CVI HENRIK HESSELMAN. 
goes on in the black soil from charcoal grounds, consisting for the most part 
of charcoal breeze. 
The tar-hollows have much the same conditions as the charcoal-grounds. 
It is true that I have not found such a rich nor such a markedly nitratophilous 
flora in old tar-hollows as in old charcoal-grounds; but the character of the 
flora tends in the same direction (see page 1052). Soil samples from tar- 
hollows can, I find, nitrify a solution of sulphate of ammonia (see table 7). 
In soil from charcoal-burning grounds and tar-hollows there thus goes on 
a process of nitrification similar to that in ground affected by forest fire. 
CHAP. X. Summary of the effect of measures taken for regeneration 
of forest on the formation of saltpetre in the ground. 
With regard to the transformation of the organically bound nitrogen, it 
is possible, as has been previously pointed out, to distinguish two types of 
forest and ground: in one type, there goes on a complete oxidation 
of nitrogenous compounds into nitric acid; in the other, on the other hand, 
the process comes to a stop with the formation of ammonia. I have given 
a detailed account of these different types, and of the conditions under which 
they come into existence, in a recently published treatise (HESSELMAN, 1917). 
The greater part of our woods belongs to the last-named type, namely all 
the mossy and lichenous coniferous forests with their different variations. One of 
the distinctive features of these types is that the covering of humus forms a 
crust lying loosely on the surface of the soil (what the Germans call "Auf- 
lage-humus”'), which goes through a peculiar and characteristic process of 
decomposition, regulated by the. soluble organic substances in the humus- 
covering and this process expresses itself in the formation of a layer of 
bleached sand, overlying a layer of rust-red soil. The whole of this type of soil 
is characterized by a special vegetation, distinguished in the first place 
by berry shrubs and carpet-forming mosses, or else, in dryer positions, of 
heath and lichens. In this humus-covering the process of dissolution of the 
organic substances comes to an end with the formation of ammonia. Under 
certain circumstances, however, as appears from this present account, certain 
long-used measures of forest regeneration can produce a radical change in 
the conversion of nitrogen, expressing itself in a more or less active forma- 
tion of saltpetre. The measures of forest regeneration which take effect in 
this way are the following: 
(TD) Im the fairly dense mixed coniferous forests! of centralfones 
den, where the ground-covering consists mainly of moss, felean 
cutting [»Kahlhieb>]|, shelterwood cutting [»Schirmhieb>], or merely che- 
querboard cutting, [»Löcherhieb>], can produce a lively nitrification 
in the ground. 
(2) A preparatrion of the soil with the Finnish plougbh orkan 
other machine that causes a mixture of the humus-covering and 
the mineral soil, produces a formation of saltpetre, even when 
the wood is so dense that nitrification does not otherwise occur. 
(3) Mouldering brushwood and old rotting timber require or pro- 
dice a nitrification in the ground, even under circumstameesmima 
whieh the formation of saltpetre does not occur on the cleamumnpgst 
