560 m Ery. — Some Types of Endolithic Limestone Lichens. 
in the condensed water vapour of the atmosphere plays a considerable part 
in the decomposition of glass. 
Summary. 
1. The investigation suggested itself during a general study of 
cryptogamic ecology, and this paper is confined to the examination of 
certain endolithic limestone lichens. 
2. The method of preparation of material for study was to decalcify, 
with dilute hydrochloric acid, the lichen thallus as a whole, then wash 
it free of acid, fix, dehydrate, embed, cut serial sections, stain, and mount 
in the usual way. 
3. The classification adopted is based on the thallus structure. 
4. Endolithic lichens have a structure similar to that of sub-aerial 
forms. 
5. The fruiting bodies originate within the rock — the deep pits being 
formed during development. 
6. In regions of special growth numerous spherically inflated hyphae 
containing oil are found. In these same regions the solution of the 
limestone is more rapid. There is probably some relation between 
growth, evolution of carbon dioxide, oil formation, and solution of the 
limestone. 
7. Inflated oil hyphae are absent in slower- growing species, but oil 
globules in the ordinary hyphae are common to all forms. 
8. The oil is not stored food, but waste material produced under 
adverse conditions during the evolution of carbon dioxide ; consequently 
there is an increased output of oil where growth is specially active. 
9. It is suggested that the boring action is brought about by the carbon 
dioxide of respiration dissolved in water. The dilute acid attacks the 
rock, the soluble bicarbonate being formed. This is precipitated at the 
surface as the stable carbonate. The precipitation causes the granular 
appearance of the surface of endolithic thalli. The granules are constantly 
replaced by the fresh precipitation of calcium carbonate. / 
I am much indebted to Professor Lloyd Williams, D.Sc., University 
College of Wales, Aberystwyth, for his kind help and encouragement with 
this investigation. My thanks are due to Miss Lorrain Smith, F.L.S., 
Mr. D. A. Jones, M.Sc., Mr. Hebden, and Mr. Wheldon, F.L.S., for their 
kindness in verifying and identifying lichens, both in connexion with this 
and previous investigations. 
