STIMULATION IN THE LEAVES OF DIONAEA 
73 
surfaces of the leaves during closure. This seems to indicate that if 
there is any change in the area of the upper surface during closure it 
is probably in the direction of an increase rather than in that of a 
decrease. Although this point is uncertain, it is still quite clear that 
if any transverse shrinkage occurs in the area of the upper leaf surface 
this must be practically negligible when compared with the expansion 
that has been shown for the lower surface. It is thus strongly sug- 
gested that the movement of closing is largely due to the increase in 
volume of tissues lying near the lower leaf surface, although, as will 
be pointed out later, there appears also to occur a decrease in the 
turgor of the tissues near the upper surface, which probably also has 
a contributory effect. This conclusion is contrary to the prevailing 
opinion in this connection, that leaf closure is due to the contraction 
of the dorsal tissues. 
The reopening of the leaf after it has closed, on the other hand, 
seems to be due to expansion of the upper layers of cells, for during 
this process the area of the lower surface changes only slightly while 
that of the upper enlarges considerably, the measurements here 
showing an average increase of 9.4 percent. 
Table IV 
Comparative Measurements of Distances Between Adjacent Dots on the Lower Surface of 
Dionaea Leaves just Before Closing, just After Closing, and 1,2, and 6 hours 
After Closing, the Dots Arranged in a Line Transverse to the Midrib 
Experiment No. 
Just Before 
Closing 
Just After 
Closing 
I Hour After 
Closing 
2 Hours After 
Closing 
6 Hours After 
Closing 
^ a 
12.0 
12.0 
12.5 
12.5 
I 
b 
5-0 
6.5 
7.0 
6.5 
, c 
16.5 
17.0 
17.0 
16.5 
la 
14.5 
15.0 
15.0 
15.0 
2 
b 
II.O 
12.5 
12.5 
12.0 
c 
18.0 
18.5 
19.0 
19.0 
\ a 
21.0 
22.0 
22.0 
22.5 
22.5 
b 
26.0 
28.0 
28.0 
28.0 
28.0 
3 
c 
37-0 
40-5 
40.0 
40-5 
40.5 
d 
25.0 
26.5 
26.5 
25-5 
25.5 
26.0 
27.0 
26.5 
26.5 
26.5 
Examination of the data for experiments I and 2, given in Table I, 
indicates that the increase in area of the lower surface during closure 
is practically permanent and that this enlargement persists after the 
leaf reopens. That this increase generally remains fairly constant 
during the period between closing and reopening is shown by the data 
