448 Dr. F. F. Blackman and Miss G. L. C. Matthaei. [Apr. 11, 
The leaf of Aponogeton, which normally floats on water, was here simply 
stood up with its cut stalk dipping in the water at the bottom of the 
chamber. The air in the chamber was quite damp, and the leaf showed no 
signs of wilting at the end of the experiment. Bomarea is a climbing 
monocotyledon with its morphologically upper leaf-surface downwards. 
The four other leaves examined, then, agree with our standard within 
5 per cent., and the diversity of type of these five seems to us to be wide 
enough to prove that leaves in general have the same coefficient of economy in 
the photosynthetre process. . 
There is, then, no difference in leaves in this direction, and it would appear 
from fig. 2 that even their temperature-maxima would be the same at very 
low temperatures. The fundamental existing specific differences would seem 
to lie in their different coefficients of acceleration of activity with increase 
of temperature. For a rise of 10°, the increase with cherry-laurel is 
2:1 [00038 at 9° and 00080 at 19° C.], while with Helianthus it is certainly 
bigger, perhaps 2°5, but we have not exact data yet for giving the coefficient 
a precise value. 
Perhaps this specific difference of the coefficient of temperature accelera- 
tion holds with growth and other metabolic processes, and a high coefficient 
might be a general characteristic of those plants which are recognised to be 
very “active” in vegetation. 
The general views expressed in this paper involve the assumption that 
with all intensities of light the amount of assimilation is proportional to the 
intensity of the light unless some secondary or limiting factor is at werk. 
Timiriazeff* has recently expressed the view that for plants (in general) 
there is a maximum of assimilation corresponding to half the intensity of 
direct sunlight, and that with higher intensities no further increase of 
assimilation takes place. 
We feel convinced that this result is due to the neglect of some limiting 
factor, probably the temperature, the effect of which has been ignored by 
nearly every investigator of these questions. By selecting an appropriate 
temperature one can get a maximum of the kind described by Timiriazeff 
at any desired low fraction of sunlight for any given leaf. 
There is certainly no general value for the fraction of sunlight utilised by 
leaves, either at a given temperature, or at the highest functional tem- 
perature, but, on the contrary, it is just on this point (being a consequence 
of the combined principles of uniform economic coefficient and varied 
* Timiriazeff, ‘ Roy. Soc. Proc.,’ vol. 72, p. 451, 1903. 
