LICHENOLOGY OF ICELAND 151 
In Cladonia foliacea the primary thallus is the chief assimilatory 
organ of any length of duration. 
Consequently, three types may be distinguished: (1) Permanent 
primary thallus, which keeps on growing along the edge and dies 
away at the base; this is found in the primary-scale-wanderers 
(Cladonia foliacea). (2) Permanent primary thallus, which does not 
die away behind, found in the hypothallus-wanderers and in the 
more primitive podetium-wanderers (Cladonia papillaria, pyxidata, 
pityrea, fimbriata, squamosa, crispata, cornuta, macilenta, Floerkeana, 
coccifera, deformis, verticillata, gracilis, rangiferina, furcata). (3) Quickly 
perishing, crust-shaped primary thallus, found in the most decided 
podetium-wanderers (Cladonia uncialis and rangiferina). 
From the under surface of the primary scales, in several cases, 
hyphæ may proceed from the cortical layer. Sometimes it is difficult 
to decide with any certainty, whether they are simply hypothallal 
hyphæ or — which may be the case — secondary hyphe, which 
from the medullary layer, push their way into the soil, and attach 
themselves to it, and are therefore, properly speaking, haptera. Un- 
doubted haptera I have found in Cladonia foliacea, where they occur 
in the form of a hyphal pencil, in C. pityrea, where they are similar 
in form, in C. squamosa, where they form solid hyphal bundles, and 
in C. pyxidata, macilenta and furcata, in which they consist of scat- 
tered hyphz, produced from the under surface of the scales. 
The haptera attach themselves to mineral-grains, humus-lumps, 
etc., in exactly the same manner as do the hypothallal hyphæ, and 
it is true also with regard to them, that it has not been possible 
to demonstrate microscopically that they have any chemical influence. 
Interwoven in a hapteron of Cladonia foliacea I found green alge, 
which were apparently uninfluenced by the proximity of the hyphe. 
Another type of primary-scale haptera I found in Cladonia foli- 
acea and in C. cornuta. By means of these the scales attached them- 
selves to one another or to podetia of the same species. 
Podetia. Of these, four types may be distinguished, which 
differ in duration of life and in mode of growth. All the fruticose 
earth-lichens are erect, and their thalli are, as a rule, called “podetia,” 
but these, however, differ greatly in the history of their development. 
Here the term is used as a biological conception to indicate the 
subeerial thallus, mainly of a radiating form; (consequently not the 
primary scales of Cladonia). Of this I have set up four types, viz. 
(1) erect, radial, permanent podetia; (2) erect, radial podetia, dying 
