66 STUDIES OF THE LEAF 



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

 jMesophyte, 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 mesoph3'tic (as the i\Iaple or Elm in summer) and 

 xei'ophytic (as the same tree in winter). 



IX. LABORATORY STUDIES OF THE LEAP 



Exercise XXIII. The Activities of the Leaf 



Experiment ii. — Select a healthy green Nasturtium plant. Place 

 it in darkness for three daj's. 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 piresence or absence of 

 starch. 



Jlean while, when tlie 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 twopins tlu'ough 

 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. Tlien 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. 



Wliere is starch formed in plants? "What is one condition of its 

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

 ditions.)^ 



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

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

 Put in, also, a small beaker with liniewater. 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 tlie experiment on respiration of 

 germinating seeds. 



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

 good number of leaves. Wra|> the pot in sheet rubbei', vhich is to 

 be l.irought u]i around the stem of the plant and securely tied. The 

 evaporation of water from the put 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 0, from Ganong's "Teaching Botaufst," may well be 

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

 important experiments are recommended. 



