THE SCALE FERN. 199 
This condition of the sorus renders it easy to confound the fructifica- 
tion of Ceterach with the truly naked sori of the Gymnogramme. 
The affinity of the Ceterach is, however, undoubtedly rather with 
the Asplenicœ than with the Gymnogramme, notwithstanding the 
anomalous condition of its indusium, as is evidenced by the lateral 
position of the spore-cases, which are developed on the side of the 
receptaeular vein, as in the true Asplenieœ, and not on the back of 
the vein, as in Gymnogramme. Though the indusium has not, we 
believe, been detected in anything like a perfect condition, we have 
occasionally found both in the native British species, and in another 
occurring in the Atlantic Islands, the small incomplete cover noticed 
by other observers, forming a narrow membranous ridge standing 
behind the line of spore-cases. We have consequently no seruple 
in placing the genus in the neighbourhood of Asplenium and Scolo- 
pendrium, as an anomalous or imperfect form of the group to which 
they belong. The thick coating of scales which invests the sori- 
ferous surface of the plant, may be a sufficient explanation of the 
obsolete condition of the proper cover to the spore-cases. The fore- 
going is, moreover, the view taken by Mr. J. Smith, who considers 
that the lateral sporangia clearly point out the relationship of 
Ceterach to be with Asplenium, rather than with any of the gram- 
mitoid genera; the absence of the indusium being entirely owing to 
its being suppressed by the density of the scales. 
Only two species of this genus are known ; the common one, 
which is widely dispersed, and a large growing kind found in the 
Canaries and other Atlantic Isles. Two South African species having 
some resemblance to them in appearance from their being clothed in 
a similar way with chaffy scales, have free veins and dorsal naked 
sori, and are accordingly referred to the genus Grammutis. 
The generic name is derived from Chetherak, which was the name 
applied to the common species by the Arabian and Persian 
physicians, among whom the plant was esteemed for its supposed 
medicinal virtues. 

BRITISH SPECIES. 
C. officinarum: a dwarf perennial, with pinnatifid fleshy fronds, clothed with 
overlying scales beneath. 

