30 
The mossy forest is ill-developed on mount Balabac. Its area com- 
prises bnt a jfew hectares and the number of ferns is insignificant com- 
pared with that on Apo. Quercus is common ; less abundant on or about 
the summit are Podocarpus, Dacrydium and Phyllocladus. Conspicuous 
companions of the terrestrial Polypodiacece are Diciesonia chrysotricha, 
Gleich&nia dolosa, and a Lycopodium of the cernuum group which spreads 
or climbs for many meters. I reached this summit but once and doubtless 
missed some characteristic ferns, but the whole number can not be large. 
Beside the species listed, there are a number of rain forest species in 
this situation. Hymenophyllacece are very abundant and comprise many 
species. Tmesipteris grows on the trunks of tree ferns. 
The startling feature of the mossy forest fern vegetation is that, in 
sharp distinction to the condition in all lower formations, the terrestrial 
species are structurally much more conspicuously xerophytie than are 
the epiphytic species. This reversal has been brought about from both 
sides. The terrestrial species have on the average thinner fronds than 
the rain forest species, because none are at all fleshy; and' the epidermal 
walls are very much thicker than in any other terrestrial group (except 
Achrostichum) ■ One of these, Oleandra, has an hyaline epidermis and 
hypodermis, resembling no other of our terrestrial ferns except Achros- 
tichum. The xerophytie character of these- ferns can be ascribed to the 
coldness of the ground and to their size. Excepting where they are 
especially -exposed, all are 1 to 2 meters in height, which height, on the 
mountain top, gives them an exposure to the wind greater than that 
possessed by the ridge-dwellers, Cheiropleuria and Taenitis, in the lower 
forests. 
The epiphytes, on the other hand, are much less xerophytie in structure 
here than in any other formation. For this also there are two evident 
reasons. These epiphytes are small plants, indeed with two exceptions 
they are very small and delicate, and their environment is moister, even 
if the atmosphere is less constantly moist, than that of the epiphytes 
anywhere else, for the thick mantle of moss and other vegetation on the 
tree trunks, where fogs are of almost daily occurrence, furnishes a supply 
of water such as is nowhere else available to epiphytes. Many species 
in the mossy forest on Apo are epiphytic or terrestrial without evident 
preference. It may be that some of these small ferns are of the biological 
type of the Hymenophyllacece , but I have never seen them dry. 
But two genera Poly podium and Lindsay a are represented in the 
typical epiphytes of this summit. Eu-P olypodium is the dominant genus 
in this formation everywhere and Lindsaya is always well represented. 
Three of the five Eu-Polypodia in this situation namely, P. cucullatum, 
P. gracillimum, and P. macrum, have erect rhizomes and nonarticulate 
.stipes. From this group (of P. cucullatum), and in the same environ- 
ment, the genus Acrosorus of Apo and of summits in Celebes and Samoa, 
has been derived. 
