Dionasa Muscipula, Ellis. 23 



fully placed on each; one closed in sixteen seconds, another 

 in twenty-five, a third in forty-two, and a fourth in ninety 

 seconds, by which time the ice had melted. The remaining 

 two did not close. These results wen- so diverse that little 

 value could be attached to them, and the experiments v, 

 made in January, when the plants were at their worst. But, 

 recently, in the natural haunts of the plant, the author was 

 able to prove that "cold " stimulus is powerful in its action. 

 On an afternoon, with the temperature at 79 in the shade, 

 small pieces of ice were placed on twenty-three leaves. Care 

 was taken to place these on the base or apex of the lamina, 

 so that even the chance of wetting the hair bases might be 

 avoided. Nineteen of the leaves closed sharply in from five 

 to eleven seconds ; three closed after sixteen to twenty-one 

 seconds, and one closed after thirty-six seconds, by which 

 time the ice had just melted. Small drops of ice-cold water 

 were placed in similar positions, and these acted like the ice. 



Leaf Closure. 



(c) By Light Stimuli. 



Darwin states 1 that concentrated light-rays are unsatisfac- 

 tory in action, and the writer's experiences corroborate this 

 so far as investigation has gone. A large leaf had the sun's 

 rays concentrated on it in a glass house with a temperature 

 at 96° F. After three and a quarter minutes the leaf very 

 slowly closed to about one-third of its extent, and about half 

 a minute later it suddenly closed completely. The leaf had 

 expanded when visited two days after, but where exposed to 

 the light a circular area of a yellowish color and thin in 

 texture showed that the leaf substance in that region had 

 been destroyed. Another leaf similarly treated, but with the 

 light more widely diffused over the lamina, closed to about 

 one-third of its extent, and it after expansion showed no 

 burning effect. Three others were tried but gave negative 

 results. Many careful studies must therefore be made before 

 definite conclusions can be reached as to light stimulus. 



1 p- 294 



