SMOOTH THREE-BRANCHED POLTPODY 
OR Oak Fern. 
Polypodium Dryopteris .* — Linnaeus. 
This, the smallest of the Polypodies, is also one of 
the most delicate of all British Ferns : very easily 
recognizable by its smooth fronds, of a bright lively 
green, divided into three branches, — the last charac- 
teristic even more obvious in the young fronds, which 
are rolled up in little balls at the ends of their three 
slender stalklets. Its height is generally not more 
than six inches, often less, but it sometimes grows to 
twelve or fourteen. It is fragile, produced about 
April, and in succession throughout the summer, soon 
withered by heat or drought, and at once destroyed 
by frost. The fronds rise from a slender creeping 
stem, which often forms densely matted roots. The 
stipes is usually much longer than the leafy part, 
thin, brittle, and dark coloured. The general outline 
is five-sided, owing to the division of the fronds into 
three triangular branches. One of the peculiarities 
of the Oak Fern is the deflection of the rachis (or 
* Also Polystichum Dryopteris, Lastrea Dryopteris, &c. 
