

372 



BOTANICAL GAZETTE 



[mat 



a much greater oxidizing power in the plants grown in the extract 

 of the more fertile soil, even under these conditions. 



Subsequent experiments were performed, the results of which 

 corroborated the foregoing. In each case where growth was good, 

 there was also good oxidation; where growth indicated a poor soil 

 extract, the oxidation was small, as will be seen from Tables IV 

 and V, . 



TABLE IV 



Comparative growth and oxidizing powers of plants in extracts of poor sandy 

 loam and garden loam. Growth expressed in terms of relative transpiration. 



^ * 



No. 



I 



2 



3 



Solutions 



Controls in distilled water 

 Extract poor sandy loam 

 Extract garden loam 



Relative 

 growth 



IOO 



77 



12* 



Relative 

 oxidation 



IOO 



103 

 275 



TABLE V 



Comparative growth and oxidizing powers of plants in extract of good and poor 

 oils. Growth expressed in terms of relative transpiration. 



No. 



i 



2 



3 



4 



Solutions 



Controls in distilled water 

 Extract Arlington clay loam 

 Extract Clarksville silt loam 

 Extract Stockton peat 



Relative 

 growth 



Relative 

 oxidation 



IOO 



75 

 123 



272 



IOO 



107 



400 



In all these experiments where direct comparisons are made 

 between the extracts of soils which were so poor as to give less plant 

 growth than pure distilled water, and other extracts giving materially 

 greater growth than the same, it appears to be unmistakably true 

 that the cultures made in extracts of good, fertile soils possess much 

 greater oxidizing powers than those made in extracts of soils of 

 relatively less fertility. 



The next question considered was concerned with the effect 

 treating the soil extract with absorbing agents. Treating the extracts 

 of a more or less unproductive soil with carbon black or other goo^ 

 absorbing agent is usually beneficial to growth. This response seem. 

 to be quite general for all poor soil extracts, although their res P ^ 

 to other treatments may be quite different. Previous work in t «s 





