184 Ingvar Jorgensen and Walter Stiles. 
here variations in light intensity are without influence on the 
assimilation, while temperature variations influence the rate of 
assimilation considerably. However, no experimental results are 
given which justify these conclusions, and however interesting they 
may be they can at present only be accepted as postulates. 
Etiolated Leaves. 
The complexity of the processes involved in carbon assimilation 
is also made clear by examination of the behaviour of etiolated leaves. 
On this subject observations were made by Miss Irving (1910) 
at Blackman’s suggestion. Blackman assumed that in the case 
of etiolated leaves “ the whole assimilatory apparatus might be 
efficiently developed except the green pigment, and as this increased 
by degrees, so the power of photosynthesis would increase. Thus 
the amount of chlorophyll present would then be the limiting factor 
for assimilation, and interesting data might be looked for relating 
the amount of pigment present to the amount of photosynthesis 
that could be effected.” 
This expectation was not confirmed by the preliminary experi¬ 
ments carried out by Miss Irving, who found not only that etiolated 
shoots possessed no power of assimilation, but that shoots that had 
developed a considerable green colour did not possess the power. 
In Miss Irving’s experimental arrangement the plants were 
supplied with their own respiratory carbon dioxide, and the light to 
which they were exposed was the feeble light from a north window. 
Willstatter, using a much stronger light intensity (48,000 lux) 
and 5% carbon dioxide, obtained results which justified Blackman’s 
expectations that chlorophyll is really a limiting factor. There is a 
possibility that in Miss Irving’s experiments light was a limiting factor. 
Table XXIII. 
Assimilation Numbers of Etiolated Leaves becoming Green. 
Phaseolus vulgaris. 
Temperature 25 n C, 5% carbon dioxide. Light intensity, 48,000 lux. 
Light. 
Appearance. 
Weight 
of Leaf 
gm. 
Dry 
Weight 
gm. 
Leaf 
Surface 
cm 1 . 
Chloro¬ 
phyll 
content 
mg. 
CO 2 
ass. in 
1 hour 
gm. 
Ass. 
No. 
Not previously 
illuminated 
Pure yellow 
5-0 
— 
— 
<0-1 
0-007 
>70 
11th June, after 6 
hrs. illumination 
Greenish 
yellow 
4.4 
— 
— 
0-3 
0-040 
133 
29th May, after 2 
days’ illumination 
Yellow- 
green 
5-0 
0-70 
216 
4-0 
0-096 
24 
31st May, after 4 
days’ illumination 
Grass green 
5-0 
0-74 
260 
7-8 
0104 
13-3 
