APPENDIX. Xlll 



humus covering and the mineral soil produces a 

 formation of nitrates, even when the wood is so dense 

 that nitrification does not otherwise occur. 



(3) MouMering brushwood and old rotting timber require or 



produce nitrification in the ground, even under 

 circumstances in which the formation of nitrates does 

 not occur on the clearings. 



(4) Where the covering of raw humus is somewhat more 



developed, chequerboard cutting, shelterwood cutting 

 or clear cutting does not by itself produce a formation 

 of nitrates. The formation of ammonia, however, is 

 substantially increased. But the formation of nitrates 

 can be produced either by a preparation of the ground 

 with machines or by the burning of brushwood. 

 His conclusions are summarised as follows : 



" If we go through our experience of the factors that favour 

 regeneration, we find throughout that in a very not- 

 able manner they coincide with the nitrification of the 

 humus nitrogen. Where the nitrogen of the humus 

 covering is transformed into nitric acid the regenera- 

 tion proceeds easily and the young pine and spruce 

 plants develop, well provided they do not have to 

 compete with an uncommonly luxuriant grass and 

 herb vegetation. Where the nitrogen of the humus 

 covering is not nitrified, natural regeneration is ren- 

 dered difficult and the spruce and pine plants grow 

 slowly. " 



Hole has shown that proper soil aeration is absolutely essen- 

 tial for the full development of sal seedlings and by soil aeration 

 he implies an adequate supply of oxygen in the soil. The researches 

 of the Agricultural Experimental Station of Cornel University 

 have shown that vigorous nitrification takes place in sealed flasks 

 as long as there is supply of oxygen and that there is an optimum 



