Fry. — Some Types of Endolithic Limestone Lichens. 553 
II. A. Aspicilia calcarea , Koerb. ( Lecanora calcarea , Sommerf.). 
Bachmann (loc. cit.) has described Aspicilia calcar ea, but only the 
endolithic part of the thallus. By his method of preparation of sections 
of endolithic lichens it is impossible to obtain the whole depth of the thallus 
in one section, but by the method adopted in this investigation it is a very 
simple matter to section the endolithic and epilithic parts of the thallus in their 
relative positions. Because such a section has not previously been prepared, 
it was thought to be advisable to add a few remarks on this type. Frag- 
ments of limestone of about 1 cm. in thickness, and having on their surface 
the crustaceous or epilithic part of A. calcarea , were chiselled from the 
surface of the rock, immersed in dilute hydrochloric acid, and the whole 
process then carried on exactly as before. Since this species grows fairly 
rapidly over the substratum, care must be taken not to confuse disorganizing 
endolithic thalli, when they are present, with the endolithic part of Aspicilia. 
In a longitudinal section of a fully developed thallus the epilithic part is 
seen to vary in thickness from 190^ to 250 /x, and to consist of cortical, 
gonidial, and medullary zones of a normal type (PL XXI, Fig. 14). The 
endolithic part is composed of gonidial groups and rhizoids, the latter 
apparently consisting of two kinds — thin and thick. The ‘ transition 5 zone 
(PL XXI, Figs. 14 and 15) of the upper to the lower part is represented 
by a dense mass of hyphal cells which are slightly enlarged and whose 
contents are very small and pressed closely against the walls. (PL XXI, 
Fig. 15). In the part of the crustaceous thallus immediately above these 
cells and directly connected with them are roundish hyphae, some of which 
appear empty while others have contents of the usual type, i. e. not 
pressed against the cell-wall. From this zone of slightly enlarged, freely 
branching hyphae arise (i) the rhizoids, (ii) the hyphae which encircle 
some of the endolithic gonidial clusters, and (iii) the hyphae which form the 
large clusters of swollen spherical cells in the upper layers of the rock 
(PL XXI, Fig. 14, and Text-fig. 9). The fine colourless rhizoids are about 
1 n wide and arise from the ends of such filaments as are represented in 
PL XXI, Fig. 15, pk. As Bachmann (loc. cit.) has stated, they are far more 
numerous than the wider yellowish ones, which are about 5 /x in diameter. 
The former branch freely and twist about in the substratum, so that in 
a longitudinal section only short portions of them are seen. They contain 
oil globules and form small clusters of inflated cells of about 6 /x diameter, 
which may be found alone or in connexion with the gonidial groups. 
Lower down in the limestone these narrow hyphae show a tendency to 
associate in strands, and remind one very strongly of the strands of ‘ oil 
hyphae ’ figured by Lang (loc. cit.) for Biatorella simplex. In longitudinal 
sections simple chains of inflated hyphae have not been discovered, but 
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