
1905.|. On the Physiological Processes of Green Leaves. 69 
carbon dioxide per square decimetre of leaf per hour, or less than one-tenth of 
the amount observed in the winter respiration of the greenhouse plants. 
The influence of increased temperature in accelerating respiration is, as is 
well known, very considerable. This is illustrated in a general way by the 
following experiments. made in the summer of 1900 on leaves of Helianthus 
annuus whilst still attached to the plant. 
Table X VII.—Influence of Temperature on the Respiration of Leaves of 
Helranthus annwus. 
CO, respired per 
square decimetre per 
Temperature, hour in cubic 
C. centimetres. 
19°°6 0579 
ol 2 1°656 
36°73 1°859 
ao 2 2°080 
41°77 2451 
The above experiments are not strictiy comparable, since they were made on 
different leaves of the same plant and on different days. A more complete 
series was made in a darkened glass cylinder immersed in water which was 
kept at a constantly regulated temperature, but the record of this experiment 
has been lost. 
Part III.—TuHE ENERGETICS OF THE LEAF. 
CONTENTS. 
PAGE 
Section (1). General Considerations of the Thermal Relations of a Leaf to its Surroundings 69 
Section (2). Experimental— 
(a) Determination of the Total Incident Radiation .............cceseeeeeee scenes 88 
(6) The Absorption of Solar Radiation by the Leaf-lamina ..................... 90 
(c) The Selective Absorption of Radiant Energy by the Leaf .................. 93 
(d) Relative Absorption of Solar Radiation by Albino and Green Leaves ... 94 
(e) The Thermal Emissivity of the Leaf-lamina ..............ccceceeese eee eeeneeees 97 
(f) Details of Experiments on Leaves submitted to Solar Radiation, showing 
the Mode of Disposal of the Incident Energy under Defined 
BP OMOAG LOUGH ee seas siincy cals dsinns oh ene dsiemeeeding desea geeiseoinerisee arm clnee Waar VE 
Section (1)—Greneral Considerations of the Thermal Relations of a Leaf to 
! ats surroundings. 
Before we can profitably discuss the general question of the exchange’ 
of energy between a living leaf and its environment, it is necessary to 
Pp 
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