104 
IOWA ACADEMY OP SCIENCE 
lacked, but there are other possible explanations, and these studies were under- 
taken to analyze this action. For convenience the work is divided into the 
following heads: 
The Acidity of the Soil. 
The Physical Effect of the Manure. 
The Bacteriological Relations. 
The Plant Food in the Manure. 
The Antitoxic Action of the Manure. 
The Toxic Effect of Cockleburs. 
As far as could be learned, very little work has ever been done along this 
line, so it was an uncharted field. There were no paths to follow, and often 
the investigations led to no profitable results. Clover was found to be a difficult 
plant to grow in the greenhouse so that the pots would each start off with an 
equal number of thrifty vigorous plants. Without this even start results are 
not comparable. The small seedlings are sensitive to any adverse infiuence, but 
after the plant becomes thoroughly established, it can shift for itself very well. 
In the series reported in this work the pots were filled with soil which was 
mellow and free from lumps, at optimum water content, and packed in with 
the hand fairly tight. This packing prevented, in large measure, the trouble- 
some settling and cracking of the soil in the pots. The optimum physical con- 
dition was obtained and the treatments thoroughly incorporated with the soil 
by the following method. Sufficient soil to fill a pot was weighed out, placed 
in a pan, the treatment, if any, was added and the whole mixed as thoroughly 
as possible. It was then wet down well and let stand until it had dried so that 
the soil could be handled readily. Then it was thoroughly mixed and rubbed 
between the hands. This process was repeated two or three times to insure 
thoroughness and the soil was then placed in the pots. The water was applied 
both at the surface and at the bottom of the pots. A small tube was placed in 
the soil leading to an inch of gravel in the bottom of the pot. This tube con- 
ducted water to the reservoir, allowing it to come up by capillarity, and pre- 
serving the physical condition of the soil. The surface watering prevented 
accumulation of salts on the surface, which the capillarity tended to bring up. 
The clover was seeded with a small dibble, one-half inch deep, one seed in a 
place, and twenty to twenty-five seeds to the pot. The plants were later thinned 
down to the required number, usually ten or twelve. When the clover was 
four weeks old it began to feed on the soil. Before this time it grew on the 
nourishment in the seed. 
THE ACIDITY OF THE SOIL. 
Clover is a plant that seems especially susceptible to the infiuence of acidity 
in the soil, and in many places, for instance Rhode Island,^ the addition of 
lime is all that is necessary to insure a good growth of clover. Furthermore, 
the soils of southern Illinois, which are in many regards similar to those of 
southern Iowa, have been found to be acid.^ It seems very possible that this 
soil is acid and to test this question a pot was treated with lime in the first 
series. The lime was added at the rate of one ton per acre, being 4.8 g. to the 
pot in the form of finely powdered limestone. 
iSixth An. Kept. R. 1. Ag. Ex. Sta., p. 227. (1893.) 
^Illinois Ex. Sta. Bull. 99. 
