458 Dr. F. F. Blackman and Miss G. L. C. Matthaei. [Apr. 11, 
of utilising for assimilation the whole of the appropriate: radiation in full 
sunlight, so experiments were made to determine what fraction of this is 
used at a given temperature. For cherry-laurel it was found that 0°28 sun, 
near noon, near the middle of August, can reduce 0:0116 gramme CO, per 
hour per 50 sq. cm. of leaf area. With Helianthus, 0°62 sunlight, at about 
the same time, reduced 00224 gramme. These indicate for full sunlight the 
photosynthetic values of 0:0414 and 0:0361 on the two occasions. Making a 
correction for the time factor, the values come out higher and still closer 
together. 
The highest assimilation actually measured (Experiment XVI) was 0:0290 
gramme COs per 50 sq. cm. leaf area per hour for Helianthus at 29° C. 
This is about 2900 c.c. COz per square metre per hour. 
The nature of the specific assimilational characteristics of different types 
of leaf was investigated, and it is shown that :— 
1. Equal intensities of light, incident upon equal areas of different leaves, 
produce, when lght is the limiting factor, equal amounts of assimilation. 
This is proved to be true within 5 per cent. for such diverse leaves as 
cherry-laurel, Helianthus, Tropeolum, Bomarea, Aponogeton. 
2. All leaves have the same economic coefficient of photosynthesis, using 
the term in the narrow sense to refer only to those radiations specific to this 
process. 
3. At low temperatures different leaves, such as Helianthus and cherry - 
laurel, have similar assimilation-maxima, but at high temperatures the 
maxima diverge. At 29°5 C. Helianthus can assimilate twice as much COs 
as cherry-laurel. 
4. This is harmonised with the first law by showing that Helcanthus 
requires just twice as much light to attain this double assimilation. 
5. The essential difference between these two leaves lies in their having 
different coefficients of acceleration of their assimilation-activity with increase 
of temperature. 
6. From this it results that the two leaves utilise different fractions of 
sunlight at any temperature: this fraction is to be found for any temperature 
by dividing the assimilation-maximum of the particular leaf at that tem- 
perature by the photosynthetic value of the sunlight. 
7. There is no optimum intensity of light for assimilation. 
In Nature, the high values of assimilation that are obtained experimentally 
cannot take place, because assimilation is limited by the small pressure of 
COs in the atmosphere. 
There is thus a general waste or diversion into other channels of the photo- 
synthetic energy in sunlight and diffuse lght. 
