192 Direct Assiitillatlon of Ammonium Salts by Plants 



centages of nitrogen in the mixed herbage from the Rothamsted grass 

 plots, which receive their nitrogen in the form of ammonium salts and 

 as nitrates respectively (see Table IV, p. 191). 



Whilst it cannot be assumed that the whole of the nitrogen of the 

 ammonia plots is taken up in the form of ammonia, the results as set 

 out in the above table increase the probability that much, at any rate, 

 of the nitrogen of the crop of plots 5, 9 and 11 is assimilated in its 

 original form. 



An explanation of the high nitrogen percentages seems to be afforded 

 by Suzuki's results {loc. cit.), which showed that ammonium salts are 

 rapidly converted by the plants into asparagine, and so give rise to 

 conditions favourable to renewed absorption, whilst nitrates tend to 

 accumulate and thus check further diffusion from outside. It would 

 seem possible that the highly nitrogenous character of leguminous 

 plants may have been acquired as a result of long continued nutrition 

 with nitrogen, supplied from the root-nodules in a form which lends 

 itself to more rapid production of proteids than is possible when 

 practically the whole of the nitrogen is taken up as nitrates, as is the 

 case with non-leguminous crops. 



Conclusions. 



Agricultural plants of various kinds can produce normal growth 

 when supplied with nitrogen in the form of ammonium salts under 

 conditions which exclude the possibility of nitrification. Some plants 

 grow equally well with ammonium salts or nitrate as source of nitrogen. 

 Other plants, while assimilating ammoniacal nitrogen in the absence of 

 nitrates, appear to prefer nitrates. It is less certain whether ammonium 

 salts can ever produce better final results than nitrates although we 

 have indications that this may be the case. 



Lehmann (17) found that whilst buckwheat failed to grow well with 

 ammonium salts, maize did far better with this form of nitrogen than 

 with nitrates during the first period of growth. Later on the nitrate 

 plants recovered, and the ammonia plants became unhealthy, "ein 

 Bild des Jammers." Kellner (19) showed that paddy rice also prefers 

 ammonium salts to nitrates to commence with, and that nitrates are 

 better than ammonium salts for the later growth. The best results 

 of all were obtained when both forms of nitrogen were employed 

 together. 



