THE FOOD OF PLANTS. 75 



But to prove directly that nitrates can actually be worked up, 

 we make the following experiment. Two pot plants of Pelar- 

 gonium zonale are placed in the dark. The quantity of nitrates 

 in the leaves of normally vegetating plants is generally very 

 slight or nil. If after four to six days we examine the leaves of 

 the darkened plants, it is found that they have become very rich 

 in nitrates. If we now place the plants at the window, so that 

 they are brightly illuminated, the nitrates disappear again from 

 the leaves in the course of eight to fourteen days. If stems of 

 Pelargonium zonale, or Fuchsia globosa, whose leaves are highly 

 variegated, are treated as just described, we find that the nitrates 

 do not disappear on illumination from the almost chlorophyll-free 

 leaves. 



Thus it follows, that the consumption of nitrates stands in 

 relation to the chlorophyll of the leaves and to light. According 

 to recent investigations, the working up of the Nitric acid and 

 formation of proteid can proceed in the organisms of the higher 

 plants only in the green cells, and under the influence of light. 



According to Schimper (see also Flora, 1890, pp. 251 and 260), 

 the working up of the nitrates, and of the sugar formed in assimi- 

 lation into amides, and finally into proteid, organic acids (Oxalic 

 acid) * perhaps being produced as bye-products, must be con- 

 sidered as quite directly dependent on light and chlorophyll 

 activity. Proteid formation in chlorophyll-free cells, such as does 

 actually take place in fungi is, according to him, excluded in the 

 higher plants. In my opinion this view is not conclusively 

 established. At the same time, the experiments by which many 

 people seek to prove the formation of proteid in the higher plants, 

 in cells which are not green, are inadequate. f The whole question 

 needs further and very searching treatment, and it is possible that 

 the light and the chlorophyll bodies are only indirectly of signifi- 

 cance for proteid formation. The formation of the secondary 

 oxalate also, might only indirectly be related to conditions of 

 illumination. 



1 See H. de Vries, Landtcirthsch. Jahrbiicher, Bd. 6, p. 900, and plate 44, 

 Fig. 3. 



* See Schimper, Botan. Zeitung, 1888. 



3 For illustrations of the Calcium oxalate crystals, see Zimmermann, Botan. 

 M'H-rotechnik, 1892, p. 56. (Trans. Humphrey.) 



* This Oxalic acid may then give rise to secondary Calcium oxalate. 



f Frank (Lehrbuch d. Botanik, 1892, pp. 568 and 570) holds the view that 

 perhaps proteid formation is possible in the higher plants in all the cells. 



