18 



A much more simple apparatus, which answers the same pur- 

 pose, is shown in Fig. 4. This method of demonstration we have 



() 



Fk;. 3. Apparatus for collcclinj; and <lett;rmiiiing ihe .■iiiinunl of oxygen given off 

 liy aijualic plants. 



required of our physiological students each year. It consists of 

 a test-tube, cither plain or graduated, placed over a glass funne 



