278 FUNDAMENTALS OF FRUIT PRODUCTION 



but may be explained in part by the lack of a sufficient amount of sap- 

 wood to serve as a local reservoir. Even prolonged cold does not affect 

 the upper part of tall trunks as much as it does the low, smaller branches 

 though conduction from the ground is conceivably as difficult; the tissues 

 on the trunk, however, have both relatively and absolutely a greater 

 amount of sapwood on which presumably they may draw. 



Where Winter Drought Conditions Prevail 



Winter drought conditions are in a measure independent of soil con- 

 ditions and can be considered as of possible occurrence over a wide range 

 of territory. The coldest weather in humid sections is accompanied by 

 dry atmospheric conditions; occasionally after a dry summer and fall 

 these sections suffer from winter killing due to desiccation. Long con- 

 tinued severe, though not excessive, cold would induce physiological 

 drought. The winter of 1895, already mentioned, was of this type. It 

 is, however, infinitely more common, in proportion to the amount of 

 fruit grown, in regions of prevailingly dry atmosphere and intense cold. 

 Wyoming, the Dakotas and parts of Minnesota furnish abundant 

 examples. Rainfall is comparatively light in those sections and the soil 

 frequently freezes with a low moisture content. Winter precipitation is 

 less than summer, frequently only a fourth as great and there is much 

 clear, cold weather. 



Protection Against Winter Drought Injuries 



Necessarily protective measures against winter injury associated with 

 drought must be preventive. They must either reduce water loss or 

 increase water supply. 



Winter Irrigation. — Buffum^^ advocates in Wyoming thorough irriga- 

 tion "late in the fall, before the ground has frozen and when growth 

 has ceased. The later this irrigation can be done the better as the 

 object is to store moisture in the soil sufficient for winter . . .where 

 orchards are planted on bottom lands that have a continual supply of 

 moisture fall irrigation may be unnecessary. But on upland it is the 

 surest way to prevent trees from winter killing and when possible irri- 

 gations through the winter will be found advantageous. " In North 

 Dakota, Waldron^^^ writes: "Parts of our own plantation have been 

 cultivated every year until the ground freezes with only the best results 

 . , . the treatment that provides the trees with the greatest amount 

 of soU moisture in the fall will tend to prevent winter kUling." Else- 

 where the same writer states: "The cause of winter killing in mild 

 weather is the drying up of the twigs .... Trees and shrubs that are 

 neglected during the latter part of summer so that the ground becomes 

 hard and dry, ripen their wood prematurely and unless fall rains are 

 abundant the drying process sets in before winter begins, leaving the 



