184 Direct Assimilation of Ammonium Salts by Plants 



The last experiments to be described are those of Ehrenberg (39), 

 who grew oats in sterilised soil, and in sterilised sand, employing seeds 

 sterilised with mercuric chloride. Nitrogen was added in the forms of 

 ammonium sulphate and sodium nitrate in sterilised solutions after the 

 sand and soil had been sterilised. Calcium carbonate was present. The 

 results of both series were negative as regards ammonium salts, the 

 plants failing to grow, and the conclusion is drawn that nitrification is 

 essential to the growth of higher plants, at any rate in the case of soils 

 of slight absorptive power. When, however, the amounts of ammoniimi 

 salts employed are considered in relation to the amount of water present, 

 it will be seen that the injurious effects were probably due to too great 

 concentration. The sand (5 kilos, per pot) contained 10 per cent, of 

 water, or 500 c.c, and the amount of ammonium sulphate present was 

 1"4 gram or 2*8 grams per litre. In the soil (3"8 kilos.) the amount of 

 water was 20 per cent., or 760 c.c, and this contained I'S gram of 

 ammonium sulphate per litre. It has been shown by Maze {loc. cit), 

 that even 1 per thousand of ammonium sulphate is very injurious\ 

 whilst in the experiment just described the amounts were nearly twice, 

 or nearly three times, as high supposing the salt to be equally dis- 

 tributed (which was probably not the case), and a good deal higher, 

 locally, if not evenly distributed. It is stated that on turning out the 

 pots a distinct odour of ammonia was noticed. 



The results of all the experiments described above may be sum- 

 marised as follows. The results of Griffiths and Maze seem to prove 

 conclusively that beans and maize assimilate ammonium salts as readily 

 as nitrates. The same may be said of Kossowitsch's experiments with 

 peas, for although sterilisation was imperfectly maintained, nitrifying 

 organisms were completely excluded. Br^al's results may also be con- 

 sidered to establish the utilisation of ammonia (by Poa annua). The 

 results obtained by Pitsch, Mlintz, Gerlach and Vogel, and Kriiger 

 indicate that the various plants employed are able to grow in absence 

 of nitrate — not with absolute certainty as regards Mlintz's experi- 

 ments — but fail to prove that ammonia was the sole source of nitrogen. 



Experimental. 



Seed Sterilisation. In order to obtain vigorous seedlings free from 

 nitrifying and other organisms, whose presence would vitiate the results, 

 some preliminary experiments on seed sterilisation were made. The 



1 See also Conpin, liev. Gen. Bot. 1900, 12, 177, and Suzuki, Bidl. Coll. Agric. Tokyo, 

 1894—7, 2, 2G5. 



