(137 ) 
if compared with 7. auratum (described at the same place) to illustrate 
the misus of the proper exciple (constituting here the inner wall of the 
exterior exciple) to become compound; and the processes which make it 
up are exactly comparable, if I do not mistake, with the similar ones in 
compound fruits of Urceolaria scruposa (Fr. Lich. Suec. n. 282) and tn 
those tending to become compound of J. ocellata (Rabenh. Lich. Eur. 
n. 122). Other compound conditions looking rather towards Pertusaria, 
are described by Montagne (Crypt. Cub. p. 167. Crypt. Guy. p. 55) and 
in the present writer’s Obs. Lich. 1. c. 5, p. 408, 411. 
Ascidium, Fée Ess. p. 42, 96, is distinguished by no generical differ- 
ence from Thelotrema depressum, Mont. (Wright Lich. Cub. 0.165, determ. 
Nyl.) beyond the peculiar thickening of the often conspicuous but finally 
even obsolete thalline exciple, and the inferior grade of evolution of the 
spores; and I incline, with Dr. Stizenberger (Beitr. 1. ¢.) and in agree- 
ment with Nylander’s earlier judgment (Enum. Gén. 1. c. p. 118) to con- 
sider it not well separable. Montagne’s view of the thickened thalline 
exciple of Ascidium, as if constituting a stroma, and of the generical 
type, as if conceivable as a ‘monocarpous Trypethelium’ (Crypt. Guy. 
p. 57) was influenced, we cannot doubt, by what he regarded the predom- 
inant Verrucariaceous affinity of the former, as of Thelotrema: but 
Nylander also (in Prodr. Fl. N. Gran. p. 50, note) keeps the two types 
distinct, even though he at the same time refers Thelotrema depressum to 
Ascidium. 
It has been remarked already of the spores of Urceolaria, that they 
suggest, in the successive changes of their evolution, the Varied differen- 
tiation of the present genus. We find here,—in TJ. lepadinum— the 
perfect expression of the coloured type, and, associable with this species 
externally more or less, a variety of forms, the spores of which, though 
now, in themselves considered, referable to the colourless series, are yet 
also well comparable with the earlier conditions of the coloured, as abun- 
dantly exemplified in Urceolaria, Graphis, & cett. And the possible 
inference is that lichens otherwise associable, are not to be dissociated be- 
cause some of the species offer only earlier gradations of the perfect spore- 
type indicated by others; and that such natural genera as the present 
may still be kept together. 
Nor are we without positive evidence looking in the same direction. 
Colour is indeed often deficient in what should be coloured spores; but 
instead we may find approximations, in the spore-cells, to parenchymatous 
complexity. And where the last clew is wanting, indications of colour 
often appear. The little group separated by Fée as Myriotrema seems 
at first possibly almost distinct; but it is interesting in this connexion, 
that 7. glauculum, Nyl., though referred to the section expressed by 
Myriotrema, is yet compared by him, than whom no one has more exten- 
sively illustrated the genus, with the brown-spored T. compunctum (Prodr. 
Fl. N. Gran. p. 47, note). With this last the other curiously agrees in 
18 
