286 CULTURE OF IRISH POTATOES 



Structure 

 Cortical Layer: 



21. Thick, thin. 

 External Medullary Area: 



22. Proportion large, small. 

 Internal Medullary Area: 



23. Large, small. 



24. Branched much, branched little. 



25. Light, dark. 

 Estimated Cooking Quality: 



26. Mealy, medium, soggy. 



LABORATORY EXERCISES 



STUDY OF POTATO TYPES 



Directions for Report. Describe each of the 11 samples of potatoes 

 exhibited, using the accompanying descriptive key and blank outline. The 

 samples here shown and described represent approximately the character- 

 istics of each of the main variety groups. 



Draw natural size the long broadside view of a tuber of each of the 

 above groups, paying special attention to size and shape of tuber, size, 

 shape and distribution of eyes. 



Draw natural size the transverse section of a tuber of each of these 

 groups, paying special attention to relative proportion of cortex, internal 

 and external medullary areas. 



Label all parts carefully in right hand margin. 



From your knowledge of descriptive characteristics of each of the 

 main groups, list the extra varieties exhibited under the proper group, i.e., 

 Irish Cobbler, Triumph, Rural, Early Michigan, Rose, Hebron, Burbank, 

 Early Ohio, Green Mountain, Pearl and Peachblow. 



MORPHOLOGY AND COMPOSITION OF THE POTATO TUBER 



The potato tuber as a part of the system of lateral underground stems, 

 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. 



Note (a) stem end; (6) bud end; (c) eye buds; (d) eyebrows; (e) 

 arrangement of eyes with reference to stem and bud end. 



Draw a tuber natural size showing correct arrangement of eyes and 

 labelling stem end, bud end, eyes and eyebrows. 



Indicate on your drawing by dotted lines how the tuber should be cut 

 for seed purposes. By a dash line indicate the phyllotaxy of the tuber. 



Make with a sharp knife, a thin longitudinal and a thin transverse sec- 

 tion of a tuber, cutting through one or more eyes in each case. Rinse in 

 water and examine carefully. 



Observe and draw natural size in both longitudinal and transverse sec- 

 tion a tuber showing in proper proportion (a) internal medullary area; 

 (6) external medullary area; (c) cortex; (d) epidermis. 



Treat a thin longitudinal section with iodine (5 per cent solution) , rinse 

 in water and observe the portion of greatest starch concentration. Indicate 

 by labelling in your drawing. 



Answer the following subsequent to reading Farmers' Bulletin No. 295, 

 pp. 5-13, and Cornell Bulletin No. 230, pp. 508-512. 



1. What differences in composition of the external and internal medul- 

 lary areas ? 



