182 LIFE AND WORK OF SIR JAGADIS C. BOSE 



phenomena so extremely diverse. What, then, is the 

 characteristic reaction in response to stimulus, and what 

 are the agents which cause stimulation ? The term 

 ' stimulus ' has been used, in vegetable physiology, in a vague 

 and indefinite sense, giving rise to much confusion. Thus 

 light and warmth have both been regarded as stimuli ; 

 but Bose was able to show that they bring about physio- 

 logical effects which are diametrically opposite to each 

 other. He carried out long series of experiments, the results 

 of which enabled him to classify factors which cause 

 stimulation. He showed that, generally speaking, agents 

 which cause a contractile twitch in animal muscle also 

 bring about the contraction of plant- tissue. The following 

 modes of stimulation are thus found effective in causing 

 excitation of vegetable tissues : (a) Mechanical (contact 

 or friction, prick or wound) ; (b) radiation (the entire 

 aethereal spectrum including visible light, radiant heat 

 and electric waves) ; (c) electrical (make or break of a 

 current, induction shock and condenser discharge) ; 

 certain chemical agents also act as stimuli. The first great 

 generalisation established by Bose is that the direct appli- 

 cation of all forms of stimuli, mechanical, electrical or radiant, 

 cause similar physiological response of contraction. 



He next shows that the excitation caused by stimulus 

 may remain localised or transmitted to a distance according 

 to the conducting power of the particular tissue. In this 

 respect there are numerous gradations of highly conducting, 

 semi-conducting and non-conducting tissues. Taking the 

 sensitive plant Mimosa as the type possessing high power 

 of conduction and a motile pulvinus, he demonstrates the 

 sensitiveness of the plant by all modes of stimulation and 

 the consequent response. He shows how the sensitiveness 

 of the under surface, eighty-fold greater than that of the 

 upper, was measured ; as also how he determined the speed 

 of transmission of excitation from petiole onwards, usually 

 at 30 mm. per second. This speed, while inferior to that in 

 higher animal nerve, notably surpasses that of lower animals, 



