182 
Ingvar Jorgensen and Walter Stiles. 
Some leaves which remain green until they fall off keep their 
assimilatory power, so that in spite of the lateness of the season 
and high chlorophyll content, the assimilation numbers are still 
high. Yet in other cases where the chlorophyll content of the 
leaves in autumn is still high the assimilation numbers are remark¬ 
ably low, while there is a considerable difference between the 
assimilation numbers of young and old leaves from the same plant. 
These results are given in Tables XX and XXI. 
Table XX. 
Autumn Leaves with High Chlorophyll Content and 
Normal Assimilation Numbers. 
Date. 
Species. 
Weight 
of Leaf 
gm. 
Dry 
Weight 
gm. 
Leaf 
Surface 
cm 1 . 
Chloro¬ 
phyll 
content 
mg. 
CO, 
ass. 
per hr. 
gm. 
Ats. 
No. 
26th October ... 
Cydonia japonica 
var. Moerlosii 
(falling leaf) 
10-0 
4-50 
301 
163 
0-119 
7.3 
27th October ... 
Clerodendron 
trichotomum 
(fallen leaf) 
6-2 
1-28 
211 
9-3 
0115 
12-3 
14th October ... 
Lonicera tatarica 
(fallen leaf) 
4-0 
1-20 
299 
3-3 
0 020 
61 
Table XXI. 
Autumn Leaves with Same Chlorophyll Content but 
different Assimilation Nlimbers. 
Date. 
Species. 
Weight 
of Leaf 
gm. 
Dry 
Weight 
gm. 
Leaf 
Surface 
cm 2 . 
Chloro¬ 
phyll 
content 
mg. 
CO, 
ass. 
per hr. 
gm. 
Ass. 
No. 
11th November 
Ampelopsis 
tricuspida 
Veitchii 
(fresh, green) 
7-0 
1-50 
— 
6-8 
0-014 
20 
16th October ... 
Ampelopsis 
quinquefolia 
(older, green) 
50 
1-05 
251 
6-4 
0-006 
0-9 
17th October ... 
Ampelopsis 
quinquefolia 
(younger leaves 
from apex of shoot) 
5-0 
1-15 
325 
6-4 
0 050 
7-9 
The low assimilation number after exposure to low temperatures 
is rapidly increased on exposure to higher temperatures. Thus in 
the case of leaves of Ampelopsis Veitchii gathered at 4"C the 
assimilation number gradually increased from less than 0-8 to 2 6 
after H hours at 25°C, and increased up to about 4 when it remained 
constant. 
