26 
available paths. On their banks are Adiantum diaphavnw and Polij- 
podium dolicliopfcnim. Onr other smaller sporios, Nephrodiutu sparsuin, 
N. canescens, Lindmija hlumeana witli its finely dissected fronds, Asple- 
nium resectum and Adiantum mindanaoensc, find sufficient ilUuuination 
on the steeper hillsides. Antrophyitm MlfoJlnm grows on sheer walls 
over cataract-carved j^ools. 
Antropliyum. laiifoUum and Adiantum diaphanum. are preeminent in 
structural adaptation to the very moist habitat. A. dlaplianum is almost 
our thinnest fern, O.OG millimeter or less in thickness, with a single 
layer of niesopliyll in part of the frond and the upper and nether epi- 
dermis in immediate contact elsewhere. The outer walls are scarcely 
1 jLt 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, whicli make the surface, especially the nether one, unwettahle. 
These water-repellant projections are aided by fme^ 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 wotting 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 rachis is underlain by the pinniE. The frond 
will shed water in any direction, but the water usually runs oi! 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 
pinnae (or pinnules, of bipinnate 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 fme 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 quasi-epiphytic habitat of Antropliyiim latifoUum probably sub- 
jects it to rare and very brief desiccation. Some of its structures, the 
mass of felty 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 
^^ r 
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 flesh}-, rather than coriaceous, as compared with its rela- 
tives, its smooth, subwaxy surface will hold practically no Avater and 
the entire margin is a sharp edge. Its epidermal walls are 2.5 fi in 
thickness. The kind of adaptation which this is appears from a com- 
parison with its local congeners; A, semicostatum has the walls 7 ja and 
G fi thick, while the average thickness of those of A. plantagineum and 
A, rcticulatum is 10 fi. A, laiifolium is without the spicnlar idioblasts 
