rUXCTIOXS OF LEAVES 137 



EXPERIMENT XYII 



Oxygen-Making in Sunlight. — Place a green aquatic plant in a 

 glass jar full of water at a temperature of about 70° Fah. in front 

 of a sunny window.^ Ou the surfaces of the plants watch for minute 

 silvery-looking bubbles. These may be partly air but some are 

 oxygen. Remove to a dark closet for a few minutes and examine by 

 lamplight to see whether the rise of bubbles still continues. 



This gas may be shown to be oxygen by collecting some 

 of it in a small inverted test-tube filled with water and 

 thrusting the glowing coal of a match just blown out into 

 the gas. It is not, however, very easy to do this satisfac- 

 torily before the class. 



Repeat the experiment, using water which has been well boiled 

 and then quicldy cooled. Boiling removes all the dissolved gases 

 from water, and they are not redissolved in any considerable quantity 

 for many horn's. 



Ordinary air containing a known per cent of carbon dioxide, 

 if passed very slowly over the foliage of a plant covered with a bell- 

 glass and placed in full sunlight, will, if tested chemically, on com- 

 ing out of the bell-glass, be found to have lost a little of its carbon 

 dioxide. The pot in which the plant grows must be covered with a 

 lid, closely sealed on, to prevent air charged with carbon dioxide (as 

 the air of the soil is apt to be) from rising into the bell-glass. 



163. Disposition made of the Absorbed Carbon Dioxide. — 



It would lead the student too far into the chemistry of 

 botany to ask him to follow out in detail the changes by 

 which carbon dioxide lets go at least part of its oxj^gen 

 and gives its remaining portions, namely the carbon and 

 perhaps part of its oxygen, to build up the siibstance of 



1 Elodea, Myriophyllum, Chrysosplenium, Potamogeton, Fontinalis, any of 

 the green aquatic flowering plants, or even the common confervaceous plants, 

 known as pond-scum or " frog-spit," wlU do for this experiment. 



