THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY, 



[SECOND SERIES.] 

 No. 106. OCTOBER 1856. 



XXV. — Monograph of the British Umbilicarui?. 

 By the Rev. W. A. Leighton, B.A., F.B.S.E. 



[With a Plate.] 



The Umbilicaria constitute a distinct and well-marked group 

 of Lichens, Their thallus bears a general external resemblance 

 to that of some species of Endocarpon (e. g. End. miniatum), but 

 the different internal structure shows these genera to have no 

 real connexion. Their apothecia approximate in external form 

 to those both of Lecidea and Opegrapha. But this resemblance 

 is limited to external character alone_, for dissection demonstrates 

 that there is no affinity in structure betw^een the plants. The 

 apothecia of the Umbilicarice are entirely destitute of that black 

 carbonaceous excipulum which is so conspicuous a feature of 

 the Lecidea. Their structure greatly assimilates, and indeed is 

 almost identical with, that of the apothecia of the plant generally 

 known as Lecidea vesicularis, Ach. With the Opegraphce the 

 resemblance is altogether external, the gyrations or redupli- 

 cations to which the apothecia are subject alone constituting the 

 similarity ; internal structure being here also entirely different. 



The structure of the thallus appears to be alike in all the 

 plants included in the genus, however dissimilar their external 

 aspect may appear. The only differences apparently arise from 

 one portion or layer being more or less developed in growth, 

 probably from local circumstances, than another. This has 

 been admirably investigated, described and figured by M. L. R. 

 Tulasne, in his " Memoire des Lichens," published in the ' An- 

 nales des Sciences Naturelles,' 3 serie, tom. xvii. The thallus 

 of U. pustulata, he says, presents a double cortical layer. The 



Ann. ^ Mag. N. Hist. Ser. 2. Vol. x > iii. 18 



