
1905.]| On the Physiological Processes of Green Leaves. 85 
temperature must in this case have been /ower than that of its surroundings, 
and this temperature difference 6—@, will again be measured by 7/2e. 
Since the average velocity of the wind during the experiment was 
120 kilometres per hour (= 200 metres per minute) and the “ emissivity ” of 
the leaf under “still air” conditions was 0:015 calorie per square centimetre 
of surface per minute for a temperature difference of 1°, the “ emissivity,” e 
for the above speed of the air is represented by 0:015 + 200 x 0:00017 = 0:0490, 
hence, 
O—0, = 0:1817+(2 x 6-049) = 1°84 C. 
The mean temperature of the surrounding air being 27°2 C., that of the 
leaf was consequently 27-°2—1:84 = 25°36. 
If, in this last experiment, we represent the sum of the energy received by 
the leaf both from solar radiation and from its surroundings by 100 we get 
the following results :— 
(w). Energy used for photosynthesis ............ 0°72 calorie. 
(W). a EPANSplratiOM...ceee. ast 80:°38\. 5 
(W+w). Total energy expended in internal work... 81:10 _,, 
R—Ra. Solar radiant energy transmitted by leaf. 18°90 __,, 
L000. “2 
Since the receipt and expenditure of energy must necessarily balance each 
other for a given period of time it is somewhat instructive to arrange the 
results in the form of a “Revenue and Expenditure Account” for the leaf. 
For the last mentioned experiment this comes out as follows :— 
Calories per square centi- 
metre of leaf-lamina 
Revenue account— per minute. 
Total solar radiation incident on the leaf ............ 0°2746 
Gain Of energy irom surroundings ...............0...0% 01817 

Total energy reaching 1 sq. cm. of leaf per min. ... 0°4563 
Expenditure account— 


Energy used up in photosynthesis ................0. 6. 00033 
: ELAMSOUEAHIOM IH!) (50). Wiad -tlddenieWeee. 03668 
Total energy used for internal work..............0..004. 03701 
Incident solar energy transmitted .................. 00s 0:0862 
0:4563 
