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Mariotte's flasks, of wich the one could be filled, while the 

 other was working. The air passed first through the plant 

 receiver consisting of a glass bottle, through the bottom of which 

 the plant could be introduced. From the receiver the air-current 

 was passed through the absorption tubes. Of these the two first 

 contained sulphuric acid to absorb the water, the two next were 

 filled with 50°/o KO H solution to absorb the C0 2 , and the two 

 last with sulphuric acid to absorb the water vapour, which might 

 be given off by the KO H tubes. The four last tubes were weighed 

 before and after the experiment, and the difference between the 

 two weighings gives the amount of C0 2 , that is not absorbed by 

 the plant. At the same time an estimation of the G0 2 content 

 in the air was made with a similar apparatus. A measured 

 amount of atmospheric air was drawn through the apparatus; by 

 weighing the absorption tubes the content of G0 2 per 1. was 

 determined. From these estimations the G0 2 taken up by the 

 plant could be calculated as a difference between the C0 2 supplied 

 and that remaining at the end. 



Giltay intented to compare the intensity of assimilation in 

 Holland and Buitenzorg. He found, that Helianthus in Wageningen 

 (Holland) assimilated 2.9 mg C0 2 in an hour per 50 cm 2 of the 

 upper surf. + 50 cm 2 of the lower surface, and in Buitenzorg 4.0 

 mg C0 2 in the same time. It is to be noticed, that Giltay's 

 experiments gave lower results than those of Sachs. 



Also Brown and Escombe (1905 p. 29) have made assi- 

 milation experiments in atmospheric air. They used an apparatus 

 of construction similar to Giltay's. The air current vas produced 

 by means of an aspirator. 



The air passed first through the plant receiver, a wooden 

 frame vith sides of glass, with the leaf, which either was attached 

 to the plant or cut off; in the latter case the leaf -stalk was 

 placed in water. Afterwards the air current passed through an 

 absorption tube with KOH, where the C0 2 that was not taken 

 up by the leaf, was absorbed, and then through a gasometer, 

 where the air was measured. The amount of the absorbed G0 2 

 was estimated by titration. Also here two experiments were carried 

 out at the same time, since in addition the G0 2 content in the 

 air was to be measured. 



Brown aud Escombe used a rather large leaf area, 300 — 800 

 cm 2 . Therefore they had also to use a very swift air current to 

 supply the leaves with sufficient C0 2 , 200 — 400 1. per hour. 



They experimented principally with Helianthus annuus, and 



