

1905.] On Vegetable Assimilation and Respiration. 417 
of its horizontal and vertical movements until the leaf was normal to the 
sun’s rays. After a quarter of an hour “preliminary ” an estimation of the 
combined effect of low direct sun and diffuse light was made—6.15 to 
7.15 AM. During this and subsequent readings the PLES was readjusted 
to face the sun every 10 minutes. 
~ Throughout the series of readings the temperature of the bath rose 
continually, as the sun, shining on the supply-water-pipe and on the bath, 
gained in power; the rate of water-flow remained unaltered. 
The graphic representation, fig. 3, allows us to gather an idea of the rapid 
UOIQe LISS 
209 sWWeUZI}IW SYyqueg 

; 4 
Ante meridian | Post meridian 
Fig. 3. 
mounting up of early morning assimilation. It is not true, however, that 
the actual amounts are measures of the increase of light. Subsequent work 
made it probable that the temperature would be the limiting factor in this 
case, the light being in excess. In Column 5d are given the temperatures 
for which the observed assimilations are maximal; we find that they agree 
well with our other experiences of how much such insolation heats up a 
leaf. The assimilation values are in this case to be taken as a direct 
measure of the leaf-temperature. 
In these early experiments we rather interpret than prove the significance 
of the assimilation numbers. Direct proof that such and such effects are 
VOL. LXXVI.—B. 2F 
