M. M. SWANN 



between nuclei which will and will not divide. Again this is correlated with DNA 

 charge and protein supply and can be upset or reversed experimentally (in Sorghum, 

 Darlington and Thomas, 1941, Proc. Roy. Soc. B 130, 127-150; in Tradescantia and 

 Scilla, La Cour, 1944, Heredity 3, 319-337). On the other hand cells can be made to 

 divide with an insufficient DNA charge on the chromosomes which have not re- 

 produced (Beadle, 1933, Cytologia, 5, 118-121, in 2ja mays). There are therefore 

 alternative and competing stimuli. 



F. J. Ebling. I should like to offer some evidence of a different kind in support of 

 Professor Swann's view that cell growth and cell division are independent. During 

 the oestrous cycle of the female rat there are significant changes in thickness of the 

 stratum germinativum but not in the incidence of cell division. It appears that the 

 rate of keratinization alters independently of the incidence of mitosis. 



196 



