IRRITO-CONTRACTILITY IN PLANTS. 197 



solution is laid on the tip of a terminal leaflet, striking changes 

 occur. Both of the terminal leaflets close within 7 seconds, and 

 the succeeding pairs below begin to close at the rate already 

 given. But before 5 or 6 pairs out of, it may be, 1922 have 

 closed, a leaflet near the base may be noticed to twitch, or, as 

 often happens, leaflets on distinct leaves, that are placed 

 however, on the same side of the plant as the excited one, may 

 twitch or even fold together in succession, or move irregularly. 

 When this was first observed, it seemed likely that the volatile 

 fumes were the cause, but though they do act as slow excitants, 

 I was soon convinced that twitches and other movements give 

 us a hint as to the true rate of propagation of stimuli through 

 the special conducting tissue, and that the rate of conduc- 

 tivity is greatly more rapid than that more specialized or 

 detailed exhibition of it which ends in the falling back of the 

 leaflets. 



Before passing from this species I may observe that the 

 leaves as a whole seem to be very feebly responsive to shocks, 

 but they, as well as the flower stalks, perform periodic move- 

 ments of great regularity. There seems to be an equally 

 marked periodic movement in the carpels at time of dehiscence, 

 for they always open in the morning while still green, and 

 after scattering of the seeds in the forenoon they close again 

 permanently. 



The above species, I believe, will prove to be the most 

 valuable plant that can be chosen for laboratory purposes, not 

 alone to the botanist, but as well to the animal physiologist. 



Mimosa pudica deserves well its common appellation, " the 

 sensitive plant" for whether we take account of its short latent 

 period, rapid contraction, relatively rapid expansion, delicacy of 

 sensitiveness and rapidity of propagation of an impulse, it 

 deservedly earns its popular name. It has engaged the 

 attention of such earnest workers as Lindsay, Dutrochet, 

 Briicke, Sachs, Batalin, Bert, Millardet, Pfeffer, and during 

 the past year or two of Cunningham and Gaston Bonnier. 

 But much yet remains to be done. 



While tracing out and comparing the contraction and expan- 

 sion periods in plants six weeks old, ten weeks old, and fifteen 



