178 THE PLANT CELL. 



Certain Experiments Demonstrating Life-processes in the 

 Cells of Plants. 



Three experunents for the demonstration of important vital 

 processes may be considered at this point (v. and vi.), viz.: — 



a. The evolution of oxygen during assimilation. 



6. The evolution of CO2 during respiration. 



c. The retention in the plant of eaPbon dlOXide during assimila- 

 tion (this being used during the formation of sugar preparatory to 

 starch-formation). 



a. The evolution of oxygen during assimilation is readily 

 demonstrated in the case of some water-plants (Fallisneria, Elodea, 

 Potamogeton). If such plants are grown in an aquarium, bubbles 

 of gas will often be seen to rise from the leaves to the surface 

 during the action of sunlight. These bubbles, if collected in 

 a test-tube (filled with water and inverted over the water in the 

 aquarium) and tested, will be found to consist of pure oxygen. 



In land-plants more care is required to demonstrate the same 

 process. A plant is taken and enclosed in a large vessel contain- 

 ing atmospheric air to which a known extra volume of CO2 has 

 been added, the whole being placed in sunlight. After some 

 hours the gas in the vessel is tested, and is found to contain 

 less CO2 and more 0^ in proportion than was originally the case. 

 Here the COg evolved during respiration may be neglected, as it 

 is relatively small in the daytime during assimilation. 



b. The Evolution of COj during Respiration (see Fig. 114). — 

 A plant is taken and placed in a vessel (bell-jar) of 10 litres 

 capacity (A, Fig. 114). Connected with this vessel are (i.) 

 two bulbs, C, containing sticks of caustic potash, and (ii.) an 

 aspirator, B. By means of the latter a slow current of air 

 (freed from COj by the absorbing action of C) is drawn through 

 the apparatus. In the vessel A is placed, previous to the start- 

 ing of the experiment, a small dish, D, which contains a saturated 

 solution of caustic potash. The aspirator is then stopped, the 

 bulbs shut off, and the whole apparatus placed in a dark place 

 for some hours. Under these conditions no assimilation of C0„ 

 can take place, for as fast as it is given off during respiration 

 it is absorbed by the potash in the dish D. 



The experiment is stopped after about twelve hours, and the 

 CO2 absorbed is estimated by precipitating with baryta water, 



