262 TRANSACTION'S OF ROYAL SCOTTISH AKBORICULTURAL SOCIETY. 



Heather raio humus results from lack of moisture in the 

 regions where the dominating heather produces a dense felting 

 or network of roots. It is often characterised by the formation, 

 at no great depth, of a brown or black grit or pan, of organic 

 oi'igin, usually called Ortstein in German, Alios in French, 

 and Moorpan in English. ^ This dark humus, of compact 

 structure, is as tough as peat. 



Forest raw humus - is derived from the material of the 

 covering [Streumull), when, either on account of the temperature 

 or the growth of the trees, moisture decreases and air no longer 

 is sitpplied in sufficient amount. Decomposition is retarded; 

 the covering becomes more and more impermeable. The plants 

 which settle on that humus, heaths and vacciniums, help by 

 the compact network of their roots and their own remains 

 to increase the deposit and exhaust the superficial layei'S of 

 the ground. 



Meadorv or Pasture raw humus originates, on the contrary, 

 from the decomposition of roots of grasses and other meadow 

 herbs, with a limited supply of air and an excess of moisture. 

 It is formed especially in the meadows or pastures, in the 

 low-lying parts of the land. 



Products of putre/action. — The result of decomposition with- 

 out oxygen is peat or acid humus, a very stable mass, which 

 may accumulate in vast beds. They are divided into lower 

 or infra-aquatic marsh or peat, and sphagnum, or supra-aquatic 

 moors. 



Lovoer or infra-aqiiatic marshes are formed in the neighbour- 

 hood of running water or in lake hollows, on physically and 

 chemically very different soils. They arise from the putrefaction 

 of grasses, sedges, and rushes, and a few mosses which grow 

 on the quiet river banks and lake shores usually covered with 

 alluvial deposits. When they thus invade ponds and lakes, 

 they restrict the surface area. 



The first condition for the occurrence of the plants of these 

 marshes is a soil rich in nutritive elements, especially lime. 



Sphagnum rnoors, or supra-aquatic moors (Haide moors), are 

 formed in hollows both in the plains and the mountains by 

 the putrid decomposition of sphagnum mosses which grow at 



' P. E. Miiller, Studien iiber die Ncdiirlkhen Humusformcn tend deren 

 Einwirkung auf Vegetation und Bodev,, Berlin, 1887. 

 - C. Grebe, Aufiorstung von Odlandercicn, 1896. 



