268 HARRIS, GORTNER, AND LAWRENCE: 
lower to higher levels. Later* he returned to the same problem, 
only to conclude that the sources of error in the use of the plas- 
molytic method are so great that it was idle to go farther with the 
study on the basis of the technique then available. After men- 
tioning certain of the difficulties he says: 
“It is more correct therefore to use the term ‘plasmalyzing concentration’ for 
results obtained in this manner, and a series of observations for leaf cells of species 
of Acacia, Eucalyptus, and Orevillea taken from 1-12 meters high show that the 
concentration may vary from 2-6 per cent. KNOs in d the same plant, and that 
the variation between’ SO at the same level is at first as great as between leaves 
at different levels, and that the size of the cell and the age of the leaf appear to 
influence the plasmolytic concentration more than any other factors apart from food 
storage and assimilation. Hence this promising line of investigation — the 
problem of the ascent of sap must be abandoned as inaccurate and misleadin 
The only exact published data of which we are aware are those 
furnished by Dixon and Atkins.} 
Dixon in his volume on the Ascent of Sap{ republishes these 
data with the same interpretation. Working with untreated 
leaves§ of Magnolia acuminata, Fraxinus excelsior and Vitis Veitchit 
they secured seven pairs of determinations, from which they 
conclude: 
“It here appears that, on the whole, taking the experiments in pairs, the leaves 
at the lower level contained sap with a lower (sometimes considerably lower) osmotic 
pressure than that of higher leaves. But the experiments are far from satisfactorily 
bearing out this view; for it will be noted that the osmotic pressure of the sap from 
leaves at the same level, but at different times and under different conditions, by no 
means corresponds in each case, although it is often higher than that of leaves at a 
lower level. The reverse, however, is sometimes found, as in a 6 and 7 where 
the pressure in the lower is much greater than in the higher leaves. 
Dixon and Atkins recognized the fact that a relationship 
between the concentration of the sap of leaves inserted at different 
distances from the root system might be due to an adjustment to 
resistance in the conducting system as well as to the hydrostatic 
* Ewart, A. J. Theascent of waterintrees, II. Phil. Trans. Roy. Soc. Lond. B. 
199: 341-392. 1906. 
i H. H., & Atkins, W. R. G. On osmotic pressures in plants; and ona 
thermo-electric method of determining freezing points. Sci. Proc. Roy. Dublin 
N.S. 42: 275-311. 1910. Alsoin Notes, Bot. Sch. Trin. Coll. Dublin 2, 1910. 
ft Dixon, H. H. Transpiration and the ascent of sap in plants. London, 1914. 
§ This work was carried out before the necessity for the preliminary freezin, 
of tissues was discovered by Dixon and Atkins. Possibly some of the inconsistencies 
in their results are due to this fact 
