
1905. ] On Vegetable Assemilation and Respiration. 455 
work actually done under various environments, the fact must not be lost 
sight of that the leaf-cells are resporing in the light, and that the CO, that they 
produce has continually to be reduced by the radiant light-energy before so 
low a partial pressure of CQz is arrived at that further supplies may diffuse in 
from the atmosphere. The amount produced in respiration will vary with 
the temperature of the cells and may, at about 30° C., be equal to half the 
possible inflow from without. 
The following table represents the waste of photosynthetic energy that may 
be considered to go on when the natural supply of COs, limits the intake 
to 0:0077, with various illumination and temperature. 
The table avoids extreme intensities of illumination and deals with two 
that we have actually observed. The assimilation-maxima given in the third 
column are all observed values except the last, which is only an approximation. 
The energy is throughout expressed in terms of the work it can do in photo- 
synthetic reduction, 2.¢., in grammes COs per hour per 50 sq. cm. leaf-area :— 









| | 
| Aug. 8, 1904, noon. 
Hypo- Intake of 
thetical | Assimila- | CO, of CO, Actual | In sun, | In shade, 
Leaf. tempera- tion- respira- + from = assimila-} 0 °0530.§ | 0 -0170. 
ture of |maximum.| tion. atmo- tion. 2aset 
leaf cells. sphere. 
Surplus | Surplus 
| energy. | energy. 
“©. 
Cherry-laurel 10 0:0042 | 0:0005 + 0:-0037 = 0:0042 | 0:0498 | 0:°0128 
Helianthus...) 19 0:0098 | 0:0008 + 0:0077 = 0:0085 | 0:°0445 | 0 -0085 
* Soo) 2) 0 -0285* | 0:0020 + 0-0077 = 0:0097 | 0:0443 | 0-0078 
Cherry-laurel 37 °5 0-0238+ | 0:0044 + 0:°0077 = 0:-0121 | 0°0409 | 00049 
Helianthus...) 35 0 -0400f | 000382 -+ 0-0077 = 0:0109 | 0°0421 | 00061 


The last two columns show how large is the waste of photosynthetic energy 
with the limited intake of CO2 that our atmosphere provides for. 
It will be observed that raising the COs-content of the atmosphere from 
three up to six parts in 10,000 will, as Horace Brown has shown, double the 
intake, and this will do away with all waste of energy in the last four cases in 
the shade. To prevent this waste in the insolated leaf an increase of six fold, 
* Observed 14 hours ab initio. 
F oD) 2 99 ” 
{ Approximately estimated. 
§ This represents the energy available for photosynthesis in Experiment XVI ; in that 
case (reading 4) 0°62 sun gave 0:0224 .. whole sun alone may be taken at 0°0360. The 
diffuse light (reading 3) was 0°0170; fora leaf freely insolated these two must be added 
together. . 
