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young plants become infected. Seed with brown discoloration should not be 

 planted. 



Black Heart. 



In this non-parasitic disease there is discoloration of the central part of the 

 tuber. Though it has been blamed upon overheating, experiments indicate the 

 cause is lack of oxygen, as in potatoes stored in large piles. It is essentially a 

 disease from imperfect ventilation. 



Frost Necrosis. 



The freezing point of the potato tuber is somewhat lower than 32°F., but 

 below 30.7° F., 50-75% of potatoes tested froze. The resulting frost necrosis 

 apears as a blackening of the water conducting tissue and is known as net, ring, 

 or blotch necrosis. As setts, frost-injured seed gave only about 50% of a stand 

 of normal production. Such injured seed thus must be planted twice as thickly, 

 but badly frozen potatoes should not be used for seed. Rotten pieces must be 

 rejected. 



Suggestions on How to Store Potatoes. 



Proved factors in good potato storage are control of temperature, of light, 

 of air movement, and of humidity. 



The temperature should be kept at 36''-40° F. All daylight should be excluded 

 from storage places, but subdued light does not cause greening of potatoes. 



Humidity may be kept fairly high at the low temperature. It prevents ex- 

 cessive loss in weight by drying. The percentage humidity must not be so high 

 that moisture condenses on the potatoes. 



Why ventilation ? Beucause pure fresh air kept in circulation maintains 

 even conditions of moisture and heat, and a sufficient supply of oxygen. It is very 

 difficult to control in pit or cellar storage. Air movement should be permitted as 

 long as temperature is above danger point. An ordinary thermometer is a neces- 

 sity in the storage place, to prevent risk of black heart and sweating. 



Treatment before storage is not generally practised. It has been shown by 

 Zavitz, however, that dusting sound potatoes and slightly decayed potatoes with 

 hydrated lime reduced decay in stored potatoes to O.S per cent, for sound, and 40 

 per cent, for slightly decayed as compared to 4.5 per cent, of decay for sound un- 

 treated, and 58.3 per cent, of decay in slightly decayed. The length of storage w^as 

 from November 7, 1912 to June 7, 1913, and November 23. 1915 to February 23, 

 1916. Twelve tests were made, and 5,000 tubers used, of three varieties. Treat- 

 ment, then, appears profitable in years when rot in severe as in 1912 and 1915. 



