119 



\v;ilci- thai [\\c soil could hold. Nine grams })t'r pol 

 o( twonly pounds of soil is approximately oquivalcul 

 to 1000 |)arls pii- million of soil. Therelore, the con- 

 centralion oT llu- solutions in which the oat croj) started 

 growth was very much greater than 1000 parts per 

 million, if the comjjound was soluble in water, and if 

 the soil did not remove the material from solution by 

 al)sori)ti()n. It api)ears remarkable, then, that the oat 

 crop, which was planted on the same day that the 

 treatments were a|)i)lied. did not show even greater 

 injury from the \anillin nnd coumarin. On the other 

 hand, neither pyrogallol nor carbon black appears to 

 have influenced the yields of oats to a noticeable de- 

 gree. In view of the fact that both of these substances 

 have been shown to exert a great beneficial influence 

 on plants grown in poor soil extracts, it might be 

 expected that a similar influence might be shown when 

 they are added to the poor soil itself, rather than to 

 the poor soil extracts. 



After the oat harvest, corn was planted in those 

 pots which had received a complete fertilizer in the oat 

 treatments. In each of these pots, the fertilizer treat- 

 ment was repeated for the corn, but no further addi- 

 tion of the special treatments was given. The other 

 pots which had been in the oat test were planted to 

 cowpeas, and the results of this test will be given 

 separately. In the fourth column of the table will be 

 found the corn yields. These results arc very interest- 

 ing. The i)ofs which had received 9 grams of vanillin 

 or coumarin in connection with a complete fertilizer, 

 ])ro(luced much lighter yields of oats than did the pot 

 which received a comjdete fertilizer alone; but the 

 crop of corn following after the oats appears not to 

 have been injured by the vanillin at all; the effect of 

 the coumarin appears to have been slightly beneficial. 

 Pyrogallol was without elTect and carbon l)lack slightly 

 reduced the yield of corn. The results here presented 

 sIhan' that this poor soil cannot be much improved in 

 fertility by the use of such materials as pyrogallol or 

 carbon black, neither of which carries plant food. If 

 this soil is j)oor because of the i)resence of toxic bodies, 

 then these l)odies are of such nature that the above 

 compounds fail to affect them, i. e., neither adsorbing 

 nor reducing agents alters the productive capacity of 

 the soil. The results show, also, that the fertility of 



