CH. Ill] NITRATE REACTION. 67 



phyll that he has shown to exist for the oxalate formation. 

 The presence of nitrates is to be tested by the diphenyl- 

 amin-sulphate test 1 ; a not too thin section of a leaf or 

 leaf-stalk is placed on a glass-slide and a drop of diphenyl- 

 amin sulphate added; if nitrate is present a deep blue 

 colour appears. Schimper recommends the leaves of the 

 elder, Sambucus nigra, adding that the large leaves de- 

 veloped on the long spring shoots should be avoided, and 

 that leaves developed in shade on short twigs should be 

 employed. The cut leaves having been tested and found 

 to contain nitrate are placed with their stalks in water 

 and exposed to light. He describes an experiment in which 

 the leaves lost the greater part of the nitrate in four 

 or five days under these circumstances 2 . When a varie- 

 gated elder is used for the experiment, the diminution of 

 nitrate takes place in the green, not in the chlorotic 

 parts. The importance of light was also shown in the 

 case of Taraxacum dens leonis, Aristolochia sipho and some 

 other plants by observing that after some weeks of sunny 

 weather the sun-leaves gave no nitrate reaction while the 

 shade-leaves showed a moderate or even strong reaction. 

 We find that plants of Pelargonium zonale, grown in pots, 

 give good results in a few days, in summer. One set 

 should be exposed to bright light, the other set kept in 

 deep shade. 



1 Molisch, Deutsch. Bot. Gesellsch. 1883. For the precautions 

 necessary in drawing conclusions from observations based on this test 

 see Zimmerman, Botanische Mikrotechnik, 1892, p. 49. 



2 According to our experience the lamina, not the leaf-stalk, of 

 Sambucus should be tested. 



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