The Food of Plants 53 
How is the surplus sugar that is made by most plants stored? 
Can it be moved. from one part of the plant to another? From 
what do plants make fats? Name some plants from which fats 
are obtained. From what are proteins manufactured? Where 
in the plant are fats and proteins manufactured? 
What minerals needed by plants are most often lacking in the 
soil? How does the gardener supply these to his plants? Name 
one difference between garden plants and weeds. 
Things to Do and Observe 
1. To examine the structure of leaves. Peel off strips of both the 
upper and lower epidermis of leaves and examine them under the 
low power of the microscope. The colorless epidermal cells and 
the ‘stomata’? surrounded by the green “‘guard cells” can be 
seen. Make thin cross-sections of leaves (most easily made from 
such fleshy leaves as the cabbage) and examine them. Perma- 
nently prepared sections may be bought from botanical supply 
houses. 
2. To show that starch is formed only in the green parts of a leaf. 
Expose a plant having white-margined leaves (variegated geranium 
is excellent) to sunlight for several hours. Then remove a leaf 
and make a tracing of it, showing the green and the white areas. 
Place the leaf in a dish with enough alcohol to cover it. Heat 
gently on a stove or over an alcohol lamp or gas flame, taking care 
not to boil the alcohol so strongly that it will catch fire. The 
green coloring matter is thus removed and the entire leaf becomes 
almost colorless. 
Obtain some iodine solution from a drug store. Add a little 
of this to thin starch paste and note the blue color of the starch. 
This is the iodine test for starch. Dip the decolorized leaf in 
water to which iodine has been added. The part of the leaf that 
contains starch will turn dark in color. Is starch found in the 
green or in the white area? 
Test cut surfaces of a potato, turnip, radish, bean seed, or other 
vegetables for starch. Do not use too much of the iodine, or the 
blue of the starch may be somewhat hidden by the brown color of 
the excess iodine. 
3. To show that sunlight is necessary for the accumulation of 
starch in green leaves. Expose a potted plant (for example, a 
