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 (b), 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 c 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 c 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 b very early in the morning and the other leaves after 

 they have been exposed to sunshine. 



