92 



£lementary Plant Physiology. 



hour or more. As soon as the animals appear to become inac- 

 tive, sluggish, or asphyxiated, because of lack of oxygen, uncover 

 the bell jar and expose it to direct sunlight. Note effect on 



Fig. 63. — Box with door at one end, and plates of colored glass, aa^ at the other. 

 After Oels. 



animals. The test may be repeated, and should be attempted 

 only on days in which good illumination may be secured. 



96. Changes produced in the air by a flame and 

 by green plants. — Provide a large bell jar with tubulure at 

 top, and a glass plate upon which it may rest. Bore a hole in 

 a block of wood to receive and hold a small candle firmly. 

 Fasten a strip of wood to one side of this block, with its upper 

 end below the level of the exposed wick of the candle. Glue a 

 strip of sanded paper to the side of this strip nearest the candle. 

 Set the candle with its holder, prepared as directed, in the 

 center of the glass plate, and near it a plant growing in a pot. 

 Close the tubulure of the bell jar with a cork or rubber stopper, 

 through which a glass rod extends down to the block in which 

 the candle is fastened. A short section of the lower end 



