Dec. x8,1916 
Assimilation of Iron by Rice 
525 
loidal and soluble iron at relatively great dilutions. From the amount of 
iron supplied and the amount absorbed it appeared that there could have 
been not more than approximately 1 part in 10,000,000 in solution at one 
time and very probably much less. The much larger quantities of iron 
found in the filtrate of the nutrient solutions were attributed to colloidal 
iron, which a previous test showed to be unavailable to the plant. 
DISCUSSION OF RESULTS 
The reactions of the solutions used in this work could not be exactly 
measured by titration because of the presence of interfering ions. It is 
evident, however, that the acid solution was relatively quite strongly acid 
as it contained only monopotassium phosphate besides a trace of sulphuric 
add, the neutral solution was nearly neutral as it contained a mixture of 
mono and di-potassium phosphates, and the alkaline solution was slightly 
alkaline from the presence of calcium carbonate and its reaction with the 
phosphates. 
The preceding tests demonstrated that the growth of rice was markedly 
dependent on the quantity and form of iron added to these nutrient solu¬ 
tions and apparently dependent on the reaction of the solution only so far 
as it affected the availability of the iron. These facts are important in bear¬ 
ing on the nature and cause of lime-induced chlorosis, rice bdng markedly 
affected with this nutritional disturbance. Previous work in soil cultures 
showed pretty decisively that lime-induced chlorosis was not caused by 
lack of any mineral nutrient except possibly iron, but did not show 
whether the reaction of the soil in itself affected the plants. The present 
study seems to substantiate the previous work and show, moreover, that 
rice is not particularly sensitive to the reaction per se, provided the iron 
supply is maintained. While in soils there are many more factors affect¬ 
ing the availability of iron than in nutrient solutions, the preceding results 
point strongly to calcium carbonate diminishing the quantity of available 
iron in a soil through affecting the reaction. Direct evidence on this latter 
point is afforded by the results of Morse and Curry (11) and Ruprecht and 
Morse (12). The results also point to different iron compounds, particu¬ 
larly the organic and inorganic compounds, varying greatly in their availa¬ 
bility in calcareous soils. The existence of organic iron compounds in the 
soil has been pointed out by Hartwell and Kellogg (8). 
While all the tests reported here were carried out with rice, certain re¬ 
sults are of general interest in relation to the proper composition of plant- 
nutrient solutions. The extent to which growth was dependent on the 
iron supply in the previous tests shows how important it may be to con¬ 
sider the form and quantity of iron used in the nutrient solution. Evi¬ 
dently the addition of a few drops of a dilute iron solution, as recom¬ 
mended in most plant physiologies, may not insure an adequate supply 
of iron. While the color of the leaves will indicate a marked deficiency 
of iron, a slight deficiency may materially diminish the yield without mate- 
