748 PLANT RESPONSE 



same dose on different constitutions were shown, again, in the 

 fact that, while a i per cent, solution of copper sulphate 

 caused depression, and subsequent death, of a plant under 

 normal tonic conditions, the same dose in the case of a similar 

 specimen, which had been raised artificially to the optimum 

 condition, brought about exaltation of response, which was 

 found to continue for a fairly long period, after which the 

 effect of the poison was completely overcome (p. 487). 



The generalisation which has thus been established will 

 be found to be of great significance. A unity of phenomena, 

 as between animal and plant, so fundamental, so detailed, 

 as has been shown to exist, points unmistakably to a basic 

 property of responsiveness common to the two, and mani- 

 fested in both alike by the same effects and modification 

 of effects under stimulation. Nor is the power of response 

 something which makes its appearance suddenly in organic 

 substances only, for it has been demonstrated as existing 

 even in the inorganic. Thus inorganic and organic are 

 held together in a linked continuity. All are responsive, 

 all are depressed by fatigue, all are made excitable by 

 stimulants and rendered irresponsive by ' poisons.' Again, 

 with regard to plants, it may be said that there is hardly 

 a responsive physiological peculiarity in the highest animal 

 that may not be found foreshadowed here. Thus the serial 

 development of the physiological functions in these two 

 cases has been more or less parallel. 



In the establishment of this generalisation, further, it 

 has been made possible to solve many of the most obscure 

 and difficult problems of Animal Physiology, by studying 

 them under the simple and more manageable conditions of 

 vegetable life. That this is the case has already been seen 

 in many instances, such as that of the polar effects of 

 currents and their reversal under given conditions ; in the 

 light shed on the nature of automatism ; in the different 

 parts played by external stimulus and internal energy, and 

 their mutual relation ; in the bifurcated expression of incident 

 stimulus as external and internal work ; and finally, in the 



