eXVI HENRIK HESSELMAN. 
the pine-plants and thus contribute to the favourable result. A further illustra- 
tion of the nitrogen problem of the young coniferous plants can be obtained 
from the nurseries. It is advantageous to manure with saltpetre, although in 
small quantities, but it is more customary to use peat, mud, compost, and the 
like, which are well worked into the nursery soil. Such treatment, as appears 
from my investigations, is very greatly calculated to produce an active nitrifi- 
cation in the ground. I have not yet devoted to nursery soil any exhaustive 
investigations; but one observation seems to me worth citing. In a nursery 
recently laid out in Sösjö Crown Park, which had only been manured with 
ashes from the fire-place in a forest hut and with the raw humus which 
existed in the place before the equipment of the nursery, there grew young 
plants of raspberry, Poa sp, Rumex acetosella. These, like some young plants 
of Eschscholtzia californica, which the ranger sowed in the nursery, all gave a 
strong nitrate reaction. As this nursery, which had not been treated in any 
special way, but was arranged on a very simple plan, showed such an active 
formation of saltpetre, it is highly probable that the nitrogen in our nur- 
series is conveyed, as a rule, to our young tree-plants in the form of 
nitrate. 
As I have previously had an occasion to point out (HESSELMAN, 1917, Page 
385), there is a considerable plant-physiological difference between a saltpetre 
manure, when a large quantity of: nitrate is put into the soil, and the more 
slowly flowing but more constant supply of saltpetre that takes place on nitri- 
fying humus soil. The saltpetre can never attain any great degree of con- 
centration, and the soil can retain its acid reaction despite the fact that it 
is the very nature of saltpetre to be, from a physiological point of view, a 
basic salt. 
Though, therefore, everything indicates that the pine is extremely grateful 
for the rather scanty supply of nitrate which takes place in nitrifying humus, 
yet I have not been able to trace the existence of nitrate in young and 
strong pine-plants growing on nitrifying peat. This negative result, however, 
is of less significance in our conception of the nitrogen problem of pine- 
plants: many plants that clearly prefer soil rich in saltpetre do not collect 
nitrate in their tissues, but use it as it is absorbed. As example of this I 
have previously mentioned Polygonum lapathifolium (FIESSELMAN, 1917). Other 
examples can be found in SCHIMPER (1890): in young tree-plants especially 
he found no saltpetre or quite inconsiderable amounts, although the plants 
occurred on a compost soil very rich in nitrates. 
So far I have chiefly spoken of the pine, but the same certainly holds 
good, in the main, for the spruce. But the spruce, as it grows older, seems 
to be more grateful for a supply of saltpetre. Our most productive spruce- 
forests—the herbulent ones—occur on ground with nitrification, although one 
also can find on ground without nitrification highly productive stands of spruce. 
From the ling-heaths of Denmark (Weis, 1908; P. E. MÖLLER and HELMS, 
1913) we have certain experience of the importance of nitrification for the 
development of the spruce. The spruces that grow most strongly are found 
on the experimental plots where the humus nitrogen is nitrified. 
Nevertheless one must firmly insist that the nitrification ofthe humus 
nitrogen is no indispensable sine gua non for the regeneration of 
coniferous forest: it is only a favourable factor. Otherwise we should 
