FOLIAGE LEAVES : FUNCTION, STKUCTUBE, ETC. 
29 
bubbles are numerous. That this activity holds a definite 
relation to light may be proved by gradually removing the 
vessel containing the leaf from the light. As the light 
diminishes the bubbles diminish in number, and when a 
FIG. 23. An experiment to illustrate the giving off of oxygen in the process of photo- 
synthesis. 
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 
