viii. c. 4 Brown: Fatigue in Stigma of Martynia 201 
it seems probable that the results observed are largely or wholly 
due to the disappearance of substances or conditions capable of 
producing the energy necessary for movement rather than to the 
inhibiting effects of substances formed as the result of movement. 
If the results were due, in any considerable degree, to the accumu- 
lation of fatigue substances, the movement should become grad- 
ually slower and slower and the stigma lips would probably not 
show such a sudden loss of the power of movement. 
After the stigma lips of Martynia had responded to stimula- 
tion a number of times it was found that the force of the 
stimulus had to be increased in order to produce complete 
closure. It is not apparent as to whether this was due to a 
decrease in the power of perception or of movement or both. 
That the power of perception and movement may be separate is 
shown by the pulvini of Mimosa, which may be insensitive to 
mechanical stimuli but respond to heliotropic and other forms 
of stimulation.* 
*Pfeffer, W. Physiology of Plants, translated by A. J, Ewart (1906). 
