4 X 6 Lewis and Tuttle. — Osmotic Properties of Plant Cells. 
2. No certain correlation between the above values and the daily or 
weekly fluctuations of air temperatures can be recognized without observa- 
tions extending over more than one season. 
3. The maximum osmotic pressure is reached in Picea and Linnaea 
towards the end of March ; in December in the case of Populus , although 
a second maximum occurs in late March nearly of the same value as the 
December reading. Pyrola shows a fairly steady decrease from the middle 
of December till June. 
4. The concentration of electrolytes shows very little variation in any 
of the plants during the whole period of observation. 
5. The variations in osmotic pressure are due chiefly to the non-elec- 
trolytes. 
6. The variation of the sugar content closely follows the variation of 
the osmotic pressure. 
7. The sugars show a decided concentration during the winter months. 
8. There is a progressive decrease of the sugars from the winter 
maximum towards the summer. 
9. Leaves of Pyrola killed by freezing in liquid C 0 2 show ice formation 
at —3-1° C. 
10. In the living leaves of Pyrola ice formation does not begin until 
a temperature of —31-6° C. is attained. 
it. During the winter months chlorophyll granules in Picea are com- 
pletely laked, the chlorophyll being localized in the region of the nucleus. 
12. During the early part of April the chloroplastids assume definite 
form and starch formation commences. 
References. 
1 . Harris, J. Arthur, and Lawrence, John V. : The Osmotic Concentration of the Tissue 
Fluids of Jamaican Montane Rain-Forest Vegetation. Amer. Jour. Bot., 1917, vol. iv, p. 5. 
2 . Muller : Landw. Jahrb., 1886, Bd. xv. 
3 . Mousson : Annal. d. Physik u. Chemie, 1858, Bd. cv. 
4 . Dufour : Annal. d. Physik u. Chemie, 1861, Bd. cxiv. 
5 . Dixon, H. H., and Atkins, W. R. G. : The Osmotic Pressures in Plants. I. Methods of 
extracting Sap from Plant Organs. Proc. Roy. Dublin Soc.; 1913, xiii. 
6. Benedict, S. R. : A Method for the Estimation of Reducing Sugars. Journ. Biol. Chem., 
1911, vol. ix. 
7 . Haas and Hill: The Chemistry of Plant Products. London, 1915. 
8. Dixon, H. H., and Atkins, W. R. G. : On the Constituents and Concentration of the Sap in 
Conducting Tracts, and on the Circulation of Carbohydrates in Plants. Proc. Roy. Dublin 
Soc., 1915, vol. xiv (N. S.). 
9 . Harris, W., and Gortner, R. A. : Note on the Calculation of the Osmotic Pressure of 
Expressed Vegetable Saps from the Depression of the Freezing-point, with a Table for the 
Values of P. for A = o-ooi° to A = 2-999°. Amer. Jour. Bot., 1914, i. 75. 
10 . Dixon, H. H., and Joly, J. : Annals of Bot., 1895, vol. ix. 
11 . Tuttle, Gwynethe M. : Induced Changes in Reserve Materials in Evergreen Herbaceous 
Leaves. Ann. of Bot., 1919, vol. xxxiii, pp. 201-10. 
12 . Pfeffer, W. : Physiology of Plants, vol. i, p. 335. English Trans, by A. J. Ewart. 
