76 
WILLIAM H. BROWN 
is 0.58 percent, while the average corresponding enlargement in the 
case of stimulated leaves, during closure alone is 6.73 percent. Thus, 
the transverse expansion of the ventral surface during closure of 
stimulated leaves is 11.6 times as great as is the average daily rate 
of transverse enlargement shown by the lower surfaces of unstimulated 
leaves. From these figures it is evident that the stimulation move- 
ments are accompanied by a greatly accelerated rate of transverse 
enlargment. 
Accelerated activity is, in general, accompanied by depletion of 
previously accumulated material, by increased formation of the pro- 
ducts of cell activity, and sometimes even by the formation of products 
not otherwise produced. It is therefore suggested that, if closure of 
these Dionaea leaves is accompanied by accelerated growth, the re- 
sponse should be less vigorous after successive closures, and the results 
of experiment i, as shown in Tables I and II, are in agreement with 
this suggestion. In this experiment the distance between the first 
and last dot increased 13.0 percent during the first closure, 9.0 percent 
during the second, and only 3.2 percent during the third response. 
Moreover, after this last closure the leaf opened very slowly and the 
process required a number of days, the extreme slowness of the opening 
movement rendering it practically impossible to decide just when the 
opening was complete. Also, it has been generally found in this study 
that plants become sickly and die when the leaves are repeatedly 
stimulated at short intervals. 
The idea is at once suggested that we are here dealing with some- 
thing closely related to the condition of fatigue, which has been 
clearly demonstrated for certain other motile responses in plants. 
For example, the stigma lobes of Martynia (Brown, 191 3) respond to 
contact stimulation by a rapid drawing together, which is followed 
by a return to the usual position, the latter process requiring from 8 to 
40 minutes. If these stigmas are repeatedly stimulated, each new 
stimulus being applied as soon as the lobes have regained their usual 
position, the period required for opening may become shorter after 
the first and second response, but it then becomes longer and longer 
as stimulation is repeated, until the stigmas at length fail to respond 
to contact stimulation at all. Here it is not clear whether the decrease 
in rate of movement is due to an accumulation of toxic substances, 
as in the case of animal muscle, or to the using up of available material, 
but the latter supposition seems to be the more probable of the two. 
