121 



was then tested with a Hghted match. This time the h'ght was 

 not extinguished, showing that the green leaves had given off 



oxygen. 



Teachers College. 



A Simple Modification of the Experiment to Show the 

 Gaseous Exchange in Plant Respiration 



By C. Stuart Gager 



In the experiment to teach the gaseous exchange accompany- 

 ing the respiration of various plant organs it is essential to show- 

 two facts : first, that the oxygen has been absorbed, and, second, 

 that carbon dioxide has been given off. The very common 

 practice of partially filling glass jars with the tissues to be in- 

 vestigated is unsatisfactory in several ways. It is not always 

 easy to lower the lighted taper as far down into the jar as is desir- 

 able, and, furthermore, when the lime-water test is applied it is 

 either necessary to remove a sample of the air from the jar, or 

 else pour the lime-water into the jar. The first operation is not 

 easy, and only invites failure. By the second method the lime- 

 water is liable to become so dirty from contact with the plant 

 material, or so obscured by it, that its change to a milky color 

 must be taken largely on faith. 



The simple device, shown in the acompanying illustration, does 

 away almost entirely with the above annoyances. A partition of 

 wire netting divides the jar vertically, and leaves a space to one 

 side into which the burning taper may be inserted as far down 

 the jar as necessary. The wire netting should be of somewhat 

 smaller mesh than that shown in the photograph, and should fit 

 snugly into the jar so that the latter may be tipped over slightly. 

 The lime-water may then be poured in at the side opposite the 

 plant-material, and (after the stopper is tightly replaced) shaken 

 well up and down the jar to insure thorough contact with the 

 carbon dioxide. By this means the Hme-water is not clouded 

 with dirt from the plants. After the netting has been once pre- 

 pared it requires practically no more time to set up the experi- 

 ment than without the netting, while the operations that must be 



