VIII, c, 4 Brown: Fatigue in Stigma of Martynia 199 
very much less sensitive. Soon after this mechanical stimulation 
does not result in closure. 
Owing to the rapidity with which the stigma lips respond 
to stimulation and then resume their original position they 
seemed to offer an easy method of determining whether or not 
such a structure would show phenomena of fatigue in any way 
similar to that exhibited by the muscles of animals. The spread- 
ing apart of the lips seemed especially favorable for this, as 
any retardation in the rapidity of this movement could be 
observed independently of any fatigue in the perception of stimu- 
lation. If this movement should show a phenomena resembling 
fatigue the time required for resuming the original position 
should increase after successive closures. In order to test this 
point stigmas of flowers one or two days old were selected. 
Since the stigma lips do not usually show a marked decrease 
in the rapidity with which, after having closed together, they 
resume the original position, until the fourth or fifth day, those 
one or two days old should have retained practically unimpaired 
the power of spreading apart for at least one or two days more 
if not stimulated. Results obtained on the first or second day 
of the experiment could therefore hardly be due to old age. 
The method of experimentation consisted in causing the lips 
to close together as the result of mechanical stimulation and 
noting the time required for them to return to their original 
position. As soon as they did this they were again stimulated. 
The same process was repeated until the lips no longer responded. 
It was found that the lips usually resumed the original position 
more quickly after the second or third closure than after the 
first, but beginning with the second or third stimulation they 
showed a marked tendency to do this more and more slowly 
after each successive closure. The increase in the time required 
for the process was quite gradual until it had been repeated 
a number of times. Finally, however, after a certain stimulus 
the time required for resuming the original position was 
increased very greatly, a number of hours being necessary. 
When the lips did spread apart after this, they either responded 
feebly or not at all to mechanical stimulation. If they did close, 
it again took a number of hours for them to spread apart and 
after this mechanical stimulation was always ineffective in 
causing closure. In Table I are given the results of a series of 
experiments which were all performed at the same time. These 
results are quite similar to those obtained from all other 
experiments. 
