47 
1914-15.] Studies on Periodicity in Plant Growth. 
taneously on the same drum, and the experiments carried out within a 
temperature of 19°-23° C., while the limits of the humidity were 40-65 
per cent. 
The external light conditions were varied for the different experiments 
as follows : — 
1. Normal Conditions : i.e. the root and shoot under natural conditions 
— the root in the dark and the shoot in intermittent light and 
darkness. 
2. Intermittent Conditions : i.e. the root under abnormal conditions — 
both root and shoot in intermittent light and darkness. 
3. All-Dark Conditions : i.e. the shoot under abnormal conditions — both 
root and shoot in continuous darkness. 
4. All-Light Conditions : i.e. the root and shoot under abnormal con- 
ditions — both in the light during the day and in electric light 
during the night. {Note. — Two electric lights, one of 50 and the 
other of 25 candle-power, were used at night, giving a diffuse 
light.) 
The hours of light and darkness were calculated from the natural 
periods of day and night at the season of the year, and not from an artificial 
12-hours day and 12 -hours night used by Sachs and Barenetzsky in their 
experiments on periodicity. 
One set of experiments was carried on during the winter months of 
February, March, and November, when the relative amounts of light and 
darkness occurring is 10:14, 12:12, and 9:15 hours respectively ; a second 
series during the summer, in May, June, and July, when the proportion of 
light to darkness is about 18:6 hours. 
Many duplicates were performed to get reliable results. 
Results. 
The auxanometer curves were divided into two-hourly intervals, the 
growth measured in millimetres, and the figures obtained plotted in 
graph form. 
From these figures were calculated the actual amounts of growth per 
day for the shoot and root under the four different conditions, and the 
amounts of growth in each during the day and night periods respectively. 
From the latter can be calculated the mean hourly growth during the day 
and night in root and shoot, and also the linear growth coefficients — i.e. 
the increment of growth of a unit of length in unit time — for each under 
all the conditions. The linear growth coefficient of an organ depends upon 
