17 



celia and is thus withdrawn from circulation, so that this soil in its most 

 distinctive forms especially the old heaths - - only has a small 

 quantity of ammonium compounds, produced mainly by physico-chemi- 

 cal means, to provide the phanerogamic vegetation with nitrogen, and 

 absolutely no nitric acid. The main character of typical mor as 

 a soil for vegetation is therefore its poverty in assimilable nitrogen, 

 and its vegetation consists, so far as known, exclusively or almost ex- 

 clusively of plant-species with endotrophic mycorhiza, which possibly 

 through their assimilation of the nitrogen of the air become independent 

 of; the assimilable nitrogenous compounds of the soil (Ericaceae etc., 

 Frank, Stahl). 



The phanerogamic vegetation varies on this soil not only accord- 

 ing to the same ecological factors as on the muld-soil, but likewise 

 according to the different biological conditions set up by the thallophytic 

 vegetation in the ground. - 



Muld and mor are therefore the results of biological processes 

 in variable combination with climatic and pedological conditions and 

 the plant-associations react in the most marked degree to the different 

 stages of this interplay. 



The old heaths in many parts are probably derived from the 

 post-glacial period of the tundras and where the soil content has 

 been most extracted, the mor -formation is carried to its greatest 

 extent with quite dominant fungal decomposition of the vegetative refuse, 

 with extreme reduction of the bacteria life and with almost complete 

 cessation of nitric acid production. It supports especially the Calluna-, 

 Empetrum- and Lichen-heaths. The young heath is better; it was covered 

 for the most part by the glacial mass of the last glacial period and 

 its soil as a rule has suffered less from the extraction of its content. 

 This young heath has in great part been covered by woods, which have 

 been supplanted by Calluna-heaths with Hypnum, Hylocomium and 

 others. Here some formation of nitric acid still occurs in the soil and 

 the vegetation is richer, more varied and with frequent occurrence of 

 remnants of woods. 



But even the dominant plant-association of phanerogams has a 

 considerable influence on whether the locality is readily exposed to 

 mor -formation or not. The Ericaceae (not only Calluna but the 

 whole series of related forms) affords ready access to malignant mor 

 with accompanying transformation of the underlying soil. Of forest 

 trees the beech, especially on dry and sandy soil, is disposed to further 

 the formation of mor, and the beech association growing on muld 

 soil can during its development change the nature of the soil in such 

 a way, that after a generation mor is formed, which hinders the 

 regenerating of even the mother association, a renewal by natural means 

 being excluded. Less exposed to mor -formation are Picea- and Abies- 



