376 



Sir J. C. Bose and Mr. G. Das. 



Calculating from the data obtained from the figure, we find : 



Absolute value of normal rate 0'457 fi per sec. 



Diminished rate under cold O'lOl „ „ 



Enhanced rate under warmth 0'737 „ „ 



Moving Plate Method. — Another experiment was carried out with a different 

 specimen of Kysoor, the record being taken on a moving plate (fig. 5, 1). The 

 left part of the curve here represents the normal rate of growth. The plant 

 was then subjected to moderate cooling, and the subsequent curve with its 

 diminished slope denotes the depression of growth. 



4. Determination of Latent Period and Time- Relations of Response to Stimulus. 



Eocpt. 4. — In the determination of time-relations of responsive change in 

 growth under external stimulus, I take the typical case of the effect of 

 electrical shock of one second's duration from a secondary coil. Two 

 electrodes were applied, one above and the other below the growing region of 

 a bud of Crinum. The record was taken on a moving plate, magnification 

 employed being 2000, and successive dots made at intervals of 2 seconds. 

 It was a matter of surprise to me to find that the growth of the plant was 

 affected by an intensity of stimulus far below the limit of our own percep- 

 tion. For convenience I shall designate the intensity of electric shock that 

 is barely perceptible to us, as the unit shock. When an intensity of 

 0'25 unit was applied to the growing organ, it responded by a retardation of 

 the rate of growth. As regards the relative sensibility of plant and animal, 

 I may say that the leaf of Mimosa pudica, in a favourable condition, responds 

 to an electric stimulus which is one-tenth the minimum intensity that causes 

 perception in a human being.* 



Inspection of fig. 6, a, shows that a flexure is induced in the curve in response 

 to stimulus, the flattening of the curve denoting retardation of growth. The 

 latent period in this case was 6 seconds. The normal rate was found 

 restored after a rest of 5 minutes. The intensity of shock was next raised 

 from 0'25 unit to 1 imit. The second record shows that the latent period 

 was reduced to 4 seconds, and a relatively greater retardation of growth was 

 induced by the action of the stronger stimulus. The recovery of the 

 normal rate was effected after the longer period of 10 minutes. I took one 

 more record, the stimulus being 3 units. The latent period was now reduced 

 to 1 second, and the induced retardation was so great as to effect a temporary 

 arrest of growth, after which there was a slow recovery. 



Uospt. 5. — As a further example of the capability of the crescograph, I will 



* Bose, ' Irritability of Plants,' 1913, p. 50. 



