REPORT OF THE SOCIETY 101 



Whether affected tubers sprout or not depends upon the extent of the 

 collapsed tissues and upon whether the injury is due to insufficient oxygenation 

 at high or low temperatures. Usualh' the latter require a longer time for 

 sprouting but if no surface injury is present and the buds sprout well there 

 is no harm in using such tubers for seed. It is obviouslj' unwise to use tubers 

 with surface lesions for seed since the lesions will become breeding grounds 

 for fungi and bacteria. 



Control 



It must be remembered that potatoes stored at high temperatures and for 

 a long period require more ventilation than those stored at lower temperatures 

 or for short periods. 



1. Potatoes should not be stored more than six feet in depth at tempe- 

 ratuies below 45° F. for a lenghh}- period of time. At temperatures of 50° F. 

 to 70° F. they should not be piled more than 3 ft. deep if they are to be kept 

 longer than a month. 



2. Small potato pits do not need extra ventilation but the tubers should 

 be protected from frost. 



(b) Frost necrosis 



In Canada, as in the northern tier of states of our neighbour, the main 

 crop is in constant danger of exposure to freezing temperatures from the time 

 of harvest to planting or to retail sale. There are two types of frost injury, 

 viz: — that in which complete freezing occurs and that in which no superficial 

 symptoms are noticeable. In the first case freezing is due to exposure to a 

 very low temperature or to prolonged freezing at a somewhat higher temper- 

 ature. The tubers are frozen solid and the tissues collapse on thawing. 

 The soft, wet condition resulting is easily recognized. 



The second type is due to exposure to temperatures just below the freezing 

 point or to a very low temperature for a short time. In this case, the tuber is 

 never frozen completely but certain tissues only are affected. Upon exposure 

 to ordinarj' storage temperatures the affected tissues become necrotic and 

 are blackish in colour after being exposed to oxidation in the air. The necrosis 

 is of three general tj-pes, viz., net, ring, and blotch. 



In "net" necrosis there is a general blackening of the finer vascular ele- 

 ments extending from the vascular ring into the medulla and cortex. 



A more pronounced blackening in the vascular ring and adjacent tissues 

 gives the "ring" tj'pe of frost necrosis. This is often most apparent at the 

 stem-end. 



When the necrotic areas are larger and less defined we have the "blotch" 

 type and this is often found in the cortical tissues. 



Frost injury before or during harvest may give rise to any of these types 

 or modifications of them, but, as a rule, the ring type predominates if exposure 



