418 Dr. FF. B lackman and, Miss G. L. C..Matthaei,. [Apr. 11, 
due to light or to temperature as limiting factors will be found: in later. 
experiments. bs at | . 
Experiment II deals with exposure of a leaf “in the shade” to thigh 
collective diffuse light of the sky, the direct sunlight being always cut off. 
by the shadow-board. In this experiment, and in this one alone, the leaf- , | 
chamber was not in the bath, but was placed horizontally in the free air 
with thermometers in contact . with it to give a rough idea of the shade-_ 
temperature around the leaf. The temperature of a leaf within a chamber 
in the shade is quite 2° above that of the mercury thermometer (see p. 409). 
We may thus assume in the first reading the leaf to have been at about 
29° C., and we find that the assimilation is maximal for 29°4 C.-(¢f p. 413) ; 
evidently the diffuse light in the shade is more than enough for an assimila- 
tion of 0:0146, but the temperature limits it to that amount. In the second 
reading the assimilation is a little lower, while in the third reading it is 
much smaller, and it is clear that this is due to diminution of light, as the 
Experiment II (July 13, 1904)—Cherry-laurel; Weight, 1°70 grammes ; 
Area, 543 sq. cm.; Current Rate, 800 ce; CO.=2:4 per cent. 
(average). . | 
Leaf exposed to Diffuse Light under Shadow-board all Day. Chamber in 
Air, not in Bath. : 
| 








vember: CO | O25 ee 
Time. | Illumination. ture of | 2 absorbed 
Sri | : supplied. he lost per hour 
pee y * | per 50 em?, 
11.45 a.M.—1 p.m.) White cumuli, with gleams 24-9 7 Dee 
| of sun i 2750" ia ry 
P.M. pa ae - 
1—2 ” oy i) 627.0 0.°0376 | 0-0187 0 0146 
2—3 » 3 |. 2277 -O 0-0387 | 0-0123 00131 
sun 2.20—2.50 | | 
3—4: White cumuli, with gleams 26 °6 0 -0397 0 0100 0 -0110. 
. of sun | . 
45.15 | Mostly. eunltue es ean 26 -0 
5.15—6.15 0 1 ERSTE Sab): Jee ately 25°2 | 0:0376 0 0048 0 -0060 
6.15—7.15 Sun; cloudless ; 6.40, sun 24 3 0 0390 0 -0046 0 0054. 
below roof 21°9 " 
7.15—8.15 | Cloudless; sunset 8.11... { Bale } 0-0386 | 0:0027 | 0:0033 — 
; lf 19-8 7 | = | f minus 
8.15—9.15 Dusk, faint clouds sarenteee { 17°8 } Pp 0 0367 0 0010 




