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of true lichens, with a well-marked thallus; and the other (confined to 
organic substrates) of plants, the thallus of which is more or less obsolete, 
and the affinity close to Pyrenomycetous Fungi. And a certain appreci- 
able difference in these groups appears further to be recognizable in the 
general features of their spore-phenomena. In the first we have a very 
regular and instructive, decolorate exhibition of the modifications of the 
muriform spore; in the other such a varied and irregular, often fungic as 
coloured presentation of the same spore-type, as we meet with in Thelo- 
trema, the analogous group of the Lecanorei. It is not difficult to trace 
the interlinks which bring together Thelidiwm and Polyblastia, or to con- 
ceive of these as making one genus with Verrucaria. But the case is, as 
we might expect, otherwise in the corticoline group (Pyrenula, as here 
taken) the irregularity of which is yet paralleled in the higher and more 
easily determined natural assemblage of Urceolariine Lecanorei above 
referred to; and may prove to be explainable. 
These chief assemblages of Pyrenulei seem none the less to touch 
each other in two principal points; and so closely that one very eminent 
writer (Nyl. Pyrenoc.) is not willing to allow of even specific distinction: 
Verrucaria conoidea, Fr., being united by him with Pyrenula gemmata ; 
and V. chlorotica, Ach., with Sagedia carpinea, Mass. In the first case 
the difficulty is notwithstanding less, possibly, than might appear. It is 
unknown to me whether or not V. conoidea agrees with P. gemmata in 
its spermatia, but in other respects the agreement is scarcely sufficient; 
bilocular, decolorate spores being (from the point of view of this treatise) 
to be looked for in either group, and this combined, a priori, with general 
structural congruity. But the questions suggested by Sagedia, Massal., 
Koerb., are much more puzzling. We might take it for possible indeed 
to refer the rock-Sagedie to Verrucaria § Thelidium, which Anzi has 
united to Sagedia, and the corticoline, with Naegeli and Hepp, to Pyrenula 
§ Arthopyrenia, with which last Mudd has associated the whole group; 
but the agreement of rock- and bark-forms is sufficiently striking, and 
the often distinct thallus of most of these forms, taken in connexion with 
their well-characterized spores lends weight rather to the view of Nylan- 
der, followed in this by Th. Fries, that a still closer relation exists between 
Sagedia and Segestria§ Segestrella. The latter differs notwithstanding in 
its coloured perithecium, and, as I have attempted to shew, the colourless 
spores are probably to be taken for a decolorate exhibition of the modifi- 
cations of the finally muriform type. In Sagedia, on the contrary, the 
ultimate modification of spore-structure as yet observed (in an American 
lichen) is the acicular; referring the group to the colourless spore-series, 
and the right extreme of the sub-family. 
Beside Sagedia, Verrucaria, and Pyrenula, this group embraces also 
some mostly inferior, and more or less questionable modifications of the 
type of the genus last named, which are commonly kept distinct. Pyren- 
astrum is to Pyrenula as Astrothelium to Trypethelium. ——Endococcus, 
