TREE FERNS OF NORTH AMERICA—MAXON. 483 
latter with a huge thick trunk that is utterly disproportionate to the 
crown of narrow, lanceolate, bipinnate fronds; C. arborea, previously 
mentioned and figured (pls. 2 and 3; pl. 10, fig. A); C. elegans (pl. 9, 
figs. A and B); C. Tussacii, a Jamaican species with coarse, tripin- 
nate fronds, everywhere shaggy with slender tawny or grayish scales; 
C. nigrescens and C. araneosa, very much alike in their harsh, exceed- 
ingly coriaceous, tripinnate blades and densely spiny trunks and 
stipes; and C. portoricensis, a species with dark, lustrous, purplish- 
brown vascular parts and large, nearly tripinnate blades. The last 
species is apparently unique in having the outer surface of the 
deeply cup shaped indusia rather densely clothed with simple yel- 
lowish hairs. 
Only a few species of the section Eatoniopteris may be mentioned. 
Perhaps the most interesting are C. Brunei and C. aureonitens, 
already referred to in the preceding pages. The Costa Rican forms, 
C. Werkleana, C. hemiotis and C. hastulata, constitute a natural group 
in having the ultimate segments of the tripinnate fronds constricted 
at the base, or even sessile. Three other species, C. Tuerckheimii, 
C. gracilis, and C. dwergens are unusual in having the larger pinnules 
(divisions of the primary pinne) mostly long-stalked. Cyathea 
insignis and C. princeps have the primary and secondary rachises 
unarmed as to spines, but yet conspicuously rough from the presence 
of the broken-off bases of the slender spiny-margined scales which 
_at first thickly invest them. At least one species, C. patellaris, has both 
veins and leaf tissue glabrous, while its nearest ally, C. mexicana, 
has the similar parts very minutely but distinctly glandular-setulose, 
and in addition many of the veins simple, an unusual feature in this 
genus. 
As to the characters which distinguish the species, it may again 
be mentioned that although minute they are usually constant, if due 
allowance be made always for minor variations which may be corre- 
lated mostly with known differences of habitat, altitude, and geo- 
graphic position; and that if a sufficient amount of well-prepared 
material be brought together the recognition of the species will not 
prove especially difficult. Indeed, the most surprising feature of all 
is that species so similar in details of leaf form have been able to 
develop such marked diversity in the general form, structure, and 
disposition of minute scales and hairs and that these differences are 
so nearly constant. An attempt has recently been made to give to 
these structures some part of the weight in classification to which 
they appear to be entitled. To this treatment ' the reader is referred 
for full descriptions of the North American species of this interesting 
genus. 
ae 
1 North American Flora, vol. 16, part 1, pp. 65-88, 1909, 
