It AvoTild seem desirable to give earnest attention to this subject 

 with plants irrown under careftil supervision in the field or laboratory, 

 as the evidence here i^jresented indicates that the removal or cropping 

 of these plants for any i:)uri3ose would result in taking from the soil 

 enormous quantities of desirable plant food and the conseqtient raising 

 of the proportion of undesirable elements in the soil. 



FU>'CTION OF THE ACID EXUDATION. 



"When the large amounts of soluble carbonates found in the soils 

 tipon which these i:)lants grow are considered, and Avhen the disas- 

 trous corrosive action of this substance is remembered, the i)roduc- 

 tion of the strong organic acid by the i)lant seems a wise protective 

 meastire of nature. The tendency of sodium carbonate to otitstrip 

 other salts in accumulating in the very top layers or crusts of a soil 

 and there corroding the root crowns of plants has been frequently 

 noted by all investigators of alkali problems. It would seem that 

 this organic acid is produced by the plant in the manner most favor- 

 able to its being brought into contact with the stirface sodium car- 

 bonate, partly converting this latter to the sodium salt of the acid 

 and partly, in all probability, to sodium bicarbonate, which, there is 

 strong reason for believing, is not itself so harmful to plant growth 

 as the normal carbonate.^ 



PHOSPHORUS IX THE PLANT. 



In the attempts to identify the organic acid on Sample I, DistichJis 

 spicaia, some leachings were obtained which contained a small amotint 

 of organic matter mechanically suspended, as well as someinsohition. 

 They were allowed to stand for several days in an Erlenmeyer flask, 

 the motith of which was covered with an inverted beaker. A rai^id 

 and voluminous growth of fungi was observed. On filtering off a 

 .small i)ortion of the solution after it had been standing a day or two 

 a decided thotigh small amotint of i^hosphoric acid was shown to be 

 present. No trace of this substance was found in freshly prepared 

 leachings of the plant. It would seem probable that it was formed 

 as a result of the action of organisms either upon dissolved organic 



'' The especially pernicious effect on plants of carbonate of sodium is in all prob- 

 ability due to the fact that this salt readih* h ydrolizes in water with the formation 

 of considerable amounts of sodium hydroxide, and it i this latter substance which 

 is in reality responsible for its great destructive power. Sodium bicarbonate or 

 hydrogen carbonate. Na-HCOg. might be expected to hydrolize to some extent 

 also, l^eing composed of a strong base in combination with a weak acid: this would 

 be equivalent to a partial inversion to the normal carbonate. But in the presence 

 of so much carbon dioxide as is present in soils this inversion to the normal car- 

 bonate would be greatly retarded or altogether prevented. The normal dissocia- 

 tion of the hydrogen carbonate would then be very small indeed and any chemical 

 activity of the compound depending on the formation of ions would be corre- 

 spondmgh" small. 



