Plate XII. Cowpeas grown in sand with all the essential mineral salts in No. 1, 

 compared with soil in No. 2. No. 3, S omitted; No. 4, Mg omitted; No. S, K omitted; 

 No. 6, Ca omitted; No. 7, distilled water; No. 8, tap water; No. 9, N omitted; No. 10, 

 P omitted. 



