55 



Effect of We.ed8 In rroduciriK a Toxic Substance. 

 Aecordmc to an old theory recently revived, 

 plants produfi in soils a subetanc© which is injurious to 

 plant growth. The work by the Bureau of Solxs sSTinis to 

 etrongly indicete the correctness of the theory. It ie 

 claimed that plants vary greatly in the toxicity produced 

 and that soils have different eapaelties in overeoming this 

 linfavortihle condition. If the theory be true, is it not 

 reasonable thttt some webde would cause toxicity for a 

 cultivat'-d plant "> • 



Clark and collaborator© (Cornell Sul. 247, 198) 

 found that soils denominated "poor spots" on -ccount of th» 

 poor crops produced, contained a high content of nitrates. 

 ThiS r>oil When transferrec t,o the cr-dsnhouS'& t-'no puiv^riz^dt, 

 produced "oetter plant /growth than that asnominat,i,cl "good 

 soil". "Good soil" refers to tht^ i;oii '.vhxch iroduced good 

 crops unc't^r field conditions. V'ae Iht* poor production 

 in the fi&id due to a toxie substance v.hich was eliminated 

 by deration or ^owi othar ag©ncy wh-e-n transfsrred to the 

 grv^nhousi- ? Was thery 4tny relation between th« conditions 

 producing high nitrogen content and th* injurious mflusne© ? 



