RESPIRATION 



237 



Light appears to have no direct influence upon it, respiration 

 continuing very similarly both in darkness and light. 



It has also been found by experiment that the process goes 

 on quite normally even when the proportion of oxygen in the 

 surrounding atmosphere is reduced to less than half that 

 ordinarily present in the air. 



Ex. 136. — Soak a handful or two of peas or barley grains in water for 

 twelve hours. Take them out of the water and allow them to germinate on 

 damp blotting-paper for twelve hours. Then put them in a wide-necked 

 bottle, cork the latter and place it in a warm, dark room. Cork and place beside 

 it another similar but empty bottle. Allow both to remain for twelve hours, 

 after which time test for the presence of carbon dioxide by introducing a 

 lighted match or taper into the bottles : the light is extinguished by carbon 

 dioxide. Arrange another similar experiment, and test for carbon dioxide 

 with lime-water : pour in the lime-water, and shake the bottles ; the lime- 

 water becomes milky if carbon dioxide is present. 



Ex. 137. — Partially fill a wide-necked bottle with half expanded young 

 dandelion or daisy ' heads' ; cork and leave for twelve hours, after which 

 time test for carbon dioxide as above. 



Ex. 138. — Repeat the experiment above, using green leafy shoots, expand- 

 ing buds, bulbs, tubers and other portions of plants. 



Ex. 139. — Soak some peas for twelve hours, 

 and after taking them out of the water allow 

 them to germinate on damp blotting-paper for 

 a few hours. Then place them in a flask ar- 

 ranged on a retort stand, with a tightly fitting 

 rubber stopper and bent glass tube as in Fig. 

 89. Slightly warm the flask with the hands 

 and dip the open end of the tube (a) into 

 mercury in a beaker (B). Leave the apparatus 

 for ten or twenty minutes and fasten a piece 

 of gummed paper on the tube (a) at a point 

 {x) up to. which the mercury rises in it. Keep 

 the whole in a room of even temperature for 

 ten or twelve hours, and observe the position 

 -of the mercury at the end of that time. If 

 ^^'^- ^5- the volume of oxygen absorbed is equal to that 



of the carbon dioxide emitted, the mercury will remain at the same place in 

 the tube. 



Repeat the experiment with oily seeds, such as hemp, linseed and turnip. 



