CH. Il] CULTURE WITHOUT CO.,. 29 



the access of COo 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 ojDen. 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 COo. 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 CO2 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 COo may also according to Pfeffer^ be removed 

 by careful treatment with lime water. 



Land-plants. 



Seedlings with their roots in water, or plants of 

 Tropceolmn 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. 



