15th. The only minimums through Dec. 15 that were below 20° were 

 15° and 18° early in the month. 



After the 60° temperature o£ Dec. 15, there was a drop to 16° 

 on Dec. 17, and minimums remained low for the next 9 days with read- 

 ings of 20, 7, 6, 10, 17, 17, 0, -1, and 5°. The first snows came 

 during this period, accumulating to 9" between Dec. 21 and 23. For 

 the rest of December, January and February, temperature records show 

 favorable conditions for acclimation. A high of 52° on Dec. 27 

 cooled gradually and single number temperatures did not appear again 

 until January 5 and 6. During that 9 day period maximums did not go 

 above 41°. By January 23, when the winter's lowest temperature (-8°) 

 was recorded, trees should have been well acclimated. The temperature 

 fluctuations during January were not great, nor as rapid as in Decem- 

 ber. 



However, trunk injury was associated with pruning done as late 

 as the 3rd week of January in some orchards. In most years, trees 

 pruned in the second or third weeks of January do not suffer cold 

 injury. Since January temperatures in 1976 were not unusual, it 

 must be supposed that the injured trees were not as well acclimated 

 as in most years. Non-pruned trees withstood subzero temperatures, 

 but the hardiness-reducing effect of pruning was sufficient to raise 

 their critical temperature level into the subzero temperatures 

 experienced in January. Possibly injury would also have occurred 

 on trees pruned in February if subzero temperatures had occurred 

 in February. 



The tree tissues that were injured at Storrs, and other orchards 

 in Connecticut were the bark or cambium of the trunk and lower scaf- 

 fold limbs. Bark separated from the wood in some cases, and remained 

 attached in others. In both cases the bark died and decayed in the 

 spring and summer. On some trees, bridges of live bark remained 

 between dead areas, connecting across the injured zone. In Connecti- 

 cut, these injured trees produced a normal crop in 1976, indicating 

 that the conducting tissue of the wood was not seriously harmed. 

 Completely girdled trees died during 1977, but some trees with very- 

 little connecting bark remained alive, and even looked pretty good 

 except for crop. 



Studies of cold hardiness have shown that bark and wood tissue 

 of acclimated apple trees survive cold temperatures by two different 

 mechanisms. Acclimated wood tissue is capable of a phenomenon called 

 deep supercooling. Supercooled water in the protoplasm remains 

 liquid even when its temperature is far below the normal freezing 

 point. It is a phenomenon that can also be shown by pure water when 

 small droplets are dispersed in a low-freezing-point liquid. 

 Researchers suspect that in the woody stem or trunk tissue, proto- 

 plasmic water may be somehow isolated from ice nucleation that 

 occurs outside the cell walls. A temperature is finally reached, 

 however, at which this protoplasmic water (or the finely dispersed 

 water droplets in a non-living system) will suddenly freeze to ice. 

 This temperature is around -40° F for fully acclimated tissue or 



