208 
AMERICAN JOURNAL OF BOTANY 
[Vol. io. 
Table 3 . Data of Growth of Wheal in Solution R%Ci, with various Planes of Added Iron 
Source of Iron 
Length 
of Tops 
in mm. 
Length 
of Roots 
in mm. 
Weight of 
dry Tops 
in mg. 
Weight of 
dry Roots 
in mg. 
Comments 
Ferric citrate, 50 
mg. Fe per 1 . 
223 ± 6* 
9 2 ± 25 
517 ± 43 
280 zb 57 
Tops dark green, roots 
yellowish and thick. 
Tops dark green, roots 
Ferric citrate, 10 
mg. Fe per 1 . 
221 ± 31 
121 zb 13 
433± 85 
206 zb 21 
Ferric citrate 2 
mg. Fe per 1 . 
209 zb 13 
206 zb 25 
3 21 ± 50 
157 zb 26 
white. 
Tops dark green, older 
Fe 2 (S 0 4 ) 3 , 50 mg. 
Fe per 1 . 
133 ± 13 
25 zb IO 
168 zb 32 
123 zb 56 
leaves dead, roots 
white. 
Tops yellowish green 
Fe 2 (S 0 4 ) 3 , 10 mg. 
Fe per 1 . 
171 db 13 
3 1 ± 6 
229 zb 70 
153 ± 28 
between fibro-vascular 
bundles, many older 
leaves dead, roots thick 
and blackened. 
Tops light green, roots 
Fe 2 (S 0 4 ) 3 , 2 mg. 
Fe per 1 . 
161 zb 13 
167 =b 13 
3 2 8 db 63 
162 zb 28 
yellowish. 
Tops dark green but pal¬ 
FeS 0 4 , 10 mg. 
Fe per 1 . 
184 zb 12 
90 zb 6 
2 50 db 31 
125 ± 5 
er than those of citrate- 
iron cultures, roots 
white, numerous later¬ 
als evident. 
Tops pale green, roots 
FeP 0 4 , 10 mg. 
Fe per 1 . 
195 zb 12 
183 =b 13 
315 ± 70 
144 zb 23 
white, numerous lat¬ 
erals evident. 
Tops dark green, older 
leaves dead, roots white. 
* Average departure from the mean of six cultures. 
Discussion 
The results of the solubility test here reported show decided differences 
between the various forms of iron employed. It was found that FeP04, 
a form commonly employed in nutrient solutions, was relatively insoluble 
at both pH values tested. FeS 0 4 , while the most soluble of the forms com¬ 
pared at the higher hydrogen-ion concentration, was relatively insoluble 
at the lower one. This result at the lower hydrogen-ion concentration 
would seem to indicate hydrolysis with the formation of insoluble Fe(OH)3 
or basic ferric salt. McCall and Haag (12) have called attention to this 
factor in the availability of iron in nutrient solutions. While Fe2(S0 4 )3 com¬ 
pares favorably with ferric citrate in solubility, it increased the hydrogen- 
ion concentration of the nutrient solution to what seems to have been an 
unfavorable extent. It was also slightly depressed in solubility in the less 
acid solution. Ferric citrate appears to possess a fair degree of solubility 
over a considerable range of pH value of the nutrient solution. With the 
