54 Gardening 
geranium) to sunlight during the day, remove a leaf (a), attach 
a label with string, and immediately place it in a bottle of alcohol. 
Place the plant in complete darkness for 24 hours. Then remove 
another leaf (5), attach a label, and place in the alcohol. Now, 
cut smoothly two disks from a cork stopper and carefully pin 
these on opposite sides of a leaf (c) so that they fit snugly and 
exclude the sunlight from the covered area. Expose the plant to 
direct sunlight for several hours. Remove leaf ¢ and also another 
leaf (d) that has been left untouched. Test all four leaves with 
iodine for starch. : 
Is starch present in a? Was starch present in the leaves when 
the plant was placed in darkness? What became of the starch 
formerly in the leaves during the time the plant was in darkness? 
Was starch formed in ¢ and d? Was it formed in the shaded 
area of ¢c? What does each leaf show concerning the influence 
of light upon the accumulation of starch in green parts of a plant? 
The above experiments can be worked with plants outdoors 
by selecting } very early in the morning and the other leaves after 
they have been exposed to sunshine. 
