232 F. J. Lewis and G. M. Tuttle 
occupied by fat. A variation was observed in different cells, some 
showing a greater disorganisation of the chloroplasts than others, 
but a definite outline was not observed at any period when exposed 
to low temperature. 
Summary 
1. Osmotic pressures, electrical conductivities and viscosities of 
the sap and the condition of the leaf cells of Picea canadensis have 
been determined through the period of change from winter to 
summer condition. 
2. There is a rapid drop in the osmotic pressure from the winter 
level of over 20 atmospheres to 16 or 17 atmospheres at the date 
when the leaf cells pass from the winter to the summer condition. 
3. The initiation of conversion from the winter to the summer 
condition is independent of a rise of temperature, starch having first 
appeared on April 5, 1920, after a period of six days, when the 
maximum temperature remained below 32 0 F. and minimum tem¬ 
peratures of — 14 0 F. were experienced. 
4. Material of other conifers from an elevation of 6500 feet in 
the Rocky Mountains shows conversion at approximately the same 
date as that from the Edmonton district at 2240 feet. 
5. Reorganisation of the chloroplast, migration of the chloro- 
plast from the nucleus, and changes in the chemistry of the pigments, 
take place in darkness at the same time and to the same extent 
as in light. 
6. The first appearance of starch in the cells takes place in 
darkness as well as light and at temperatures below freezing-point. 
REFERENCES 
(1) Lidforss, B. Die Wintergriinen Flora. Lunds Universitats Arsskrift. 2 , 
No. 13. 1907. 
(2) Lewis, Francis J. and Tuttle, Gwynethe M. Osmotic Properties of 
some Plant Cells at Low Temperatures. Ann. of Bot. 34. 1920. 
(3) 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. Amer. Journ. Bot. 1 , p. 75. 1914. 
(4) Dixon, H. H. and Atkins, W. G. R. The Osmotic Pressures in Plants. 
I, Methods of Extracting Sap from Plant Organs. Proc. Roy. Dublin 
Soc. 13. 1913. 
(5) Sinnott, E. W. Factors Determining Character and Distribution of Food 
Reserve in Woody Plants. Bot. Gaz. 66, pp. 162-175. 1918. 
