Fry. — Some Types of En do lit hie Limestone Lichens . 555 
processes the spherules are brought into immediate contact with each other, 
the whole mass constituting a complex of ceils having the appearance of 
a bunch of grapes in which it is no longer possible to distinguish the cells 
of the principal hypha from those of the lateral branches.’ As Bachmann 
(loc. cit.) states, they are most frequently found in the uppermost layers of 
limestone (PL XXI, Fig. 14), but since he had not the' epilithic part 
of the thallus in situ he was not able to see the relative position of the 
largest and more frequent clusters. In the present investigation by far the 
largest and most conspicuous masses of inflated hyphae are found in the 
limestone beneath or in the immediate neighbourhood of the apothecia 
Text-fig. 9. Aspicilia calcarea, showing apothecium and large clusters of inflated cells. 
Tr. = ‘ transition 5 zone ; inf. oil hyphae — complex mass of inflated oil hyphae. 
which occurs in the epilithic part of the thallus (Text-fig. 9). In such 
clusters the spherical hyphae have a diameter of not more than 6 or 7 /x. 
It should be mentioned, both as regards the masses of spherically inflated 
cells and the endolithic gonidial groups, that they are not equally 
abundant in all parts of the thallus ; in fact, in many parts they may be 
completely absent. 
General Discussion. 
One of the most striking facts about the endolithic lichens here 
described is that, although they are embedded in the rock, their thalli 
have a structure similar to that of the sub-aerial forms to which they are 
related. For example, the genus Lecidea includes both sub-aerial and 
endolithic species, and both exhibit the heteromerous structure. In both 
types growth in area goes on at the circumference, where the thalli are thin 
and consist of fungoid elements alone. Towards the centre, where they are 
fully developed, the thalli present the typical heteromerous structure. The 
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