1905.] On Vegetable Assimilation and Respiration. 427 
iting: _off characteristic of the afternoon diffuse light. The temperature of 
the bath was- 30° C., and that of the-leaf would be. about 32°. The absolute 
amounts of real assimilation in the first three readings 0:0122, 00118, 0:0109, 
are such as would be maximal for the temperatures of 26° C., 25°26, 247 C= 
the diffuse light is evidently, though adequate for the possible assimilation at 
.. these temperatures, not adequate for that at 32°. To provide evidence in this 
~ direction, the shadow-buard was removed at 3.30, and the leaf adjusted normal 
* to the sun’s rays, when the assimilation at once went up to nearly double, ie., 
to 0:0200. The bath became 1° hotter and the leaf would be heated 5° to 6° C. 
higher still by the sun’s direct radiation, so that in substantial harmony with 
this we find the new amount of assimilation to be that maximal for 34°-6 C., or 
for a degree or two higher when allowance is made for the fact that the 
heating has been prolonged for four hours: at this temperature the time factor 
is not negligible. 
_ Experiment VIII (July 18, 1904).—Cherry-laurel ; Weight, 1:98 grammes ; 
Area, 60 sq. em.; Current Rate, 800 cc; CO2=24 per cent. 










(average). 
| | Pember CO OOF Pee 
- Exposure. Time. Illumination.| ture of | | . absorbed a 
naan supplied. by leaf per hour 
j a | * | per 50 cm?. 
| Leaf-chamber ex- | 11.30 a.m.— Cloudless, 30 2 Prelimjinary 
posed to diffuse} 12.30P.m. thin haze 
light only over sun 
Shadow-board | P.M. ; 
12.30—1.30 re 30 ‘1 0 -0375 0 °0115 0 ‘0122 
1.30—2.30 — 30°1 0-0392 | O-0111 | 0°0118 
2.30—3.30 of 30 *1 0 0362 0 -0100 0 ‘0109 
| 3.80 p.m, leaf ex-| 3.30—4.30 " 3th 0-0350 | 0:0197 | 0-0200 
exposed to sun 
plus diffuse light 







The assimilation-value in the diffuse light is here an exact measure of its 
intensity, as the temperature is not limiting. It is thus proved not to be 
very intense, which is due to the fact that the day was cloudless, and but 
little sun was therefore reflected by clouds into the “shade.” A distinctly 
higher value 0°0146 was obtained in Experiment II, and even that was limited 
by the temperature of 29° C., while in the next experiment a very much 
higher value is obtained ona day with abundant white cumull. 
Experiment [X.—In this experiment with Helianthus the temperature of 
