276 FUNDAMENTALS OF FRUIT PRODUCTION 



Bailey^"^ estimates that a large apple tree loses from 250 to 350 grams 

 of water each day through the winter. Observations on moisture content 

 of apple twigs in Iowa show an actual increase from November to Decem- 

 ber in many varieties; on Jan. 15, however, following several days of 

 severe cold, there was a very marked decrease, though the respective 

 intervals between observations were 5 weeks and 3 weeks^*^ (see Table 13). 



Water Conduction in Trees During the Winter 



Bailey ^° cites evidence gathered in New York showing loss of moisture 

 in twigs during winter and a higher moisture content during a thaw than 

 during a previous period of cold weather, indicating a conduction of sap 

 during the milder weather. Indeed such a conduction must be conceded 

 else the tree would inevitably dry out. Wiegand^i"* showed a conduction 

 of water to Pinus Laricio buds at temperatures between — 18°C. and 

 — 6.7°C. Buds severed from the tree but sealed immediately on the 

 cut surfaces showed an average water content of 41.2 per cent, after 3 

 days while buds taken fresh from the tree at the end of this time, even 

 though the twigs had been frozen, showed an average content of 47.5 

 per cent. It is probable that interference with conduction, or an evapora- 

 tion rate much higher than conduction, is just the condition requisite for 

 winter drought injury. 



Relation of Freezing to Water Conduction. — It is well known to every 

 wood-chopper of the northern woods that trees freeze even to the center 

 in prolonged cold weather. Investigations have shown that in trees of 6 

 to 8 inches diameter the difference in temperature between the center and 

 the outside in the morning is only 1 ° or 2°R. , though in trees 2 feet in diam- 

 eter it may be on single days 5°, 6° or 7°Il. ; with air temperatures of — 13° 

 to — 15°R. the tree temperature was —12° to — 14°R.; most important, 

 the longer the temperature of the air remains uniform the more the tem- 

 perature of the tree approaches that of the air.^^^ The temperature of the 

 alburnum or sap wood in maple has been shown to follow the air tempera- 

 tures fairly closely. ^^^'^ More detailed figures taken morning, noon and 

 night, at a depth of 8 centimeters in a box elder tree, indicate that tree 

 temperatures follow the trend of the air temperatures very closely, not, 

 however, reaching the full extremes of the outside fluctuations unless 

 these are maintained for some time.'^^ Figure 27, arranged from a part 

 of these figures, shows typical daily fluctuations of air and tree tempera- 

 tures. Table 22 shows the averages of the temperatures recorded during 

 January and February. Observations in Lapland show winter tempera- 

 tures in live and dead trees to be practically the same."^ 



Grape vines have been grown in a greenhouse, so trained that certain 

 canes passed outside and were then brought back into the house. The 

 base and the upper parts, inside the greenhouse, opened their buds 

 quickly and continued to grow. On cold mornings, however, with the 



