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EXPLANATION OF PLATE IV 
Fig. a. Relative growth in solutions "A" and "H" when FeP04 was supplied as a 
source of iron. Numbers i, 2, and 3 are in solution "A," with 3.5, 14, and 35 mg. FeP04 
per 1., respectively. Number 4 is solution "H " with 7 mg. FeP04 per 1. 
Fig. B. Effect of 0.0004 ^ acids and their aluminum salts in solution "H." 
Fig. C. Effect of 0.0004 ^ acids and their ferric salts upon root development in 
solution "H." 
