430 Dr. F. F. Blackman and Miss G. L. C. Matthaei. [Apr. 11, 
Experiment ‘X (August 11, 1904)—Helianthus tuberosus ; Weight, 1:20 
grammes; Area, 61:2 sq. em.; Current Rate, 800 cc. -" CO; =4 per 
cent. (average). © 7 i | | | 
Leaf-chamber stationary all Day, facing South, elevated 30°. 








Tempera- | Tempera- | CO _, Beal 
Time. Illumination. ture of ture of ee d Abaca assimilation 
bath. leaf, | S*PPUPM- | by teat. || eeu aes 
per 50 cm*. 
lisa es | ; | | 
A.M. é g 
9.30—10.30 | Very overcast ......... — = Prelim |inary ae, 
10.30—11 say beeen se _ ie far 0 -0362 000384 | 0 :0062 
11—11.30 | Raining, but lighter 17-0 18 ‘0 0 -0362 0:0050 | 0-:0089 
11.30—noon | Raining, lighter still) 17:1 18 ‘0 0:0377 | 0-0051 | 0-0090 
P.M. 
noon—12.30 | Raining, heavy clouds 17:0 mil ecr, 0 0390 0 0050 0 0089 
Be 4 Heated 
MLO——2.20) |; Raimime | Leiie ese. "298 
2.20—2.50 PRM EAR CML AR Ann 18, Wisur-32¢s} 30 °5 0 -0240 0 -0087 0 0163 
Ree | J Cooled 
2.50—8.12 | No rain, lighter ...... 166 | 
3.12—3.42 | Much brighter ...... | 16°6 18 *2 0:0235 | 0-0050 0 0089 
3.42—4.12 |Sun out, but leaf 16 °6 18 *4 0 -0254 0 0052 0 0092 
shaded by the 
shadow-board | 








the last two readings. This can only be interpreted as being due to the fact 
that the assimilation is limited by the temperature, which has been kept 
steady throughout. 
Striking confirmation of this is obtained by raising the temperature for the 
fifth reading. The sky was no lighter than before, but yet, on the tempera- 
ture being brought up to 30°5, the assimilation at once doubled, becoming 
0:0163. This number will then be the exact expression of the intensity of the 
illumination only, fur an assimilation of at least 0°0289 is possible at this 
particular temperature. 
Nothing could show better than this experiment the impossibility of 
investigating the effect of varying illumination while ignoring the leaf- 
temperature. | 7 
In Experiment XI with Helianthus, the temperature of the bath was varied 
up and down several times for alternate pairs of readings, and careful records 
of the temperatures of the leaf and of the bath were made euely, 10 minutes, 
or less, according to the variability of the insolation. ; 
