Fry. — Some Types of Endolithic Limestone Lichens . 549 
particularly by those with dense contents. Those in the gonidial region 
are much narrower than similar hyphae in the cortex. From each of the 
little clusters filaments branch off and cross over or pass down to the 
neighbouring groups when the latter are situated some distance apart. 
When the clusters are close together these hyphae pass downwards, 
forming a dense strand of parallel filaments. 
Rhizoidal zone. From the gonidial zone hyphae of both kinds pass 
downwards, branch very freely, and appear to form a dense network. In 
this region of transition from the upper zone to the rhizoidal region nearly 
all the hyphae appear to have the power of producing small inflated cells. 
These may be formed in continuous rows, or with 
short lengths of narrow hyphae in between. They 
resemble very closely the ‘ empty * cells of the cortical 
and gonidial zones. From this mass of hyphae spring 
the ‘ rhizoids \ These are narrow filaments, except 
when inflated to 1 4 /a, or thereabouts, with cross-walls 
far apart. They contain small globules of oil which 
is of the same nature as that found in the spherical 
dilations. Instead of the swellings occurring singly 
at the end of filaments as in V. calciseda, they are 
seen in 1 X ’ to be most frequently in simple chains 
(Text-fig. 6) and sometimes in very small clusters. 
Frequently in a longitudinal section one can see that 
the structure of the rock has some influence on the 
rhizoids. The parallel lines of cleavage of large calcite 
crystals are often followed by branches of smaller 
inflated hyphae which join on to the main filament at 
an angle of 6o°. 
Reproductive organs . Ascus-bearing bodies and 
asci have not been found in lichen ‘ X \ but there ‘ x^ Inflate’d hyphae 1 
are two kinds of spore-bearing organs apart from 
these. Both form pits which penetrate the limestone to more than twice 
the depth of the gonidial zone. 
Spermogonia . The first kind one recognizes as simple immersed sper- 
mogonia (Text-fig. 7) bearing on their infolded walls countless spermatia of 
the club-shaped type. Numbers of these spermogonia have been cut both 
horizontally and longitudinally. At the apex the neck is narrow and 
generally circular in cross-section and measures about 70 fi in diameter ; if 
oval in outline the measurements are about 55 ju x 180 ju. Lower down in 
the rock where the spermogonium reaches its greatest breadth the average 
measurement is 200 ju. 
The second spore-bearing bodies appear very like pycnidia, but they bear 
macrospores „ In general appearance they resemble the spermogonia, but 
