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With regard to the susceptibility of apple stocks it has 

 been noted at- East Mailing that the different sorts of Paradise 

 differ markedly. The most susceptible are certain types which 

 root rather poorly when layered and which consequently have 

 to be torn or broken from the stool, instead of being cut with 

 the knife, e.g., the Doucin. While evidently this is due partly 

 to the ragged wound made by tearing the stock from the stool, 

 there is, apart from this, evidence of variation in susceptibility. 

 No kind of apple stock has yet been found to be immune, and 

 traces of the disease have been seen on several kinds of " Free " 

 stocks, which have been propagated by layers, as well as on 

 all the common forms of " Paradise." 



Distribution in Britain. The Crown Gall bacterium is 

 widely distributed in gardens and orchards and especially in 

 the soils of nurseries. This is evident from records kept by 

 the Ministry of Agriculture and receives confirmation from 

 the frequent occurrence of galls on stocks, canes and trees 

 received from all parts of Western Europe at the East Mailing 

 Research Station over a period of nine years. Judging by the 

 large percentage of attacked plants it would appear that the 

 disease must be exceedingly prevalent in certain localities. 

 From Erwin F. Smith's work it is clear that the bacteria* 

 causing the galls show little specialisation into distinct races 

 according to their hosts, but can, if opportunity offers, attack 

 a large range of plants. The importance, therefore, of pre- 

 venting the distribution of diseased stock and the infection of 

 clean areas is obvious. 



Measures of Control 1. Clean Soil. In the cas'e of 

 Manetti roses which are particularly liable to infection it is 

 highly desirable when propagating these plants to avoid soil 

 badly infested with the Crown Gall bacterium. If possible new 

 or entirely clean land should be selected. 



2. Prevention of Wounds. It has been shown that the bac- 

 teria invade the plant through wounds, and that in all probability 

 they cannot enter an uninjured surface. The greatest care, 

 therefore, should be exercised in not injuring the stocks more 

 than necessary. This applies not only to their . propagation, 

 but to subsequent cultivation; all unnecessary shifting, 

 heeling-in, &c., should be avoided. 



3. Budding and Grafting. Where Crown Gall is liable to 

 occur, special care should be exercised in the operations of graft- 

 ing and budding, since very frequently the junction or point of 

 union is subsequently planted below ground, thus offering a 

 wound for immediate infection. Scions should be placed on 

 stocks of appropriate size and the graft protected by careful 

 wrapping. 



4. Treatment of Attacked Stocks and Trees. It should be 

 clearly understood that the removal of a gall from a plant does 



