REGENERATION MEASURES AND THE FORMATION OF SALTPETRE CXXI 
that the man in Sweden who has perhaps worked most zealously for the intro- 
duction and development of the practice of select cutting, namely UNO WALLMO 
(1897), had to do with forests where gap cutting produces the nitrification 
ofthe humus nitrogen (see fig. 41). I do not wish here to enter into a detailed 
discussion of select cutting from an economic standpoint: that would take me too 
far outside the subject of this treatise; but this method of forest management 
has one great merit, namely, that the productive power of the ground is pre- 
served, provided it is of such a nature that select cutting produces regrowth, 
which is usually the same thing as saying that select cutting produces a 
nitrification. On ground where this takes place, the regrowth in the gaps 
proceeds very rapidly. Even woodsmen who consider that the practice of select 
cutting is not very advantageous from an economic point of view acknowledge 
its power of promoting regeneration. (See ADOLF WELANDER, 1910.) 
A later development of select cutting practice is represented by the method 
of select cutting in strips (> Blendersaumschlag») elaborated by A. WAGNER (1912). 
Here, too, the result of the regeneration depends upon the nature of the 
ground. The description he gives of the conversion of the humus-covering 
on the clearing (1912, pages 56—58) points to the appearance of nitrifica- 
tion—a thing which is extremely probable when we consider the nature of 
these forests. In his photographs of very fine regrowths, too, we can see 
nitratophilous plants among the tree-plants (1912, page 89). Where the hu- 
mus-covering has a less favourable quality, some preparation of the soil is 
also undertaken in order to favour the regeneration (1912, pages 114, 115). 
In this connection, it is of great interest to find that, where the strip-cutting 
method has been more or less unconsciously adopted in Sweden but has given 
very fine regrowth results, namely at Lanfors under Alkvättern in Värmland, 
there such a method of cutting produces a nitrification in the humus-covering 
(see page 94). 
Questions as to the treatment of the ground assume quite a different shape 
when the humus-covering is more markedly of the raw humus type, so that the 
nitrification of the humus nitrogen encounters considerable difficulties. Here, 
too, one can find in the ground-flora some guidance in the transformation of 
the humus-covering. Where the mosses and berry shrubs, despite abundant 
access of light, do not fade away, or where the ground is covered with a thick 
carpet of Azra flexuosa, there, too, there is, as a rule, no formation of saltpetre. 
'The dry moss carpet on the surface and the tangled mat formed by Aira flexuosa 
form a germinating bed unsuitable for the seeds and throw great difficulties 
in the way of natural regeneration. Even the planted plants that are deve- 
loped on such a clearing grow distinctly worse than where the humus nitrogen 
is nitrified, unless they have to fight against a very powerful clearing vege- 
tation, in which case the opposite may occur. 
We may justly say that the question of regeneration which has been so 
keenly discussed amongst us of late years refers principally to areas of the 
last-named quality. Disputes have chiefly raged round the question as to 
how such areas are properly to be treated. All the investigations of which 
I have given some account above show the immense importance of the nitri- 
fication of the humus nitrogen. All the old methods of promoting regenera- 
tion, e. g. preparation of the soil, burning, breaking up the stumps, pro- 
duce a nitrification of the nitrogen of the humus-covering. The coniferous 
