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Scientific Proceedings, Royal Dublin Society. 



water, as previously shown by the authors (1). Evidently, then, the true 

 concentration of tlie sap in the tracheae may be very different from that of 

 the liquid pressed from the wood. 



The possibility of centrifuging the sap from the tracheae of pieces of 

 freshly cut wood subsequently suggested itself, and this method was found 

 very successful. 



The buckets of our centrifuge conveniently held cj'clinders of wood 10 cm. 

 long by 2 cm. in diameter. These were cut from stems and roots, and the 

 amount of sap yielded, even when the wood appeared dry, was often surprising. 

 A cylinder of the dimensions just mentioned rendered as much as 1-5 c.c. 



The sap obtained by this method was found to be much less concentrated 

 than that obtained by pressure. In the following table (Table II) are given 

 measurements made on sap derived by centrifuging pieces of the same branches 

 and roots as those which supplied the sap for the determinations recorded in 

 Table I. 



Comparison of the depressions of freezing-point and the conductivities of 

 the liquids obtained by the two methods from the wood shows conclusively 

 that pressure, by bursting the cells in the wood, liad contaminated the sap of 

 the tracheae both with electrolytes and non-electrolytes. This contamination 

 was further shown by the fact that while the sap pressed from the wood 

 became more or less deeply coloured brown owing to the presence of a 

 chromogen and an oxidase (1), that centrifuged from it remained almost colour- 

 less, indicating that either or both of these bodies were retained in the substance 

 of the wood, or, more precisely, in the living cells. Moreover, the centrifuged 

 sap is neutral to litmus, whereas that obtained by pressure is acid. 



At the same time the interesting fact was made clear that even in the 

 month of August the carbohydrates present in the tracheae are sufficiently 

 concentrated to produce a depression of freezing-point amounting to 0'030° 

 and 0'038° in stem and root respectively. It thus appears that the solution 



