LICHEN COMMUNITIES 391 



country is Dermatocarpon aquaticum, with thick coriaceous rather contorted 

 lobes; it inhabits rocks and stones in streams and lakes. Somewhat less con- 

 tinuously aquatic is D. miniatum var. complicatum which grows on damp rocks 

 exposed to spray or occasionally to inundation. Lindsay 1 has described it 

 " on boulders by the side of the Tay, frequently covered by the river when 

 flooded, and of a deep olive colour when under water": both these lichens 

 have a wide distribution in Europe, Africa, America and New Zealand. 



In a discussion of lake shore plants Conway Macmillan 2 describes on 

 the flat shores a Dermatocarpon zone on the wet area nearest the lake, behind 

 that a Biatora zone and further landward a Cladonia zone. On rounded 

 rocky shores the same zones followed each other but were less broad : they 

 were so close together that the Cladoniae, which with Stereocaulon paschale 

 grow in profusion on all such shores, occurred within a couple of feet of the 

 high-water mark. 



M. C. Knowles 3 reports concerning the lichen flora of some mountain 

 lakes in Waterford, that a band of Dermatocarpon miniatum var. complicatum 

 six feet wide grew all the way round the lakes between the winter and 

 summer level of the water. Below that zone D. aquaticum formed another 

 belt mingled with the moss Fontinalis and several species of crustaceous 

 lichens Staurotheleae, Polyblastiae, etc. 



Bruce Fink 4 gives as a typical "amphibious angiocarpous lichen forma- 

 tion" of wet rocks in Minnesota: Dermatocarpon aquaticum, D. miniatum var. 

 complicatum, Staurothele clopima and Verrucaria viridula. These "forma- 

 tions," he says, " may be seen complete in places along the shores of Ver- 

 million Lake and less well represented at other portions of the lake shore." 

 Macmillan found that on the rocky shores of Lake Superior the Dermato- 

 carpon zone also occurred nearest the water. 



Species with closed fruits such as Pyrenolichens, or with apothecia 

 deeply sunk in the thallus and thus also well protected, seem to be best 

 adapted to the aquatic life. Such in our own country are Lecanora lacustris, 

 Bacidia inundata and others, with a number of Verrucariae : V. aethiobola, 

 V. hydrela, V. margacea, etc. 



Lettau 5 gives as "formations" on rocks or boulders in the beds of streams 

 in Thuringia : 



Verrucaria aethiobola. Bacidia inundata. 



Verrucaria hydrela. Lecanora aquatica. 



Dermatocarpon aquaticum. 



In their ecological study of Perthshire lichens Wheldon and Wilson 8 

 give two " formations." The first is on rocks submerged for long periods, 



1 Lindsay 1856. 2 Macmillan 1894. Knowles in lift. 4 Bruce Fink 1903. 



5 Lettau 1911. 6 Wheldon and Wilson 1915. 



