86 PLANT RESPONSE 



holding the specimen horizontally, as would be necessary 

 in using the Optic Lever. 



In the records obtained with Cucurbita (fig. 39), it will 

 be noticed that the recovery was not very complete, even 

 though an interval of five minutes elapsed between successive 



Fig. 39. Responses of Piagiotropic Stem of Cucurbita 



stimuli. In the case of Convolvulus (fig. 40), however, the 

 recovery was almost complete in two minutes. But of the 

 two, Cticurbita was the more sensitive, Convolvulus requiring 

 a stimulus about four times as great, in order to produce the 



Fig. 40. Responses of Piagiotropic Stem of Convolvulus 



same amplitude of response. Both records show evidence 

 of fatigue. 



Response by collapse of divergent halves of Allium 

 peduncle. — The effect of the anisotropy thus induced by the 

 unilateral action of light may also be exhibited by taking 



