XCVIII HENRIK HESSELMAN 
berry shrubs and to some degree woven together by their roots. Under this 
we come to a less compact layer of peat-like or peat-formed consistency, 
tough and tenacious, which only in the immediate neighbourhood of mineral 
soil has a distinetly loose and flocculated structure (see fig. 8 and 9). The depth 
of the humus covering is as much as 7—9 cm., that is to say, nearly twice 
as much as in the Jönåker woods (see fig 4). Beneath this raw humus 
covering we come to a layer of bleached soil, having a very distinctive cha- 
racter of its own and with a depth of as much as 10 cm., more or less. 
The samples here figured may be regarded as very representative of the 
thoroughly cleared spruce forests of upper Norrland (see fig. 10). 
As in our mossy coniferous forests, with favourable conditions of ground, 
there are also lacking nitrification organisms in the more distinctly marked 
raw humus covering. Samples of soil do not produce any formation of salt- 
petre in a suitable solution of sulphate of ammonia; and only very small 
quantities of saltpetre are formed on storing (cf. HESSELMAN, 1917) Nor do 
the samples of earth denitrify GILTAY'S solution, and the capacity of produc- 
ing ammonia in a pepton solution is weak. 
The change of vegetation which occurs on cutting in these forests is far less 
radical than in the types described in the preceding chapter. Even in dense 
woods, or in woods which through select cutting of the timber are only half 
dense, the Azra flexuosa plays a very important part, which, however, is not 
very obvious so long as the plant does not blossom. On a complete clear- 
ing, however, it becomes much more frequent, and, moreover, by passing into 
the blossoming stage it becomes very much more obvious to the eye. A com- 
plete clearing in these old spruce forests often resembles a grass-field, grass- 
stalks sometimes stand as close together as on ploughland, and the brown- 
ish violet stems and flowers give to the ground a distinctive shimmer of 
violet. Simultaneously with this change in vegetation the hummus covering 
is more or less transformed. It is woven together by the numerous fine roots 
of Arira flexuosa, the mouldering is oiten very much accelerated, the layer 
of humus diminishes and gets a more mould-like structure, and occasional 
worms are encountered in the ground. But they do not bring about any con- 
siderable mixture with the underlying bleached soil, and it is only in the very 
uppermost part of it that that layer becomes mixed with humus (compare, 
OO; CDG IE). 
The raw humus covering thus undergoes certain changes through complete 
cutting. These changes also show themselves in the more powerful activity 
of the micro-organisins; the capacity to produce ammonia in the clearing is 
much greater than in the woods—the difference is often very considerable 
(see Table I, Nos. 1—7). The bacteria of nitrification do not immigrate, 
however, and the samples of earth do not nitrify a solution of sulphate of 
ammonia. The soil forms only quite inconsiderable quantities of 
saltpetre on being stored, often not more than samples of the 
same kind from the neighbouring forest (see too Table 12, Nos 1—4). 
On the raw humus clearings that are characterized by a richly 
developed vegetation of Azra /flexuosa, the transformation of nit- 
fogen becomes more active, it 1isctrue, but no change tfakestplace 
in tite Tie ammonia formed in the process of momderimenms 
