Grade. 

 Date. . 



EXERCISE 25 



STUDY OF POTATO 



Object. To study the morphology and composition of the potato tuber. 



Explanation. The potato tuber is part of the system of lateral under- 

 ground stems, and corresponds largely in its morphology to aerial stems. 

 It serves as a storage part to the underground stem and enables the plant 

 to live over from one year to another. 



Part I. (a) Draw a tuber natural size showing the correct arrangement 

 of eyes. Label stem end, bud end, eyes, and eyebrows, (b) Show on your 

 drawing by dotted lines how the tuber should be cut for seed purposes. 



Part II. (a) Make with a sharp knife a thin longitudinal and a thin 

 transverse section of a tuber cutting through one or more eyes in each case. 

 Rinse in water and examine. (6) Draw natural size in both longitudinal and 

 transverse section a tuber showing in proper proportion: (1) internal medul- 

 lary area; (2) external medullary area; (3) cortex; (4) epidermis. 



Part III. (a) Treat the thin longitudinal section with dilute iodine, 

 rinse in water in a pie tin and observe the portion of greatest starch concentra- 

 tion. Indicate concentrations by labeling the drawing in Part II. 



Reference. Montgomery, E. G., Productive Farm Crops (LIPPINCOTT), 

 Chap. XXX. 



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