ACTION OF CHEMICAL AGENTS 39I 



60° C, however, a spasmodic reversal of torsional movement 

 occurred, which w^as so violent that the record went down 

 off the plate in a very short time. 



Explanation. — I have shown that an erectile movement is 

 produced in the leaf of Mimosa, under rising temperature, 

 by the expansion of the more excitable lower half of the 

 pulvinus. But a sudden spasmodic fall takes place at 

 the critical temperature of 60° C, which is the spasm of 

 death. This critical temperature is more or less definite 

 in fresh and vigorous specimens. Growing organs like- 

 wise exhibit a sudden contraction at the fatal tempera- 

 ture (p. 37). It may fairly be inferred that the sudden 

 reversal of normal torsion at this critical temperature is 

 due to the violent death-contraction of the more active 

 longitudinal half of the stem. 



Action of Chemical Agents on Torsion 



A chemical solution applied to the cut end of the stem 

 ascends with the rising sap and affects the torsional 



Fig. 220. Effect of Formaldehyde applied at arrow, showing 

 prehminary acceleration followed by reversal. A prelimi- 

 nary portion of the record is omitted. Successive dots at 

 intervals of 3 minutes. 



activity. A certain interval necessarily elapses betw^een the 

 application and the responsive reaction. In an experiment 



