80 AMERICAN FERN JOURNAL 
Suksdorfiana. The stipes of the three species differ in 
both external appearance and internal structures. Those 
of P. glabella are dark red-purple, becoming almost black 
in old age; those of P. Suksdorfiana are somewhat 
lighter in tone, and more reddish brown, while those of 
P. pumila are rather bright chestnut brown, becoming 
darker in old age, but entirely without any purple tinge. 
Those of the last mentioned species differ also from the 
others in their great brittleness, a character which has 
led to some confusion between this species and P. 
Breweri. 
The most characteristic microscopic differences in the 
stipes are in the epidermal and immediately subjacent 
layers of cells. The stipes of P. glabella have fibrous 
epidermal cells, which are of rather even size and uni- 
formly very thick-walled (average size in cross-section, 
12 x 19y, with the lumen 3 y or less in width). The 
hypodermal cells are mostly similar, but slightly larger 
and less thick-walled, and some similar cells occur in the 
third layer. In P. Suksdorfiana the epidermal cells are 
less uniform, 8» 11 u-19 x 22u in cross-section, 
moderately thick-walled with the thickening heaviest 
on the outer wall, and with the lumen 3.5-5.5 p wide. 
. The hypodermal cells are somewhat thick-walled, but 
otherwise resemble the internal parenchyma rather than 
the epidermis. In P. pumila the epidermal cells are 
nearly circular in cross-section, 9-15 in diameter, 
moderately and uniformly thick-walled with the lumen 
4-74 wide. The hypodermal layer, with the exception 
of a few scattered fibrous cells, consists of thin-walled 
parenchymatous cells. 
The vascular bundle of the stipe, and particularly the 
form of the xylem, is quite distinctive in the three 
species, though there ‘is enough variation between 
larger and smaller stipes, and between the proximal and 
distal parts of the same stipe to confuse somewhat the 
points of difference. In all the species the xylem con- 
