524 
Journal of Agricultural Research 
Vol. Vlf, No. 12 
could have elaborated scarcely any organic matter; the leaves were 
especially thin and often withered as soon as formed. It is possible that 
the high percentage of iron in the dry substance might have been due to 
the fact that enough iron was not present in the plant to start the pro¬ 
duction of carbohydrates, which would have lowered the percentage. 
While this explanation opens up several points not covered by the present 
investigation, it is supported somewhat by the following test (Table XV, 
first test), where plants grown for 13 days with iron and then for 13 days 
without iron contained a lower percentage of iron than plants grown the 
full 26 days without iron. 
Table XV .—Percentages of iron in rice plants grown with and without iron 
Test and treatment of plants. 
Average 
dry weight 
of stalks 
and leaves 
per plant. 
Percentage 
of iron 
(F2O3). in 
dry stalks 
and leaves. 
First test: 
Grown for 13 days, without the addition of iron to the solu¬ 
tion.. 
Grown for 26 days, without the addition of iron to the solu¬ 
tion. 
Grown for 13 days, without the addition of iron to the solu¬ 
tion and then for 13 days with iron. 
Grown for 26 days, with the addition of iron to the solution.. 
Second test: 
Grown 13 days, without the addition of iron to the solution.. 
Grown 26 days, without the addition of iron to the solution.. 
Grown 40 days, without the addition of iron to the solution.. 
Grown 40 days, with the addition of iron to the solution. 
Gm. 
0.017 
0. 020 
00 
H 
O 
. 026 
.097 
. 020 
* 3 11 
. 027 
. 016 
.015 
. 019 
. 024 
. 026 
.049 
547 
. 030 
In the first test plants grown 26 days without iron contained a higher 
percentage of iron than those grown 13 days, although there was practi¬ 
cally no increase in growth. This peculiarity was repeated in a second 
test (Table XV). 
From the regularity of these results it appears they were due to pecu¬ 
liarities in the metabolism of plants grown without iron. That plants 
grown for 40 days in the iron-free solution made only slightly more growth 
than those grown for 13 days, although they contained much more iron, 
is probably due in part at least to the immobility of iron in the plant (7). 
Considering the extremely low concentration from which plants absorb 
their iron in solutions supplied with iron, it is probable that the plants 
obtained traces of iron even from the “iron-free” solutions, as it 
would be very difficult to exclude one part of iron in several hundred mil¬ 
lion of solution. 1 
The attempt to determine the soluble iron in the various solutions was 
unsuccessful because of the impossibility of distinguishing between col- 
1 If the difference between the Iron present in plants grown 13 days and 40 days (Table XV) is due to iron 
absorbed from the solution, 0.0000055 gm. of ferric oxid (FetOs) was absorbed between the thirteenth and 
fortieth day by the three plants grown in each flask. As 1,600 c. c. of solution were supplied per flask during 
this interval, the concentration of soluble iron, expressed as Fe*Oj, would have been less than parts in 
1,000,000,000. 
