196 BOTANICAL GAZETTE [MARCH 
with the smallness of the leaves in others, excluded from use all 
but Trichomanes crispum, T. radicans, and T. rigidum. Similar 
mechanical difficulties made it impossible to investigate the root 
pressure, so it is not possible to state what relation the facts ascer- 
tained by the potometer method as to the intake of water by tran- 
spiring leaves may bear to those which hold true for intact plants 
in a state of nature. In plants in which the transpiring surface is 
also capable of absorption, and in which there is no structural nor 
functional means by which transpiration is limited or regulated, it 
is to be expected that the rate will be largely a function of the 
conditions governing evaporation. 
A single leaf of Trichomanes crispum, freshly cut from the plant 
and mounted on the potometer, was placed under a bell jar and 
kept wet by a drip from an opening in the top of the jar. There 
was no forward movement of the bubble in the potometer tube 
during the nine hours through which the test was run. In one of 
_ the two repetitions that were made there was a backward movement 
of the bubble at the rate of 1 mg. per hour during the early alte 
noon, suggesting a backward movement of water in the vessels 
due to the absorbing activity of the leaf surface. In order to 
compare the behavior of leaves only partially wet, the test was 
repeated so as to have the leaf wet at the start but without drip 
to keep it so. The following figures are the total losses jn mg. 
for the intervals indicated: 
aX ttm AGE, leak partly wel os eo eee 
32°88 OM. leaf just dey. oc | os isa 13-5 
1:15 P.M., leaf beginning to curl......... 61.0 
1:16 P.., leaf wetted again...........-- 
2:45 P.M., leaf beginning to dry off....... 4.9 
Similar results were obtained with Trichomanes radicans. 
Neither in the dull diffuse light used in all other experimentation 
with the Hymenophyllaceae nor in bright diffuse light did thor 
oughly wet leaves show an intake of water through the petiole. . 
single test was made with a partially dry leaf of this species. The 
leaf had been mounted on the potometer since 9:00 A.M. an kept 
wet until evening. At 5:30 P.M. the drip was stopped and the bell 
jar left over the leaf during the night. At 9:00 the next morning 
