THE FOOD OF PLANTS. 59 



since the protoplasm of the cells is of course rich in such bodies, 

 and only non-nitrogenous organic substances and ammonia have 

 been employed. 



While the higher plants can readily utilise Nitric acid for the 

 formation of proteids, the yeast cell is not in a position to make 

 use of it. If we replace the Ammonium tartrate of Pasteur's food 

 solution by Potassium nitrate, and add yeast cells to the fluid, the 

 fungus behaves exactly as it does in a solution to which no nitro- 

 genous substances at all have been added. On the other hand, by 

 experiments in which we replace the Ammonium tartrate of the 

 Pasteur's solution by peptone, we can ascertain that this last 

 body is a more favourable source of Nitrogen for the yeast plant 

 than ammonia. 



That not only yeast cells but also other organisms not possess- 

 ing chlorophyll can prepare proteids from sugar and ammonia can 

 readily be determined. Two small vessels, a and 6, are pro- 

 cured. Into a we pour 25 c.c. of Pasteur's solution, into 6 25 

 c.c. of a fluid of similar composition except that the Ammonium 

 tartrate is absent. We now place both vessels under a bell-glass, 

 and let them stand for about eight days. The fluid in a very 

 soon becomes turbid, owing to copious development of bacteria. 

 Other organisms also may appear (in my experiments, for example, 

 the red Saccharomyces glutinis). The fluid in b becomes only 

 slightly turbid since there is no source of Nitrogen. Feeble indi- 

 cations of the life of the germs which are present may appear, 

 since the fluid may perhaps absorb some ammonia from the air. 



1 See A. Mayer, Untersuchungen uber die alkoholische Gahrung> 1868, and 

 Lehrbuch der Gdhrungschemie, 1&74, p. 108. 



19. Can Seedlings Make Use of the Free Nitrogen of the 

 Atmosphere for the Formation of Proteids ? 



Plant cells can produce proteids from non -nitrogenous organic 

 material and nitrogenous inorganic compounds (Nitric acid and 

 ammonia). It is another question whether free atmospheric Nitro- 

 gen can be employed for the same purpose, and this question is 

 not only of theoretical but also of great practical interest. We 

 first of all make experiments which teach that seedlings under 

 particular conditions neither take up free Nitrogen nor experience 

 loss of Nitrogen in their development. 



