8o 
WILLIAM H. BROWN 
more at the time of killing showed all of the cells between the veins and 
the dorsal surface packed with starch, while the cells between the veins 
and the ventral surface contained no starch. The formation of starch 
thus indicated can not be considered as responsible for closure, since 
it did not occur until after the leaf had been closed for some time, but 
this starch formation may have been connected in some way with 
the same conditions as those that led to closure. 
According to Pfefifer (1900, p. 326), Bohm was able to produce a 
deposition of starch by plasmolyzing cells with potassium nitrate 
solution. This suggests that the formation of starch occurring soon 
after closure in the cells of the dorsal region of Dionaea leaves may be 
caused by a pronounced extraction of water from these cells, such an 
extraction being brought about through a greatly increased absorptive 
power of the cells of the ventral region. It seems unlikely, however, 
that the osmotic concentration of the solution in the latter cells 
may become great enough to withdraw water from the cells of the 
dorsal region in sufficient amount to bring about the deposition of 
starch in the quantities observed. 
It seems more probable that the sugar in the cells of the dorsal 
region of the leaf becomes less active osmotically as a response to 
stimulation, perhaps by being changed into some substance inter- 
mediate between sugar and starch, and if this occurs it should allow 
a movement of water out of these cells into the cells of the ventral 
region. Whether or not this sort of removal of sugar from solution 
in the dorsal cells does actually occur as a concomitant of leaf closure, 
it appears highly probable that there occurs, with stimulation, an 
increase in the osmotic attraction for water in the cell sap of the 
ventral cells. As has been mentioned above, it seems improbable 
that a sufficient amount of water to cause the observed stretching 
may pass into the cells of the ventral region unless this movement is 
preceded by an increase in the osmotic attraction for water exerted 
by the latter cells. That the causal change may be an alteration in 
the cell walls of the ventral region appears highly improbable, as has 
been noted. 
In connection with the changes in the starch content of the tissues 
of these leaves, it may be mentioned that leaves that failed to respond 
to stimulation showed peculiarities in their starch content. There 
appeared to be two classes of leaves that did not respond to stimulation 
in these studies. Those of the first class were exceptionally thick and 
