The production of deleterious excretions by roots * 
OSWALD SCHREINER AND Howarp SPRAGUE REED 
It is our purpose to show in the following paper that the roots 
of certain higher plants may produce substances which have a 
deleterious effect. The undue accumulation of these substances is 
unfavorable for the growth of plants, and hence this study throws 
some light upon problems of soil conditions and ecological 
relations. 
A number of typically unproductive soils from different parts of 
the United States have been under study in the laboratories of the 
Bureau of Soils of the United States Department of Agriculture 
for several years, and some of their properties are now understood. 
It has been demonstrated that many soils are unproductive, not 
because proper nutrients are lacking, but because they contain 
substances actually deleterious to plant growth.+ 
An aqueous extract of an unproductive soil, though contain- 
ing nutrient materials, is often a poorer medium for the growth of 
plants than distilled water. Wheat seedlings will grow for about 
three weeks in good distilled water, but various experiments de- 
scribed in the publications just cited show that seedlings grown in 
the extract of an unproductive soil give a much poorer growth in 
both top and root, and the plants often die within two weeks. 
Wheri such an extract of a poor soil is treated with an insolu- 
ble, finely divided solid it loses its toxicity for plant development 
and gives (as might be expected) a better growth of plants than 
distilled water. The method usually followed is to add carbon 
Merck to the soil extract.’ ‘The carbon black is sdried. or shaken 
With the soil extract for a few minutes and, at the expiration of a 
half hour, filtered out. The carbon black contains no nutritive 
Substances, It is practically pure carbon obtained by burning 
* Published by permission of the Secretary of Agriculture. ; : 
A great deal of evidence on this point has already been presented = — 
28 and 36 of the Bureau of Soils, and a general presentation is given in Farmers’ Bul- 
letin 257 of the United States Department of Agriculture. 
279 
