180 Direct Assimilation of Ammoniimi Salts by Plants 



compound produced, and that the nitrous acid is immediately reduced 

 to ammonia. An experiment we made with beans taken from a garden, 

 showed the presence of ammonia both in the root and in the nodules. 

 A few grams of fresh nodules, and about the same weight of the roots 

 from which they were taken, were extracted with 75 per cent, alcohol 

 and the extracts distilled under reduced pressure with magnesia. The 

 amounts of nitrogen as ammonia were as follows : — 



In Roots N. = 001G per cent. 



In Nodules N. = 0043 per cent. 



If it should be shown that nodules generally contain more ammonia 

 than the roots, and that ammonia is readily assimilated by leguminous 

 plants, the results would lend some support to Loew's suggestion. In 

 this connexion it may be mentioned that Frank (27) looked for nitrates 

 in the nodules of peas grown in soil and failed to find any, whilst the 

 roots showed a distinct nitrate reaction both above and below the point 

 at which the nodules were attached. In the case of plants grown in 

 sand free from nitrogen, no nitrates could be detected in any parts. 

 Frank also detected the presence of asparagine in lupin and pea nodules 

 as well as in the roots. Assuming the initial process in nitrogen fixation 

 to be the production of an ammonium salt, it is probable that some of 

 the ammonia would at once pass into the roots. It does not follow, 

 however, that all the nitrogen derived from the nodules is taken up in 

 the same form, and it seems equally possible that the asparagine found 

 in the roots may have been partly produced in the roots themselves and 

 partly obtained from the nodules. 



Before describing the experiments on assimilation of ammonium 

 salts it will be desirable, as the prevailing ideas on the subject are 

 anything but clear, to show in some detail what has been already 

 done. As, however, the number of papers on the subject is consider- 

 able, attention will be confined chiefly to the more recent experiments 

 in which nitrification has been taken into accounts 



The first experiments in which precautions were taken to avoid the 

 possibility of nitrification were made by Pitsch (21) at Wageningen. In 

 these experiments, which were commenced in 1885 and continued every 

 year until 1894, various plants were grown in humus sand contained in 

 metal pots, holding about 30 kilos. The general method employed was 

 first to sterilise the contents of the pots, covered with cotton wool, by 



1 The earlier exijcrimeuts are summarised iu S. W. Johusou's IIow Crops Feed, New 

 York, and references are given at the end of this paper. 



