Dixon and Atkins — Osmotic Pressures in Plants. 



59 



Table IX. 



Cotoneaster frigida, June 21st, 1915. 



Perhaps the most striking fact brought out by Tables VIII and IX is the 

 peculiar distribution of sugars in the stem-sap. Sucrose is invariably 

 present, the quantities found in June being on the whole decidedly greater 

 than in February. Eeducing sugars, hexoses, on the other hand, are in each 

 case absent from the root and higher portions of the stem except for traces 

 in two instances. Yet from the ground-level up to a height of two metres 

 about one-half per cent, is found both in spring and summer. Why a 

 sugar should be present in quantity in one part of an ascending stream 

 and absent in the parts below and above is a subject pressingly calling for 

 investigation. 



As compared with Acer and Ulmus the electrolyte content of Cotoneaster 

 is low throughout the whole year. Possibly the vernal rise in electrolytes 

 which occurs in deciduous trees is connected with the escape of organic acids 

 and salts from the cells along with sugar. 



Variations in the electrolyte concentration at different levels may be 

 more or less explained by the action of cells adjoining the transpiration 

 stream in abstracting materials for the growth of the cambium, &c, and by 

 the concentration effected by evaporation taking place in the leaves. In 

 several instances there appears a greater concentration of electrolytes at the 

 base of the stem than in the roots. This seems to necessitate a passage of 

 electrolytes from the cells of the wood into the transpiration stream. 



SCIENT. PROC. E.D.S., VOL. XV., NO. VI. K 



