IV. THE REACTIONS OCCURRING IN SOILS 69 



Department of Agriculture fail to show any great advantage attend- 

 ing the use of either the new German or the American preparation. 



In South Africa, many parcels of lucerne, peas, beans, etc., have 

 been inoculated in the Government laboratories, but, with few excep- 

 tions, very little advantage has been attained. The writer has seen 

 many instances of leguminous plants grown without any inoculation 

 well provided with root nodules, though where inoculated seed has 

 been used the nodules certainly appear to be more abundant. 



On the whole, the value of these preparations was not clearly 

 marked, so that they, like their forerunner, fell into comparative 

 obscurity. 



More recently (1907) the subject was again brought into promin- 

 ence by Bottomley, and for a time excited considerable popular atten- 

 tion, especially as it was hinted that it might be possible to cause 

 nitrogen fixation in the roots of cereals and crops other than legumin- 

 os(&, by the use of the so-called " Nitro-bacterine ". 



Nevertheless, Hellriegel's discovery is very important and affords a 

 satisfactory explanation of many hitherto puzzling facts in reference 

 to the nitrogen question. Some investigators have obtained results 

 which show that plants other than the leguminous ones assimilate 

 free nitrogen, but to a much less extent. 1 With the exception of 

 lupines, the author just- quoted found that all the plants he tried were 

 developed best when combined nitrogen was also supplied. In many 

 cases the amount of free nitrogen assimilated was increased if 

 combined nitrogen was also supplied. 



Other experimenters, e.g., Lotsy,' 2 do not confirm the fixation of 

 free nitrogen except in the case of leguminous crops. 



According to later investigations the bacteria in the nodules of 

 leguminous plants secrete an enzyme (i.e., a so-called unorganised or 

 soluble ferment) and the assimilation of the atmospheric nitrogen 

 really occurs in the leaves of the plant under the influence of the 

 enzyme. 3 That the fixation takes place in the leaves is denied by 

 Nobbe and Hiltner, 4 who found that if the nodules on the roots were 

 kept under water, fixation of nitrogen ceased. 



The symbiosis of certain moulds with the roots of heaths and 

 some forest trees the production of the mycorrhiza in which the 

 fungus prepares and hands on certain items of plant food to the host 

 plant, is a process of a somewhat similar kind, but has not so much 

 importance from an agricultural point of view. 



Denitrification. A chemical change involving the liberation of 

 free nitrogen from nitrates takes place under certain circumstances in 

 soils and in manure heaps. This process is effected by the agency of 

 micro-organisms, several species of which appear to exist. The loss 

 of nitrogen consequent upon this reaction is of serious importance and 

 the subject has, of late, attracted considerable attention in France and 

 Germany, as well as in England. 



1 Frank, Jour. Chem. Soc., 1892, Abstracts, 370. 



2 U.S. Dept. of Agric., Bull. 18, 1894. 



^Stoklasa, Jour. Chem. Soc., 1900, Abstracts, ii. 610. 

 4 Jour. Chem. Soc., 1900, Abstracts, ii. 234. 



