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external characters. The spores vary indeed, occasionally, in these sub- 
tropical representatives of G. elegans, so far as to present a larger num- 
ber (12-16) of spore-cells (such spores measuring, in specimens from 
South Carolina, and Texas, 0,039-0,069™- in length, and 0,009-0,011™™- in 
width) but I have found no reason to reckon this difference as expressing 
any more than an occasional exuberance.— Much more important how- 
ever is the fact that it was among these tropical forms, now approaching 
so closely to G. elegans, if now again, as might perhaps be expected, 
receding from it, that the muriform modification of the spore was first 
observed (G. substriatula, Nyl.) in the species-group before us. No reason 
appears for estimating the value of this difference any higher here than 
in G. scripta ; and the lichens exhibiting it must, in this view, be brought 
together as a variety (substriatula) either of G. elegans, or, if the sub- 
tropical lichen really prove, in the end, to be distinguishable in species, 
of G. striatula ; and will, in either case, correspond, as does the plant 
sometimes, most closely in other respects, to G. scripta, v. sophistica. It 
is observable, as illustrating the intimate relation of the lichens we have 
been considering, that while some forms of the tropical G. elegans, Vv. stri- 
atula (G. striatula (Ach.) Nyl.) as, for instance, Opegr. rimulosa, Mont. 
Guy. (Herb. Mont.) offer exactly the spores of G. elegans, a specimen of 
the Opegr. elegans of the same work (Herb. Jfont.) most readily compar- 
able, externally, with the European lichen (as in Moug. & Nestl. n. 360) 
and almost equally so with Herb. Lindig n. 862 (G. striatula, Nyl.) which 
last is assimilated by the spores also to G. elegans, proves yet to be differ- 
enced, internally, by muriform spores. I have not yet met with muriform 
spores in my North American specimens referable to the stock of G. ele- 
gans, and the hymenium is but imperfectly developed in many of these 
specimens; but Dr. Nylander recognized a South Carolina lichen as 
belonging to his G. striatula. To judge by the Cuban lichens of the 
affinity we are now considering, in the collections of Mr. Wright, the 
elongated spore with entire spore-cells is far more common than the more 
advanced, muriform one. And there is, if I mistake not, some evidence 
in these collections, that the condition of the v. striatula above-noticed, 
which is distinguishable from other conditions, as from G. elegans, a, only 
by an increase in the number of (entire) spore-cells, is finally further 
differenced by apothecia not a little like those of G. tumidula (Fée) Nyl. 
(Lindig Herb. N. Gran. n. 2723) towards which — separated by its very 
large spores—the specimens we refer to may then be said to look.— 
G. rigida (Fée) Nyl., is another tropical lichen, to a form of which (v. enter- 
oleuca, Nyl.) specimens from Texas (Mr. Wright) were referred by Dr. 
Nylander. Spores solitary, and in fours; oblong-ellipsoid ; muriform- 
multilocular ; the length twice to thrice exceeding the diameter; colour- 
less, or at length brownish. —  G. Pavoniana, Fée, one of the lichens 
found on Cinchona bark, and with a little of the aspect of some Ustalia, 
has occurred in Texas (Mr. Wright) as determined by Dr. Nylander. The 
