286 FUNDAMENTALS OF FRUIT PRODUCTION 



influence acts upon the plant. It follows, then, that the earlier the plant 

 enters upon its period of rest the earlier the period is over. This is a 

 matter of some practical import, as appears later. 



The rest period can be shortened, or broken, by various treatments. 

 Etherization, light, wounding, desiccation, hot-water baths and exposure 

 to freezing all bring it to an early end. For the forcing of certain flowers, 

 such as lilacs, etherization is sometimes used; the greenhouse man who 

 wishes to force fruits exposes the trees to cold. Northern greenhouses 

 in Europe can force fruit and have it on the markets somewhat in advance 

 of the greenhouse fruit crop from many more southern parts because the 

 trees can be exposed to a freezing temperature earlier in the north and 

 the rest period broken earlier. For the orchardist, however, the chief 

 interest is in prolonging the rest period; this can be done in some cases, 

 discussed later, by postponing its advent. In northern sections, though 

 the temperatures are undoubtedly severe enough early in the winter to 

 break the rest period, they are low enough to prolong dormancy and the 

 rest period is relatively of less importance there. Farther south, where 

 warm periods come during the winter, it is of much greater significance. 



The exact natures of the changes involved in the beginning and the end of the 

 rest period are not known. A puzzling fact is mentioned by Schimper: A low 

 temperature in the growing season will not have the same effect as in the dormant 

 season; the change of starch to sugar in the potato accompanying cold in the 

 winter is not dupUcated in the summer. Since ordinary growing temperatures 

 are without effect on the rest period, chemical changes appear not to be the con- 

 trolUng factors. Since time is a recognized factor a physical change is suggested. 

 It seems significant that all processes known to shorten the rest period are known 

 also to increase permeability. 



Injuries to Fruit Buds 



The killing of fruit buds which have started into activity is more 

 evident in southern sections. Whitten^i" discusses winter killing of the 

 peach in Missouri as of this nature. He states: "The growth of buds 

 during warm weather in winter renders them very susceptible to injury 

 from subsequent freezing. This is the most common cause of winter 

 killing to peach buds in this state. Very often a warm spell as early as 

 February causes peach buds to make considerable growth. If growth 

 starts to any great extent the subsequent cold weather is almost sure to 

 kill the buds." Chandler^^ states that "there has very seldom been a 

 year when buds in the peach section of southern Missouri have not been 

 started sufficiently by Feb. 1 to be killed by a temperature considerably 

 higher than would be required to kill buds in northern Missouri, or 

 certainly in Michigan, New York or New England on the same date." 



It is possible that occasionally the injury in these cases of warm 

 weather followed by cold is due merely to the sudden drop in temperature. 



