REGENERATION MEASURES AND THE FORMATION OF SALTPETRE CV 
On the other hand, it is easy to find examples of the cessation of nitri- 
fication power a comparatively short time after the burning. In the autumn 
of 1915 some samples of soil were taken from a severely burnt part of the 
1911 burn near Selsjön under a thick carpet of Polytrichum juniperinum. On 
storing the samples formed only quite inconsiderable quantities of saltpetre, 
the content of saltpetre nitrogen not being more than 1.6 mg. per kg. of soil 
after two months” storage. If these experiences be compared with the fact 
that samples of soil from the more severely burnt portions of the Krokmyrs- 
hygget nine summers after the burning formed still smaller portions of salt- 
petre nitrogen, it is evident that the effect of the burning with regard to the 
transformation of nitrogen is sometimes very transitory. 
All the denshired or burnt grounds that are here mentioned belong to 
the type which on clean cutting without burning is overspread with Azra 
/flexuosa. "The increased access of light caused by the felling cannot by 
itself produce such changes that nitrification appears in the ground. But fire 
does bring this about. The importance of forest fires and burning with 
negard to the transtonrmationN ofnitrogen thus consists in thel fact 
that on areas covered with tough raw humus they can bring about 
such alterations that the organically bound nitrogen can be trans- 
formed into nitric acid. On the areas with a more favourable, but not 
nitrifying, humus-covering the changes requisite for this are produced solely 
by the increased access of light that follows felling. 
CHaP, IX. Charcoal-burning grounds and tar=hollows. 
(Detailed description on page 1050.) 
From old times it has been customary to use earth from old charcoal-burn- 
ing grounds as filling soil in planting holes or in the laying out of nurseries. 
In North America, too, the same method has been employed with success, 
and even pure charcoal has proved to give a good result (RETAN, 1915). The 
flora which occurs on charcoal-burning grounds has a composition which is 
highly illustrative of the supply of nitrogen in the ground. We find there, 
for instance, quite commonly Fpilobium angustifolium and also a number of 
tilth-weeds and plants from our hay-fields. Some very characteristic examples 
of the flora of charcoal-grounds are given on pages 1050-—- 1052. If one examines 
the charcoal-ground flora with regard to the nitrate-content of the plants, we 
usually find that that is very considerable, not only in such a plant as Kpi- 
lobium angustifolium, but also in many others such as Matricaria inodora, Phle- 
um pratense, Poa trivialis, Taraxacum officinale, Achillea millefolum, etc., and 
even in the semi-parasitic MKhinanthus minor. To judge by the high nitrate- 
content of the plants, the nitrification in the soil must be very active. Bac- 
teriological examinations show, too, that the bacterial life is very rich. Soil 
samples nitrify a solution of sulphate of ammonia and denitrify GILTAY'S 
solution with a development of gas-bubbles (see table 7). The power to pro- 
duce ammonia has in the cases examined proved about as great as in soil 
from burns. 
There is thus no doubt whatever that a very active formation of saltpetre 
