: 
ON THE RESPIRATION OF PLANTS. 345 
Taking these precautions, a satisfactory series of estimations through 
a range of temperature from — 6° C. to + 45° C. was obtained. 
The general conclusion is that there exists for each temperature a 
maximal assimilation specific to that temperature. The amount of light 
required to produce the specific maximal assimilation varies directly with 
the magnitude of the maximum. When this is once reached further 
increase in the illumination or in the amount of CO, supplied produces 
no longer any augmentation of the assimilation. 
The amount is just determinable at — 6° C., and then rises rapidly 
with higher temperatures, giving a curve which is convex to the tempera- 
ture abscissa. The curve is similar to the accepted curves for the effect 
of temperature on respiration, and it rises more and more steeply at 
higher temperatures—certainly up to 38°C. 
At temperatures about this point the leaf is not capable of maintain- 
ing its initial high rate of assimilation for any long time, so that the 
values obtained for successive hourly estimations with the same leaf form 
a rapidly declining series. The higher the temperature the shorter the 
duration of the period of maximal assimilation, and it becomes experi- 
mentally impossible with hourly estimations to obtain the maximal value 
at temperatures close to the fatal temperature of 45° C. The final 
numbers actually obtained, which can be only swb-maximal, show a 
conventional ‘optimum’ at a temperature about 38° C., with a subsequent 
very rapid decline. 
The relation between CO,-assimilation and various intensities of 
natural illumination has been worked out by Dr. Blackman and Miss 
Matthaei conjointly. The detailed research is in course of publication, 
but it may be stated here that determinations have been made of the 
assimilatory value of the natural illumination at dawn, at midday, in sun 
and shade, during rain and storm, and at dusk. It is shown that the 
diffuse light of the whole heaven compares favourably with feeble direct 
sunshine as an illuminant. Estimations have also been made of the 
exact fraction of sunshine which is required to produce the specific 
maximal amounts of assimilation for a given temperature (50° C.) both 
with cherry-laurel leaves and with leaves of Helianthus tuberosus. 
From these and other determinations it seems to follow that equal 
areas of different leaves (though of very dissimilar types) require iden- 
tical amounts of light te produce the same amounts of CO,-assimilation. 
Botanical Photcgraphs.—Report of the Committee, consisting of Pro- 
fessor L. C, MIALL (Chairman), Professor F, E. Weiss (Secretary), 
Mr. Francis Darwin, and Mr. A. G. TANSLEY, on the Registrution 
of Photographs of Botanical Interest. 
Firty photographs have been added this year to the Register, which now 
contains 230 photographs. The additions have been contributed by the 
Rev. T. A. Lea, Mr. Francis J. Lewis, Professor F. W. Oliver, Mr. A. G. 
Tansley, and Mr. Arthur Reid. They illustrate some of the botanical 
features of the British coast and British moorlands, the flora of the 
Alps, and of the Mediterranean, and are the type of photograph of which 
it will be very useful to have a record. 
