Researches on Growth and Movement in Plants. 397 



Should the tonic condition of the plant happen to be below par, the effect of 

 stimulus will be an abnormal acceleration of growth, but during the course 

 of the experiment (owing to the continued action of stimulus) the effect will 

 mysteriously revert to the normal retardation. The point of application of 

 stimulus will introduce further complication, indirect stimulation inducing 

 an effect precisely the opposite to that of direct application. The response 

 under unilateral stimulation is further modified by transverse conductivity, 

 by the intensity of stimulation, and the differential excitability of the organ. 

 In an actual experiment the permutation and combination of these different 

 factors will give rise to effects which will, no doubt, appear as highly 

 capricious. These complexities have led Pfeffer to state that an empirical 

 treatment of the subject of growth is all that is possible in the present state 

 of our knowledge. He, however, adds that "deductive treatment still 

 remains the ideal of physiology,, and only when this ideal has been attained 

 shall we be able to obtain a comprehensive view of the interacting factors at 

 work in the living organism."* 



I have attempted in the present paper to contribute towards a deductive 

 treatment of the subject by investigating the isolated effect of each of the 

 numerous complicating factors. 



Among these, we have the changing influence of the environment, which 

 cannot be kept strictly constant for more than a short time. Besides this, 

 " there are the numerous and varied stimulating and mechanical interactions 

 between different organs." The changing influence of the environment cau 

 in practice be eliminated by reducing the period of experiment to a very 

 short time (rendered possible by the employment of the high magnification 

 crescograph) and studying the influence of one factor at a time. Shortening 

 the period of experiment also excludes the interaction of distant organs, for 

 its influence can only be exerted after a certain lapse of time. The organ to 

 be experimented on can thus be isolated from the influence of changing 

 environment and from the interactions of neighbouring organs. In this state 

 of isolation the response under normal conditions is found to be very definite. 

 A given modification of normal response can, moreover, be traced to the 

 definite variation of effect due to the change in the intensity and point of 

 application of stimulus, or in the tonic condition of the reacting organ. 



Summary. 



The most important results that I have so far obtained from experiments 

 with the crescograph are briefly as follow : — 



1. Under lowering of temperature the growth-rate undergoes a diminution 

 * Pfeffer, ibid., vol. 2, p. 1. 



2 I 2 



