448 Scientific Froceedings, Royal Dublin Society.. 



Eefereiice to the graphs shows that the osmotic pressure rises sharply in 

 February, viz., from 13'3-15'0 atm. Little of this rise is due to the 

 electrolytes, for the graph Ae shows only a small elevation in concentration. 

 Consequently by far the larger part is to be attributed to an increase of 

 sugars. As the buds are only just beginning to expand, this rise in coneen- 

 tratio!! of tlie carbohydrates can scarcely be attributed to photosynthesis. 

 With much greater probability it is to be assigned to the translocation of 

 stored carbohydrates from tlie lower parts of the tree. It has already 

 been shown that sucli a transference takes place from below upwards 

 through the wood, especially in the early spring (7). The sugars in the 

 sap liave been in part previously stored as such in tlie wood parenchyma, 

 and have in part arisen from colloidal storage carbohydrates. 



The irregular fall in the osmotic pressure taking place between the end 

 of February and tlie end of June may be in a large degree assigned to the 

 expansion of the cells of the leaves, leading to an increase in the size of the 

 vacuoles, with which the production and translocation of carbohydrates do 

 not keep pace. It is to be observed that the greater part of the irregularities 

 in the graph for the depression due to the total solutes is to be attributed to 

 variations in tlie carbohydrate content of the vacuoles, probably connected 

 with the erratic nature of the external conditions upon which photosynthesis 

 depends. Also the diminution in the osmotic pressure during this period is 

 due to the diminution in concentration of the carbohydrates only ; for the 

 lowest curve plainly indicates that during the same time the concentration 

 of the electrolytes has increased. 



From June till September the osmotic pressure rose, attaining the 

 maximum observed in this town plant at the end of the latter month, 

 viz., 18*3 atm. Here, again, the carbohydrates are the important factor. 

 Less than one-quarter of the total pressure is attributable to the electro- 

 lytes. Fluctuations in concentration also characterize the carbohydrate 

 content of the vacuoles during the end of the season, while the concentration 

 of the electrolytes steadily grows. Disregarding the fluctuations, we see the 

 osmotic pressure rises during the period the leaves are on the tree, from 

 about 13-5 to 16'0 atm. Although the carbohydrates maintain the major 

 part of the osmotic pressure, the rise seems just what is due to the increasing 

 concentration of the electrolytes, viz., 2-7-5'7 atm. It is to be noted that 

 when the leaves are falling from the tree they contain quite a large amount 

 of non-electrolytes. 



The dotted graph indicates the concentration of solutes in sap pressed 

 from untreated leaves in our previous research. It is inserted here and in 

 the other figures to institute a comparison between the results obtained by the 



