APPLE DISEASES 



109 



for at least a half century. It is now found on practically every 



continent of the globe. Records come from Europe, South 



Africa, Asia, New Zealand and 



North America. It occurs in 



practically every state in the 



Union, but is most abundant in 



the more southern states of the 



apple-growing belt, from Virginia 



to Texas. The disease is also 



known in Canada. 



As already intimated, crown- 

 gall is most damaging in the 

 nursery, and becomes most 

 prominent and important where 

 root-grafts are carelessly made. 

 In many instances the affected 

 plant shows no ill effects, and 

 trees are said to outgrow the 

 disease if they are well rooted. 

 In certain other cases affected 

 plants are dwarfed, which of 

 course renders them less valu- 

 able. A common source of loss 

 lies in the fact that other patho- 

 genes enter plants through the 

 gall-lesions. 



Symptoms. 



The disease may exhibit itself 

 in two' forms: (1) as galls (Fig. 

 30), and (2) as hairy-roots (Fig. 

 31). The galls are either hard or 

 soft and occur at the ground- 

 line or on limbs. It is estimated that fully 90 per cent of 

 the galls appear, in the nursery, on the scion just above the 



FIG. 30. Crown-gall on apple 

 roots. 



