No. 606] 



MUTATION IN DIDINIUM NASUTUM 

 TABLE I (concluded) 



355 



Total a 



duced at practically the same rate, but those in the former, 

 considerably more rapidly than those in the latter. Dur- 

 ing the 315 days each line in the one group produced ap- 

 proximately 838 generations, 2^ per day, and each line in 

 the other group approximately 634 generations, 2 per day. 



The averages for the five lines in each group for five- 

 day periods are presented in Table I and plotted in Fig. 1. 

 By referring to this table and the figure it will be seen 

 that the difference in rate of fission in the two groups 

 remained fairly constant throughout the entire 315 days, 

 and that in both groups the rate was high in July and 

 August, 1912, after which it decreased considerably and 

 then remained fairly constant. 



The fluctuations in rate of fission were closely asso- 

 ciated with variations in temperature. This was true for 

 twenty-four-hour periods as well as for the five-day 

 periods given in the table. During July and Au.nnist, 

 when the fission rate wa^; liigli, tlie tcm]n'i-atnre wn> in 

 general much higher than it was during tlip rest of the 

 time, when the fission rate was relativelv low. At the 



