WINTER INJURY TO THE ROOTS 313 



roots; Green and Ballou^^ indicate peach root killing in Ohio. Macoun^^^ 

 reports similar injury to thousands of peach trees in southern Ontario 

 in the winter of 1898-1899. However, root killing without any appreci- 

 able amount of injury to the top, as occurs from time to time in the apple, 

 is extremely rare in the peach; conditions severe enough to injure peach 

 roots generally will work far greater damage to the tops. 



Carrick^^ summarizes the results of laboratory freezing of peach roots as 

 follows: "As a general rule the order of resistance of the various tissues in the 

 peach root seems to be as follows: pith, cortex, phloem, cambium, xylem. At 

 — 18°C. or below, the xylem was usually killed during the hardiest period. In 

 most cases during February and March the pith is the tissue most easily killed, 

 but in April the cambium is the least resistant. 



"It is not so easy, with the data at hand, to assign an arbitrary hmit within 

 which the peach root is injured by freezing. This is because of the great varia- 

 tion in the root tissues. The peach cambium certainly is as hardy as the pear 

 cambium, tho less so than the apple. Regardless of the size of the root, most 

 of the peach material tested showed some injury at — 10°C., and, except in 

 unusual cases, serious injury occurred at —11°. This would then place the 

 hardiness of the peach root very close to that of either pear seedHng." 



The Cherry. — Sour cherries frequently suffer from root killing on the 

 northern margin of their range, sometimes under conditions such that the 

 top is uninjured. Hansen*^ states: "One great difficulty in cherry grow- 

 ing in this state is the tender imported Mahaleb and Mazzard stocks upon 

 which we are compelled to bud and graft at present. These root-kill in 

 severe winters." Under some conditions the flower buds of sour cherry 

 may be more resistant than the roots. Craig^^ reported on damage to 

 cherry stocks in Iowa in 1898-1.899: "In nursery, the former [Mazzard] 

 was practically a total loss of 2-year-olds and a complete loss of 1-year-old 

 in the region of the severe root killing. Mahaleb suffered less, Morello 

 stock and own-rooted Morello trees generally escaped with slight injury, 

 except in exposed situations. ... In the college nurseries the practice 

 of root grafting the cherry received commendation by the fact that the 

 only trees which escaped were those which were partly on their own roots." 

 Prunus pennsylva7iica is reported from several sources to be hardy but is 

 difficult to work commercially. 



Carrick^^ places the relative hardiness in cherry stocks in descending 

 order as follows: Mahaleb, Prunus Besseyi, Prunus yennsylvanica, 

 Mazzard and he finds the Mahaleb generally much hardier than the apple 

 roots investigated. "In large Mahaleb roots during their hardiest 

 period," he states, "little injury is found under — 14°C., while at — 15° the 

 injury is relatively small. . . . The Mazzard roots in no instance with- 

 stood — 11°, but the number of tests run at — 10° was insufficient to place 

 this as its minimum. From these results the Mazzard cherry stock does 

 not appear hardier than Keiffer pear stock." 



