22 
heteroclitus, L. hydrophyllus and Polypodium macrophyllum grow on 
and between rocks, in gulches usually without running water. The 
rockiness of this habitat makes it, during the dry season, approach the 
character of the dry woods. 
The narrow belt of low ground along the river and the bottoms of 
the moist tributary depression of course permit a decidedly luxuriant 
growth as compared with the savanna- wood or the drier high forest. 
N ephrodium seiigerum, N. immersum, Aspidium leuzeanum , Microlepia 
Speluncce, Diplazium meyenianum, D. polypoclioides and Odo'ntosoria 
' retusa have ample fronds, usually more than 1 ni'eter high; while 2 
meters is a commoner height for N. ferox, Dennstaedtia cuneata, D. 
Smithii and Pteris tripartita. In the wettest part of the savanna-wood 
only Polypodium Schneideri, and, among the plants of the drier high 
forest, only Pteris opaca, -reach a height of 1 meter. Stature is as much 
an index of the character of the. environment as is structure, sometimes 
a much better one, because great size may require some xerophytic struc- 
tures in plants having moist habitats. 
Thickness of . frond is a xerophytic character, as exhibited by many 
epiphytes of coriaceous texture , but it is also often an hygrophytic char- 
acter, exhibited by many moisture-loving plants with fleshy but not at 
all coriaceous fronds. One of these is Scolopendrium pinnatum, the 
mesophyll of which is composed of large, roundish cells with copious 
intercellular spaces. Its veins are sometimes 2 millimeters apart. Its 
stipe and rhizome are also fleshy. Polypodium macrophyllum as well 
has . an open mesophyll, with intercellular spaces, even in the uppermost 
layer. Except for these two, the thickness of which is itself an hydro- 
phytic character, the average thickness of these leaves (0.122 millimeter) 
is slightly less than that in the low part of the savanna-wood. . 
Eloristically, this division is characterized by the development of 
A! ephrodium § Lastraea, and of Diplazium. 
The more xerophytic terrestrial part of the high forest flora includes 
several elements which have nothing in common except the comparative 
physiological dryness of the environment. Pteris opaca and P. melano- 
caulon grow only over the river but in sunny places almost without soil. 
P. opaca is especially xerophytic in structure because of its size; it has 
a waxy upper surface, no chlorophyll in the thick-walled epidermis, 
sharply differentiated palisade-like mesophyll, and veins only 0.19 mil- 
limeter , apart, hut, like Aclirostichum, it is adapted to life in damp air 
also, having a likewise well-developed spongy parenchyma and numerous 
large, mobile stomata. Sheer banks above creeks, sunny and often devoid 
of other vegetation, are the habitat of Onychium, here and throughout 
the Islands.' 
On small breaks in very steep shaded ground, as under the brow of 
ridges, are found Cyclopeltis presliana in the lower woods and Microlepia. 
pinnata at altitudes above 400 meters. Lindsaya decomposita, and a 
