374 BOTANICAL GAZETTE [may 



oxidizing powers of the plants subsequently grown in the extracts, 

 and the growth of the plants was also increased. 



The increased oxidation, as well as the increased growth, points 

 directly to the conclusion that the soil extracts have been so improved 

 by the treatment given as to induce a more active functioning of 

 processes necessary to secure the best conditions for growth. In 

 the single case of No. 2 the growth was increased as a result of the 

 treatment with carbon black, but the oxidation was not. This 

 result was frequently obtained with the Takoma lawn soil; in some 

 cases the oxidizing power was even slightly decreased as a result of 

 treatment with absorbing agents, although growth was increased. 

 No satisfactory explanation has as yet been obtained for this appar- 



* ■ 



ently exceptional action. It may be found upon further investigation 

 that the lack of response was due to the presence of matter inhibiting 

 oxidation, which was not removed by the carbon black. This 

 question seems worthy of more study than we have been able to 

 give it. 



Extracts of poor soils sometimes contain volatile bodies of a 

 deleterious nature, which can be driven off by boiling and collected 

 in the distillate. The writers have described^ 1 the behavior of 

 plants grown in such distillates. Where the deleterious bodies are 

 volatile, the distillate usually exhibits the same toxic properties which 

 the original extracts previously possessed, and the residue is corre 

 spondingly improved. 



To study the effects of these distillates upon the oxidizing powers 

 of the plants the following experiments were made. One liter o 

 such soil extract was placed in a distilling apparatus and distil^ 

 until 200" of distillate had passed over and been condensed. * 

 fluid was made up to 500" by adding water and designated r> 

 portion. When a second 200" of distillate had been collecte , 1 

 was likewise made up to 500" and designated second porti 

 Cultures were made in each portion, together with controls inp 

 distilled water. At the end of a week the plants in the dltere " n 

 solutions showed marked differences. The plants in the first portio^ 

 of the distillate were very small and were dying ; those in the scco^ 

 portion were much better, in fact, were equal to the controls ero 



3' Bur. of Soils, U. S. Dept. Agric. Bull. 40. 1907. 



This 



on. 



1 



