244 BOTANICAL GAZETTE [OCTOBER 
of an indigenous epiphytic association is excluded from the begin- 
ning.” This Polypodium seems evidently an endemic epiphyte of 
the temperate zone, and not one imported with this habit already 
formed from the tropics. It might well be designated a facultative 
epiphyte. In its ability to live on various substrata it closely 
resembles dozens of species of ferns and seed plants of the tropical 
forests which can be found growing, now on soil, now on dry rocks, 
and again as epiphytes on tree trunks. 
It might perhaps be suggested that more of our temperate 
zone plants should prove able to live on trees. As a matter of 
fact, however, few of our saxicolous vascular plants are really as 
hardy as this polypody, the thick-cuticled leaves of which are 
capable of rolling up in dry weather and so of lessening transpira- 
tion. The combination of these two features, uncommon in plants 
of this region but common in epiphytic ferns of the tropics, is 
probably an important:one in'enabling this fern, and likewise its 
relative Polypodium polypodioides, to adopt the epiphytic habit. 
The evergreen leaves of Polypodium vulgare, which are also char- 
acteristic of most, although not of all epiphytes,:are probably of 
great importance to this plant of shady deciduous forests. They 
enable it to carry on an important share of its photosynthetic 
work on any mild days between October and May, when abundant 
light reaches it because the surrounding trees are bare of leaves. 
In other words, while growing on soil or rocks this fern has developed 
more of these xerophytic characters, which fit it for living.as an 
epiphyte, than perhaps any other vascular plant of the north- 
eastern United States. It seems at the present time to be an 
indigenous temperate-zone epiphyte in the making. 
Jouns Hopkins UNIVERSITY 
BALTIMORE, Mp. 
