ROCK BRAKES. 
107 
Withering and Smith in his second. Roth makes it an Onoclea, 
associating it with O. Strut1iiopte7'is, the Struthiopteris germa- 
7 iica of later writers. By three eminent botanists it has been 
made the type of a new genus, viz., by Bernhardi, under the 
name of Allosorm ; by Desveux, under the name Phoroholus ; 
and by Robert Brown, under the name Cryptogramma. Of 
these three names, Allosorus has been adopted on the ground of 
priority, by Sprengel, George Don (in Loudon’s ‘ Hortus Bri- 
tannicus’), Sadler, Presl, the compilers of the ‘ Edinburgh Cata- 
logue,’ and Babington ; and Cryptogramma by Hooker and 
Mackay. The principal characters by which to distinguish this 
plant from our other British Polypodies, are that its fronds are both 
barren and fertile, and that the margins of the pinnules in the 
fertile frond are indexed or convolute, covering the clusters of 
capsules. Mr. Gibson objects to the first of these characters ; 
and I have to acknowledge my obligation to him, as well as to 
Miss Beever and Mr. Cruickshank, for fronds partially fruitful 
and partially barren. Mr. Gibson objects to the view I take of 
this character, on the ground of what he considers its incon- 
stancy; but with great deference to the opinion of so excellent 
a botanist, 1 must acknowledge that I still continue to regard 
the fertile and barren fronds of the Rock Brakes as perfectly dis- 
tinct : in the British ferns, Lomai’ia spicant, Allosorus crispus, 
and Lastrcea Thelypteris, we observe a marked and constant 
difference between the two kinds of fronds, whereas in all our 
other species the want of fruit is the result of immaturity, un- 
congenial situation, or some other casualty. I will not contend 
that such a character is sufficient for the establishment of a ge- 
nus, but that it is one of great interest, and not to be neglected 
on the ground that an intermediate and somewhat monstrous 
production may be occasionally found. Still, as regards the ge- 
nus, the present species is in every respect a Polypodium, even 
as restricted by Presl’s description in his recent work,^' and his 
figure of the venation of this speciesf appears to me incorrect. 
The roots are fibrous, numerous, tough, and adhere tenaciously 
to the earth or stones : the rhizoma is procumbent, extending 
^ Tentamf’n Pteridographise, p. T76. 
t 1. c. tab. 26, f. 3. 
