74 MASS. EXPERIMENT STATION BULLETIN 190. 



Another advantage in having trees grafted on roots of known varieties 

 lies in the greater resistance to insects and diseases of the roots that can be 

 secured in this way. This idea is in practical use in Austraha and South 

 Africa, where the method is used to avoid serious trouble with the root 

 form of the woolly aphis. This insect was early imported from America, 

 and is there known as the American bhght. It was found that Northern 

 Spy roots were highly resistant to this insect, and it is now the usual 

 practice in those countries to propagate all varieties on roots of the North- 

 ern Spy, or some other resistant variety.^ 



It has been the observation of the writer that roots of different varieties 

 differ in their susceptibihty to crown gall, and it is reasonable to suppose 

 that the same may be true with other root diseases. Root troubles are 

 the cause of failure of bearing trees more often than is generally reahzed. 

 Propagating varieties on known roots offers a chance of overcoming, to a 

 considerable degree, at least, many of these root troubles. 



In the northern part of the apple belt, especially in the prairie north- 

 west, resistance of the roots to extreme cold becomes important, and it is 

 considered higlily desirable to get varieties on their own roots in order 

 to avoid root killing in winter, when the temperature of the soil falls to 

 an extremely low point. If trees of the varieties suited to these conditions 

 could be worked on roots known to be of exi,reme hardiness, it would con- 

 tribute to the longevity and consequent fruitfulness of the orchards. 



If we concede that trees growing on roots of known varieties, either as 

 own-rooted trees or trees on roots of other known varieties, may be more 

 desirable for orchard purposes than trees on miscellaneous unknown 

 seedling roots, there are suggested many problems for investigation. For 

 example, what varieties on their own roots are resistant to the various 

 insects and diseases, and what ones possess extreme hardiness to severe 

 cold? What is the effect of different varieties used as root systems on 

 the growth and fruitfulness of the scion variety? 



Before these problems can be solved it is necessary to propagate trees 

 on their own roots. The general question of the interrelation of stock 

 and scion is under investigation at this station, and it is the purpose of 

 this paper to set forth some of the results obtained in propagating trees 

 on the roots of known varieties. 



The first step in securing trees on known roots is to induce the forma- 

 tion of roots from the stem of the chosen variety. The methods most 

 used in practice are by cuttings and by layers. It is known that apple 

 wood roots from cuttings with the greatest difficulty, and that only 

 certain varieties root readily by the somewhat slow and cumbersome 

 method of layers. The method of growing trees on Northern Spy roots 

 to secure resistance to the woolly aphis may be termed the nurse-root 

 method. In this method a rather long scion is grafted by any appropriate 

 method on a short piece of seedling root, and planted out in the usual way. 

 Roots arise from the Spy scion, and the seedling nurse root may be re- 

 moved, leaving the tree on its own roots. 



» Cole, C. F.: Jour. Agr. Victoria, 9: 338 (1911). 



