30 
LABORATORY EXERCISES 
II. Early in the morning, carefully cover one half of the leaf of 
a growing plant with tin foil. After allowing the plant to stand 
in the sunlight for several hours remove the tin foil. Carefully 
warm over a flame some 95% alcohol, the ordinary commercial 
form, and place the leaf in the alcohol so that the chlorophyll may 
be dissolved out of it. Next test the leaf for starch. Do you find 
starch in both the part which was covered and that which was 
not? Explain. Under what conditions is starch manufactured? 
What is photosynthesis? Compare respiration and photosyn¬ 
thesis. (See Waggoner, Fig. 88.) 
III. Temporary Storage of Starch in Leaves. In the latter 
part of the afternoon, dissolve out the chlorophyll of a leaf of a 
geranium plant with alcohol. Then test the leaf for starch. Re¬ 
peat in the early morning with another leaf from the same plant. 
Compare the results. Explain any differences in the amounts of 
starch found in each case. 
EXERCISE 33 
TRANSPIRATION 
For this experiment use a rather small but vigorous potted 
geranium. The plant should be one with a single stem. 
I. Water the plant well. Cover the pot with heavy paraffined 
paper or with sheet rubber — the inner tube of an automobile tire 
may be used — and secure this covering tightly about the gera¬ 
nium stem. Place the pot under a bell jar. (See Waggoner, Figs. 
89 and 90.) Observe frequently. What soon appears on the inner 
surface of the bell jar? What is its origin? What purpose does 
the paper or rubber covering of the pot serve? The cool bell jar? 
II. Weigh the potted plant after the covering is placed over the 
pot. Repeat at intervals of an hour throughout the day. Record 
the results. What must be the cause of any change in weight 
which occurs? What is transpiration? 
(Note — Make preparations for Exercise 35 several days before 
the materials are needed for class use.) 
