394 



BOTANICAL GAZETTE 



[may 



me 



approximately the same relation to each other irrespective of the 

 nature of the filter used. It was intended to use types of soil ranging 

 progressively through the weathering products from feldspars to 

 kaolin. But the feldspars are highly alterable minerals, and the 

 chemical products of feldspathic and 



granitic rock-decomposition 



Fig. 



i. 



._ .. Diagram showing growth-rate of wheat seedlings in treated ^j*^ 

 The ordinates represent transpiration in grams; the abscissas show e p ° ^^ 

 addition of quartz to bog water. Unbroken lines for bog water collecte . ep ^^ 

 12, 1908. Broken lines for bog water of October 16, 1908. Broken line sing 

 for boiled bog water; broken line double dotted for distilled water. 



are extremely varied (4) . In the residues, however, which remai^ 

 after leaching, free silica as quartz, and a number of rather inc e^ 

 substances known as clays, are the most abundant. In e I ^ 

 case the efficiency of the following substances, characteristic ^ 

 final residue of soil-forming rocks, and their allied substan ^' c in 

 tested: Si0 2 coarse; SiO, fine; kaolin; CaC0 3 ; SiC; an u?h 

 the form of air-dried humus. The materials were obtame 



