THE WORK OF LEA VES 



193 





under water. When sufficient gas has collected, the 

 cork is removed from the neck and a glowing splinter 

 is quickly thrust into the neck. If it glows more 

 brightly or bursts into flame, it indi- 

 cates that the gas in the funnel is richer 

 in oxygen than ordinary air, and, 

 consequently, that the plant is giving 

 off oxygen. 



These results, taken in connection 

 with the fact that the formation of 

 starch is prevented by depriving the 

 leaf of air, make it highly probable that 

 the leaf makes starch by causing car- 

 bon dioxide and water to unite, accom- 

 panied by the giving off of oxygen. 

 It would lend greater certainty, how- 

 ever, if we could deprive the leaf of 

 carbon dioxide without at the same 

 time depriving it of the other constitu- 

 ents of air. We may do this by means 

 of the apparatus shown in Fig. 112. A bottle or 

 fruit -jar is fitted with a stopper of cork or wood, 

 through which passes a funnel filled with lumps of 

 lye which will absorb the carbon dioxide from the 

 air as it enters the bottle. On the bottom of the bottle 

 we place some lumps of lye and a small bottle of 

 water in which is a leaf of Nasturtium (or some other 

 leaf which normally gives a good starch test) which has 



M 



Apparatus for 

 growing a leaf in 

 air deprived of car- 

 bon dioxide: lumps 

 of lye are placed in 

 the funnel and on 

 the bottom of the 

 bottle. 



