git] SHREVE—JAMAICAN HYMENOPHYLLACEAE 203 
leaves under water without squeezing out the bubbles of air among 
the hairs, and found them still very imperfectly wetted up after 
24 hours, and has watched dry leaves becoming wet during the 
commencement of rain in the forest, noticing that a heavy downpour 
of an hour’s duration does not completely wet the leaves. It is a 
very uncommon thing even in the wettest weather to see leaves in 
the field which look saturated. The writer has no experimental 
evidence as to the possible réle of the hairs in preventing water 
loss by the leaf cells themselves, but it is obvious that they do so to 
some extent, and also that they play a part in the ability of this © 
species to withstand a greater amount of insolation than others do. 
AUTONOMY OF THE LEAF AND ITS CELLS.—The extremely low 
degree of differentiation in the leaf tissue of the filmy ferns, and 
the fact that the same cells are at once capable of the functions of 
absorption , photosynthesis, and transpiration, seemed to indicate 
that the behavior of individual leaves when severed from the plant 
might be taken as a perfectly good criterion of their performance 
when in situ. As isolated leaves had been used in experimentation, 
it seemed desirable to determine their capacity for survival under 
the most favorable conditions. In order to do this leaves were 
taken from fresh plants of several species and hung in a moist 
chamber with wicks of cotton cord running from a pan of water so 
as to keep them constantly wet. The forms used were Trichomanes 
rigidum, T. radicans, T. crispum, T. capillaceum, Hymenophyllum 
asplenioides, H. polyanthos, and H. sericeum. At the end of 14 
days all of these were in good condition, looking normal under 
the microscope, excepting H. sericeum, the inability of which to 
withstand submergence has already been noted. Its leaves had 
blackened and its chloroplasts become disorganized. 
There being no reason to suppose that even portions of leaves 
would not survive equally well when removed from the whole leaf, 
a smaller series of leaf fragments was arranged, which were put in 
watch glasses of cistern water that was changed every other day. 
The only forms used were Trichomanes capillaceum, T. rigidum, 
and T. crispum, from each of which was taken a single pinna, a 
Portion of a pinna 1 cm. long, and a portion 3mm. long. The frag- 
ments were frequently examined under the microscope and were 
