CH. Il] CULTURE WITHOUT CO2. 23 



graduated as follows : into one 550 c.c. of water is poured 

 and the level marked with a diamond, a second mark 

 being made after the addition of 50 c.c. The other beaker 

 is marked at 300 and 600 c.c. The beakers are filled 

 with water and inverted in saucers, and the rosettes of 

 Callitriche floated up under the rims of the beaker. 

 Three hundred c.c. of air are now introduced into one 

 beaker and 550 c.c. into the other, using a finger bellows 

 for the purpose ; afterwards CO^ is added until each beaker 

 contains 600 c.c. of mixed gas, one containing 50 p.c, the 

 other 8 p.c. of CO,. In our experiments the Callitriche 

 exposed to 50 c.c. CO^ showed hardly any starch, while the 

 control-plants were black with it. 



The experiment may be more accurately performed 

 with a pair of graduated tubes inverted over mercury 

 (covered with a few drops of water) and containing leaves 

 of land-plants. 



(34) Plants deprived of 00^. 



To show that the formation of starch depends on 

 the presence of CO^ it is necessary to cultivate plants in 

 such a way that they have access to oxygen but not to 



Water-plants. 



Water which has been boiled and allowed to cool in a 

 closed flask will be free from both and CO^. But if the 

 flask is in connection with an arrangement for preventing 



1 Godlewski, Flora, 1873, p. 378. 



