THE BREATHING OF THE PLANT 71 



are being carried on. To prevent this the experiments 

 may be made in the dark, or some part of the plant 

 that does not contain chlorophyll may be used for the 

 experiment. 



Experiment 42 



Aim. — To find out if a plant gives out carbon- 

 dioxide. 



Method. — Any one of the three following methods 

 can be used : 



1. Into the bottom of a bottle or fiask two or three 

 pieces of blotting-paper are put. The paper is made 

 damp and then covered with a layer of peas. The 

 peas should have been soaked in water for a day or 

 two so that germination is just beginning. A test-tube 

 filled with lime-water is placed in the bottle. The 



Fig. 33 



Fig. 34 



bottle is then securely corked (Fig. 33). A control 

 experiment, in which the peas are omitted, is also 

 set up. 



2. A layer of peas is put into a bottle together with 

 damp blotting-paper as in the first method, but the 

 lime-water is omitted. The bottle is well corked and 

 left for some hours. The air inside the bottle is then 

 tested by means of a lighted taper. 



3. A potted plant is placed under a bell-jar together 

 with a dish of lime-water; and a black-covered box is 

 placed over the whole (Fig. 34). 



