300 SWEET POTATOES 



known as black rot. Black rot (Fig. 122) gives some trouble in 

 the field, but is most injurious in the warehouses. It appears as 

 rather large black spots on the potato, soon causing the rot. The 

 principal method of control is to provide against infection in the 

 field. It is usually carried over in the soil or on the plants. Great 

 care should be taken to use seed free from the disease. For this 

 reason many growers use seed grown from slips, planting it in soil 

 where potatoes have not been grown in recent years, in this way 

 getting disease-free seed. Other rot diseases, known as stem rot, 

 soft rot, and dry rot, are less common, but similar in their attack 

 to the black rot. They are all controlled much in the same way, 

 namely, rotation of crops and use of clean seed. 



The sweet potato borer is the only insect that injures the plant 

 to any extent. Its injury is caused by boring through the sweet 

 potato tubers, and sometimes it is the cause of considerable injury 

 along the Atlantic Coast. 



LABORATORY EXERCISES 



SWEET POTATOES 



1. Compare the structure and anatomy of a sweet potato and Irish 

 potato. Does the sweet potato have similar cortical and medullary parts? 

 Does it have the same kind of eyes? (See laboratory exercise on 

 Irish potatoes.) 



Draw longitudinal sections of sweet potato and Irish potatoes. 

 Place both sweet potato and Irish potato in a moist chamber in a warm, 

 dark place. Make drawings illustrating the origin of sprouts on both. 



2. If possible the students should take part in making a hot-bed, 

 setting plants or in any other field operations that may be under way 

 in the neighborhood. 



3. Storage Experiment. Place a half-bushel of freshly dug sweet pota- 

 toes in a tight box or can, and a second lot in a ventilated crate. Make 

 notes on comparative keeping quality under the two conditions. 



QUESTIONS 



1. How does the sweet potato resemble the morning-glory? 



2. Compare the tuber of the sweet potato and the Irish potato. 



3. Give the history of sweet potatoes. 



4. Describe the principal types of sweet potatoes. 



5. Where are sweet potatoes grown principally? 



6. Describe the best climatic and soil conditions. 



7. State the best manure and fertilizer treatment for sweet potato land. 



8. Compare merits of ridge and level culture. 



9. Describe briefly all the details in propagating sweet potato plants. 



1 0. Describe methods of setting plants. 



11. Describe methods of harvesting. 



12. Principles to be observed in storing. 



13. Describe construction of pits. Storehouses. 



14. Describe construction of pits. Storehouses. 



