12 BULLETIN 42, U. S. DEPARTMENT OF AGEICULTTJKE. 
In each treatment two cultures containing 20 wheat plants were 
used. Comparison was made with an equal number of plants growing 
in an untreated portion of the soil extract under the same conditions. 
At the end of two weeks the green weight of each culture was taken. 
In addition the oxidizing power of the plants subjected to various 
treatments was determined. 
The method used to determine the oxidizing power of the roots 
in these solutions is the one described by Schreiner and Reed in 
Bulletin 56 of the Bureau of Soils. One hundred milligrams of aloin 
were added to each 250 c. c. culture jar. Aloin is a yellow powder and 
when dissolved in water gives a pale yellow solution, which is changed 
by oxidation to a deep red wine color. The aloin was added to 
the solution the last day of the cultural experiment; that is, after 
the plant had grown for two weeks. It remained in the solution and 
was subjected to oxidation by the plant roots for 12 hours before a 
comparison of the various treatments was made. The intensity of 
color of the solution was estimated by means of a Schreiner colori- 
meter. The untreated soil solution was used as the standard for 
comparison. It is sometimes difficult to make comparisons where 
there is a wide difference in the degree of oxidation. When this 
was the case the solutions were arranged in the order of their apparent 
color intensity, and the weakest colored solution was used first as 
a standard, being compared with the second weakest. Number 2 
was then compared with the third weakest. In turn the third solu- 
tion can be used as a standard against the next strongest, and so on. 
In this way the necessity of comparing a solution strongly tinged 
with yellow against a solution which has a deep red color is avoided. 
Finally, all readings were reduced to the basis of the untreated soil 
solution as the standard. 
EFFECT OF MANGANESE IN EXTRACTS OF UNPRODUCTIVE SOILS. 
The first experiments were made with the poor sandy loam soil, 
which responded to manganese when tested in pots. Extracts were 
made of the soil, in the manner described above, and wheat plants 
were grown in the extracts with additions of manganese in several 
forms. The manganese was added at the rate of 50 parts per million 
of the element Mn. The chloride, sulphate, nitrate, and carbonate 
were used. The plants grew from May 11 to May 22. Two cultures 
were run with each treatment. Aloin was added to the solution the 
last day of the experiment and the oxidizing power of the plants 
taken. The comparative growth and oxidation is given in Table III. 
