704 PLANT RESPONSE 



ments of plants which are seen in nature, under the action of 

 external stimulus, are but different expressions of a single 

 fundamental response by contraction. 



Kunchangraphic records. — By taking advantage of this 

 responsive contraction, we are able to study all the physio- 

 logical modifications induced in the vegetable tissue by 

 various reagents, with as great ease and certainty as similar 

 phenomena can be studied in animal muscle, using myographic 

 records. By such study, again, we are once more led to 

 see how misleading has been the superficial distinction be- 

 tween sensitive and non-sensitive plants, since the latter, 

 or so-called ordinary, plants also exhibit contraction under 

 stimulation. 



Direct and indirect effects of stimulation. — The living 

 organism is thus a delicately responding machine, whose 

 responsive movements are brought about by external stimulus ; 

 but this complex machinery has also the power of holding 

 part of the energy of the external stimulating shock latent, 

 for a longer or shorter time, so that part only may find 

 immediate expression, while the rest is stored up as internal 

 energy to be given out after the lapse of an intervening 

 period. These two factors, of external stimulus and internal 

 energy, again, induce opposite effects, of contraction and 

 expansion respectively. And the infinite multiplicity of 

 responsive processes in the life-cycle of the plant is brought 

 about by their mutual play. That the combination of these 

 two elements in varying degrees of each, finding expression in 

 different ways, creates a tangle which would at first sight appear 

 inextricable, can be easily understood. And it was the bewilder- 

 ment which this fact imposed upon the observer, that drove 

 US to postulate the existence of an unknown and indefinable 

 vital force, whose mysterious working was to be held to 

 account for the occurrence of all those phenomena that we 

 were otherwise unable to explain. 



It is possible, however, as we have found, going back step 

 by step, to trace out the different expressions of these two 

 distinct factors, of external stimulus and internal energy, and 



