TBE WORK OF LEA VES 



191 



affect starch formation ? Keep a plant in the dark until 

 the leaves no longer give a good starch test. Remove 

 the plant to the light and treat several of its leaves by 

 covering both sides of a portion of the leaf with vase- 

 line. Remove some of the untreated leaves from the 

 plant, and place them in tumblers of water so that the 

 stalk of the leaf and about half of the blade dip under 

 water. Place all of the leaves where they will get 

 abundant sunlight. In two or three days, test all the 

 leaves for starch (removing them from the plant at 

 sundown). Do you find starch in the portions from 

 which air has been excluded? 



Does the leaf decompose carbon dioxide? Invert a 

 large bottle or fruit-jar in water, as shown in Fig. 110, 

 and introduce a lighted 

 candle set in a cork. 

 After a short time the 

 candle goes out, indicat- 

 ing that some of the 

 oxygen of the air has 

 been converted by burn- 

 ing into water and car- 

 bon dioxide. Withdraw 

 the candle by means of a string attached to it and 

 introduce a leaf, the stalk of which passes through a 

 hole in the center of a cork, as shown in the figure: do 

 this without lifting the bottle above the surface of the 

 water. The experiment should be commenced in the 



110. Arrangement for investigating the power 

 of a leaf to " restore " air wliich has been 

 "vitiated" by a burning candle. {Sec- 

 tional view.) 



