LICHENOLOGY OF ICELAND 153 
the relation of the podetia to the substratum and mutually to one 
another. 
As already mentioned, the oldest podetia die away below, and 
form thereby a peaty mass, while they keep on growing at their 
apex “per secula” as Wainio writes. 
The question now arises how the podetia, on a century-old 
cake of lichen-peat, obtain their mineral food. So long as the lichens 
are in somewhat close contact with mineral soil, every shower will 
saturate the upper layers of earth, and the water will become nu- 
tritive to a certain extent. But later on, when the cakes of lichen- 
peat are formed, they will no doubt gradually become washed free 
from minerals, and the water which the lichens can absorb from 
the substratum (which is, as is well-known, very little, because they 
lead the rainwater down into the ground much more easily than 
upwards from it, as demonstrated by Zukal, 1891—96) must be- 
come poorer and poorer in nutriment. Can this ultimately bring 
about the result that the lichen-covering, by its continued growth, 
brings about its own destruction? It is a question which lichen- 
ologists, who have easy access to Alpine lichen-heaths, ought to 
take up for investigation. 
Haptera have been first demonstrated and described by Ser- 
nander (1901) in a small and very interesting, but unfortunately 
only too brief, treatise. Sernander distinguishes several types 
(Cladonia-type, Alectoria-type, etc.). I prefer another classification, 
because haptera of several different types occur on the same plant, 
and cannot therefore be named after different genera. Sernander 
does not describe them anatomically. In my "Forberedende Under- 
søgelser” (1913) they have been very fully treated and figured, and 
the chief points will now be recapitulated here. 
According to my classification the types to which the haptera 
may be referred, are the following: — 
(1) Apical haptera, 
(2) Lateral haptera, 
(3) Primary-scale haptera, 
(4) Podetium-scale haptera. 
Some of these, especially the two last, have not been mentioned 
at all by Sernander. 
The haptera may attach themselves to the ground (when the 
podetia are procumbent); or to other individuals of the same species 
(but no parasitic relation ever arises from this contact); or to other 
