DETERMINATION OF CRITICAL POINT OF DEATH 1^3 



A few words may be said here with regard to these 

 successive movements. As in animals the rigor mortis is 

 succeeded by relaxation, so also in radial organs, as has been 

 said, we see relaxation succeeding the death-contraction. It 

 may then be asked whether the second half of the present 

 curve, in fig. 87, giving the rise of the leaf, does not simply 

 represent a similar relaxation, in the case of the pulvinus of 

 Mimosa. But we have to notice that, in taking records with 

 the Lever, the weight of the Lever ensures the indication of 

 any passive relaxation of the specimen. If we inspect a 

 Mimosa leaf, however, during the death- spasm, the leaf 

 being free, i.e. unconnected with the Lever, we find that it, 

 after its first fall, becomes again almost vertically erected, 

 evidently in consequence, at least to some extent, of some 

 process of active contraction, which must be that of the upper 

 half of the organ. Had there merely been a general relaxa- 

 tion of the whole pulvinus, caused by death, then the weight 

 of the leaf might have caused it to fail. 



The slope of the curve of relaxation, again, is, generally 

 speaking, relatively gentle. Its comparative steepness, in the 

 case o( Mimosa, after the passing of the death point, seems to 

 indicate that the movement of relaxation was partially aided 

 by later contraction of the upper half of the pulvinus. 



Constancy of death-point. — Before concluding the present 

 chapter, I must refer to the remarkable fixity of the death- 

 point in all the phanerogamous plants which have come 

 under my observation in normal conditions. Thus, on re- 

 peating my experiments at the end of spring, by the perfected 

 method of morographic record, I invariably found that the 

 point of inversion was at, or within -^^ of a degree of, 60° C. 

 Other and less perfect modes of investigation, such as the 

 spasmodic lateral movement of a dorsi-ventral organ, the 

 movement of uncurling, the sudden expulsion of water, and 

 those opening and closing movements of flowers which are to 

 be described in the next chapter, enabled us to obtain death- 

 points which were not very different from this. I give below 



