CH. Il] CULTURE WITHOUT CO 2 . 29 



the access of CO 2 while allowing other gases to pass in, 

 the boiled water will after a time become oxygenated. 



A convenient method is the following. A flask A 

 (fig. 7) is filled with spring water which has been freshly 

 boiled, and filtered from precipitated calcium carbonate; 

 it is connected with the bottle B, half filled with strong 

 KHO solution. The water in A is boiled 20 minutes, 

 with the stop-cock C left open. The flame is now 

 removed and C is closed. As the flask A cools, air is 

 sucked in by D, and in passing through the KHO in 

 the bottle B, is freed from C0 2 . The water so prepared 

 is now used for the culture fluid: the vessel containing 

 the plants must be closed by a rubber cork through 

 which passes a tube of soda-lime like the one shown in 

 fig. 8. 



A similar flask filled with spring water (to which a 

 little extra C0 2 may be added by blowing air from the 

 lungs through it) and closed by a U tube containing 

 coarse sand, will serve for a control. 



The CO 2 may also according to Pfeffer 1 be removed 

 by careful treatment with lime water. 



Land-plants. 



Seedlings with their roots in water, or plants of 

 Tropceolum or clover in small pots, are to be used. The 

 pot is supported in a crystallising glass (G, fig. 8) half filled 

 with soda-lime, which rests on a ground glass plate, and 

 is covered by a tubulated bell-jar, the lower edge of which 

 is ground, but need not be welted. The ground edge is 



1 Pfeffer, Physiologic, I. p. 111. 



