130 RESEARCHES ON IRRITABILITY OF PLANTS 



Effect of Temperature 



The effect of temperature on the latent period is shown 

 in the next two sets of records (figs. 80, 81). In fig. 80 

 we have three sets of records, taken with a 100 D.V. 

 recorder at the three different temperatures of 23 C, 28 C, 

 and 33 C. respectively, under a uniform stimulus-intensity 

 of 2. These temperatures were maintained by means of the 

 thermal chamber, heated electrically. From the lowest 

 record at a temperature of 23 C. the latent period is seen to 

 be -165 second. At 28 C. in the middle record, it is found 



Figs. 80, Si. — Effect of temperature. 



to be reduced to -125 second. And at 33 C. it becomes 

 still further reduced to "065 second. 



In fig. 81 these results are corroborated by records taken 

 with a different specimen, under stimulus-intensity of 2, the 

 vibration-frequency of recorder being 50 D.V. The three 

 records are for temperatures of 24 C, 29 C, and 33 C. 

 respectively. The shortening of the latent period with 

 rising temperature is also shown here in a very striking 

 manner. The lowest of the records, taken at 24 C, gives us 

 a latent period of '14 second. The next, at 29 C, shows a 

 reduction to -102 second. And the last and highest, at 

 33 C., gives us a latent period of only -07 second. 



The increase of vigour in the responsive movement 

 under rising temperature is also very clearly apparent in the 



