358 ECOLOGY 



globulifera formed a continuous crust on the trees as much as 120 x 90 cm. 

 Lecanora tartarea seemed to thrive exceptionally well when subject to 

 driving mists and rains from mountain or moorland, and was in these cir- 

 cumstances frequently the dominant epiphyte. Bruce Fink' also observed 

 in his ecological excursions that the number of species and individuals was 

 greater near lakes or rivers. 



Though a fair number of lichens are adapted to life wholly or partly 

 under water, land forms are mostly xerophytic in structure, and die off if 

 submerged for any length of time. The Peltigerae are perhaps the most 

 hydrophilous of purely land species. Many Alpine or Polar forms are 

 covered with snow for long periods. In the extreme north it affords more 

 or less protection; and Kihlman^ and others have remarked on the scarcity 

 of lichens in localities denuded of the snow mantle and exposed to severe 

 winter cold. On the other hand lichens on the high Alpine summits that are 

 covered with snow the greater part of the year suffer, according to Nilson', 

 from the excessive moisture and the deprivation of light. Folio.se and 

 fruticose forms were, he found, dwarfed in size; the crustaceous species had 

 a very thin thallus and in all of them the colour was impure. Gyrophorae 

 seemed to be most affected : folds and outgrowths of the thallus were formed 

 and the internal tissues were partly disintegrated. Lichens on the blocks 

 of the glacier moraines which are subject to inundations of ice-cold water 

 after the snow has melted, were unhealthy looking, poorly developed and 

 often sterile, though able to persist in a barren state. Lindsay* noted as 

 a result of such conditions on Cladoniae not only sterility but also de- 

 formity both of vegetative and reproductive organs ; discolouration and 

 mottling of the thallus and an increased development of squamules of the 

 primary thallus and on the podetia. 



c. Wind. Horizontal crustaceous or foliose lichens are not liable to 

 direct injury by wind as their close adherence to the substratum sufficiently 

 shelters them. It is only when the wind carries with it any considerable 

 quantity of sand that the tree or rock surfaces are swept bare and prevented 

 from ever harbouring any vegetation, and also, as has been already noted, 

 the terrible winds round the poles are fatal to lichens exposed to the 

 blasts unless they are provided with a special protective cortex. After 

 crustaceous forms, species of Cetraria, Stereocaulon and Cladonia are best 

 fitted for weathering wind storms: the tufted^ cushion-like growth adopted 

 by these lichens gives them mutual protection, not only against wind, but 

 against superincumbent masses of snow. Kihlman^ has given us a vivid 

 account of wind action in the Tundra region. He noted numerous hollows 

 completely scooped out down to the sand : in these sheltered nooks he 



' P'ink 1894. 2 Kihlman 1890. ' Nilson 1907. 



^ Lindsay 1869. 6 Sattler 1914. 



