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 



