Some Types of Endolithic Limestone Lichens. 
BY | 
E. J. FRY, M.Sc , 
Assistant Lecturer in Botany , University College of Wales, Aberystwyth. 
With Plate XXI and nine Figures in the Text. 
Introduction. 
AN investigation of the pioneer cryptogamic vegetation of the Carboni- 
l \ ferous crystalline limestones of the Great Orme and in S.E. Anglesey 
was begun in 1918. The present paper deals with the study of several of 
the more common endolithic lichen thalli found on those outcrops. 
Up to the present time little work on embedded lichens has been 
published, and it was thought that, since new and better methods of 
sectioning the endolithic thalli had been found, it might be advisable to 
make a detailed study of certain forms which Bachmann (1) did not describe. 
It is to Bachmann that we owe our present knowledge of the anatomy of 
such plants. 
General Notes. 
Investigation of the outcrops under discussion shows there is scarcely 
a square inch not occupied by lichen thalli of some kind, and of these by 
far the most numerous, both in species and individuals, are the endolithic 
forms. The majority of these can be detected with the naked eye, since 
their fruiting organs at maturity appear at the surface, and frequently the 
endolithic lichens give a tinge of colour to the surface of the rock. The 
presence of other forms — which fruit but rarely and give very little, if any, 
colour to the limestone — is betrayed only by the scratching of the rock 
surface, which gives a bright green or orange ‘ streak ’ according to whether 
the algal constituent of the embedded lichen belongs to the Chlorophyceae 
or the Trentepohliaceae. In some species, e. g. Verrttcaria calciseda , the 
boundary of the thallus is clearly marked by a black line. In this region 
the limiting lichen hyphae are dark coloured and in some cases are raised 
just above the level of the rock. 
Over these embedded thalli creep the epilithic forms such as Xanthoria 
parietina , Lecanora murorum^L . cirrochroum, and species of Physcia , of which 
only the rhizoids penetrate the limestone already partly broken up by the 
[Annals of Botany, Vol. XXXVI. No. CXLIV. October, 1922.] 
