158 CHAP. XIX. THE DAILY VARIATION IN ACTIVITY 



change which is continuously taking place in the assimila- 

 tory activity under the combined influence of changes of 

 light and temperature which are registered by the Electric 

 Photometer and the Thermograph (fig. 43). For our present 

 purpose it is sufficient to take simultaneous observations 



'jWilf ■<?■'■■ — — M8M ' '""■'■"'"■"■ '■'■'■'■ ■ ' L ~ -- 



W 



f^ 1 Z ""1 g Gj5 // Jw'Jss 



To Iht fflecordinq Drum >-«*„ l_jL_ '■''■V'f/c 



Fig. 43. The Complete Apparatus 

 b, the Bubbler ; R, the Electric Photometer ; and T, the Thermograph. 



once every half-hour during periods of rapid change, and 

 once in an hour when the variation is less rapid. 



The method of procedure in taking the observations is 

 as follows. The activity of photosynthesis at different 

 periods is given by an automatic record lasting for five 

 minutes ; the record commenced two and a half minutes 

 before the hour and continued for two and a half minutes 

 after the hour. The mean of these gives the average 



