Fry. — Some Types of Endolithic Limestone Lichens . 547 
I. A. a. Lecidea immersa , Acb. 
The external appearance of Lecidea immersa is not unlike that of 
V. calciseda . There is the white or pale grey, granular surface, but except 
for the marginal regions fewer black dots, representing the external hyphal 
ends, are present. The black or dark-brown fruiting bodies appear 
larger than those of V. calciseda , and although the general shape of the 
apothecial area is circular, yet not uncommonly one finds them with an oval 
outline — probably this is the result of fusion of two apothecia developing 
closely together. After treatment with hydrochloric acid, the thallus of 
Lecidea is still very like Verrncaria , although it is thinner and only 
penetrates the limestone to a depth of 400 fi. The vertical section also shows 
certain similarities, and because of this a detailed description will not be 
given. The main points of differ- 
ence are as follows : The cortex 
is . 34 /x wide, and between the 
hyphal groups — even at the margin 
•where the tissue is denser — there 
are fewer hyphae passing from 
group to gronp. Near the margin 
there are many hyphae with brown 
external tips. 
The gonidial zone is wider, 
varying between 80// and 100 /x, 
but this is due to the fact that the 
clumps are somewhat scattered in the vertical direction. Apart from this 
the two gonidial zones are rather alike, except that, as in the cortex, there 
are fewer hyphae crossing from group to group. 
The rhizoidal zone offers the most striking difference between the two 
species. In L. immersa there are no inflated hyphae in the thallus. Cells of 
about twice the width of the ordinary hyphae are present, but even these 
are very few. The hyphae of the rhizoidal region of Lecidea are very much 
narrower than those of Verrncaria ; also, the width of the rhizoidal zone as 
a whole is considerably less in the former type. 
The apothecium. Although from the surface the young state of the 
fruiting body appears very like the perithecium of Verrncaria , its construction 
is very different. This is clearly seen in the longitudinal section (Text-fig. 5). 
It is of the ordinary lecideine type and needs no description. The pit 
which has been formed during the development of the apothecium reaches 
down to about 200 /x or more. In the tissue of the hypothecium there are 
many small crystals which have not been dissolved by the acid. Although 
inflated hyphae are not found in longitudinal section either in the young 
apothecium or in the thallus tissue, yet in freshly decalcified material mature 
Text - fig. 5. L ecidea im ?nersa . Y o un g ap oth e ci u m 
(longitudinal section). 
