Carbon Assimilation. 
183 
Leaves poor in chlorophyll (Yellow Varieties). 
Leaves poor in chlorophyll, e.g., yellow varieties with a chloro¬ 
phyll content of from 15% to 3%, or even less, of that of the leaves 
of the normal green varieties, exhibit a marked deviation in the 
proportionality between chlorophyll and assimilation. The numbers 
given in Table XXI1 for the yellow varieties are not maximal values 
of the assimilation, for it was found impossible to use the maximum 
light intensity without injuring the leaves. Under certain conditions 
it was found that at 15 n C instead of 25°C the absolute amount of 
carbon dioxide absorbed by equal surfaces of yellow and green 
varieties can in the former reach a value as high or even higher 
than that taken in by the leaf of the normal variety. 
Table XXII. 
Assimilation Numbers of Leaves of Green and Yellow 
Varieties of Elm. 
Ulmus, 5% C0 2 , 3000 candle power at 35 cm. distance (24,000 lux). 
Variety. 
Temp. 
Weight 
of Leaf 
gm. 
Dry 
Weight 
gm. 
Chloro¬ 
phyll 
mg. 
Leaf 
Surface 
cm 2 . 
CO 2 
ass. 
per hr. 
gm. 
CO 2 
per sq. 
metre 
gm. 
Ass. 
No. 
Chlorophyll poor ... 
25° 
8-0 
20 
0-95 
321 
0-075 
2-3 
79 
do. 
15° 
the 
same leaf 
2-0 
0-95 
321 
0 056 
1-7 
59 
Chlorophyll rich ... 
25° 
80 
2-35 
130 
421 
0-089 
2-1 
6-9 
do. 
15° 
8-0 
2-35 
130 
421 
0-059 
1-4 
4-5 
Willstatter points out that from this table it may be observed 
that the assimilation of chlorophyll-poor and chlorophyll-rich leaves 
is very similar at lower temperatures, but that the quantity of 
assimilation per unit quantity of chlorophyll is much greater in the 
yellow varieties. 
Willstatter seems to indicate that the conditions in the yellow 
varieties are of great importance in judging the factors which 
influence the assimilation. As temperature variations do not 
influence the assimilation in such leaves, while decrease in light 
decreases the assimilation, he concludes that in this case the 
enzymatic system is more developed than the chlorophyll system, 
which thus controls the rate of assimilation. The reaction of the 
chlorophyll system being photochemical it may be assumed to have 
a temperature coefficient not far from unity, while the enzymatic 
process has a temperature coefficient of a magnitude of 2 to 3. In 
the normal leaf the chlorophyll system is more developed and the 
enzymatic process limits the rate of assimilation. Consequently 
