16 
HISTORY OF BRITISH FERNS. 
the earliest of them do not last till autumn ; in others they 
continue until touched by frost, from which the more 
robust of them shrink, even as the tender sorts do from 
drought as well as frost. Others are much more durable, 
and the plants, if in a moderately-sheltered situation, be- 
come evergreeu. These latter should be most extensively 
adopted for culture where ornamental effect is an object. 
We shall point out these peculiarities as we describe the 
different species. 
The fronds of Ferns consist of two parts — the leafy 
portion, and the stalk, which latter is often called the 
stirpes. The continuation of the stalk, in the form of a 
rib extending through the leafy portion, and becoming 
branched when the frond is divided, is called the racMs, 
If the frond is compound, that is, divided, so that there 
is another set of ribs besides the principal one, the latter 
is called the primary rachis, and the former the secondary 
rachis. Few of our native species are so highly compound 
as to possess more than a secondary rachis. In practice, 
when the outline or division of the frond is mentioned, it 
is generally the leafy portion only that is referred to, ex- 
clusive of the stipes. 
The stipes is generally furnished more or less with mem- 
