STANDLEY — TREES AND SHRUBS OF MEXICO. 39 



edge, both of the species actually occurring there and of their geographic 

 distribution, is very incomplete. Tree ferns are, as a rule, of restricted 

 range, yet many of the Mexican species are known from Alta Verapaz, Guate- 

 mala, and of the remainder most, at least, may be expected to occur there. 

 With a very few exceptions, the Mexican species are exclusively continental, 

 and only a few extend as far south as Panama. 



Aside from the attention attracted by their beauty and stately habit of 

 growth, tree ferns are decidedly interesting because of their marked diversity 

 in structural characters and, unfortunately, their difficult classification. Lo- 

 cally, at least, they serve varied economic uses also, the most important being 

 the use of the trunks as building timbers. These are composed largely of a 

 branched network of hard fibrovascular elements, resistant to decay and the 

 attacks of termites alike, permitting the use of the trunks over and over again 

 in the supporting framework of native houses. Occasionally they are made to 

 serve as telegraph poles. Small pieces of the fibrovascular elements are em- 

 ployed in inlay work. In Costa Rica the succulent unrolling young fronds or 

 " crosiers " of a Cyathea called " I'abo de mico " are eaten as a salad. The 

 scales of a related species (probably Cyathea mexicana), known in Veracruz 

 as " ocopetate " or " cola de mono," are applied topically as a hemostatic. A 

 like use of the matted capillary scales or " pulu " of Hawaiian species of 

 Cibotivni is, of course, well known. Several species of Hemitelia and Alsophila 

 are known as " tatahueso " in Oaxaea, according to Reko. 



Sori borne upon the back of the veins, commonly near the costule or at least 



not marginal; Indusium (if present) not formed in part of the modified 



leaf margin. 



Sori distinctly indusiate, the indusium attached at the base of the receptacle. 



Indusia either (1) cup-shaped or saucer-shaped, never wholly inclosing the 



sporangia, persistent, or (2) globose, at first wholly containing the 



sporangia, rupturing at maturity, the divisions persistent to fugacious. 



1. CYATHEA. 

 Indusia inferior, more or less semicircular in outline, often lobed and scale- 

 like or sometimes cleft or lacerate, never inclosing all the sporangia. 



2. HEMITELIA. 

 Sori usually uonindusiate, a very minute basal scale present in a few species. 



3. ALSOPHILA. 



Sori terminal upon the veins at or near the margin; indusium bilobate or 



bivalvate, the outer portion a more or less modified, concave lobule of the 



leaf margin. 



Outer lip of the indusium formed of slightly modified leaf tissue, unlike the 



rigid brownish inner one 4. DICKSONIA. 



Outer lip of the indusium formed of highly differentiated cartilaginous 

 tissue, similar to the inner one 5. CIBOTIUM. 



1. CYATHEA J. E. Smith, Mem. Accad. Sci. Torino 5: 416. 1793. 

 Caudex erect in most species, arboreous, bearing numerous adventitious 

 roots in the basal part, in mature individuals usually smoothish above, with 

 close-set to distant scars ; fronds borne in a terminal crown, oblique, spreading, 

 or rarely drooping, the stout stipes strongly aculeate to muricate, tuberculate, 

 or nearly smooth, paleaceous toward the base ; blades 2 or 3-pinnate, usually 

 1 to 3 meters long, lanceolate to oblong or ovate, the rachises variously 

 pubescent, furfuraceous, or minutely paleaceous, glabrescent with age ; pinnules 

 subentire to pinnate, sessile to long-petiolate, deciduous or not; veins free, 

 usually branched; sori dorsal, apart from the margin; indusium either (1) 

 inferior and saucer-shaped, never wholly inclosing the sporangia, persistent, 



