THE DEATII-SPASM IN PLANTS 



153 



one young, of each plant tested. These experiments were 

 carried out at the beginning of spring. 



Table showinc Death-points in Old and Young Leaves of 

 Different Specimens of Mimosa 



From these results it will be seen that there is a mean 

 difference of r5° C. between the death-responses of old and 

 young leaves. It would thus appear that the age of a cell 

 must be the occasion of a certain amount of protoplasmic 

 change, as manifested in the retardation of death-response. 

 We may also infer that sudden change to unfavourable 

 physiological circumstances — before the plant has accommo- 

 dated itself to the changed condition — will tend to lower the 

 death-point. This fact I found illustrated during the preva- 

 lence of an extraordinary wave of cold, which supervened 

 recently, during the progress of these experiments. I then 

 found that the mean death-point, in the case of various plants, 

 was reduced by several degrees. In Mimosa it fell from the 

 average of 59° C. to 55° C, i.e. as much as 4° C. We have 

 thus seen that the physiological differentiation concomitant 

 on protoplasmic change is attended by variation of death- 

 point. 



Explanation of the subsequent erection, — In animal 

 tissues, the contraction produced by rigot^ mortis is succeeded 

 by a relaxation. The contractile death-spasm in a plant is, 

 similarly, followed by the relaxation seen in the subsequent 



