486 ANNUAL KEPORT SMITHSONIAN INSTITUTION, 1911. 



miles all drawn out to long, slender, nearly linear points, thus 

 suggesting the species name; A. microdonta, a lowland species 

 already mentioned, easily distinguished by the remarkably large, 

 strong, narrowly conical spines which occur at irregular intervals 

 the whole length of its stipe and primary rachis; A. stipularis, a 

 plant of the mountains of Costa Rica and western Panama, with a 

 trunk 30 to 40 feet high and enormous spreading, nearly tripinnate 

 fronds which show the very interesting adaptation of having the 

 primary pinnae (particularly in the basal part of the blade) directed 

 backward from their insertion upon the rachis at an acute angle; 

 A. armata, which, with several related species, has the stipes and 

 rachises densely soft-hairy; A. myosuroides, previously mentioned, 

 with very minute, thickly set spines closely associated with an 

 abundant covering of glossy brown, slender scales at the base of the 

 stipe, and the pinnules of the deeply tripinnatifid fronds ending in 

 narrow greatly elongate tips, "mouse-taillike," as the specific name 

 implies; A. Schiedeana, a much more leafy plant of Mexico and 

 Guatemala, with broader and larger rounded segments; and A. 

 Salvlnii of Chiapas and Guatemala, a species with leaf blades fully 

 tripinnate, the elongate, crenate, leathery segments sessile or short 

 stalked, the rachises firm and woody and of a polished, dark 

 purplish-brown color. The naked (nonindusiate) sorus of this 

 group is indicated in plate 10, figure C, representing a portion of a 

 very young pinnule of A. myosuroides, in which the sporangia are 

 all in place. In figure D, of the same plate, is shown a similar por- 

 tion of A. Schiedeana at a later stage, in which the sporangia are 

 nearly all fallen away from the roundish elevated receptacle. 



The section Lophosoria contains a single species, Alsophila quad- 

 ripinnata, which offers several peculiar structural characters, possibly 

 warranting its separation as a distinct generic type; the trunk and 

 fronds have already been described. 



The section Amphidesmium likewise contains a solitary species, 

 Alsophila blechnoides, which is unique among American tree ferns in 

 the production of more than one sorus upon the veinlets of its large 

 simply pinnate fronds. A partial section of one of the long slender 

 pinnae of this species is shown in plate 13, figure A. Both this and 

 the preceding species are peculiar in the silky hairlike scales of the 

 rhizome and stipe, their form and structure being that of the tribe 

 Dicksonieae and very different from the usual flat scales of the 

 Cyatheae. The fourth section, Trichipteris, which is essentially a 

 group of fully bipinnate South American species, with sessile or 

 stalked pinnules and sori borne in a dense row, is represented in 

 North America by a single species, Alsophila marginalis, first described 

 from British Guiana but gathered once since in Mexico. The scales 

 in this section are like those of Eualsophila. 



