ON THE CHEMICAL CONSTITUENTS OF SOILS. 



221 



tacks the stem and leaves, and is quite different from 

 the brand {uredo ghimarum) which appears on the 

 seeds and organs of reproduction. Rust is most fre- 

 quently detected on plants growing on soils which 

 contain bog-ore, or turf iron-ore. According to 

 Sprengel, rust contains phosphate of iron, to which 

 this chemist ascribes the origin of the disease. It 

 is very possible that other causes may operate in the 

 production of similar diseases. 



8. Soil, a fine-grained loamy marl, from the vicin- 

 ity of Schoningen. It produces corn, w^hich is, how- 

 ever, very liable to blight. 100 parts contain : — 



100-000 



It will be observed that a considerable quantity of 

 phosphate of iron is contained in this soil, and the 

 corn which grows upon it is, as in the former case, 

 disposed to rust. 



9. Surface-soil (A) a loamy soil, from Brunswick, 

 remarkable on account of producing buck-wheat, 

 which is exceedingly poor in the grain. (B) analy- 

 sis of the subsoil at a depth of IJ foot. 100 parts 

 contain : — 



Silica, with coarse siliceous sand 



Alumina .... 



Protoxide and peroxide of iron . 



Protoxide and peroxide of manganese 



Lime, in combination with silica 



Magnesia, idem 



Potash, with silica . 



Soda ..... 



Phosphate of iron 



Sulphuric acid with lime 



19* 



