Aero 0. | On Vegetable Assimilation and Respiration. 397 
higher assimilation was noted than with much lower temperature at the 
same light intensity, 5°7. 
There were also other small indications in the same direction, 
When this work was taken up again in 1907 and 1908 definite experi- 
ments were made to determine what limit was actually set to assimilation by 
the light and the temperature employed respectively in the long series of 
earlier experiments. Five such experiments, all made with Elodea, may now 
be described briefly, and these will serve to exemplify the general principle. 
that is employed for experimentally determining which of the possible factors 
is actually limiting the function in any specific case. This principle may be 
formulated as follows :— When several factors are possibly controlling a Function, 
a small increase or decrease of the factor that is limiting, and of that Jactor 
only, will bring about an alteration of the magnitude of the functional activity. 
Hach of our experiments accordingly will involve the change of some one. 
factor in the middle of the experiment to test whether the assimilation 
responds to this change or not. 
Lixperiment A: COs-Supply the Limiting Factor.—-In this case the light 
intensity was 8 and the temperature 19° C. throughout the experiment. The 
! 2 3 4 S 6 7 p.m. 
ees ion | eeeeca| 
Ely aaa 
Light =8.0 Throughout 
emperature  19°OC Throughout. 
Fig.2 Exp.A. 
‘000 
+ 
COs-supply was at first 0:0032 grm. CO: per 100 c.c. solution, and at 3 p.m. it. 
was suddenly increased. The diagram in fig. 2 shows the course of the 
assimilation. As in all experiments in this section the abscissce are time 
and the ordinates grammes COQ. ; two separate curves‘are given, one for the 
assimilation (in grammes CO: assimilated per hour), and the other for the 
COs-supply in grammes COz dissolved per 100 c.c. of the solution,* 
* It is, perhaps, slightly unfortunate that the weight of CO, assimilated is greater, than 
the number given for the CO,-supply. This, of course, is only a question of units, as the. 
plant has in each hour ¢hree hundred cubic centimetres of the solution to draw from. 
