250 RESEARCHES ON IRRITABILITY OF PLANTS 



of such excitation than the nerve-and-muscle preparation 

 of a frog. This preparation is an exceedingly sensitive 

 detector of induction-current. A shock too feeble to be 

 felt by the intact human subject when passed across the 

 body through two fingers, will, when applied to the exposed 

 nerve of the frog, provoke vigorous movement in the 

 attached muscle. The intact plant, like the human 

 subject, is not so sensitive to an induction-shock as the 

 bare nerve. 



But the case is different when we come to the question 

 of excitation by a constant current. In order to compare 

 the relative excitatory effects here, in plant and animal, 

 I carried out two different investigations, comparing the 

 sensitiveness of the plant on the one hand with that of 

 frog's nerve-and-muscle preparation, and on the other, 

 with that of intact human subject. 



In the first of these I placed an intact petiole of 

 Biophytum in series with a nerve-and-muscle preparation of 

 frog. A gradually increasing e.m.f. was applied by means 

 of a potentiometer-slide arrangement, till one of the two 

 specimens showed excitation at make. The intensity of 

 the exciting current was now measured by means of micro- 

 ammeter. The e.m.f. was then further increased till the 

 second of the two specimens gave excitation at make, and 

 the current again measured. From the value of these two 

 effective currents the relative sensitiveness of the two 

 specimens can be gauged. Instead of measuring the 

 current, we may take, if we wish, the readings of the 

 slide-wire for the two effective values. 



These experiments were carried out in August, during 

 the rainy season. As regards the specimen of Biophytum, 

 it should be mentioned that the vitiated atmosphere of a 

 town is particularly inimical to the sensitiveness of this 

 plant. I have succeeded in raising Mimosa, Desmodium, 

 and other sensitive plants in Calcutta, without much loss 

 to their sensitiveness ; but I have invariably failed to do 

 this in the case of Biophytum. It always becomes stunted 



