S. 46:466-467. 1917. 
, The basis of sex inheritance in Sphaerocarpos. Proc. Amer. Phil. Soc. 
58: 289-316. 1910. 
2 Scuacke, M. A., A chromosome difference between the sexes of Sphaerocar pos 
texanus. Science, N.S. 49:218. 1919. 
245] [Botanical Gazette, vol. 72 
