767 
Moto-excitability in Mimosa. 
Effect of transition from darkness to light . Here we have to deal first 
with the immediate effect of sudden transition, and then with the persistent 
effect of continuous light. In the record given in Fig. 6 the plant had been 
kept in the dark and the responses taken in the usual manner. It was 
then subjected to light ; the sudden change from darkness to light acted as 
a stimulus, inducing a transient depression of excitability. In this con- 
nexion it is interesting to note that Godlewski found that in the pheno- 
menon of growth, transition from darkness to light acted as a stimulus, 
Fig. 6. Effect of change from darkness to light. The first three records are normal under 
darkness. Horizontal line below indicates exposure to light. Note preliminary depression followed 
by enhancement of excitability. 
causing a transient decrease in the normal rate. The effect of continued 
light on Mimosa is an enhancement of excitability. 
( 2 ) Effect of Enhanced Turgor. 
I have often found that the moto-excitability is depressed under 
excessive turgor. Thus the over-turgid leaf of Biophytum sensitivnm does 
not exhibit any mechanical response on rainy days. The effect of excessive 
turgor on moto-excitability may be demonstrated in the case of Mimosa by 
Fig. 7. Effect of enhanced turgor, artificially induced. First two responses normal. 
Application of water, at arrow, induces depression of moto-excitability. 
