66 CALCIUM OXALATE. [CH. Ill 



(78) Calcium oxalate formation. 



The leaves of ^sculus hippocastanum, of Acei^ negundo, 

 Ulmus campestris, and Humulus lupulus are according to 

 Schimper^ useful to demonstrate the fact that calcium 

 oxalate accumulates in leaves with age. Young and old 

 leaves of some of these species, having been rendered 

 transparent by chloral hydrate, should be compared under 

 the microscope. The method described in Chapter v. of 

 detecting small amounts of calcium oxalate with the 

 polariscope may be used, but will probably not be needed. 

 The formation of the oxalate is connected with illu- 

 mination: in jEscuIus, as Schimper states, this is 

 especially noticeable, leaves which have grown in full 

 sunshine having far more crystals than 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 instructive. In the white leaflets 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 nitric acid is assimilated. The disajDpear- 

 ance of nitrate out of leaves shows therefore the same 

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



i Botan. Zeitmirj, 1888, p. 83. 



