THE ALGJE. 101 



light ; notice bubbles of gas given off by the plant. This 

 gas is oxygen set free in the chemical changes that occur 

 in the formation of the starch. 1 ; i% V 



In a vessel containing healthy Spirogyra ^rovYing^ki 

 Sachs' solution in the sunlight, arrangte a/feft&tAfte 'kO'C'oi-' 

 lect the gas given off. The tube is filled with the solu- 

 tion and supported bottom up with its mouth just below 

 the surface of the solution. Let the stem of an inverted 

 funnel rise into the tube, the flaring portion of the funnel 

 being in position to catch the bubbles of gas. Let the 

 apparatus stand until a quantity of the gas has collected, 

 agitating the Spirogyra below the mouth of the funnel 

 from time to time to dislodge the bubbles which cling to 

 the plant. Test the gas by introducing a spark on the 

 end of a splinter of wood. The spark glows more brightly, 

 or kindles into a flame, showing that the gas is oxygen. 



7. Run glycerine under the cover glass of a specimen 

 that has been treated with iodine solution. Note that the 

 slightly stained protoplasm shrinks from the cell wall. 

 The cells may also be plasmolyzed by running ten per cent 

 salt solution under the cover. The protoplasm contracts 

 and the primordial utricle is brought into view. Notice 

 the large centrally situated vacuole. 



A short piece of glass tubing closed at both ends and 

 covered with paper gives a good idea of the Spirogyra cell. 

 The paper represents the transparent cell wall ; the glass 

 represents the thin lining of protoplasm or primordial 

 utricle ; the hollow interior, which in the Spirogyra is, 

 of course, filled with cell sap, represents the vacuole. The 

 nucleus is suspended in the center of the vacuole. 



8. Run solution of caustic potash under the cover glass. 

 This brings the cell wall into more prominent view. Trace 

 a filament to its end. Notice that the filament is of uni- 

 form width, with perhaps an occasional accidental enlarge- 

 ment or contraction, the cells being of the same shape with 



