52 



Scientific Proceedings, Royal Dublin Society. 



the values of electrical conductivity measurements, expressed in mhos, upon 

 the same sap. A e represents the depression of freezing-point occasioned by the 

 electrolytes ; this is calculated by finding the value of A for a solution of 

 some standard substance, such as potassium chloride, which has an electrical 

 conductivity equal to that of the sap. As explained in an earlier paper (1), 

 this is an approximate value, but it is sufficiently accurate for dilute solutions. 

 Accordingly, A - A e is a fairly reliable measure of the non-electrolytes, which 

 are almost entirely sugars, dissolved in the saps under examination. 



In the two columns at the right are shown the percentages of reducing 

 sugars (R) and of sucrose (SI found. The reducing sugars include the 

 mono-saccharides, glucose, (dextrose) and d-fructose (laevulose) and the 

 disaecharide maltose. The latter was found only in a few instances. Its 

 presence was detected by means of its phenylosazone, and a rough idea of the 

 relative amounts of the two hexoses and maltose was obtained by micro- 

 scopic examination of the osazone crystals. It must be remembered that 

 these hexoses yield the same osazone. The percentages shown are only rough 

 estimations carried out upon the sap by Fehling's solution. The figures for 

 sucrose were obtained by treating sap, inverted with hydrochloric acid, in 

 the same manner. Allowance was of course made for tbe reducing sugars 

 previously found. The figures under R are calculated as if only glucose were 

 present ; thus when maltose is present the value will be too low, as the 

 reducing power of maltose is only about half that of glucose, weight for 



weight. 



Deciduous Trees. 



Below are recorded the results afforded by the examination of portions 

 of the stem of a large elm, felled on March 3rd. The sap was extracted by 

 centrifuging small cylinders of wood, as previously described (1). 



Table I. 

 TJlmus campestris. Wood-sap from tree, March 4th. 



