METHOD OF CONTINUOUS OBSERVATION 37 



between the successive dots is the same ; but for completing 

 the same length of growth-elongation the number of dot- 

 intervals is different. At 30° C. it is eight, at 35° it is six, 

 at 40° it is ten, and at 45° it is twenty-two. The rate of 

 growth at 35° is thus nearly one and a half times that at 

 30° ; at 45°, on the other hand, the rate has fallen to nearly 

 a third. In some cases there was no growth even at 40°, 

 when pulsations were exhibited in each of which the up- 

 and down-curves are nearly equal. 



For Kysoor the optimum temperature is about 35°, but 

 there are plants in which the optimum is as low as 28°, 

 and continues for about the next eight degrees. 



Experiment 11. The temperature minimum. — The ex- 

 periment was carried out with Kysoor subjected to a 

 continuous lowering of temperature by adjusting a flow of 

 ice-cold water into the thermal regulator. It was found 

 that the rate of growth underwent continuous depression, 

 till arrest took place at 22° C. The temperature was 

 then gradually raised, growth being feebly revived at 23°. 

 The minimum temperature may therefore be regarded as 

 22-5° C. 



Experiment 12. Effect of higher temperatures. — Growth 

 was found to be greatly retarded at 55° ; at 60° there 

 occurred a sudden spasmodic contraction, which I have 

 shown elsewhere to be the spasm of death. ^ This spasmodic 

 death-contraction is the immediate effect of the fatal 

 temperature. Prolonged exposure to a temperature a few 

 degrees below 60° would no doubt be followed by the death 

 of the organ. 



Method of Continuous Observation 



The above method of observation, though not ideally 

 perfect, was fairly satisfactory ; a minor defect was, how- 

 ever, discovered as the result of further observation. The 

 plant, according to the method described, was surrounded by 



^ Plant Response (1906), p. 1O8 ; Comparative Electro-physiology (1907), 

 pp. 202, 546. 



