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SCIENCE PROGRESS. 



ACIDITY OF THE ROOT SAP OF PLANTS (DYER). 



The mean acidity of the 103 determinations of root sap 

 is 0*85 per cent., reckoned as crystallised citric acid ; and 

 the mean acidity of the twenty orders is 0*91 per cent. 

 When we look, however, at the agricultural crops, we find 

 the acidity less, the mean acidity of the Leguminosae, 

 Cruciferae, Gramineae, Chenopodiaceae and Solanaceae being 

 0-63 per cent. 



The difficulty of determining exactly the effective acidity 

 of the sap present in the root hairs is very great, and the 

 results of the numerous experiments just quoted are natur- 

 ally only approximate. Nor does Dr. Dyer assume that 

 the acid present is necessarily citric acid ; the results are 

 given in terms of this acid for a reason which will presently 

 appear. 



It has been recognised by many agricultural chemists 

 that we should obtain a much more correct idea of the 



