355 



I^OTES ON BRITISH LICHENS: 



LECANORA MURORUM AND ITS MORE IMMEDIATE 



ALLIES. 



JOSEPH A. MARTINDALE, 

 Staveley, near Kendal, Westmorland. 



Much fresh light has recently been cast on the species allied to 

 Lecaiiora nmrortmi (Hoffm.) Nyl. i^Placodium Leight. Lich. Flora), 

 as well as on the limits of the species itself, by continental botanists, 

 and more especially by Dr. Nylander in the pages of ' Flora,' and it 

 may, perhaps, be of some service to point out the characters of the 

 British members of the group by the aid of information derived from 

 those sources. 



Formerly too much reliance was placed on external appearance, 

 as on colour, in determining the species, while the definite and trust- 

 worthy characters to be derived from a careful examination of the 

 apothecia and spermogonia were but little regarded. With respect 

 to colour, Dr. Nylander has pointed out that all the yellow Placodia 

 readily assume a more or less miniate hue when growing in dry and 

 open situations. Nothing, certainly, can well present a greater 

 contrast to the eye than a deep red ' obliterata ' set by the side of a 

 pale yellow or vitelline lobulata, or than a ' ininiata ' beside a pale 

 greenish-yellow form of tegidaris ; but the fallaciousness of resting 

 specific distinctions on such contrasts is readily seen when the 

 identity of the apothecia and spores in these cases is proved by 

 examination, more especially as plants of intermediate shades con- 

 nect the two extremes. 



But if placing undue importance on colour has led to the making 

 of bad species, the trusting too much to another external matter, the 

 pulverulence which more or less covers certain species, has also led 

 to false division, as where plants really belonging to sympagea are 

 confounded with muroruvi. Certainly the evidence afforded by the 

 spores and spermatia as to specific relationship is much stronger than 

 that of a variable suffusion of the thallus. If species are to be correctly 

 recognised, the characters afforded by the apothecia and their con- 

 tents, and by the spermatia, must be held to be of fundamental 

 importance. Guided by these it will, I believe, be possible to refer, 

 with a great deal of precision, to their proper species forms which 

 would otherwise be most perplexing, or at best uncertain. 



The following descriptions are limited to the more immediate 

 allies of L iniiroruni^ that is, those with a distinctly flavescent thallus 



Dec. 18S7. 



