190 NATURE-STUDY REVIEW [14:5— May, 1918 



dotted lines. Lead class to infer that the potato is a stem. Have 

 pupils reason out: Why leaf is reduced? Show class a potato 

 which has been exposed to sunlight and one that has been in the 

 dark. How account for difference in color? Conclusion: The 

 potato is an enlarged underground stem. 



Apply a weak solution of iodine to the cut surface of a potato. 

 Observe results. Iodine colors starch blue. Infer that starch 

 has been stored in the potato or underground stem. 



About a month before this lesson remove the skin from a 

 potato and weigh. Leave in a warm place. Pupils now observe 

 changes in size and weight. Lead class to infer that its loss in 

 size and weight is due to evaporation of water. The composition 

 of potato is 78.3 per cent water, 18 per cent starch, 2.2 per cent 

 protein, 1.0 per cent ash, and 0.1 per cent fat. Show by diagram 

 about how much of a potato is water and how much starch. 



Show class a potato which has sprouts upon it. How does it 

 differ from a potato without sprouts? (Wrinkled). Why? New 

 growth eating the starch which was stored in it. Infer that starch 

 is stored in the potato as nourishment for new plants. Note 

 that sprouts are long white stems with small white leaves. Why 

 white? Why long stems? Why small leaves? Leave specimen 

 exposed to light and observe changes. Why are potatoes with 

 sprouts not desirable for the table? 



Pupil dig up a piece of potato which has been planted. From 

 what does the sprout start? From what do the roots come? 

 Do the shoots or roots start first ? In what direction do the roots 

 go? Why? Why should the earth be kept loose about the 

 growing plants?" 



Teach class why potato has large leaves above ground. Show 

 flowers. Show "seed-balls". These should be collected the 

 year before and preserved in formalin in a small bottle. Explain 

 law of disuse. When the potatoes are ripe the parts above ground 

 wither and die. Why? (They have served their function.) 



If possible show a potato plant with the new potatoes. Have 

 class review by giving life history of this plant. A diagram may 

 be substituted if the plant is not available. 



III. Potato Gardening 

 A. Organizing Club. Send to the U. S. Department of Agri- 

 culture and to the State Agricultural College for all literature 

 related to the Potato Club Work. 



