HEAUTIPUL FERNS. 
41 
specimens from California and Oregon they are wider and consid- 
erably deeper. The lobes are from four to six or seven in num- 
ber : in sterile fronds they are minutely toothed at the end ; but 
in the commoner fertile fronds they are reflexed and changed in 
character, so as to form somewhat crescent-shaped or transversely 
elongated involucres of a pale-brownish color. The tips of the 
veinlets extend into these involucres, and bear the sporangia on 
the under or inner surface. In this peculiarity is the essential 
generic character of Adiantum. The spores of this species are 
spheroid-tetrahedral, the three radiating angles marked with slen- 
der vittae, or bands. They are mature in the latter part of summer ; 
but the fronds remain until frost, often changing from green to 
variegated shades of brown. 
There do not seem to be any well-marked variations in this 
fern. Ruprecht has a “ var. A leuticum'd the Ad. boreale of Presl, 
separated mainly on account of its smaller size and fewer parts. 
The genus Adiantum contains eighty-three species, accord- 
ing to Mr. Baker’s estimate; but this number is reduced to sixty- 
seven by the more recent and very careful recension of Keyser- 
ling. The species vary in form from a simple and reniform frond 
an inch or two in diameter to others with ample tripinnate and 
even quadripinnate fronds. The species with distinctly bipartite 
and radiated fronds are Ad. patens, hispiduluni, and fiabellula- 
tum. A. patens is found in Mexico and Central America. It is 
a smaller plant than A . pedatum, and has deeply-sunken reniform 
involucres. The other two occur in South-eastern Asia, the his- 
piduluni extending to Africa and to New ‘Zealand, and the fla- 
