74 Studies in Forestry [CHAP. iv. 



bated by Ville all along, and since 1888 it has been abundantly 

 proved by Hellriegel, B. Frank, Wilfarth, and others, that this 

 can and does take place indirectly, more particularly in the case 

 of Leguminosae (e.g. in the Acacia among our common trees). So 

 long, however, as a supply of nitrogenous food is available in 

 the soil, this capacity, for which the symbiotic aid of a Bacillus 

 (Bacillus Radicicola or Rhizobium leguminosarum} is requisite, is 

 not called into play *. The researches of these last-named scien- 

 tists during the last decade have shown that all leguminous 

 plants possess, by means of their root-nodules or tubercules, 

 which contain these bacteria, the power of withdrawing from the 

 air a sufficient supply of nitrogen for the requisite formation 

 of essential albuminoid substances when these are not other- 

 wise easily obtainable. According to Frank's researches also 2 , 

 the Alder is endowed with similar capacity to the Leguminosae 

 for the formation of nitrogenous and albuminoid substances ; 

 for the tubercules on its roots are found to contain an albu- 

 minoid protoplasma filled with the germs of a bacteroid fungus. 

 Through a symbiotic process quantities of albumen are pro- 

 duced within these root-nodules, which become gradually 

 absorbed into the tree and utilized for general requirements. 

 Alders therefore thus appear, like the Acacia, able to derive 

 supplies of nitrogen from the air, when requisite, through this 

 symbiotic aid. So far, however, as woodland crops are con- 

 cerned, though any abnormal increase in the ordinary supply 

 of nitrogen obtained from the soil might probably exert great 

 influence on the extent of seed-production and the frequency 

 of mast-years, it certainly would not stimulate the increment 

 in timber 3 . The precise manner in which woodland trees 

 obtain the supplies of nitrogen requisite for their development 

 has not yet been satisfactorily determined. But as woodland 

 soils contain at best very small amounts of nitric acid, and are 



1 Ramann, op. cit., p. 306. 



2 Report of the Deutsche Botanische Geselhchaft for 1891, p. 250. 



3 R. Hartig, op cit., p. 221. 



