CII HENRIK HESSELMAN. 
<burnberry” (Rubus idaeus), both markedly nitratophilous plants (see, too, 
fig. 16). 
It is not without interest to remind the reader that the burn flora of North 
America is characterized by raspberry and still more by Epilobium angusti- 
folium (COOPER, 1913; RÖBEL, 1916, page 16)); the latter grows in masses 
over wide areas devastated by forest fire. Another burn plant is Rubus stri- 
gosus (CLEMENTS, 1910)—a species of raspberry very closely akin to our own. 
In Colorado this and Kpilobium characterize the grounds devastated by fire 
which before the fire were covered with forests of he lodgepole pine (Pinus 
contorta). 
The kind of flora found on burns thus shows that the fire either produces 
or else increases the process of nitrification going on in the ground. The 
process has been closely studied by me both on the great burns between Sel- 
sjön and Skorped stations on the northern trunk line in Ångermanland (see 
fig. 17), and also on a number of denshired clearings and older burns in 
Norrland. 
The Selsjön—Skorped burns came into existence in the early summers of 
1909 and 1911 in consequence of sparks from locomotives. I have examined 
them on several occasions during the summers and autumns of 1913, 1914 
and 1915. A detailed description will be found on page 1046, and numerous 
observations are rendered in tables 3, 6, 10, 14. The investigations have 
chiefly comprised: (1) Observations of the nitrate content of the plants; 
(2) Studies of the changes in the bacterial flora of the ground, (3) 
Determination of the capacity of the soil-samples to form salt- 
petre during storage. 
Before the fire there was within the region devastated by the fire a mOSSy 
mixed coniferous forest of the ordinary type, which, however, in those Parts 
where the ground contained a large amount of clay, was somewhat richer in 
herbs than perhaps can be regarded as usual. A pretty full description has 
been given in a treatise recently published by the present writer (HESSEL- 
MAN, 1917, page 470). In the parts of the wood still undisturbed by the 
fire the humus covering has the character of raw humus, but in some small 
patches the raw humus has a more mould-like structure. "There are no 
nitrification bacteria, and on being stored the samples of soil 
form . only very small quantities of saltpetre. There is no complete 
clearing in the stand, it is true, where we can study the effect that felling 
without burning may have on the ground; but both my experience from simi- 
lar woods in Norrland and observations on small unburnt patches of the burn 
show that the ground belongs to the type which on clean cutting is principally 
clothed with a carpet of Azra flexuosa. The nitratophilous flora which marks 
the burn, therefore, has the fire to thank for its appearance. 
The young plants of grass and herbs that are to be found on the burn 
yield a very powerful nitrate reaction, as a rule, and this is especially the case 
with pilobium. Even where the ground has been extremely badly burnt, so 
that the humus covering has practically disappeared and the ground lies 
bleached and naked, the presence of saltpetre can be demonstrated in £p:- 
lobium (see fig. 18). As examples of other nitrate-gathering plants on the 
burn may be mentioned KRubus 1daeus and RK. saxatilis, Luzula pilosa and 
Arenaria trinervia (see, too, the detailed description, page 1046). 
