IO2 



PLANT BIOLOGY 



covered area. 88. Plants or parts of plants that have developed 

 no chlorophyll can form no starch. Secure a variegated leaf of 

 coleus, ribbon grass, geranium, or of any plant showing both white 

 and green areas. On a day of bright sunshine, test one of these 

 leaves by the alcohol and iodine method for the presence of starch. 

 Observe that the parts devoid of green color have formed no 

 starch. However, after starch has once been formed in the leaves, 

 it may be changed into soluble substances and removed, 



to be again /-^ converted into starch in certain other parts of 



tissues. 



To test the giving off of oxygen by day. 

 89. Make the experiment illus- 

 trated in Fig. 122. Under a fun- 

 nel in a deep glass jar containing 

 fresh spring or stream water place 

 fresh pieces of the common 

 waterweed elodea (or anacharis). 

 Have the funnel considerably 

 smaller than the vessel, and sup- 

 port the funnel well up from the 

 bottom so that the plant can more 

 readily get all of the carbon dioxid 

 available in the water. Why would 

 boiled water be undesirable in this 

 experiment? For a home-made 

 glass funnel, crack the bottom off 

 a narrow-necked bottle by press- 

 ing a red-hot poker or iron rod 

 against it and leading the crack 

 around the bottle. Invert a test- 

 tube over the stem of the fun- 

 nel. In sunlight bubbles of 

 oxygen will arise and collect in 

 the test-tube. If a sufficient 

 quantity of oxygen has collected, 

 a lighted taper inserted in the 

 ube will glow with a brighter flame, showing the presence of 

 oxygen in greater quantity than in the air. Shade the vessel. 

 Are bubbles given off? For many reasons it is impracticable 

 continue this experiment longer than a few hours. 90. A 

 ampler experiment may be made if one of the waterweeds 

 wrnba (water-lily family) is available. Tie a lot of branches 

 sther so that the basal ends shall make a small bundle. Place 

 : m a large vessel of spring water, and insert a test-tube of 

 5 before over the bundle. The bubbles will arise from the 

 surfaces. Observe the bubbles on pond scum and water- 

 weeds on a bright day. To illustrate the results of respiration 



Fiu. laa. To SHOW THE ESCAPE 

 OF OXYGEN. 



