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, cornnta, 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, 

 hyphae may proceed from the cortical layer. Sometimes it is difficult 

 to decide with any certainty, whether they are simply hypothallal 

 hypha? or which may be the case secondary hyphae, 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 hyphae, 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 hyphae, 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 algae, 

 which \vere apparently uninfluenced by the proximity of the hyphae. 

 Another type of primary-scale haptera I found in Cladonia foli- 

 acea and in C. cornnta. 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 

 subaerial 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 



