— 243 — 



(In Helianthus Blackman found 0.7mgCO 2 per hour per 50 

 cm 2 at 19°). 



Hence it may be calculated that the maximal C0 2 assimilation 

 is about 8 times as great as the respiration. 



In the stems of Sinapis alba the respiration was estimated as 

 0.16 mg C0 2 per lg per hour (20°). 



3a. Percent production of matter calculated. From 

 the data given above it is possible approximately to calculate the 

 percent production of matter, this value being defined in the 

 manner stated on page 219. We will work out the calculation in 

 Sinapis alba for the month of July. A determination of the average 

 intensity of light in the different hours of a day in this month is 

 given on page 234. The average temperature in July is reckoned as 

 20° to facilitate the calculations. To the sure the mean temperature 

 for this month is in Denmark only 16.0°. But in sunshine the leaf 

 temperature will be some degrees above the temperature of the air. 



The calculations are carried out for a plant with a leaf area 

 of 100 cm 2 (upper + lower surface). Such a plant was found to 

 have the following composition. 



Weight. dry matter. 



Leaves 1.30 g 0.168 g 



Stem -'- root 0.96 g 0.111 g 



2.26 g 0.279 g 



Hornberger (1885 p. 415) found in Sinapis grown for 28 days, 

 for a leaf area of 50 cm 2 : 



Weight. dry matter. 



Leaves — 0.170 g 



Stem -f root — 0.075 g 



2.24 g 0,245 g 



The result of the calculations is as follows: 

 Gain of dry matter: Assimilation. 



Time 



Intensity of light 



Real Assimilation 



in Bunsen units 



(per hour per 50 cm 2 ) 



12-1 



39 



67 



1—2 



38 



6.7 



2-3 



36 



6.7 



3—4 



33 



6.7 



4-5 



29 



6.6 



5—6 



22 



6.4 



6—7 



14 



5.6 



7—8 



4 



2.6 



48.0 mg CO a assimilated per \ day 

 per 1 day per 50 cm 2 96 mg = 60 mg dry matter. 



