140 OLAF GALL@E 
The course of development in the decomposition of the bark, and 
the consequent change of vegetation from hypophlæodal to epi- 
phloeodal and other bark lichens, may be studied on almost every 
old tree. 
How many of Iceland’s bark lichens are hypophloeodal, has 
not been investigated. 
The epiphlceodal 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 hypophloeodals, in which anything like it appears to 
be rare. 
With regard to competitive capacity, in most of the habitats 
the epiphloeodals stand above the hypophlceodals, 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. Lecania cyrtella Ach. 
= punctiformis Ach. Lecanora atra (Huds.) Ach. 
Arthopyrenia analepta Ach. = Hageni (Ach.) Koerb. 
— grisea Schleich. = pallescens (L.) Schaer. 
Bacidia abbrevians Nyl. = protuberans Sm. 
— arceutina Ach. — subfusca (L.) Ach. 
—  atrosanguinea Schaer. = tartarea L. 
—  Beckhausii Koerb. = varia (Ehrh.) Nyl. 
— rubella Ehrh. Lecidea crustulata (Ach.) Koerb. 
— sphaeroides. —  Diapensiz Th, Fr: 
Buellia myriocarpa (D C) Mudd. —  elaeochroma (Ach.) Th. Fr. 
— ) -parasema-(Ach:) ‘Th: Fr, —  erytrophæa Flk. 
Caloplaca cerina (Ehrh.) Th. Fr. —  fuscescens Sm. 
— citrina Ach. —  helvola (Koerb.) Th. Fr. 
— ferruginea (Huds.) Th. Fr. —  Nylanderi Anzi. 
Diploschistes scruposa L. —  Tornoensis Nyl. 
Lecania athroocarpa (Dub.) Nyl. Lepraria. 
