26 
available paths. On their banks are Adiantum diaphanum and Poly- 
podium, dolichopterum. Our other smaller species, N ephrodium sparsum, 
N. canescens, Lindsay a blumeana with its- finely dissected fronds, Asple- 
nium. resectum and Adiantum mindanaoense , find sufficient illumination 
on the steeper hillsides. Antrophyum latifolium grows on ' sheer walls 
over cataract-carved pools. 
Antrophyum latifolium and Adiantum- diaphanum are preeminent in 
structural adaptation to the very moist habitat. A. diaphanum .is almost 
our thinnest fern, 0.06 millimeter or less in thickness, with a single 
layer of mesophyll in part of the frond and the upper . and nether epi- 
dermis in immediate contact elsewhere. The outer walls are . scarcely 
1 fx thick. The epidermal cells are very rich in chlorophyll, very wavy 
in surface view and irregular in section, with outgrowths half as deep as 
the cells, which make the surface, especially the nether one, unwettable. 
These water-repellant projections are aided by fine, dark hairs, 0.5 mil- 
limeter long, scattered over the nether surface but only near the basiscopic 
margin above. The stomata are in the general level of the epidermis, 
protected against wetting by the projections, which, however, as they do 
not form any closed wall, do not seriously interfere with the circulation 
of the air. Acroscopic and outer margins are shallowly lobed by sharp 
incisions. The filiform raehis is underlain by the pinnse. The frond 
will shed water in any direction, but , the water usually runs . off at the 
apex. In this forest a low plant is likely to receive a nightly sprinkling 
from those above it, although the sky be clear. The margins of the 
pinnse (or pinnules, of bip innate individuals) are almost, parallel ;■ the 
frond presents a practically unbroken surface to the light, almost without 
waste by overlapping. The sori are at the bottom of fine sinuses in the 
middle of the lobes, certainly the driest spots on the nether surface, and 
the indusia are beset with long hairs. The filifom stipe allows the frond 
to be agitated by any breath of breeze. 
The quashepiphytic habitat of Antrophyum latifolium probably sub- 
jects it to rare and very brief desiccation. Some of its structures, the 
mass of f elty roots, for instance, may be correlated with this danger ; but its 
general structure is- as truly hygrophilous as that of Adiantum, diaphanum, 
yet two ferns could hardly be more unlike. Instead of being delicate, 
the Antrophyum has a frond 0.64 millimeter thick, which in its best 
development is orbicular, with a diameter , of 17 centimeters, a glabrous 
surface, and entire margin. Even in these it is a hydrophyte. In its 
thickness it is fleshy, rather than coriaceous, as compared with its rela- 
tives, its smooth, sub waxy surface will hold practically no water and 
the entire margin is a sharp edge. Its epidermal walls are 2.5 y in 
thickness. The kind of adaptation which. this is appears from a com- 
parison with its local congeners; A. semicosfatum has the wads .7 y and 
6 y thick, -while the average thickness of those of A, plantagineum and 
A. reticulatum is 10 y. A. latifolium is without the spicular i dioblasts 
