TREE FERNS OF NORTH AMERICA—MAXON. 467 
of Cyatheacez are known from Mexico, but almost the only recent 
material of these is that secured upon occasional excursions from the 
table-land into the moist lower regions bordering the tierra caliente 
of Vera Cruz. 
In the several regions mentioned a few tree ferns are found to be 
partial to the lowlands. Among the West Indian species of this class 
may be noted Cyathea arborea which, however, as already explained, 
exceptionally occurs high up on the southern slopes of the Sierra 
Maestra, finding there congenial surroundings which are wanting at 
a lower altitude in this region. Upon the continent Alsophila micro- 
donta is found near sea level from Mexico along the Atlantic to South 
America. Alsophila myosuroides shows a similar preference for low 
altitudes, its known range extending on the mainland from Vera 
Cruz to Honduras, and including also Cuba and the Isle of Pines. 
Another and very remarkable species of Alsophila (A. blechnoides, 
described hereafter) ranges along the Atlantic coast from Guatemala 
to Trinidad. The occurrence of Hemitelia petiolata in the moist coastal 
woods and thickets of the Canal Zone has already been mentioned. 
Further examples might be cited. 
There are still other species which, though occurrmg commonly 
at a low elevation, yet show a considerable altitudinal range; for 
example, Alsophila aspera, which in Jamaica extends from about 
1,000 to 4,000 feet altitude. A better instance is that of Hemitelia 
multiflora (Hemitelia nigricans), which exists mainly as a sea-level 
species from Guatemala to Panama, along the Atlantic, but never- 
theless ascends to nearly 4,000 feet in Costa Rica. There are, 
doubtless, many tree ferns which are more resistant than others 
to untoward conditions of environment, or less particular in their 
requirements of soil, shade, and moisture, which occupy similarly 
broad belts. In fact, local and hardly appreciable conditions of 
exposure and air drainage, as well as more obvious differences of 
humidity and topography, may be supposed to exercise great influ- 
ence in determining the distribution of tree ferns as of other plants. 
Certain tree ferns occur typically as undergrowth in the dense 
shade of lofty forest trees; for example, Cyathea gracilis, a Jamaican 
species which grows usually in peaty soil in wet, sheltered depressions. 
The trunks of this, though commonly short, sometimes reach 8 to 
12 feet, whereupon, according to Jenman, they “frequently fall and 
lie procumbent, though this does not much affect the growth.” In 
the mountain ravines of Java and Malaya there occurs also, accord- 
ing to Christ, a definite thicket formation of tree ferns, “over which 
the crowns of the forest trees form a second forest.’ A similar 
‘“‘under-forest’’? formation in which screw pines (Pandanus) are 
associated with tree ferns is mentioned from Celebes. These dwarf 
tree-fern associations at high altitudes are believed to fill the impor- 
