66 STUDIES OF THE LEAF 



It must be understood that the terms, Xerophyte, Hydrophyte, 

 Mesophyte, are merely abstract designations for general types of 

 adaptation. When we say Xerophyte, we mean any plant showing 

 adaptation to a dry habitat. The same plant may be at different 

 periods of the year mesophytic (as the Maple or Elm in summer) and 

 xerophytic (as the same tree in winter). 



IX. LABORATORY STUDIES OP THE LEAF 

 EXERCISE XXIII. THE ACTIVITIES OF THE LEAF 



Experiment n. Select a healthy green Nasturtium plant. Place 

 it in darkness for three days. Then cut one or two leaves, boil them in 

 water, decolorize them in strong alcohol (this may take a day or so), 

 and then treat with iodine to determine the presence or absence of 

 starch. 



Meanwhile, when the plant is first taken from darkness, cover a part 

 of one of the leaves in the following manner : Cut disks from a cork 

 stopper ; place them on opposite sides of the leaf ; stick two pins through 

 both corks and leaf, to hold the corks in place. A portion of one leaf 

 being thus entirely darkened, expose the plant for at least a day in 

 sunlight. Then test two or three of the leaves, including the partly 

 darkened one, for the presence or absence of starch, in the same man- 

 ner as before directed. Compare with the former results. 



Where is starch formed in plants? What is one condition of its 

 production, as determined by this experiment ? (There are other con- 

 ditions.) 1 



Experiment 12. Pour a little water into a fruit jar, enough to 

 cover the bottom. Put in a few leaves, with their stalks in the water. 

 Put in, also, a small beaker with limewater. Close the jar tightly. 

 Place the jar in the dark. 



Arrange a second jar, water and limewater, without leaves, and 

 place it beside the first. 



After twenty-four hours examine the limewater in both beakers for 

 the action of carbon dioxide, as in the experiment on respiration of 

 germinating seeds. 



Experiment 13. Select a plant with a single stem below, bearing a 

 good number of leaves. Wrap the pot in sheet rubber, which is to 

 be brought up around the stem of the plant and securely tied. The 

 evaporation of water from the pot and soil is thus prevented. 



Weigh the plant as thus fixed, and record both weight and time. 

 In doing this, set the scales in the sun if possible, and having found 



1 Experiment 6, from Ganong's "Teaching Botanist," may well he 

 introduced here if the apparatus is available. See also Appendix, where 

 important experiments are recommended. 



