— 250 — 



The result of the calculations (for full daylight) is: 

 Gain of dry matter (C0 2 assimilation). 



Time 



Intensity of light 



Real assimilation 



in Bunsen units 



per hour per 50 cm 2 



12—1 



39 



0.9 



1-2 



38 



0.9 



2—3 



36 



0.9 



3-4 



33 



0.9 



4—5 



29 



0.9 



5—6 



22 



0.9 



6—7 



14 



0.9 



7—8 



4 



0.8 



7.1 mg C0 2 assimilated per § day; 

 per 1 day per 50 cm 2 14.2 mg = 8.9 mg dry matter. 



Loss of dry matter (respiration). 



Leaves 24 X 0.1 = 2.4 mg 



Leaf -stalk 24 X 0.85 X 0.20 = 4.1 - 



6.5 mg C0 2 = 4.0 mg dry matter. 

 The production of dry matter per 50 cm 2 per day = 8.9 — 4.0 = 

 4.9 mg = 2.1 °/o of the dry matter of the plant. 



6. Summary. 



Finally to summarise shortly the difference between Sinapis 

 alba (a light plant) and Oxalis acetosella (a shadow plant): 



In Sinapis the intensity of the G0 2 assimilation is very great, 

 rising to at least 6 mgC0 2 per 50 cm 2 per hour at 20°. Also the respi- 

 ration in the leaves is great, about 0.8mgCO 2 per 50 cm 2 per hour at 

 20°. The point of equilibrium between G0 2 assimilation and respi- 

 ration lies at a light intensity of 1.0 (Bunsen units x 100). The de- 

 velopment of a Sinapis plant is very quick. In 4 weeks the dry 

 matter content rises from 0.5 g to 38 g per 100 plants. In favourable 

 conditions the daily percent production of dry matter can be esti- 

 mated as about 15. 



In Oxalis the maximal intensity of G0 2 assimilation is very 

 small, about 0.8 mg G0 2 per cm 2 per hour at 20°. Also the respi- 

 ration of the leaves is small, about 0.1 — 0.2 mg C0 2 per 50 cm 2 per 

 hour at 20°. The point of equilibrium between G0 2 assimilation and 

 respiration lies at a light intensity of 0.2. The daily percent pro- 

 duction of dry matter is 2.1. 



Febr. 9. 1918. 



