4 BULLETIN" 916, U. S. DEPARTMENT OF AGRICULTURE. 



posed to a temperature of 8.7° froze in 6 minutes when the actual 

 internal temperature had reached 23° F. The other potato was 

 exposed to 15.8° and froze in 12.5 minutes when the internal tem- 

 perature had reached 20.2° F. The actual freezing point of both 

 potatoes was 29.15° F. This substantiates the results obtained by 

 Jones, Miller, and Bailey (4) . They cite an instance of a tuber freez- 

 ing in 80 minutes when undercooled to 24.44°, while another exposed 

 to a slowly diminishing temperature did not freeze until 13.1° F„ 

 was reached. Another specimen froze in 40 minutes when under- 

 cooled to 26.4° while exposed to a rapidly diminishing tempera- 

 ture which had reached 12.2° F. They state that, in general, po- 

 tatoes do not freeze until exposed to 26.6° F. or lower. To judge 

 from the results submitted in this report it is possibly safe to state 

 that except in the case of accidental inoculation the degree of under- 

 cooling at which freezing occurs depends upon the variety, the 

 rapidity with which undercooling progresses, and the length of ex- 

 posure to a given degree of undercooling. 



PLAN OF THE WORK. 



In order to apply to the handling of potatoes the knowledge of the 

 process of undercooling and freezing already gained, a series of ex- 

 periments was conducted at the Arlington cold-storage plant of the 

 Bureau of Plant Industry. It has been noted by potato growers and 

 shippers that sometimes one lot of potatoes while being handled or 

 otherwise disturbed in transit will freeze when another left undis- 

 turbed at the same temperature remained uninjured. Some apple 

 handlers are very careful not to jar or jolt frosted apples, because 

 they say it will cause them to bruise and rot. It is a practice among 

 some onion growers to store their onions through very severe winter 

 weather in mows or buildings between layers of hay where they are 

 undisturbed during the winter. These persons will often .guard 

 against loose doors or shutters which can be slammed by the wind, 

 as this is liable to cause the onions to freeze and subsequently to rot. 

 Numerous instances are reported where potatoes have been exposed 

 for hours or even days to temperatures below their freezing point 

 without injury. Miiller-Thurgau reported having stored potatoes 

 at 32° to 26.6° F. for two weeks without injury. Of course, internal 

 frost injury may have been present without its being detected unless 

 the potatoes were cut open and examined. 



In the present work seven standard varieties of potatoes, all true 

 to name and grown under the same conditions by the Bureau of 

 Plant Industry at the Aroostook Farm of the Maine Agricultural 

 Experiment Station, were used. These varieties were the Triumph, 

 Irish Cobbler, Spaulding No. 4, American Giant, Rural New Yorker, 



