310 



ALLEN— SEX INHERITANCE IN SPH^ROCARPOS. 



in rate of growth of the respective gametophytes may well result 

 from the difference in bulk of chromosome substance present in the 

 cells of female and male respectively. The size of the X-chromo- 

 some is such that the chromosome group of the female exceeds in 

 bulk that of the male, at a rough estimate, by perhaps fifty per cent. 

 In view of this difference, and of the differences in cell size which 

 in many cases have been shown to result from differences in chro- 

 mosome number — as, for example, between haploid and diploid 

 moss gametophytes (fi. and £. Marchal, 1909), between haploid 



Fig. 25. A typical fully developed lateral lobe of a female gametophyte. 

 Fig. 26. A similar lobe of a male gametophyte, drawn to the same scale. 

 Both from greenhouse cultures of Sphccrocarpos Domicilii. X 36. 



and diploid Spirogyra cells (Gerassimow, 1901), and between the 

 ordinary and gigas forms of tomato and nightshade (Winkler, 

 1916), it would not have been surprising to find a marked difference 

 in cell size between homologous members of the male and female 

 gametophytes of Sphccrocarpos. However, some measurements 

 made to test this possibility showed that in corresponding parts, 

 such as the lateral lobes, the range of cell sizes is substantially the 

 same in the two sexes. This fact appears clearly in the camera 

 lucida drawings of typical mature lobes from a female and a male 



