496 PLANT RESPONSE 



accelerated growth of the convex side, is apparently supported 

 by Elfving's experiments on grass haulms in which growth 

 had been at standstill. ' He found that the pulvini of grass 

 haulms placed on the klinostat increase in length. This 

 experiment shows incidentally that the klinostat does not 

 remove but merely distributes equally the geotropic stimulus ; 

 also that geotropic stimulus leads to increased, not to 

 diminished, growth. The same thing is proved by the simple 

 fact that a grass haulm shows no growth in its pulvinus while 

 it is vertical, so that when curvature begins (on its being 

 placed horizontally) it must be due to acceleration on the 

 convex, since there is no growth on the concave side in which 

 retardation could occur.' l 



In the cases of response to stimulation, hitherto studied, 

 however, it will be remembered that the fundamental effect 

 was always a contraction and concomitant retardation of 

 growth, the expansion and acceleration of growth being 

 always a secondary and indirect effect ; but in the case of 

 the response to stimulus of gravity, the interpretation of 

 results which has just been quoted would make it appear 

 that the responsive action brought about by gravity was 

 essentially distinct in its character from the responsive re- 

 action with which we have hitherto been familiar. 



Experiment demonstrating responsive curvature as 

 brought about by unilateral pressure of particles.— My 

 own object in the course of the present chapter is, however, 

 to demonstrate the fact that the curvature of an apogeotropic 

 plant-organ in response to gravitation is the result of the 

 direct effect of stimulus, its reactive peculiarities being in no 

 way different from those other instances of the response of 

 the plant to stimulation, which we have already studied 

 And in order to simplify my explanation, I shall here 



1 B.A. Report, 1 891, p. 671. It ought to be mentioned here that in other 

 plants when placed on the klinostat this increased rectilinear growth was not 

 observed, leading to the supposition that in such cases a simultaneous increase 

 and decrease of growth-rate on opposite sides of the rotating plant is produced. 

 Ibid. : Nature, 



