242 THE THEORY OF THE GENE 



ondary sex-organ, the sex-comb (present in the normal 

 male, absent in the female). In the mosaic the sex-comb is 

 absent in the region that is haploid. In other words the 

 haploid group of chromosomes consisting of three auto- 

 somes and one X gives, as anticipated, the same kind of 

 result as six autosomes and two X's. The balance is the 

 same in each although the haploid region of the mosaic 

 has only one X, as has the normal male ; but in the male 

 this is offset by six autosomes. 



The converse case is reported by Wettstein who pro- 

 duced by artificial means gametophyte moss plants that 

 were diploid. If these arise from a haploid female game- 

 tophyte cell they are female, and if from a haploid male 

 gametophyte cell they are male. In both cases the balance 

 remains as before. It is apparent that sex-determination 

 is not in these cases regulated by the number of chromo- 

 somes but by the relation of contrasted sets of genes or 

 chromosomes to one another. 



Sex and its Definition in Lower Plants. 



The question of sex terminology appears in its most 

 acute form in the results of recent work on certain groups 

 of gilled fungi or toadstools, Basidiomycetes. In this 

 group, according to the recent statement by Hanna ' ' The 

 problem of sex has occupied the attention of mycologists 

 for more than a hundred years." The discoveries of Miss 

 M. Bensaude (1918), of Kniep (1919-23), of Miss Mounce 

 (1921-22), Buller (1924) and Hanna (1925) have brought 

 to light an extraordinarily interesting situation. In order 

 to simplify the description of this work, the recent paper 

 of Hanna is here followed closely. By means of a new and 

 refined technique, single spores from the gills of the toad- 

 stool can be isolated. From each spore a single mycelium 

 of hy|Dhae can be grown in dung-agar cultures. Each such 

 monosporous mycelium can then be tested by bringing it 



