24 
main river bed, because rocks nowhere else receive sufficient illumination ; 
but some are scattered through the forest on the trunks of trees. Polypo- 
dium albido-squamatum, Pliotinopteris, and Drynaria rigiduld are not un- 
common terrestrial plants, on arid, treeless mountain sides in'Benguet; 
and on the edges of cliffs in forests, various normally epiphytic plants 
are found on the ground. These cases illustrate what everyone knows, 
that the epiphytic habit has been assumed by plants because of the more 
ample light ; they are a caution against" any disposition too much to 
accredit the abundance of epiphytes along rivers to the moisture of 
the air. 
Another group of species finds adequate illumination only in the tops 
of the upper-story trees, the spreading branches of which are veritable 
gardens. This tree-top vegetation is of necessity most imperfectly known 
in a forest in which the timber has never been cut. Ferns mixed with 
mosses, orchids, etc., which are encountered in such windfalls as may be 
present are Oleandra neriiformis, Humata heterophylla, II. gaimardiana, 
H. parvula , Davallia brevipes , Polypodium incurvatum, Lecanopteris 
pumila, Drynaria quercifolia, and D. rigidula. Along the river, but 
never elsewhere, the tree-top species of Humata come down to the crowns 
and trunks of the smaller trees. Niphobolus Lingua and Dryostachyum 
pilosum grow with them and should probably be added to this very 
imperfect list of tree-top species. 
Growing on tree trunks at the lower border of the high forest are 
Lindsaya Merrilli and Asplenium epiphyticum. Just as thickness of 
frond, usually a xerophytic character, is also under opposite conditions 
at times an appropriate adaptation to a very wet environment, so thinness 
of frond although usually a character of moisture-loving plants, is char- 
acteristic as well of one highly developed type of xerophytes. 12 * This 
type, familiar in the cases of mosses, many lichens, and the Hymenophyl- 
lacece, endures dryness, not by devices to prevent the loss of water, but 
by becoming dry with impunity. Lindsaya Merrilli is a plant of this 
type. Growing in what, during a part of the year, is the driest environ- 
ment to which any Lindsaya of our flora is exposed, it has still the 
thinnest leaves in its genus. Where it grows, on the trunks* of small 
trees in the densest part of these lower woods, the illumination during 
the wet months is quite inadequate for any plant with structures which 
would allow it to retain any activity through the dry season. Asplenium 
epiphyticum is less specialized, in the same direction, and does not grow 
quite to the boundary of the savanna-wood. Somewhat above it but to- 
gether with it, are Asplenium caudatum and two or three other Asplenium 
la A xerophyte is a plant adapted to enduring great dryness; one which, as 
compared with other plants, can endure a desiccating environment at any time. 
A tropophyte is a plant adapted to a periodically very drying environment. 
Bull. Bureau of Education. Manila (1906), 24. 
