m\ 



SCHREINER 6- REED— OXIDIZING POWER OF ROOTS 



375 



in distilled water. One hundred milligrams of aloin was added to 

 each of the culture bottles, and on the following day the amount of 

 oxidation was noted by comparing the intensity of red color in each 

 culture. The cultures in the first portion showed much less oxidation 

 than either of the other two. The most oxidation appeared to have 

 gone on in the cultures in the second portion, which was slightly 

 in excess of that in the control cultures in pure distilled water. 



The question was studied further, and in a more quantitative 

 manner, by the following experiment. An extract of Elkton silt 

 loam, having a volume of 750", was placed in a flask connected 

 with a condenser and distilled. The distillate, amounting to 500", 

 was collected in two portions of 2 5 o cc each and used as a culture 

 medium in which plants were grown. The res 

 flask, which was diluted to its original volume, was also used for 

 growing plants. For comparison, cultures were also made in the 

 original soil extract. The wheat plants were allowed to grow in 

 the various solutions for 13 days, and then their oxidizing powers 

 were estimated by means of phenolphthalin. The growth and 

 oxidation are shown in Table VII. 



d 



TABLE VII 

 Growth and oxidation in distillate and residue of extract from Elkton 

 Growth expressed in terms of relative transpiration. 



silt loam 



No. 



Solutions 



Relative 

 growth 



Relative 

 oxidation 



I 



2 



3 

 4 



Original soil extract untreated 

 First portion of distillate 

 Second portion of distillate 

 Residue after distillation, diluted 



volume 



to 



original 



100 



53 

 70 



!3 2 



100 

 20 



19 



180 



These results show that the distillates of this soil «*«*""! 



STOW 



soil extract, while the residue from 



distillation was materially 



^ ** extract, wnue me resiuuc **w ,., 



^proved. This seems to indicate that the origmal sod «*£•»? 

 rs which have been investigated,., contame^ a volau e «ox,c 



othe 

 subst 



en nave Deen investigate., --- tbi 



stance which inhibited oxidation by the roots, an 

 Stance was driven off by the process of distillation, with resulting 



m 



3J Bur. Soils, U. S. Dept. Agric. Bulls. 28, 36- and 40. 



