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Profs. Percy Frankland and Marshall Ward. 



division which initiated these new septa, because the fall in tempera- 

 ture seemed probably too gradual and slow to account for it. No 

 doubt these septa were already present at 6.45, and the increased 

 rate of growth followed on their inception, but, with the power 

 employed, they would be invisible for some time, as experience had 

 shown me in other cases. 



The following series were traced on a segment broken off from one 

 of the filaments of the same culture as the last, and is therefore 

 practically a continuation of that series into the night. It clearly 

 bears out the same conclusion, that the period of cell-division entails 

 more or less cessation of growth. In this case the temperature was 

 12 C. throughout the whole period during which the rod was kept 

 under observation, and the whole growth took place in the dark, 

 consequently the variations noticed cannot have been brought about 

 by recognisable changes in the environment, but must be referred to 

 internal causes. 



In this case no septum was visible at 7.8 P.M., but there was one at 

 7.34 P.M., and the rod consisted of two cells. At 8.39 to 9.28 we 

 have another period of slower growth, and during this interval each 

 cell put in another septum ; then it increased again, up to 10.48 P.M., 

 when the observations ceased for the night. 



At 8.30 on the following morning the filament measured 144 /*, 

 having grown 106 /t during the nine hoars and forty-two minutes, 

 which would give 0'18 /* per minute as the approximate average if 

 the rate were constant. This seems a somewhat high rate for the 

 temperature (12 C.), and suggests a question which I afterwards 

 tested ; the question is, does the average rate of growth, other things 

 being equal, increase during the dark hours of the night ? 



The following series, however, drew my attention to some questions 

 of temperature more definitely than hitherto, and led, as we shall see, 

 to some interesting results in this connection. 



A spore, sown soon after 10 A.M. in dilute broth, was kept entirely 



