STIMULATION IN THE LEAVES OF DIONAEA 
89 
zontal) and with intervals longer than 3 minutes it is somewhat 
steeper (more nearly vertical). The curve is thus roughly divided 
into two portions, the upper of which is steeper than the lower. This 
main bend in the curve may be of considerable importance, but the 
physiological conditions determining it appear to be as yet quite 
unknown. 
Summary 
The closure of Dionaea leaves is due largely to an increase in the 
size of the cells of the ventral or convex region, this increase being 
due to stretching of the cell walls, which soon becomes fixed by growth. 
The opening of the leaf is due to slow enlargement, by growth, of 
the cells of the dorsal or concave region. 
Stimulation of the leaf results in a greatly accelerated rate of 
growth. 
Stimulation appears to be immediately followed by a decrease in 
the osmotic pressure of the cells of the dorsal region, resulting in a 
passage of water from these cells to those of the ventral region. 
A large quantity of starch is deposited in the cells of the dorsal 
region soon after closure occurs. 
Leaves that have been killed in boiling water just after closure, 
open if transferred through alcohol to xylene and close again when 
replaced in water. 
The mechanism of movement in Dionaea leaves shows many points 
of apparent similarity to that of geotropic curvatures. 
At 21° C. two mechanical stimuli are usually necessary to produce 
closure in these leaves, but if the time interval between the successive 
stimuli is increased the number of stimuli necessary for closure also 
increases, though the latter increase is not proportional to the total 
time period involved in the reaction. 
In one case when stimuli were applied at 20-minute intervals, 
closure was not complete until eight hours and twenty minutes after 
the application of the first stimulus. 
Bureau of Science, 
Manila, P. I. 
LITERATURE CITED 
Batalin, A. Mechanik der Bewegungen der insektenfressenden Pflanzen. Flora 35: 
54, 105, 129. 1877. 
Brown, Wm. H. The mechanism of curvature in the pulvini of Mimosa pudica. 
Philippine Journ. Sci. C. Bot. 7: 37. 1912. 
The phenomena of fatigue in the stigma of Martynia. Philippine Journ. Sci. 
C. Bot. 8: 197. 1913. 
