386 Scientific Proceedings^ Royal Dublin Society. 



In this plant the only observations made show the concentration of the 

 wood-sap of the root to be less than that of the stem, even during the summer 

 and autumn months. At the same time the curve of the root-sap follows that 

 of the stem-sap. 



Concentration of Sugars and other Non-electrolytes. 



The form of these curves is not greatly altered if we deduct from each 

 observation the amount of depression due to the electrolytes. Hence the 

 curves given convey a fair impression of the variations in the concentration 

 of the soluble carbohydrates in the traelieae, and it has not been thought worth 

 while to plot special graphs for the carbohydrates in the sap. 



From inspection of the tables it is quite clear that, except occasionally in 

 the summer and autumn, the molecular concentration of the carbohydrates 

 in the transpiration stream in deciduous trees is greater than that of the salts. 

 Furthermore, since the sugars have high molecular weights (glucose 180, 

 sucrose and maltose 342) the actual percentage weights of these substances 

 in the sap must be far greater than that of the electrolytes, which have low 

 molecular weights, and are more or less ionised. Hence we must admit that 

 the translocation of carbohydrates is at least as important a function of the 

 transpiration current as the transference upwards of nutritive mineral salts. 



In the roots even a similar relative concentration is often found, as a 

 comparison of the columns under Ac and A - A^. clearly shows. 



The balance of salts and carbohydrates is more evenly kept in the 

 evergreen Ilex, and the concentration of the two throughout the year more 

 closely approximates ; so that the function of wood here in conveying the 

 electrolytes may be regarded as being as important as that of transporting 

 carbohydrates. 



Concentration of Electrolytes. 



With the exception of the two observations made in June on Cotoneaster 

 frigida and in October on Populwi alba, it appeal's from the experiments quoted 

 that the concentration of electrolytes was greater in tlie wood of the roots 

 than in tliat of the stems. This would seem to suggest that while the 

 quantity of dissolved carbohydrates in the transpiration stream may be 

 added to on its upward passage, the amount of dissolved electrolytes is not 

 thus reinforced, but usually is diminished as the stream rises. Doubtless 

 some of the dissolved salts are abstracted and used in various processes of 

 metabolism. The observation on Cotoneaster, however, shows that this does 

 not always hold good, for in it the concentration of electrolytes in the stem 

 was slightly greater than in the roots. And in a number of observations 

 made on Acer macrophylkim (see Table X) no steady gradient from below 

 upwards is revealed. 



