altering the Daily Period of Light, 
79 
Flax , u)20. 
The three pots exposed to light were labelled L i, L 2, and L 3, while 
the three darkened periodically were marked D 1, D 2, and D 3. The 
seeds were sown on 31 May, and after they had germinated and grown 
considerably several of the seedlings were pulled up in order to give the 
remainder more room to grow. The final thinning out took place on 
8 June, ten seedlings of nearly equal vigour being left in each pot. The 
heights of these seedlings were carefully measured before any of the plants 
were darkened ; the heights were again taken at the end of the experiment, 
as well as the total weight of the plants after they had been pulled up by 
the roots and the earth shaken off. 
The dates, duration of darkening, and weather conditions were as 
follows: 
9 J une 
Darkened 
10.30 
to 
n.30 
Sunny 
10 
y y 
yy 
9-3° 
yy 
10.30 
Cloudy, then sunny 
10 
y y 
yy 
3.20 
yy 
4.20 
Sunny 
11 
yy 
yy 
10.20 
yy 
11-20 
Cloudy 
12 
yy 
yy 
10.35 
yy 
n-35 
Cloudy 
14 
yy 
y y 
10.30 
yy 
11.30 
Mostly sunny 
15 
yy 
yy 
10.30 
yy 
11.30 
Mostly cloudy 
l6 
yy 
yy 
10.25 
yy 
n.25 
Sunny 
17 
yy 
yy 
IO.IO 
yy 
11-40 
Mostly sunny 
18 
yy 
yy 
10.15 
y y 
11.15 
Cloudy 
J 9 
yy 
yy 
10.05 
yy 
n-35 
Sunny 
21 
y y 
yy 
10.15 
yy 
11.15 
Cloudy 
23 
yy 
y y 
10.00 
yy 
12.00 
Sunny and cloudy 
24 
yy 
yy 
10.30 
yy 
11.30 
Sunny 
25 
yy 
yy 
10.00 
yy 
11.00 
Mostly sunny 
25 
yy 
yy 
2.30 
yy 
3-30 
Sunny and cloudy 
26 
y y 
yy 
11.40 
yy 
12.40 
Sunny and cloudy 
28 
yy 
yy 
9-35 
yy 
10.40 
Cloudy 
29 
yy 
yy 
10.15 
yy 
11.10 
Cloudy 
3° 
yy 
y y 
9-35 
yy 
11.35 
Cloudy 
2 
July 
yy 
1 o. 2 5 
y j 
11.25 
Cloudy 
3 
yy 
yy 
10.00 
yy 
12.00 
Sunny 
5 
yy 
yy 
10.00 
yy 
11.00 
Sunny 
6 
y y 
yy 
I 0.0-, 
yy 
11.03 
Sunny 
It will be seen, therefore, that the period of darkening extended from 
9 June to 6 July. The plants were darkened on twenty-two days. The 
total period of darkening amounted to twenty-eight hours, namely, nineteen 
times for one hour, two times for one and a half hours, and three times for 
two hours. All the occasions of darkening were a.m., except three which 
were partly or wholly p.m. About half of the times of darkening were 
sunny and the other half cloudy. 
The results obtained from each set of plants were as follows : 
The first column gives the average height of each plant on 9 June; the 
second column the average height on 7 July; the third column the height 
of the tallest plant on 7 July; and the fourth column the total weight 
(including roots) on 7 July. 
