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C. Islandica ; or, notwithstanding the difference in the spermatia, that 
C. Islandica is congenerical with C. cucullata: and the bridge is in fact 
an old and well-accepted one which unites together these parts of one 
natural whole. We do not then leave the fruticulose Cetrarie without 
finding them inseparably related to foliaceous forms; and these latter 
pass insensibly into that Parmelioid type, the varied expressions of which 
make up the great bulk of the genus. The relations of the plants before 
us to Parmelia are yet, for the most part, practically without difficulty ; 
but the remark seems certainly less true of the relations of certain Parme- 
lie to Cetraria. Here however, not to refer again to. Scherer’s sweeping 
judgment, corrected later by himself, the question may be raised if too much 
has not been made of the alleged distinction in the spermogones. It is 
difficult, in a full view of the lichen, to appreciate the real difference in this 
respect which, according to Nylander, should refer Parmelia Fendleri, Tuck- 
erm., to Platysma of the former writer. And the case is perhaps only less 
clear as respects Parmelia Fahlunensis. So closely related is this plant 
to P. stygia, and so considerable is the amount of variation, as in all other 
respects so also in the spermogones of each, that, practical and useful as 
the asserted distinction undoubtedly is for the most part, there is perhaps 
some reason for the suspicion that it does not always hold good, and that 
even this criterion is insufficient to separate the species. ——Cetraria chry- 
santha, Tuckerm. Suppl. 1 (Amer. Journ. Sci. 25) p. 423 (Platysma septen- 
trionale, Nyl. Syn. 1, p. 315) an arctic lichen which Mr. Wright first found 
fertile in Japan, has the habit and size of the wide-lobed condition of 
C. glauca, but differs conspicuously in colour. 
The European Cetrari@é are almost all known to be also North Ameri- 
can, and a considerable part extends into Northern Asia; but we possess 
several unknown to Europe, and a larger proportion, including some of 
the most remarkable forms, is peculiar to Asia.—C. tristis is supposed 
by Dr. Th. Fries (Lich. Arct.) to be scarcely known beyond the European 
arctic regions, and he cites J. Vahl to the effect that he never saw it in 
Greenland. It is however reckoned by Hooker (Append. Frankl. Narr. 
p. 762) among the lichens collected by Richardson in the ‘Barren Grounds’ 
of Arctic America.—C. odontella was reckoned by R. Brown an inhabit- 
ant of Melville Island (Parry’s Ist Voy.) but what Mr. Babington has 
sent me as C. odontella of Melville Island, is, I think (the specimen is in 
fragments) C. Islandica v. Delisei. Bory sent out Newfoundland speci- 
mens of the same lichen (Herb. Kunth) as C. odontella ; and these led, in 
the absence of the true plant, to the reference to it (in Syn. Lich. N. Eng. 
p. 14) of other arctic American specimens (Herb. Hook. Herb. Grev.) of 
the cited variety of C. Islandica, which is very distinct.——C. lacunosa, 
Ach., a very common North American lichen, known to me however only 
as growing on trees and dead wood, has lately been recognized (Th. Fr. 
le. Nyl. Lich. Scand. p. 289) in rock-specimens, which were also infertile, 
of the coasts of Norway.——C. ciliaris, Ach., a widely diffused and abund- 
