PLATE LXXXVIlt 



Fig. i. Comparative growth of wheat in sand and in dolomite. The dolomite con- 

 tained 96 per cent of carbonates of calcium and magnesium and 4 per cent of insoluble 

 silica residues. 



Fig. 2. Comparative growth of wheat in magnesium chlorid and magnesium 

 sulphate. 



