ASSIMILATION OF CAEBON 5 



(comparatively pure oxygen') given off, in light, from the cut end of a piece of 

 the water plant Elodea, submerged in water saturated with carbon dioxide, 

 as shown in Fig. 2. If a number of such green water plants are placed under 

 water in sunlight and are covered by an inverted funnel, over the neck of 

 which is inverted a test-tube of water (Fig. 3), the test-tube soon becomes 

 filled with a gas that is nearly pure oxygen. 



Schiitzenberger's reagent (a solution of indigo carmine or nigrosine, de- 

 colorized by sodium sulphite) can also be used to demonstrate that oxygen is 



O 



Fig. I. — Leaf in 

 position in a measuring 

 tube, for demonstration 

 of absorption of carbon 

 dioxide and elimination 

 of oxygen during photo- 

 synthesis. 



Fig. 2. — Elimina- 

 tion of oxygen bubbles 

 by Elodea in sunlight. 



Fig. 



3. — Collection of oxygen 

 water plants in light. 



from 



liberated by water plants; this solution is yellow when prepared, but turns blue 

 in the presence of oxygen. If a shpot of Elodea, or other aqmtic, is placed 

 in a dilute solution of this reagent and exposed to sunlight, the solution surround- 

 ing the leaves becomes blue in a few minutes.^/ 



§3. Chlorophyll.- — Since the decomposition of carbon dioxide is effected exclu- 

 sively by the green parts of plants, the properties of the green pigment — called 



' This method was perfected by Kohl. See: Kohl, F. G., Die assimilatorische Energie der blauen und 

 violetten Strahlen des Spektrums. Ber. Deutsch. Bot. Ges. is: 111-124. 1897. 



' ^ Kny, L., Die Abhangigkeit der Chlorophyllf unction von den Chromatophoren und vom Cytoplasma. 

 Ber. Deutsch. Bot. Ges. IS: 388-403. 1897- [See also: Kolkwitz, R., Pflanzenphysiologie. Jena, 1914. 

 P. 3.1 



