THE REQUIREMENTS OF PLANTS 



found that asparagine was the most effective nutrient for the de- 

 tached embryo of barley, followed by other relatively simple sub- 

 stances like nitrates, glutamic and aspartic acids, ammonium sulphate, 

 etc., the more complex substances being less useful. The experimental 

 study of the nitrogen nutrition of adult plants is complicated by the diffi- 

 culty of growing plants under sterile conditions and thus obviating the 

 decompositions effected by bacteria ; much of the earlier work is vitiated 

 by this circumstance. Later work has satisfactorily shown that am- 

 monia is readily assimilated from solutions of ammonium sulphate, if 

 the concentration is not too high ; but even cri per cent, was found 

 injurious by Maz6 (196). Kriiger (157) concludes that ammonium 

 sulphate is less beneficial than sodium nitrate for mangolds, both 

 compounds are equally useful for oats, barley and mustard, while am- 

 monium sulphate is better for potatoes. Hutchinson and Miller (140^) 

 found that peas assimilate nitrates and ammonium salts equally well, 

 while wheat showed a decided preference for nitrates. 



None of these preferences has been correlated with any other pro- 

 perty of the plants, nor is it easy to explain the fact, on which all 

 experimenters agree, that plants fed on ammonium salts contain a 

 higher percentage of nitrogen than those fed on nitrates (Table VIII.) : 



TABLE VIII. PERCENTAGE OF NITROGEN IN DRY MATTER OF PLANTS. 



The fact indicates that each unit of nitrogen taken up as ammonia 

 is less effective in the growth process than a unit of nitrogen taken as 

 nitrate, and the plants in spite of their high nitrogen content are really 

 suffering from nitrogen starvation. 



Nitrites are also assimilated so long as the solution is not too con- 

 centrated or too acid. 1 



In spite of a considerable amount of work it is not known whether 

 other nitrogen compounds are assimilated by plants. That many other 

 compounds serve as nitrogen nutrients even without the intervention of 



Perciabosco and Rosso, Staz. Speriment. Agrar. ital., 1909, xlii., 5. 



