CH. Ill] CALCIUM OXALATE. 59 



of calcium oxalate with the polariscope may be used, but 

 will probably not be needed. The appearance of the 

 oxalate is connected with illumination: Schimper states 

 that in the Horse Chestnut this is especially noticeable, 

 leaves which have grown in full sunshine having far 

 more crystals than older leaves developed in the shade. 

 The formation is also connected with the presence of 

 chlorophyll. The comparison of a pure green and a 

 white leaflet of a leaf of Acer negundo is, as Schimper 

 states, especially instnictive. In the white leaflet only a 

 small amount of minute crystals occur. The variegated 

 Pelargonium may also be used. 



(79) Nitrate reaction. 



Schimper has shown that the appearance of calcium 

 oxalate is connected with the decomposition of calcium 

 nitrate in the leaf. The calcium being deposited as an 

 oxalate while the nitrate is assimilated. The disappear- 

 ance of nitrate out of leaves shows therefore the same 

 relation to light and to the presence or absence of chloro- 

 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^; 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, Samhucus nigra, adding that the large leaves de- 

 veloped on the long spring shoots should be avoided, and 



' MoUseh, Deutsch. Bot. Gesellsch. 1883. For the precautions 

 uecessaiy in drawing conclusions from observations based on this test 

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



