440 BOTANICAL GAZETTE [JUNE 
appeals at first sight to its availability for popular demonstration. 
Even for purposes of investigation it is free from most of the objec- 
tions to the bubble-counting method, and subject only to such as 
necessarily attend work on water plants. 
Submerged plants of some kind are fastened where the oxygen they 
set free as gas is collected under an areometer. They may be fastened 
Fic; 2.7 Fic. 3. 
into a funnel, whose upper end is sealed into a tube of uniform external 
diameter, closed at the top (fg. 2). Or they may merely be tied into 
a beaker, or any other vessel, which is inverted and hung by a uni- 
form rod. Because it is allowed to contain air, or preferably as it is 
held up by a counterpoise, this funnel or other vessel containing the 
plants stands with the uniform tube partly out of the water. As the 
plant assimilates, the oxygen set free displaces water, making lighter 
the vessel with its contents, which accordingly rises, lifting above the 
water a volume of the tube or rod equal to that of the oxygen evolved 
in the water below. It is indifferent whether the bubbles rise and 
*Used by courtesy of the West Virginia Experiment Station. 
