Carbon Assimilation . 
179 
Expressing this in terms of Blackman’s principle it must mean 
that neither light nor carbon dioxide is a limiting factor. The 
amount of carbon dioxide assimilated can then only depend on 
internal factors and the temperature. 
The ratio between the quantity of chlorophyll and the 
carbon dioxide assimilated in a certain time is termed by 
Willstatter the assimilation number (assimilation number = 
amount of C0 2 assimilated in one hour.\ 
chlorophyll content. ' 
Approximately constant values of the assimilation number 
would indicate that the assimilation depended only on the amount 
of chlorophyll, if variable values are obtained it means that other 
factors come into play. 
It is to be regretted that only the tables which illustrate the 
conclusions are given by Willstatter; none of the preliminary work 
necessary for the justification of the conclusions is quoted. 
Normal Leaves. 
In Table XV we give the results obtained by Willstatter for 
normal leaves. 
Table XV. 
Assimilation Numbers of Normal Leaves. 
Concentration of C0 2 , 5%. 
Rate of Gas Current, 4-5 litres per hour. 
Species. 
Temp. 
Light 
Int. 
in Lux. 
Wt. of 
Leaves 
gm. 
Dry 
Weight 
gm. 
Leaf 
Surface 
sq. cm. 
Chloro¬ 
phyll 
content 
mg. 
co 2 
ass. 
in 1 hr. 
gm. 
Ass. 
No. 
Rubus Eubatus 
25° 
48000 
5-0 
1-80 
356 
16-2 
0 094 
5-8 
Syringa vulgaris 
25° 
48000 
12-0 
3-45 
371 
141 
0-091 
6-5 
Sambucus nigra 
25° 
48000 
80 
2-20 
343 
17-8 
0117 
6-6 
Ulmus 
25° 
48000 
80 
2-35 
421 
13-0 
0-089 
6-9 
PrunusLaurocerasus 
30° 
75000 
100 
3-40 
— 
12-2 
0 098 
8-1 
Primula 
30° 
75000 
100 
0-90 
— 
11-4 
0105 
9-1 
Hydragea opuloides 
30° 
75000 
10-0 
1-20 
— 
9-2 
0 060 
6-5 
Pelargonium zonale 
30° 
75000 
100 
0-96 
— 
12-5 
0 093 
7-4 
From the numbers given in this table there would seem to be 
a rough parallelism between the amount of chlorophyll and 
assimilation. But in all the cases given the leaves were in the 
same stage of development and all were rich in chlorophyll. On 
the other hand leaves from the same plant, but in different stages 
of development, exhibit much wider variations in the assimilation 
number, as the following table shows. 
