branch generally hearing a sorus at about midway its length.
The sori are thus generally numerous, and rather irregularly
disposed; and it often occurs that they are so numerous as,
when fully grown, to become confluent into a mass of fructification
covering the whole under surface of the frond. The
number of sori produced, and consequently the sparse or
crowded disposition of the fructification, is a matter altogether
dependent upon the circumstances of growth, and
hence exceedingly liable to vary even in the same plant, and
within the same year, as heat or cold, drought or moisture,
may preponderate. The sori, which are nearly circular, are
covered while young by a concave or hood-shaped indusium,
which is attached by its broad base on one side beneath the
sori, and has its apex ultimately free ; this part usually becomes
torn or split into narrow segments, and the whole soon
becomes pushed back or cast off by the growing spore-cases.
There are many forms or varieties of this species. Two
of them, called cynapifolia and anthriscifolia, do not seem
to need any distinct description. Another, called angmtata,
is rather larger, generally, than the typical form, but differs
more by having the points of its pinnæ and the apex of the
frond itself drawn out considerably into very narrow points
than in any other circumstance readily pointed out.