486 KELLERMAN: EFFECT OF BORON ON VEGETATION 



the stimulating effect to be due to a suppression of the growth 

 of competing organisms such as bacteria and molds on the con- 

 trol plants of water cultures and the bacteria and protozoa in 

 the sand and soil cultures. It may be doubted also whether the 

 • conclusion regarding the relative toxicity of boron compounds 

 and compounds of zinc and copper is valid. If one is considering 

 plants growing in natural soil, zinc and copper compounds are 

 certain to become transformed into insoluble compounds much 

 more rapidly and completely than is the case with boron form 

 deposits that represent natural accumulations. Therefore, it 

 may not unfairly be presumed that boron will prove to be a 

 more toxic element than either zinc or copper. 



The toxicity of boron compounds to different crops under 

 field conditions has not been adequately investigated. It will 

 almost certainly be found that different crops will show a great 

 range in their resistance to borax poisoning, and it is probable 

 that there may be found to be some direct correlation between 

 the action of the plant in absorbing boron compounds and the 

 limit of the toxic concentrations. In rather extensive experi- 

 ments upon the efifect of manure treated with different com- 

 pounds of boron, Dr. Cook makes the following statement :'' 



"It apparently made little difference in the quantity of boron ab- 

 sorbed by the plants tested whether boron was added to the soil as 

 borax or as calcined colemanite. The addition of lime with borax 

 had no definite effect in preventing the absorption of boron. Wheat 

 and oats absorbed very little boron, while leguminous and succulent 

 plants absorbed comparatively large amounts." 



It seems clear that much additional investigation, both in the 

 field and laboratory, is necessary before it will be possible to 

 determine the significance of borax either in its relation to 

 natural vegetation or its bearing upon agricultural development 

 in irrigation projects or in the use of fertilizers. In taking up 

 new studies it should be emphasized, however, that the inves- 

 tigator should not remain blind to other compounds that might 

 prove even more important in their relation to vegetation than 

 compounds of boron ; for example, in several of the regions where 

 borax has been produced commercially, quicksilver ores also occur. 



6 Cook, F. C. Journ. of Agric. Res. 5: 888. 



