INTRODUCTION 43 



it. As there are none at night that can do this it is 

 given off to the atmosphere. Hence, too, the oxygen 

 required for respiration at night is obtained from 

 outside and not from within. 



Dry seeds do not respire because they are inactive, 

 but as soon as they germinate carbon dioxide is given 

 off and growth begins with the commencement of 

 energy. 



Some germinating seeds are placed at the bottom 

 of a flask, which is corked, and has a small test-tube 

 containing lime-water suspended from the cork. A 

 second flask is arranged in the same way, but without 

 the seeds. After about twenty-four hours the lime- 

 water in the test-tube in the first flask will have 

 clouded and a lighted taper held in the flask will 

 go out. In the second flask the lime-water will 

 show a very slight film on the top and a lighted taper 

 will burn. The presence of the germinating seeds 

 has increased the amount of carbon dioxide in the 

 air and decreased the amount of oxygen. The same 

 result is obtained both in the light and in the dark. 

 It can also be carried out with roots and portions of 

 stems. In the case of leaves the flasks must be 

 kept in the dark, as in the light carbon assimilation 

 is so active that the respiration is difficult to trace, 

 and a more elaborate experiment is required to 

 demonstrate it. Such experiments show that all 

 parts of plants respire by day and by night (Figs. 5 

 and 5 a). 



