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several others have shown, is much accelerated with the rise of 

 C0 2 content in the surrounding air. 



The following investigations aim at determining the amount 

 of the G0 2 assimilation at the same C0 2 tension as in atmos- 

 spheric air. 



Weber (1879 p. 346) tried to measure this value by estimating 

 the gain of dry matter in an experimentation time of 43 — 50 days. 

 Every day he estimated the leaf area in m 2 and the time during 

 which the plants were illuminated in hours. Hence the C0 2 assi- 

 milation per hour per 1 m 2 could be calculated. 



Sachs (1884 p. 1) attempted to determine the intensity of 

 assimilation by his weighing method. From leaves, which were 

 as symmetrical as possible, he removed during the morning the 

 one half, while he let the leaf stalks with the other half remain 

 on the plant till the evening, when they also were cut off. From 

 both the half-parts, known areas were cut out and the dry 

 weights of the two samples were determined; the difference be- 

 tween them indicated the amount of the C0 2 assimilation during the 

 day. In addition a correction for the migration of the synthesised 

 carbohydrates had to be applied. By this method Sachs found, 

 that the assimilation for Helianthus annuus was 1.88 g and for 

 Cucurbita Pepo 1.5 g dry weight per m 2 per hour. 



Sachs' method was sharply criticised by Brown and Escombe 

 (1905 p. 29). They maintained, that the two half parts of a leaf 

 may vary much in weight and that the area of the leaves may 

 be altered during the time of the experiment. And it is to be 

 remembered, that a small percentage error in determining the 

 weight of te two samples of leaf pieces will cause a considerable 

 error in the determination of the intensity of assimilation. Accor- 

 ding to investigations of Thoday (1910 p. 1 and 421) these errors 

 can be avoided by suitable precaution. 



The C0 2 assimilation can also be estimated from the intake 

 of G0 2 . In these experiments the plant is placed in a stream of 

 atmospheric air. The amount of air, which is drawn through the 

 apparatus during a definite time and the G0 2 tension in the air 

 is determined ; hence the amount of the G0 2 , with which the plant 

 is supplied during the experimentation time, may be calculated. 

 When the air current has passed the plant, it is conducted through 

 absorption-tubes, which take up the remaining G0 2 , and thus 

 may be calculated how much C0 2 the plant has absorbed. 



Such an apparatus was constructed by Giltay (1898 p. 43). 

 The air current was produced by the suction of two calibrated 



