231 
Seasonal Changes in Leaf Cells of Picea canadensis 
ments did not take place until the beginning of May and at this 
period no distinction could be recognised between the experiments 
and controls. In both cases the chlorophyll had changed from the 
winter brownish yellow colour to the normal vivid green and the 
chloroplasts had become completely reorganised with normal 
grouping in the cells. 
The regularity of these changes regardless of the influence of 
light and the first appearance of starch at temperatures below the 
freezing-point are interesting features. 
Table II 
Condition of the chloroplasts and the appearance of starch in 
light and darkness 
Date 
Location 
1920 
in 
Material 
Condition of the chloroplasts 
Starch 
Oil 
6. iv. 
6. iv. 
Shade 
Covered Mar. 23 
As in winter 
Small amount 
Abundant 
6. iv. 
99 
In light 
” ” 
” ” 
” 
12. iv. 
” 
Covered Mar. 23 
Mostly distinct, frequently 
localised around nucleus 
Abundant with chloral 
hydrate and iodine 
” 
12. iv. 
,, 
In light 
As in covered material 
Abundant with iodine 
99 
12. iv. 
Sun 
Covered Mar. 23 
Faint, but evenly distrib¬ 
uted, generally distinct 
Abundant with chloral 
hydrate and iodine 
12. iv. 
99 
In light 
Rather less organised than 
in preceding 
Abundant with iodine 
” 
4. v. 
Shade 
Covered Mar. 23 
Chloroplasts fully formed 
Trace with iodine, abun¬ 
dant with chloral hy¬ 
drate and iodine 
99 
4. V. 
99 
„ Feb. 1 
” 
Abundant with iodine 
and chloral hydrate 
99 
4. V. 
99 
In light 
99 99 99 
Abundant with iodine 
99 
25 - V. 
” 
Covered Feb. 10 
99 99 99 
Small amount with 
chloral hydrate and 
iodine 
99 
Observations have been carried out every year since 1920-1 and 
the changes recorded in a former paper (2) have been substantiated 
and further facts brought to light. The change from summer to 
winter condition seems to be very gradual. On October 28 the 
contents of the mesophyll cells were tending to become localised. 
The chloroplasts, still definite in outline, were crowded round the 
nucleus in which the chromatin was very distinct, indicating the 
progress of rapid chemical changes in the cell. Cells examined during 
November and December showed the chloroplasts becoming less 
distinct in outline until in many cells no trace of their form could 
be distinguished. The extreme winter condition was observed in 
cells examined on January 26. At this time the green colour was 
confined to a small portion of the cell, while the major portion was 
