THE FOOD OF PLANTS. 



important to prepare first of all absolutely pure distilled water, 

 and food stuffs which contain not a trace of organic material. 



1 See Eeichardt, Grundlagen zur BeurtliAlung des Trinkwassers, 1880, pp. 

 154, 143. 



2 See Molisch, Berichte d. Deutschen botan. Gesellschaft, 1 Jahrg., p. 150. 



3 See Berthelot and Andre, Annal. de chem. et de physique, Ser. 6, T. 8. 



4 See Schimper, Botan. Zeitung, 1888, p. 120. 



5 Literature on Nitrification: see especially Schlosing and Miintz, Compt. 

 rend., T. 84, 85, and 86; Winogradzki, Landwirthschaftl. Jahrbucher, Bd. 20, 

 p. 175 ; Godlewski, Anzeiger der Altad, d. Wiss. in Krakau, 1892. 



22. Nitric Acid as a Nutrient Substance. 



In the soil and in water occur nitrates which can be utilised as 

 food by the higher plants. That the nitrates can actually furnish 

 the Nitrogen needed for the production of proteids and the 

 normal development of the plants, can be demonstrated by the 

 water-culture method. Maize, oats, or buckwheat may be used 

 for the experiments (I used maize with very good results). The 

 experiments are carried out as described in 1. One or two plants 

 are grown in a food solution, a, having the composition given 

 in 1. Others are cultivated in a solution of similar com- 

 position, but containing, in place of Calcium nitrate, 1 gr. of 

 Calcium sulphate per litre, fo. The plants in a developed very 

 normally in my experiments ; those in &, on the other hand, 

 presented after a few weeks a very distressed appearance. (See 

 Fig. 22.) The lower leaves dried up, and the plants grew ex- 

 tremely slowly. They had at their disposal only the nitrogenous 

 reserve materials of the seed. They could at most take up only 

 small quantities Qf ammonia from the air, but these were not 

 nearly sufficient for vigorous development. 



23. Ammonia as Nutrient Material. 



To convince ourselves that the higher plants can utilise for the 

 formation of proteids, Ammonium salts absorbed by means of their 

 roots, we grow maize or other plants in a food solution having 

 exactly the same composition as that given in 1, but containing in 

 place of Ca (N0 3 ) 2 , 0*5 gr, of Ammonium phosphate, and 0'5 gr. 

 of Calcium sulphate. Great care must be taken that the reaction 

 of the solution does not change much during the experiments, but 



