558 Fry . — Some Types of Endoiithic Limestone Lichens. 
investigation L. immersa only penetrates to a depth of 1,100 /x, and no 
inflations, of the complicated type figured by Fiinfstiick, are found. 
Fiinfstiick states that Opegrapha saxicola is one of the richest in oil cells. 
He also says in another connexion that O. saxicola and V. calciseda are 
rapidly growing forms. The rate of growth of lichen ‘ X ’ is not known. 
It is interesting to note, in connexion with the development of the perithecia 
of V. calciseda and the apothecia of L. immersa, that oil cells are prominent. 
It is also curious that, even in the case of A. calcar ea, where the apothecia 
are in the epilithic part of the thallus, there is in the rock below an 
unusual formation of these cells full of oil. It may be worth mentioning 
as a characteristic feature of the genus that during its early development 
the apothecium remains immersed in the thallus tissue. In regions of 
growth, or any other plant activity, carbon dioxide is given off, and in 
regions of rapid or locally concentrated growth one would expect a pro- 
portionally increased evolution of the gas. In these endoiithic lichens it is 
in such regions that one finds the main masses of oil cellules, and it is in 
these same places that the more rapid solution of the limestone goes on. 
It seems natural to conclude, therefore, that growth, formation of oil, 
evolution of carbon dioxide, and solution of the limestone are intimately 
related. If this is so, then one can suggest a solution of the phenomenon 
of limestone penetration by these lichens. Such a solution would also 
explain penetration of the rock by Trentepohlia and moss rhizoids. 
Various theories have been advanced to explain the use of the fatty 
material. It was stated by Zukal (15) to be a food reserve in case of drought 
or extra strain on the resources of the lichen. This has been disproved by 
Fiinfstiick’s (loc. cit.) experiments on V. calciseda and O. saxicola . The 
researches of Beyerinck (12), Wehmer (13), and Stahel (14) all go to show 
that the formation of the fatty material is due to adverse conditions, such as 
absence of nitrogen or excess of calcium carbonate, while respiration is actively 
proceeding. Some of the material used in the present investigation had 
been kept dry and in the dark for two or four years, and it is interesting to 
note that the inflated cells and hyphae were full of oil at the end of those 
periods. As stated by Miss Lorrain Smith (8), the results obtained by the 
above investigators show how the fatty substance may be formed in those 
lichens which are deprived of nitrogen and have an excess of carbon dioxide 
which is not readily removed. This is clearly brought out in the present 
investigation, for wherever carbon dioxide evolution is at its greatest, there 
one finds the greatest formation of inflated oil hyphae. Furthermore, in 
the slower-growing species, inflated hyphae are absent, the oil being stored 
as small globules in the ordinary narrow hyphae. From the above con- 
siderations one can conclude with Fiinfstiick (loc. cit.) that the oil is a waste 
product formed under the special endoiithic conditions. 
Various theories have also been put forward by different investigators 
