43 



Table II. — The Effect of Dilution and of Precipitation, 



on the Toxicity of a Soil Extract Containing a 



Higli (lonccntration of NO- and Mn. Weight in 



(irains of Air Dry Roots and Tops. 



Nature of Solution 



Untreated 



Precipitated 



Root Top Total Root Top Total 



Tap water 



Soil extract 



Soil extract 50 per cent 

 dist. water 50 per cent 



Soil extract 25 per cent, 

 dist. water 75 per cent 



Soil extract 10 per cent, 

 dist. water 90 per cent 



Second leaching 



.135> 

 .287 

 .332 

 .563 



When this soil extract was made alkaline with 

 XaOH, a voUiminoiis precipitate came down, which 

 precipitate gradually darkened on standing. The pre- 

 cipitate was filtered out and HNO-; added to slight 

 acidity. Sufficient c. p. CaCO.; was added to bring the 

 extract back to the neutral point. In the last three col- 

 umns of the table are given the yields of oats from the 

 solutions so treated. On account of the wick-like ac- 

 tion of the cotton wrapping around the seedlings, salts 

 accumulated around some of the seedlings to 

 such an extent as to become very injurious. In spite 

 of this defect in the method used, the soil extract from 

 which the elements precipitated by NaOH had been 

 removed, proved to be a much better medium for 

 growth than the original extracts of similar dilution. 



A chemical examination of the second leaching from 

 this soil showed that practically all of the manganese 

 had been removed in the first extract. This second 

 leaching was used as a medium for growth, with the 

 results shown in the last line of Table II. 



The evidence presented thus far shows that the 

 l)rown crusted soil under discussion contains a very 

 large amount of nitrates and soluble manganese; that 

 this soil is a poor medium for plant growth; that leach- 

 ing removes, in a large measure, the toxic l)ody; that 

 the water extract of this soil is highly toxic to seedling 

 plants; and that the use of an active base markedly 

 improves both soil and extract. 



To obtain further evidence as to the cause of the tox- 

 icity of the extract of this soil, another supply of ex- 

 tract was obtained, and the culture method described 

 by McCooI was used. If the toxic body present were 

 organic in nature, in all probability the extract would: 



