(261) 
uncertain line of separation between lower Lichens and Fungi finally dis- 
appears. So slight indeed are often the indications of thallus in these 
groups, and so little satisfaction is to be had in the application of any 
supposed rules of discrimination, that it may well seem nearly indifferent, 
and to competent enquirers, whether a plant (Verr. rhyponta, Ach., Fr. 
L. E. p. 448) shall be saluted as a Pyrenula or a Spheria. In this view 
jt is natural to enquire if we cannot eliminate these myco-lichens, all of 
them corticoline, from the true lichens with which they are still in a tribal 
sense associable, and have undoubtedly so muchin common; and there is 
no lack of evidence that the thoughts of lichenographers have turned not 
seldom in this direction. Thus Fries (S. O. V. p. 264) concludes his dis- 
cussion of the insufficiency of the characters by which Acharius attempted 
to distinguish his Verrucaria from his Pyrenula, with the observation : 
‘ne quidem ut tribus’ (h. e. sectiones) ‘servande ; et st restituende, plane 
reformande ; terrigenus et saxicolas Pyrenulas, corticolas Verrucarias 
dicas.’ The important thing here being the suggested discrimination of 
the saxicoline groups from the corticoline, it is of less consequence that 
Fée’s subsequent restriction of Pyrenula to bark-lichens (Suppl. p. 76) has 
since been followed, and Verrucaria retained for saxicoline. Fries has 
not indeed recurred to his early suggestion any further than to distinguish 
and give prominence in his Verrucaria (L. E.) to the saxicoline types ; 
those confined to bark being relegated, as inferior, to the end: but Naegeli 
and Hepp have renewed the generical distinction in their Pyrenwla ; and 
there is not a little in modern views of the Lichen-system, as for instance 
the generally admitted naturalness of the group of rock-Verrucarie 
(Verrucaria, Koerb., Syst.) and the close relation to this of such species, 
otherwise agreeing, as are differenced by bi-quadrilocular (Thelidium, 
Massal., Koerb.) or muriform-multilocular spores (Polyblastia pro p., Auct.) 
which looks the same way. Satisfactory differences for these saxicoline 
and corticoline groups are still not easily indicated. So reduced is apothe- 
cial structure in the present tribe, and so often obscure, that it does not 
appear to be always sufficient in itself to determine generical relations ; 
or even to discriminate Lichens from Fungi; and though the naturalness 
of his results may satisfy the lichenist of the probable value of the subtle 
distinctions which have led to them, it may be difficult for him to express 
these in words. Natural genera are notwithstanding to be preferred to 
artificial ones; ‘ and inthe present state of the study of our lower Verru- 
cariacet, it is possible that the arrangement now to be proposed shall 
prove to be of service. 
The Pyrenulei, as here taken, are readily conceivable as falling into 
two principal assemblages, —the one (confined to inorganic substrates) 
1 “ Unica antiqua et bene evoluta species per omnia evolutionis stadia rite obser- 
vata majoris momenti est quam novum genus — el genus naturale majoris quam 
systema artificiale.” Fr. 8. V. 8. p. 427, not. 
