
1905.] 
On Vegetable Assimilation and Respiration. 
421 
Experiment IV (July 30, 1904)—Helianthus tuberosus; Weight, 1-47 
grammes; Area, 70-1 sq.cm.; Current Rate, 800 c.c.; COz = 2°5 per cent. 





(average). 
Leaf-chamber faced towards the Approximate Position of the Sun, at 
Intervals. ) 
Tempera- co CO, Rata 
Time. Illumination. ture of ae absorbed | 98S ation 
bathe supplied. by leaf. per hour 
per 50 cm?. 
P.M. ° 
12.30—1.30 — — Preliminary 
1.30—2.30 Heavy leaden clouds; 18 -2 0 :0426 0 -0011 0 0015 
storm drifting up 
2.30—3.30 Violent thunderstorm at 18 °3 0 0384: 0 -0032 0 ‘0030 
first, then slowly clear- 
ing up 
3.30—4.30 Brighter; no rain..........:. 18°3 0 0386 0 0073 0 0059 
4.30—5.30 Sun at first, then clouded 18 °3 0 -0394 0 -0050 0 0043 
over; storm drifting up 
5.30-—6.30 Overcast, steady rain; 18 ‘0 0 :0380 0 0007 0 :0010 
6.10, heavy storm 





In the third reading rain ceased, and 0:0059 marks the brighter period. 
Soon, after a few gleams of sun, a second storm began to drift up, and this 
burst at the end of the fifth reading. These assimilation values are plotted 
in fig. 3, and show the passage from one big storm to another through a 
brighter interval. The assimilation is in no case near the maximum for the 
temperature, and is a measure of the light only. Possibly the vitality of the 
leaf has been lowered by prolonged sojourn in the chamber not far from the 
mercury connecting cups. 
We now come to a group of three experiments under the natural sequence 
of illumination, in which the temperature of the leaf was actually determined 
thermo-eleetrically throughout the experiment. 
Experiment V took place on a day which was dull up to about 3 o'clock, 
when the sun came out brightly ; at the same time the temperature of the 
bath was raised by the circulation of hotter water. The leaf is thus in the 
last reading both hotter and better lighted than in the first three readings, 
and there is a marked change in the assimilation. | 
The first three readings give assimilation values of 0:0073, 0:0065, 0-0077, 
the average temperature of the leaf being about 20°5 C. Now, the assimilation 
