1905. | On Vegetable Assimilation and Respiration. 441 
These data are plotted in fig. 6, where the line from 0:0167 to 0:0140 
represents the fall of the assimilation maxima at 295 due to the time-factor. 
We see from this, that at 10.30 am, 14 hours ab initio, we should 
expect a value of 0°0148. With 0°28 sunlight at this time in Experi- 
ment XV we get a value of 0:0116—“.2., 0-28 sunlight gives 116/148 of 
maximal assimilation at 29°'5. Therefore, to give the whole maximal assimila- 
tion (14 hours abd initio), there will be required 0°36 (= im x 0:28) sunlight. 
One might make an apparently more direct and absolute statement to the 
effect that the photosynthetic energy in 0°28 sunlight is sufficient to reduce 
0:0116 gramme COs, but we shall see presently reason for regarding the 
statement which takes notice of the time-factor as a more critical and precise 
one. 
Before going further into this matter, let us take a similar experiment with 
a leaf of Helianthus. 
After several failures, in Experiment X VI we succeeded in getting all our 
data into one experiment. 
The leaf was set up at 8 A.M. exposed to full intense sunlight plus diffuse 
light, and the assimilation value of 0:0290 was obtained at about 30° C. This 
we regard as obviously maximal for the temperature. To make certain of 
this, a second estimation was made with direct sunlight only, the diffuse 
light being cut out by the wooden tube. Again, in spite of the diminution of 
light, about the same assimilation, 0:0284, is obtained, and this point is proved. 
Then the diffuse light alone is employed (and, indeed, the sky had clouded 
up), giving a value of 0:0170, which is not nearly maximal for the tempera- 
ture of 29°-5, but only about 2 of the maximal amount. On the clouds clearing 
right away an estimation was made with 0°62 sunlight at 30° C., and this 
gave a value of 00224, large, but not maximal as was the case with cherry- 
laurel in this intensity of light. To conclude this satisfactory series, an esti- 
mation was again made in full sunlight, plus diffuse light, to get a maximal 
reading (one cloud came up at 2.6 P.M., and the current was shifted back to 
the preliminary tube till 2.29 p.m.). The value obtained was 0:0238, showing 
the usual effect of the time-factor, and falling off from the early value of 
00290. 
Connecting up (in fig. 6) the maximal values by a line, we find that at 
1.15 the value would have been 0:0248. So at that hour 0°62 sunlight gave 
224/248 of maximal assimilation at about 29°-5 (5 hours ab initio); therefore, 
for the whole maximal assimilation, 0°69 sunlight is required. 
The absolute form of statement would be that 0°62 sunlight can reduce | 
0:0224 gramme CO». — | 
