Igri] SHREVE—JAMAICAN HYMENOPHYLLACEAE 197 
the leaf was partly dry, but not sufficiently so for the tips of the 
pinnae to have begun to curl, and the basal pinnae were still wet. 
The intake of water during the 153 hours was 39 mg. 
The backward movement of the bubble in the test with Tricho- 
manes crispum suggested determining the behavior of a leaf kept 
completely wet for several days. Trichomanes rigidum was used 
in this experiment, and in order to prevent any portion of the leaf 
from becoming dried the whole was submerged under a water- 
tight bell jar in the manner shown in fig. 6. The following figures 
show a continuous and uniform retreat of the potometer bubble: 
Readings Amts. per hr. 
Ot 88 20° SO AML: o.oo is ce 65.5 
AN GC Be 63.5 0.60 
ee OO AM Ak. je 59.5 0.24 
med, S:80PR. Ce 57.8 0. 26 
mee. y, Gr00 BAL... ee 57.0 0. 26 
PS GOO AM. a 54.0 0.20 
NOY. 2. <92*00 Noon, 66 0. os 53-0 0.33 
Ot 4, 50100 AM. oi. ee 47-3 o. 26 
NOV, 45° £2100 Noon... -. ss 46.5 0.40 
eee Sew 45.5 0.30 
We sO a ee 44.5 0. 33 
Dey 4 SOO AW AS ee 40.5 0.27 
meek, fas00 MOON. a 30-5 0.33 
POUL, S60 PM ae 38.5 0.33 
That the pressure of the water surrounding the leaf had to do 
with this retreat is scarcely probable, in view of the hourly rate at 
hight being always less than by day. While an intake of the 
amount here observed would be impossible in intact plants without 
exudation at the roots, the experiment gives an excellent demon- 
stration of the absorbing power of the leaves, and the greater 
amounts absorbed by day than by night point to an influence 
exerted by photosynthetic activity on the absorption rate. 
The extreme slenderness of the petioles of the ferns most capable 
of resisting surface dryness made it impossible to experiment with 
them on the potometer, but the experiments on root-absorption 
Indicate that those forms are capable of maintaining a regular 
transpiration rate when atmospheric conditions do not make it 
too rapid. 
