316 FUNDAMENTALS OF FRUIT PRODUCTION 



roots when they come from cions of extremely hardy varieties are gen- 

 erally hardier than the stocks commonly used. In those of the northern 

 sections where root killing is most likely there is a tendency to grow trees 

 formed by grafting long cions on short pieces of root for the purpose of 

 inducing cion rooting, thus securing increased hardiness in the roots. 

 No experimental evidence is available to show clearly whether cion roots 

 of hardy apple varieties are hardier than those of tender varieties, but 

 Craig^^ records numerous instances when cion roots proved more hardy 

 than the stocks on which they were worked. Hansen, ^^ writing in South 

 Dakota, says: " . . .in ordinary winters the roots emitted by the 

 scions of hardy varieties are sufficiently hardy but . . . they are not 

 proof against such winters as that of 1898-1899." 



Use of Hardy Stocks. — Top working on stocks of known hardiness is 

 another method of combating root killing in those sections particularly 

 subject to it. Pyrus baccata is said by Hansen to succeed in the Trans- 

 baikal section of Siberia where the mean annual temperature is 27'°F. 

 and the mean temperature of the coldest month — 18.4°F. and where 

 the annual rainfall is 11.42 inches. He reports young seedlings of this 

 species to have wintered perfectly despite a temperature of — 40°F. with 

 no snow. The "Virginia crab" is also reported to be more hardy than 

 French crab. However, these have more or less dwarfing effect and do 

 not make an altogether satisfactory union. '^^^ 



Pruning. — After the damage has occurred, there is little that can be 

 done. If the killing is complete or nearly so the trees should be removed. 

 However, many times the root destruction is incomplete; some of the 

 roots that start straight down from the crown on old trees will frequently 

 escape. In many of these cases a heavy pruning back, or, if there is 

 also injury in the top, a moderate pruning back, will enable the tree to 

 survive and still have many years of usefulness. Very young trees 

 that have suffered only partial destruction of the roots can be restored 

 in many instances by banking the trunks with earth, inducing the for- 

 mation of additional cion roots. 



Handling Nursery Stock in Cold Weather. — One form of root injury 

 likely to be encountered in regions remote from the territory commonly 

 subject to killing of this type is that occurring on nursery trees. Root 

 growth in apple trees in Missouri has been shown to continue long after 

 the top has assumed a completely dormant appearance, in fact until 

 winter has well set in. 212. In a growing state, it will be recalled, roots 

 are damaged by temperatures only a few degrees below freezing and 

 even in a dormant state they will stand only comparatively high tem- 

 peratures.^^ Chandler states: "In case of 1-year-old roots of the French 

 crab, used as stock by most of the nurserymen, about —5 to — 8°C. (23 to 

 15.8°F.) is as low a temperature as they can be depended upon to with- 

 stand with no injury." Fall dug trees, necessarily hfted before the 



