470 



PLANT RESPONSE 



of these pulsations during a period of twelve hours, by means 

 of photography. The record began at 6 P.M. and ended at 

 6 a.m. During this time there were no fewer than 1 80 con- 

 stituent pulses, and it will be noticed that these again fall 

 into groupings, whose average period is a little over an hour, 

 there being about ten such groups in the course of twelve 

 hours (fig. 1 87). 



Returning now to the question of periodic growth-fluctua- 

 tions, Sachs and others have measured the different rates of 

 growth at various hours within the twenty-four, and from the 

 data thus obtained have constructed curves which showed 



2 3 A.M. 6 A.M. 



FlG. 187. Continuous Photographic Record of Autonomous Pulsation of 

 Desmodium gyrans from 6 P.M. to 6 a.m. 



The lower record is in continuation of the upper. 



the periodicity of the rate of growth. These curves exhibit 

 the daily period in a marked manner ; but the subordinate 

 waves are more or less obliterated, in consequence of the 

 fact that the data from which the curves were constructed 

 were obtained from discontinuous observations. The curves 

 thus deduced show marked differences also, according as. 

 their points were determined frequently or at long intervals. 

 Record of periodic variation of rate of growth. — For 

 this reason it appeared to me important to devise means by 

 which, not the growth, but the variations, of its rate might 

 be automatically recorded, directly and continuously, for any 



