214 Prof. Bose and Mr. Das. Physiological Investigations ivith 



In order to remove the drawback connected with the supply of sufficient 

 material, I commenced an investigation to find whether a detached leaf- 

 preparation could be made as effective for the study of irritability as the 

 whole plant. Here we have at the central end of the leaf the pulvinus, 

 which acts as the contractile organ ; the conducting strand in the interior of 

 the petiole, on the other hand, is the vehicle for transmission of excitation. 

 The problem to be solved is the rendering of an isolated petiole-and-pulvinus 

 of Mimosa as efficient for researches on irritability as the nerve-and-muscle 

 preparation of a frog. On the success of this attempt depended the practical 

 opening out of an extended field of physiological investigation which would 

 be unhampered by any scarcity of experimental material. 



In connection with this it is well to note the surprising difference in 

 vegetative growth as exhibited by plants grown in soil and in pots. A 

 pot-specimen of Mimosa produces relatively few leaves, but one grown in the 

 open ground is extremely luxuriant. As an instance in point, I may state 

 that for the last five months I have taken from a plant grown in a field 

 about 20 leaves a day for experiment, without making any impression on it. 

 A large box containing soil would be practically as good as the open ground, 

 and the slower rate of growth in a colder climate could be easily made 

 up by planting half a dozen specimens. The protection of the plants from 

 inclemencies of weather can be ensured by means of a glass cover with 

 simple heat-regulation by electric lamps, in place of an expensive greenhouse. 



Eeturning to the question of the employment of an isolated leaf, which 

 I shall designate as a petiole-pulvinus preparation, instead of the entire 

 plant, the first attempts which I made proved unsuccessful. The cut leaf 

 kept in water would sometimes exhibit very feeble response, at other times 

 all signs of excitability appeared to be totally abolished. It was impossible 

 to attempt an investigation on the effect of changing environment on 

 excitability when the normal sensitiveness itself underwent so capricious 

 a change. 



These difficulties were ultimately overcome from knowledge derived 

 through systematic investigations on the relative importance of the different 

 parts of the motor apparatus, on the immediate and after-effect of section on 

 the excitability of the leaf, and on the rate of decay of this excitability 

 on isolation from the plant. The experience thus gained enabled me to 

 secure long-continued and uniform sensibility under normal conditions. 

 It was thus possible to study the physiological effects of changing external 

 conditions by observing the responsive variation in the isolated petiole- 

 pulvinus preparation. I propose in this paper to deal with the different 

 aspects of the investigation in the following order : — 



