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 

 (Cladohia-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- 

 sogelser" (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 



