FOLIAGE LEAVES : FUNCTION, STRUCTURE. ETC. 29 



bubbles are numerous. That this activity holds a definite 

 relation to light may be proved by gradually removing the 

 vessel containing the plant from the light. As the light 

 diminishes the bubbles diminish in number, and when a 



Fig. 23. An experiment to illustrate the giving ( 



synthesis. 



of oxygen in tho process of photo- 



certain amount of darkness has been reached the bubbles 

 will cease entirely. If now the vessel be brought back 

 gradually into the light, the bubbles will reappear, more 

 and more numerous as the light increases. That this gas 

 being given off is oxygen may be proved by collecting the 



