81 
altering the Daily Period of Light . 
measured, and on 8 July the heights were again measured, after which the 
plants were pulled up and weighed after the earth adhering to the roots had 
been removed as far as possible. The figures were: 
Average height 
Average height 
Tallest on 
Total 
on 9 June. 
on 8 July. 
8 Jiily. 
xveight. 
mm. 
mm. 
mm. 
grm. 
Li 
3 6 -3 
554-5 
607 
124.820 
L 2 
29.8 
563-5 
635 
I 35 - 38 o 
L3 
30-3 
537-5 
580 
121.130 
Average 
32.1 
551-8 
607 
127.IIO 
D 1 
37 *i 
548-7 ' 
650 
119.020 
D 2 
36-5 
585-7 
625 
132.120 
D 3 
2 5-9 
484.4 
54 ° 
109.650 
Average 
33 -i 
539-6 
605 
120.260 
While the average height of the unshaded plants on 9 June was 3-3 per 
cent, less than that of those subsequently darkened, the height of the 
unshaded plants on 8 July was 2-2 per cent, more than that of the other set. 
White Mustard , ig20. 
The seeds of this species were sown on the same date as those previ¬ 
ously mentioned, and the period of darkening was similar, but towards the 
end of the experiments all the plants became so badly affected with green 
fly that no satisfactory results could be deduced from them. Accordingly 
another set of experiments was started. 
The plants were darkened on sixteen days between the 12th and 29th 
of July. They were covered altogether eighteen hours, the sky during one 
half of the time being sunny and during the other half cloudy. The 
heights and final weights of the plants were determined as in the foregoing 
experiments. In addition, the number of flower-buds present in each pot 
was observed before the plants were pulled up in order to be weighed. 
The seeds were sown on 8 July. On 12 July the seedlings were 
thinned, ten being left in each pot, the heights of which were determined. 
The heights were again measured on 23 July. The complete figures were 
as follows : 
Average 
Average 
Average 
Tallest on 
1° July. 
No. of 
'Total 
height on 
12 July. 
height on 
23 July. 
height on 
30 July. 
flower 
buds. 
J. ULUu 
weight. 
mm. 
mm. 
mm. 
mm. 
grm. 
Li 
13.0 
73-9 
146.3 
173 
7 
20-000 
L 2 
13.2 
7 2 -5 
146-0 
194 
10 
I 7-950 
L 3 
I2-I 
78.9 
176-6 
215 
9 
22.750 
Average 
12-8 
75 -i 
I 56-3 
r 94 
8.7 
20-230 
D 1 
12.1 
55 -° 
114-6 
T 45 
5 
13 - 57 ° 
D 2 
10.6 
58-3 
126-2 
158 
4 
16 .OOO 
d 3 
12-0 
67-5 
134.6 
169 
7 
I 4 .O 50 
Average 
11-6 
60.3 
125.1 
157 
5-3 
T 4 - 54 ° 
G 
