98 



PHYSIOLOGICAL PROCESSES IN PLANTS 



them in iodine solution. Which leaves show the presence of 

 starch ? 



Conclusions. 1. What else besides sunlight, carbon diox- 

 ide, and water is a necessity to a leaf for starch formation? 



2. If the leaf is alive and is doing work (making starch), 

 what element is needed to release energy for doing the work ? 

 How does this element get into the leaf? (Respiration.) 



2. FOOD MAKING AND ITS BY-PRODUCTS (PHOTOSYNTHESIS) 

 (a) Starch Making (Important) 



Observations. 1. Place some 

 green water plants under a funnel 

 in clear water as in Figure 28. 

 Note. Bubble carbon dioxide 

 through the water (not under the 

 funnel) several times in the course 

 of the experiment. Cork the 

 end of the funnel, or invert a test 

 tube filled with water over its 

 neck. In either case see that the 

 funnel tube is filled with water. 

 Place the jar in sunlight for sev- 

 eral days, and collect any escaping 

 gas, either in the funnel tube, or 

 in the test tube. Thrust a glow- 

 ing splint into the gas. Result ? 



2. Set the apparatus as before, 

 and let it stand overnight, or where 

 the light cannot strike it. Has 

 any gas been formed ? 



3. (Optional.*) Immerse a sprig 

 of geranium in water under a 

 corked funnel, and set the jar in 

 sunlight. Are bubbles given off ? 



Place some mold, or toadstools, or other fungi under another 

 funnel. Observe as before. 



FIG. 28. Experiment to show 

 that oxygen is given off by 

 green plants in sunlight. 



