544 Fry. — Some Types of Endolithic Limestone Lichens . 
I. Wholly Endolithic Types . A. 
a. Vermtcaria calciseda , D. C. 
Under the microscope the surface of the limestone immediately above 
V errucaria calciseda appears white and rather granular, exhibiting very 
numerous black spots and empty pits. The spots are of two kinds. The 
larger circular patches are the carbonaceous lids of the perithecia, while the 
smaller dots are the dark external ends of hyphae of the cortical zone, or, 
as is often the case in these endolithic forms, they are small colonies of 
minute blue-green algae, which adhere to the surface. The pits are the 
positions of the old perithecia. 
After decalcification the thallus is very thin, soft, and delicate, the upper 
surface having a fine woolly appearance. Both the upper and lower surfaces 
are white, as are also the short rhizoids. In a vertical section (PL XXI, 
Fig. i) can be seen the three zones : cortical, gonidial, and rhizoidal. From 
the cortex to the limits of the rhizoids measures 670 \ a. The whole thallus, 
except for the short dark hyphal tips, is embedded within the rock. 
Cortical zone. The cortex has an average thickness of 28 \k. Although 
it appears fairly continuous the hyphae are not evenly distributed. In 
certain regions, i. e. just above the main groups of gonidia, the hyphae are 
shorter and more closely packed, forming a dense tissue. Linking up these 
clumps one with another are many branching hyphae which are composed 
of the short cells or more elongated ones. Towards the surface of the rock 
the cortical hyphae tend to be of a greyish brown colour. Those that are 
actually at the surface are a deep brown or black (PI. XXI, Fig. 1, a). 
. Gonidial zone. The average width of the gonidial zone is about 75 /x. 
In a longitudinal section the bright green gonidia are arranged in more or 
less regular, elongated groups. These branch in one or more directions. 
The long axis of the gonidial group usually is at right angles to the surface 
of the rock, though frequently it may run almost parallel with it (PI. XXI, 
Fig. 1). The gonidia are wound round by innumerable hyphal threads 
(Text-fig. 1), which, besides enclosing the whole group in a kind of envelope, 
push their way between the individual gonidia. These hyphae are continuous 
with the hyphal tissue immediately above the group. The gonidial groups 
with their hyphal caps are situated in hollows in the limestone, and it is 
from these that the gonidia are so easily lost in the rubbing process in 
the preparation of the rock sections by Bachmann’s method. From the 
common envelope of short hyphae with dense contents there are given 
off numerous branches which connect up the neighbouring groups of algal 
cells (Text-fig. 1). Other branches- pass in a downward direction, branch 
freely, and anastomose while still in the region of the gonidial zone. 
Rhizoidal zone. The hyphae which are deepest in the rock are narrower 
