100 
ADIANTACEiE. 
dered analogous to the usual involucre, or one of them only; 
and if one only, then which are we to select ? Roth does not 
appear to have observed the inferior membrane, but describes 
the superior one as an involucre originating in an elongated epi- 
dermis.^' Sir J. E. Smith, although aware of this inner mem- 
brane, unhesitatingly speaks of the outer one as the cover. 
Mr. Wilson, who has most obligingly favoured me with many va- 
luable observations on this remarkable structure, seems to regard 
the inferior membrane as the involucre; the occasional presence 
of the superior membrane in the total absence of capsules, prov- 
ing, in his opinion, that it is not necessarily connected with fruc- 
tification. Still, although I may state that I do not detect its 
presence in seedling or barren plants, and am therefore led in 
a measure to associate its appearance at least with the power of 
producing fruit, yet I am quite inclined to consider it distinct 
from a true involucre, and more analogous to the indexed por- 
tion of the pinnule in Adiantum and Allosorus, which, although 
considered an involucre by Sir J. E. Smith, and all our more 
eminent authorities, and although there can be no question that 
its presence is connected with fructification, since in both these 
instances it is absent when the frond or pinnule is entirely bar- 
ren, yet 1 have always regarded as perfectly distinct : instances 
however occur, in all the genera here cited, in which this in- 
flexed or folded margin of the pinnule is totally unaccompanied 
by the presence of capsules, as pointed out to me in Pteris by 
Mr, Wilson. Mr. Jenner, who has most obligingly taken the 
greatest pains to assist me in the enquiry, as regards Pteris, also 
appears to consider the exterior membrane as nothing more than 
a prolongation of the outer epidermis. The question as regards 
the interior membrane seems much more restricted : we are com- 
pelled to regard this as an involucre, from the absolute absence 
of any other analogous part to which, with any show of plausi- 
bility, it can possibly be referred. I have stated that the margins 
of each lobe are convolute, so that the marginal vein and its 
Involucrum in plantis hujus generis ortum suum trakit ex epidermide 
elongata, &c. — Roth, Flor. Germ. hi. 42. 
f Eng. Flor. iv. 304. 
