ASSIMILATION OF CARBON 5 



(comparatively pure oxygen 1 ) 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. 



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

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



Pig. 2. — Elimina- 

 tion of oxygen bubbles 

 by Elodea in sunlight. 



Fig. 3. — Collection of oxygen' from 

 water plants in light. 



Fig. 1. — Leaf in 

 position in a measuring 

 tube, for demonstration 

 of absorption of carbon 

 dioxide and elimination 

 of oxygen during photo- 

 synthesis. 



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

 in the presence of oxygen. If a shoot of Elodea, or other aquatic, 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. 2 



§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 



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

 violetten Strahlen des Spektrums. Ber. Deutsch. Bot. Ges. 15: 111-124. 1807. 



- Kny, L., Die Abhängigkeit der Chlorophyllfunction von den Chromatophoren und vom Cytoplasma. 

 Ber. Deutsch. Bot. Ges. 15: 388-403. 1897. [See also: Kolkwitz, R., Pflanzenphysiologie. Jena. i<H4- 

 P. 3-1 



