INTERNAL ENERGY AND EXTERNAL STIMULUS 43 1 



corresponding phenomena in growth-response. It will be 

 shown in the next chapter that the rate of growth increases 

 with the rise of the temperature up to a certain optimum. 

 At a determinate maximum, however, which is about 44 C, 

 growth is arrested, but this arrest does not, as we have just 

 seen in the corresponding instance of Desrnodium, imply a 

 total cessation of internal activity. In making experiments 

 on a seedling of Balsam, I obtained the record shown in the 

 upper part of fig. 176, the temperature being 34 C, which is 

 below the optimum. The average period of a single pulse 



Fig. 175. Photographic Record showing the Slow Pulsations of Large 

 Amplitude of Desmodium Leaflet at 30 C. to become very much 

 Quickened and Reduced in Amplitude at 42 C. 



was in this case 125 seconds, and owing to the considerable 

 amplitude of each pulsation, combined with its incomplete 

 recovery, the average of the resultant rate of growth was as 

 much as '074 mm. per minute. 



On now raising the temperature to 44 C. I obtained the 

 lower of the two records in fig. 176, showing no resultant 

 growth. It is interesting to observe the process by which 

 the cessation of growth comes about in this case. For it is 

 clearly seen from the record that there is no cessation of 

 activity. On the contrary, we find that the frequency of 

 oscillation has become increased from four pulsations to ten, 



