(70) 
and modern science, with all its decided advantage as respects both extent 
and minuteness of knowledge, has still, it is admitted, to solve the prob- 
lem of a satisfactory arrangement of it. 
It isin his section Mallotium that we find the centre of the typical 
Collema, Ach., and the highest expression of Collemeine vegetation 
(“quasi Sticte hujus generis.” Fr., sub Leptogio, S. O. V. p. 255). 
From this centre the more pulpy Collemas diverge in one direction, and 
the submembranaceous ones (C. nigrescens, C. thysaneum) meet finally 
the membranaceous ones (§ Leptogiwnz) in the other. Scarcely anything 
was then known of crustaceous types referable here, but Synalissa, Fr. 
S. 0. V., is included among pulpy Collemas, while several more or less 
degenerate forms, in question between Paunnariei and Collemei, are thrown 
together at the beginning of the enumeration; as what is now Thermutis, 
Fr., is appended to it. Leaving out of sight the last, it is easy to admit 
the simplicity and elegance, from his own point of view, of the concep- 
tion of Acharius: and this shall perhaps excuse now an attempt to glance 
at the principal members of the whole sub-family, enriched with the dis- 
coveries of fifty years, from a still not dissimilar standpoint; or as con- 
stituents of but a single, most closely associable group. 
The embarrassing relations of certain types and groups of Lichens at 
once to Pannariei and Collemei have been already considered; and the 
results are before the reader. It has appeared impossible to escape the 
conclusion that Pterygium pannariellum, Nyl., if, as should appear, it be 
identical with Lecothecium asperellum, Th. Fr., is other than congeneri- 
cal with the type of Lecothecium ; or that this type is other than cor- 
rectly referred by Nylander to Pannaria. The plus minusve, say even 
the final obsolescence, of the hypothallus in these plants, is far from 
enough to obscure their admitted resemblances; and if the cited Ptery- 
gium exhibit, in all other respects, a sufficient congruity with Pannaria 
nigra, the microscope reveals to us no important structural difference be- 
tween the latter and P. tryptophylla.1 Butit is perhaps not alone in 
Pterygium, Lecothecitum, and Collolechia of authors that Pannariine struct- 
ure has proved at length indistinguishable from Collemaceous. Not to 
1“ Die Gattungen dieser Familie” (Lecotheciew, Koerb.) “vermitteln sowohl 
hinsiehtlich des dussern wie des inneren Lagerbaues die heteromerischen Flechten 
mit den homeomerischen und zeigen sich namentlich der Gattung Pannaria in 
hohem Grade verdhnelt.” Koerb. Syst. p. 397; and vide Parerg. p. 405. ——“ Vix 
specie differt” Pannaria nigra “a tryptophylla. . . <Accedere quoque videtur 
versus Pterygia, at apud hec nullum adest stratum hypothallinum.” Nyl, Lich. 
Scand. p. 126. What we cannot but call indications of such hypothalline layer 
are however to be seen in the figure of Pterygium centrifugum given in Nyl. Syn. 
t. 2, and are observable, under the microscope, in P. Petersii; while, in the latter, 
and perhaps even more evidently in P. pannariellum (Lecoth. asperellum, Th. Fr.) 
descending (hypothalline) cells, that is to say an imperfectly developed, true 
bypothallus is now to be made out. 
