Seasonal Changes in Leaf Cells of Picea canadensis 229 
This was not done in a previous paper, neither was the viscosity of 
the sap considered by Dixon and Atkins in their earlier work ( 4 ). 
Conditions affecting Conversion 
In 1919 the change from the winter condition in the organisation 
of the cells and the first appearance of starch began to take place 
on April 7. The stages in the gradual re-formation of the chloroplasts 
and their movement from the region of the nucleus and the appear¬ 
ance of starch, were described by us in a former paper(2). 
One of the most suggestive features is the apparent want of 
connection between the first appearance of starch in outside material 
and the daily temperature curve. Examination of the graph shows 
that from March 29 to April 7 the maximum temperature never rose 
above freezing-point and on April 3 a minimum temperature was 
recorded of — 15 0 F., yet on the afternoon of April 5 the first trace 
of minute starch grains could be demonstrated with the use of 
iodine and chloral hydrate. Leaves had been examined daily for 
some two weeks previously, and more frequently as the suspected 
time of conversion approached, but no trace of starch could be 
demonstrated with the use of iodine and chloral hydrate; material 
outside still began to form starch at a certain date, although the 
temperature never rose above 32 0 F. and fell to — 15 0 at night. 
The evidence strongly suggests a certain rhythmic change, inde¬ 
pendent, as regards its initiation, of external factors such as tem¬ 
perature. This is supported by an examination of coniferous material 
in the neighbourhood of Edmonton, at 2240 feet, and from altitudes 
up to 6500 feet in the Rocky Mountains. The date of the change 
from winter to summer condition in Picea canadensis was the same 
in trees grown at Edmonton, and at Banff at an altitude of 4600 feet. 
It was found that Picea Engelmanni (Parry) Engelm. from 6400 feet, 
Abies lasiocarpa (Hook.) Nutt, from 6400 feet, Pinus Murray ana 
Balf. from 4600 feet, Pinus albicaulis Engelm. from 6500 feet, all 
in the neighbourhood of Banff, showed the same changes in the 
reorganisation of the chloroplasts and the appearance of starch at 
the same date as white spruce material at Edmonton, where spring 
conditions are at least six weeks in advance of the sub-alpine zone 
in the mountains. But temperature evidently acts as an accelerator 
for it was not until April 29 that outside material showed as much 
starch as that obtained from material exposed to laboratory tem¬ 
perature for 24 hours on April 5. It is suggested that an activator, 
