44 EXPERIMENT STATION EECOED. 



of rapid growth there is little difference in hardiness of the different tissues. 

 The root tissue is the most tender at all seasons and the difference in the killing 

 temperature of roots in summer and winter is much less than that of the 

 killing temperature of twigs or other wood in summer and winter. The resist- 

 ance of the root system is greater in the parts nearest the surface. Roots of 

 the French crab apple stock seemed to be more tender than roots of the average 

 apple variety. Marianna plum roots were found to be more hardy than Myro- 

 bolan roots and Mahaleb cherry roots were slightly more hardy than Mazzard 

 roots. 



Pollen of the apple was found to withstand much lower temperature than any 

 other tissue when in full bloom. Peach buds frozen in the laboratory with 

 the scales removed were slightly more resistant to low temperature than were 

 buds with the scales not removed. 



With reference to the killing of the wood of peach trees from freezing the 

 author concludes that little can be done to influence the amount of killing ex- 

 cept to have the trees started into winter in proper condition of maturity. Trees 

 one or two years in the orchard or old weak trees are most liable to succumb 

 to the effects of low temperature. With trees that have been winterkilled, al- 

 though apparently in the best condition of maturity, pruning the trees severely 

 seems to reduce the subsequent amount of killing. On the other hand, when the 

 wood has been winterkilled because it has not reached the proper condition of 

 maturity in the fall subsequent heavy pruning is liable to result in greater loss. 

 The hardiness of peach buds when in fully dormant condition seems to be 

 greatly increased by continuous low temperature previous to unusually severe 

 temperature. The most important factor influencing the loss of peaches from 

 low temperature in winter is keeping the buds from starting into growth dur- 

 ing warm periods in winter. In south Missouri and Arkansas at least the best 

 means of accomplishing this end is prolonging the growth of the trees in 

 autumn, either by heavy pruning or by fertilizing with nitrogen the spring be- 

 fore. Some varieties of peaches have a much longer rest period than other 

 varieties and therefore start into growth more slowly during warm winter 

 periods. 



For Missouri conditions the killing temperature of peach blossoms when the 

 tree is just coming into bloom varies from 22 to 26° F. After pollination and 

 until the peaches are a half inch in diameter at least they continue to become 

 more tender until they will withstand but very few degrees below the freezing 

 point, the seeds of young peaches killing at a higher temperature than other 

 peach tissue. No evidence was secured from the author's investigations to 

 show that early varieties of peaches start into growth more readily during 

 warm periods in winter than do later varieties. After blooming time, how- 

 ever, the early peaches grow much more rapidly and are much more liable to 

 be killed by a freeze after the fruit is set. 



The killing of apple w^ood is of considerable importance in some apple-grow- 

 ing sections, among the common injuries being root killing, crown rot, crotch 

 injury, sunscald, trunk killing, and killing back of top and branches. The 

 killing of apple buds from low temperatures has not been commonly observed. 

 The blossoms and young fruit of the apple, however, will not generally with- 

 stand as low temperature as will the blossoms or young fruit of equal age of 

 the peach. Cherry and plum buds are more resistant than peach buds but are 

 frequently killed in some sections. The young fruit of the Wild Goose plum 

 is among the most resistaut to late frost in the spring. 



In connection with this study temperature records were secured and a chart 

 is given showing the maximum and minimum temperature curves at Columbia 

 and Koshkonong, Mo., during the years 1901-1912, including the season begin- 



