2 RESEARCHES ON IRRITABILITY OF PLANTS 



whether a given influence has contributed to the plant's 

 well-being or the reverse, whether it has left it more 

 or less excitable, whether it has rendered it more or less 

 energetic ? 



It is conceivable that internal changes which eluded our 

 direct vision might nevertheless be brought within the 

 range of our observation if we could obtain any sort of 

 answer from the plant itself to a questioning shock. In 

 such a case, the feebleness or vigour of the reply would in 

 itself doubtless constitute a measure of the vitality of the 

 organism. It appears obvious that if any given influence had 

 rendered the plant more excitable, this fact would be mani- 

 fested by the greater intensity of its response. In a very 

 excitable condition we may suppose the slightest shock of 

 stimulus would evoke a very large responsive expression ; 

 in a state of depression, on the other hand, the strongest 

 stimulus would induce only a feeble reply. The relation 

 between the stimulus and the response would thus form a 

 gauge of the physiological condition of the organism. The 

 invisible fluctuating changes taking place in the plant, under 

 the changing conditions of the environment, might in this 

 way be made to reveal themselves. 



All this presupposes, however, that the plant will answer 

 in some tangible way to the impinging testing stimulus, 

 and that it may be possible to obtain some record of this 

 answer. The possibility of this will be further discussed 

 presently. There are many important problems which wait 

 for their solution till some such means of inquiry is found. 

 What, for instance, are the various forms of stimulus which 

 evoke an answering reaction in the plant ? Again, has a 

 given plant-tissue, like animal muscle, any definite percep- 

 tion-period capable of exact measurement ? Is the respond- 

 ing tissue susceptible of fatigue ? Is the intensity of its 

 answer dependent on the intensity of the blow ? Is the 

 excitation that may be caused at one point transmissible 

 to a distance, as along animal nerve ? Is such transmission, 

 supposing it to occur, fundamentally of the same nature 



