WINTER INJURY 



285 



winter. The data are summarized in Table 27, which is arranged from a 

 more detailed statement in Chandler's report. The relation is close 

 enough to indicate why a given variety, of the Persian type for example, 

 may be tender in the south where its rest period is likely to be broken 

 and still be hardy in the north where cold weather is constant, or why in 

 the same orchard it may be hardy during a winter of steady and fairly 

 severe cold and still be tender during a mild winter. 



Recent studies indicate some correlation, even in Minnesota, between 

 hardiness and the intensity of the rest period in certain plums, as shown 

 in Table 28. These suggest that the rest period may be more important 

 in the north than it generally has been considered, though they do not 

 explain observed differences in bud killing early in the winter. 



T.^£LE 27. — Percentage of Buds Starting Early and of Buds Killed''' 



Table 28. — Time Required for Blooming under Laboratory Conditions at 

 Different Intervals During the Winter 



{After Straushaugh^^^) 



Different plants appear to have rest periods of unequal length; in fact 

 some, such as certain spiraeas, seem to have none. However, the rest 

 period for each plant seems to be fairly constant provided no disturbing 



