398 Dr. F. F. Blackman and Mr. A. M. Smith. [Dee. 19, 
The mean of the two assimilation estimations, each representing 40 minutes, 
taken before 3 o’clock is 0:0073 grm. CO, per hour. With so low a CO>- 
supply we expect this factor to be the limiting one, and at 3 p.m. the supply 
bottle of CO:-solution was opened and filled up with a stronger solution. 
Owing to excessive generation of CO, in the tower, and perhaps also to 
imperfect mixing in the supply bottle, the final strength of the new affluent 
was only slowly attained, continuing to increase until 7 p.m. The behaviour 
of the assimilation after the change shows clearly that, in this particular 
combination of factors, the CO:-supply actually was limiting, for the assimi- 
lation increases suddenly at 3 P.M., and goes on rising continuously till 7 P.M., 
about in proportion to the altering the CO,-supply. 
Lxperiment B: COz-supply the Limiting Factor—In this case the tempera- 
ture was 19° C. throughout, and until 5 p.m. the light was 6. At 5 pM. the 
light was increased to 8:3. It was intended to maintain the COs-supply at 
00090 grm. per 100 cc. throughout, but, as the diagram of fig. 3 shows, its 
concentration declined in the last half of the ae 
7 8 p.m. 
- ae 
“O10 pane e 
000 
Tempe rarars [sere ThESUOKGHE 
Fidg.3 -Exp. B. 
The assimilation values for the first half average 0-0265, which might 
possibly be limited by either the light or the CO, (see fig. 1). On increasing 
the light it becomes clear that the latter is true, because not only is there 
no increase of assimilation, but there is a decrease due to the fall that has set 
in with regard to the COs-concentration. 
Luperiment C: Light the Limiting Factor.—An experiment was carried out 
at a temperature of 29° C. and a CO;-supply of 0:0490 grm. per 100 ce, 
