70 PLANT RESPONSE 



anther-tube, in consequence of the general shortening. After 

 a few minutes the filaments again elongate, returning to 

 their original arched position. They are now once more 

 irritable. Again, if one of the filaments be freed, and 

 stimulation be applied to its outer surface, this convex surface 

 becomes concave, returning to the original convex form during 

 recovery. But if the inside of the filament be touched the 

 reverse action takes place, that is to say, the inner side now 

 becomes strongly concave. On excitation, the expelled 

 water passes from the excited cells into the intercellular 

 spaces. This excitatorily expelled water was observed by 

 Pfeffer to well forth from the cut end of the filament. He 

 also studied the contractile shortening, using a magnification 

 of one to two hundred diameters, and found it to amount in 

 various cases to from 8 to 22 per cent of the original length. 



It will be seen that in this case of Cynere<E we find those 

 conditions of extensibility and elasticity which are so charac- 

 teristic of muscle, to be present, though not in an extreme 

 degree. In muscles, contraction is brought about by re- 

 distribution of fluid, as between the constituent isotropic and 

 anisotropic elements. In CynerecE, also, the phenomenon is 

 not altogether different, for here it is known to be brought 

 about by a redistribution of water as between the cells and 

 intercellular spaces. It will be well to remember here that 

 the effect of stimulus acting on an organ from without is, in 

 general, to force the expelled water inwards, whence it may 

 be driven, through intercellular spaces and fibro-vascular 

 elements, out of the excited region, into the interior, or the 

 rest, of the plant. On the cessation of stimulus, the water, 

 thus expelled under tension, returns into the contracted cells, 

 and this fact aids the process of recovery. 



I have already demonstrated in the beginning of this 

 chapter the contraction and concavity of the excited side of 

 an organ, in response to unilateral stimulus. The responsive 

 concavity of either side of the filament of Cynerece when 

 excited, as observed by various investigators, is simply ar 

 instance of this. 



