2 1 8 PICTURESQUE EXPERIMENTS 



ceased to move because they and the leaves between 

 them have consumed the oxygen dissolved in the 

 water, and bacterial activity being dependent on 

 oxygen naturally came to an end. The preparation 

 is placed under the microscope and illumined with 

 bright incandescent gas, and after a short time the 

 bacteria begin to stir and are soon once more 

 whirling in their insensate dance. The reason is 

 obvious — the green leaves under the influence of 

 light were able to seize the carbon from the CO^, 

 and the O thus set free put the bacteria in motion. 

 The bacterial dance is therefore evidence of the act 

 of assimilation carried on by the Elodea leaf. 



Yet another method is worth mention, viz., that 

 of Boussingault, The plant is placed in an 

 inverted glass vessel resting in a dish of water, and 

 is filled with hydrogen mixed with a percentage of 

 CO2. Inside the vessel a fragment of phosphorus 

 is suspended, and as a small amount of oxygen 

 is sure to be mixed with the hydrogen the phos' 

 phorus will be oxygenated and white fumes will 

 fill the vessel. The observer must wait until these 

 clouds have subsided, which may need a couple of 

 hours. This must take place in the dark, and as 

 soon as the atmosphere is clear, the whole prepara- 

 tion is placed in bright light, when obvious clouds 

 will again appear — a proof that oxgyen has been 

 set free by the assimilation of the green plants. 

 With this example I must bring my short series of 

 experiments to a close, with the hope that my 

 readers may not deny that they are picturesque. 



