1921] JOHNSON—POLY PODIUM 239 
The two forks of the trunk stood almost in a north and south line, 
and the crotch between them in an east and west direction. The 
larger clump of polypody, which bore more than forty full grown 
leaves, grew just below the fork on the east side of the tree (fig. 1). 
At 6 inches and at 2 feet below this, on the same side, were two 
smaller tufts of this fern (fig. 1). Both the latter evidently profited 
from the collection of considerable water by the fork above, part 
of which water was directed down the shallow grooves of the bark 
in which these two clumps grew. This somewhat more abundant 
water supply, which is likewise more constant, probably explains 
_ the presence of these tufts on the east side of the tree, while all 
the other clumps of this polypody seen were confined to the north 
sides of the trees. The other five trees on which this fern was 
growing had trunks that were perfectly straight and without forks 
or any branches for many feet above the ferns (fig. 3). There was 
thus no collection of rain, as in the forked trunk, but each clump of 
polypody was dependent entirely on the portion of water that 
chanced to run down the particular furrow in which it grew. The 
fronds of the polypody on the unbranched trunks, although barely 
half as large as those on the forked trunk, were quite mature, and 
many of them bore spores. The more favorable growing conditions 
on the forked tree were indicated not only by the larger size of the 
polypody itself, but also by the richer growth of bryophytes and 
lichens, which were much more abundant below the fork ee above 
it on this tree, or than on any of the erect trunks (fig. 
Aside from the smaller fronds of the epiphytic apie they 
apparently were not different from those growing on the soil. 
In both the rhizome was largely covered by epiphytic liverworts 
and lichens and sometimes by more or less humus. The external 
character and internal structure of the rhizome and of the leaf, even 
to the thickness of the cuticle and of the mesophyll of the latter, 
were quite alike in plants of both habitats. The roots of both 
epiphytic and terrestrial plants were abundant, closely matted, and 
thickly beset with root hairs. Many of these root hairs had one 
or more fungous hyphae running lengthwise through them. These 
hyphae could often be seen entering at the tips of the root hairs. 
Whether they have the function of mycorhizal fungi has not been 
determined. 
