482 
IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
The graph (figure 97) shows the comparative merits of ferric 
phosphate for the Canada field pea. All the cultures of the 
series, except No. 4, give an increase in yield on the addition 
of iron. Where 0.0050 grams of ferric phosphate are added to 
a liter of the solution the total dry weight amounts to 7.2132 
grams. Whether or not this is the upper limit of ferric phos- 
phate cannot be stated at this time. 
In the series (figure 98) where ferrous phosphate is used, the 
behavior is somewhat different. Here No. 4 gives the highest 
yield, producing 7.1146 grams. Number 5 in the ferric phos- 
phate has the same amount of iron, but the total yield is only 
6.2774 grams. In comparing the two series further it is noted 
that there is not a great deal of difference between the total 
yield (7.1146 grams) of No. 4 of this series and the total yield 
(7.2132 grams) of No. 6 in the ferric phosphate series. 
The results obtained in this study show that the amount of 
iron is probably of more importance than is generally supposed. 
The yield of the two kinds of plants, varying widely in mor- 
phological character, and growing in water cultures, is depen- 
dent- upon iron. Ferrous phosphate is less efficient than the 
ferric form, yet in the case of the Canada field pea, the varia- 
tions are not nearly as well marked as for wheat. Iron in 
the form of ferric phosphate to an amount equal to 0.0044 grams 
to a liter of the solution (as used by Shive) gives the greatest 
yield for wheat. The series with wheat show that this plant 
is more suitable for experiments of this kind. 
Iowa State College. 
