TREE FERNS OF NORTH AMERICA MAXON. 467 



of Cyathcacese 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 tins class 

 may be noted Cyaihea 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 AlsopMla micro- 

 donta is found near sea level from Mexico along the Atlantic to South 

 America. AlsopMla 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.m 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 occurring commonly 

 at a low elevation, yet show a considerable altitudinal range; for 

 example, AlsopMla aspera, winch in Jamaica extends from about 

 1,000 to 4,000 feet altitude. A better instance is that of Hemitelia 

 multijlora {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, Cyaihea gracilis, a Jamaicar* 

 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 winch 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- 



