88 PLANT RESPONSE 



through the specimen, the divergent curled portions are seen 

 to fall together, the observed effect being very like the 

 sudden collapse of the divergent leaves of a gold-leaf electro- 

 scope. The experiment described becomes very striking 

 when magnified by optical projection. 



In the response-phenomena of anisotropic organs we meet 

 with instances in which the continuous action of stimulus 

 gives rise to alternate movements up and down. One factor 

 of this obscure phenomenon may be determined by a modi- 

 fication of the experiment just described. Since we have 

 seen that in a typically anisotropic or dorsi-ventral organ 

 the excitabilities of the two halves are different, there must 

 also exist a difference of time-relations as between their 

 responses ; that is to say, the beginning of response, the 

 attainment of the maximum, and so on, will take place earlier 

 in the one half than in the other. The response of the organ 

 as a whole will thus be the resultant of the curves of response 

 of its constituent halves ; and since these latter differ, in 

 amplitude and phase, we are in a position to understand how 

 we may have great variations in the resultant effect. In 

 order to show the difference of phase I shall take a simple 

 case of induced anisotropy. One half of the bifurcated 

 peduncle is cooled by immersion for a time in ice-water. 

 The two halves are now dipped in a vessel of water, as in the 

 last experiment, and electric shocks are passed through the 

 peduncle as a whole. It will now be found that we obtain 

 successive, instead of simultaneous, excitations of the two 

 halves. For the uncooled half responds at once, whereas the 

 cooled half only begins to respond after ten or more seconds. 

 It is thus clear that had the two halves been joined to form 

 a single organ, the observed response would have been a 

 compound of these two constituent responses. The first part 

 of this response would be due to the active contraction of the 

 uncooled half, but, later, the contraction of the cooled half 

 would reverse this first movement. 



Response by uncurling 1 . — Having now studied the 

 anisotropy, and consequent differences of excitability, caused 



