58 LABORATORY AND FIELD EXERCISES 



b. Place a bleached and a fresh leaf in separate watch 



glasses and flood with iodine solution. After a half 

 hour rinse the two leaves in water and place in watch 

 glasses of water for observation. Test some starch 

 with iodine in a watch glass. Compare the starch 

 reaction with that of the leaf. Is starch present in 

 Pelargonium leaves ? If so, where is it located and 

 where did it originate ? How and when is the starch in 

 a leaf used ? Have you had any clue to the answer 

 to this question in your work with woody stems ? 



c. Record the object, method, and results of, and the con- 



clusions to be drawn from, the above experiments, 

 as indicated above under Recording of Experiments. 

 Include in the results a drawing of the bleached 

 leaf, showing the distribution of starch. 



2. Test as above leaves of young growing corn or bean plants 



about six inches high. Individual experiment. 

 a. Use two plants which have been in the dark overnight 

 or for at least six hours. Why is this precaution 

 necessary ? 



' b. Expose one plant to bright sunlight for an hour or 

 more and leave another in darkness. Remove a leaf 

 from each plant, boil, extract chlorophyll with warm 

 80 per cent alcohol, and test for starch. 



c. Results ? Do the two leaves show a different reaction 



to iodine? If so, be able to state why. What im- 

 portant conclusions are to be drawn from this 

 experiment ? 



d. Record your results and conclusion as prescribed above. 



3. Gaseous exchanges in water plants during photosynthesis. 



Class demonstration. 



a. Observe plants of Elodt><t (water weed) which are ex- 

 posed under water to bright sunlight. Are bubbles 



