542 Fry . — Some Types of Endolithic Limestone Lichens. 
action of the endolithic thalli. Apart from such epilithic types there are 
a few whose thalli are partly epilithic and partly endolithic, e. g. Aspicilia 
calcarea , the endolithic part only of which has been described by Bachmann 
(loc. cit.). 
Method of Preparation of Material. 
Bachmann prepared and examined slides of the rock with the lichen 
in situ. To examine the thallus in greater detail he removed the limestone 
by treating the rock section with hydrochloric acid or Perenyi’s fluid ; but 
before this could be done all trace of the Canada balsam, used in fixing the 
rock section to the glass slide for the rubbing-down process in the prepara- 
tion of rock sections, had to be removed by special methods. It was 
necessary that this process of decalcification should be carried out on the 
slide, since the thallus sections were too delicate and of too loose a texture 
to allow of the usual manipulation. The disadvantages of such a method 
are obvious. In the first place, rock sections, thin enough to show sufficient 
detail of the hyphae, cannot be prepared without loss of a certain number — 
perhaps the majority — of the gonidia, which come out fairly easily in the 
rubbing-down process. Secondly, in the decalcification of sections, a number 
of the short portions of hyphae and algae readily break away from such 
a loose structure, so that a perfect section can rarely be obtained. In the 
present investigation, rock sections having proved unsatisfactory, the follow- 
ing method was adopted for the preparation of sections of endolithic thalli. 
From the surface of fairly pure crystalline limestone bearing the endolithic 
lichens, fragments of about i cm.-i*5 cm. thickness were chiselled. These 
were then immersed in hydrochloric acid. In order that the effervescence 
might be very slow the acid was made very dilute. This precaution allowed 
the true structure to be preserved, which might have been destroyed by 
too violent a reaction. The process in a number of cases has been observed 
under the microscope. Effervescence was less rapid from the upper surface. 
This became woolly in appearance as the limestone was dissolved, and the 
degree of coarseness of the texture varied with the different lichens. At 
the end of three or four hours all the calcium carbonate was removed. 
To the naked eye the thallus, freed of the rock, appeared as a thin rind, 
from the underside of which spread out a meshwork of very fine, soft hyphal 
threads, the length, number, and colour of which varied with the different 
species. When the thallus was touched an impression was given as of a mass 
of sodden silken threads. This mass collapsed on removal from the liquid. 
The whole was washed gently in running water for twenty-four hours, then 
fixed in chrom-acetic, washed, dehydrated, embedded, and serial sections 
cut in the usual way. It should be- mentioned that before washing free of 
the acid the underside of the material was examined under the microscope 
for insoluble impurities. These, when present, were removed, care being 
