ALLEN— SEX INHERITANCE IN SPH^ROCARPOS. 311 



plant respectively (Figs. 25, 26), and of mature archegonial and 

 antheridial involucres (Figs. 27, 28). These figures, while not 

 negativing the possibility of a small difiference between the sexes in 

 average cell size — a possibility to be tested only by a great number 

 of measurements — demonstrate that such differences, if they exist, 

 are negligible as compared with the difference either in total chro- 

 mosome volume or in the total surface area of the chromosomes ; 

 and, what is more significant from the present point of view, that 



Fig. 27. A typical fully developed archegonial involucre. Fig. 28. A 

 typical fully developed antheridial involucre, drawn to the same scale. Both 

 from greenhouse cultures of Sphccrocarpos Donncllii. X 36. 



such possible differences in cell size play no important part in bring- 

 ing about the marked differences in size of homologous organs. On 

 the other hand, as the figures referred to demonstrate, the charac- 

 teristic differences in size between male and female plants result 

 from the presence of a much greater number of cells in correspond- 

 ing parts of the female. Since these size differences appear be- 

 tween plants of the same age, it follows that cell growth and divi- 

 sion go on more rapidly in the female than in the male. If, there- 

 fore, the size and related differences between plants of opposite sex 

 are determined by the diff"erence in chromosome bulk, this quanti- 

 tative difference produces its ultimate visible effects by means of its 



