140 



OLA I (',. \LL0E 



The course of development in the decomposition of the hark, and 

 the consequent change of vegetation from hypophkeodal to epi- 

 phla-odal and other bark lichens, may be studied on almost every 

 old tree. 



Ho\v many of Iceland's bark lichens are hypophlcoodal, has 

 not been investigated. 



The epiphlu-odal crustaceous-lichens are fastened to the sub- 

 stratum like the hypophloeodal; they have been investigated by 

 Lindau (1895). They have a hyphal tissue that sinks into the bark 

 and ruptures the cells of the bark, but is not able to dissolve their 

 cellulose. The gonidia-containing part of the thallus is on the sur- 

 face of the bark, hence their name and is more or less dis- 

 tinctly covered with a cortex, showing all transitions between species 

 with the thinnest and the thickest cortex. 



In several crustaceous lichens soredia are formed which can 

 propagate the plant, for instance in the Variolaria spp. This 

 mode of propagation indicates a higher morphological stage than 

 that of the hypophlceodals, in which anything like it appears to 

 be rare. 



With regard to competitive capacity, in most of the habitats 

 the epiphlceodals stand above the hypophlu'odals, but they generally 

 appear to need a more advanced stage of decomposition of the bark, 

 than do the latter, so that they frequently succeed to them as the 

 bark gradually gets older. It is possible that they also require 

 more light. 



Of crustaceous bark-lichens Iceland has the following: 



Arthonia proximella Nyl. 



punctiformis Ach. 

 Arthopyrenia analcpta Ach. 



grisea Schleich. 

 Hacidia abbrevians Nyl. 

 arceutina Ach. 

 atrosanguinea Schaer. 

 Beckhausii Koerb. 

 rubella Ehrh. 

 sphaeroides. 



Bucllia myriocarpa (D C) Mudd. 

 parascma (Ach.) Th. Fr. 

 Caloplnca cerina (Ehrh.) Th. Fr. 

 citrina Ach. 



ferruginea (Huds.) Th. Fr. 

 Diploschistes scruposa L. 

 Lecania athroocarpa (Dub.) Nyl. 



Lecania cyrtella Ach. 

 Lecanora atra (Huds.) Ach. 



Hageni (Ach.) Koerb. 

 pallescens (L.) Schaer. 

 protuberans Sm. 

 subfusca (L.) Ach. 

 tartarea L. 

 varia (Ehrh.) Nyl. 

 Lecidea crustulata (Ach.) Koerb. 

 Diapensias Th. Fr. 

 elaeochroma (Ach.) Th. Fr. 

 erytrophoea Flk. 

 fuscescens Sm. 

 helvola (Koerb. Th. Fr. 

 Nylanderi Anzi. 

 Tornoensis Nyl. 

 Lepraria. 



