Knowles — The Maritime and Marine Lichens of Howth. 83 



species in liis list. In tlie short introduction to the paper he divides the lichens 

 of the rocky shores into three groups: (1) Marine — those growing on the 

 rocks that are covered at every tide ; (2) Semi-marine, those that, without 

 requiring a complete immersion, benefit by the splashings they receive from 

 the waves breaking at the base of tiie rocks, of which they occupy the sides ; 

 (3) Maritime — those that grow beyond reach of the waves, but come under 

 the influence of the salt breeze. Verruearia maura and Lichina confinis are 

 mentioned as belonging to tlie semi-marine group, and Lichina pijgmaea as 

 an example of the marine group ; but no further reference is made to this 

 classification in the paper. 



More recently, Sanstede has published several important papers on the 

 lichens of the German North Sea islands (24 and 25). He also is mainly 

 concerned with the systematic side of the subject, but there are some 

 ecological notes, and references are made to the species that grew on rocks 

 splashed by the salt water and to those preferring higher levels, and lists of 

 species are given. 



In his treatise on plant-ecology, Warming (29) refers to the zonal 

 distribution of the vegetation of the sea-shore, and describes three belts 

 of lichens as characteristic of the coasts of Denmark and Sweden, and 

 of other northern countries. He says : " Lying lowest on the shore, where 

 the rocks are very frequently wet, is Verruearia maura, a very tiiin black 

 scaly lichen divided into small pieces. . . . Higher up the rocks are reddish 

 yellow with Placodium murale, which is accompanied by Xantlioria parietina. 

 Above this follows a belt of Ramalina scopulorum ; here the action of the salt 

 water is reduced to almost nothing." There are scattered references to 

 the liclien vegetation of the sea-coasts in other publications ; but, so far, 

 the ecological side of the subject has received very little attention from 

 liclienologists. • Practically all that has been written about the ecology of 

 the lichens of the sea-coasts refers to the marine group and is to be found in 

 the writings of marine algologists such as Borgesen (2), Jonsson (9), 

 Joubin (10), Cotton (3), and others, who, in describing the various marine 

 algal associations, incidentally give some account of the lichen vegetation 

 found betweeu tide-marks. By far the most complete account, and the only one 

 that has been published for our own coasts, is that contained in A. D. Cotton's 

 paper on the Marine Algae of the Clare Island Survey. Here we find a very 

 full and interesting description of the Lichina communities of those coasts, and 

 in his account of the " Hildenbrandtia- Verruearia association " Mr. Cotton 

 supplies a good deal of information about the distribution and habitat of 

 Verruearia mucosa and V. maura, and suggests that there may be other species 

 in the association. 



