The efficiency of the usual trace of iron when employed in culture solutions may be expected to vary with the nature of the compound in which it is supplied, with the composition and reaction of the solution in which it is employed, and with the species of plant. Gile and Carrero have shown that the reaction of the nutrient solution (whether acid, neutral, or alkaline) (6), as well as soil conditions (7), have a marked influence upon the availability of iron to the rice plant. Corsan and Bakke (4) count ferrous iron less efficient than ferric iron, when used in the forms of phosphates. Jones and Shive (9) have pointed out that, in the nutrient solution which they employed, iron in the form of ferrous sulphate was very readily available to the wheat plant, but was evidently somewhat toxic in the highest concentrations used. Ferric phosphate, on the contrary, was very slowly and difficultly available to these plants, even when supplied in relatively large quantities. In later work (10) they found that ferrous sulphate was superior to ferric phosphate as a source of iron for plants grown in a nutrient solution containing calcium nitrate. When ammonium sulphate was employed as the source of nitrogen, however, the solution increased in acidity and ferric phosphate supported growth of the plants better than did ferrous sulphate. Hoagland (8) has suggested that the presence of sufficient dissolved iron in the culture solution will depend upon the form and quantity of the iron salt used, and considers iron citrate and tartrate the most effective forms. Duggar (5) has recommended a special form of "soluble" iron prepared from ferric citrate and sodium phosphate. EXPERIMENTATION SolubilityIn the present investigation an attempt was made to determine which of the following salts of iron, namely: ferric citrate, FeP0 4, Fe2(S04)a, and FeS04' would remain in solution in the greatest amounts at the two hydrogen-ion concentrations of pH 4.2 and pH 6.0, using the Livingston-Tottingham nutrient solution; and also to determine which of these forms of iron would be most available to the wheat plant when supplied in varying amounts, at the latter pH value of the nutrient solution.

The following brief notes relate to collaborative work of the writers upon a project outlined by a special committee of the National Research Council (17). Publication in the present rather fragmentary condition is ventured in the hope that our observations may be of aid to others operating in the same field. Acknowledgment is hereby made of a grant from the research funds of the University of Wisconsin in support of this investigation.Of the six possible three-salt combinations which can supply the six essential elements of a nutrient solution, exclusive of iron, as arranged in the plan for collaborators, Type VI was chosen for the present investigation. This type is composed of KH2P04, CaS04' and Mg(NOah. Cultures of wheat were conducted in duplicate in the series of solutions of this type, following the prescribed plan. The results appear to justify no further statement here than that the agreement between duplicate cultures was' generally very poor. It seemed probable that this condition was due in part to the very poor root development of the seedlings employed. The roots were short, and usually curved and discolored where they came in contact with the nutrient solution.Shive's nutrient solution RsC2 (IS) diluted to 0.1 the usual concentration is the medium prescribed for germination in this work. The pH of this nutrient solution, at the concentration commonly employed, is approximately 4.7 (16). It.appeared possible that the poor root growth observed here was due partly to the acidity of this solution. With this possibility in mind, the following tests were undertaken. The seed used throughout was wheat of the Marquis variety, provided for collaborators by the committee in charge of the project. In tests other than the comparison of continuous with intermittent renewal of the solution, ferric citrate was used instead of ferric phosphate, as a source of iron.