318 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



towards resisting rust. A somewhat cursory survey shows that some 

 are as susceptible to orange rust as the Hybrid Perpetuals. Examples 

 which will occur to most rose-growers are ' Mrs. W. J. Grant,' ' Lady 

 Ashtown,' 1 Liberty,' and ' Camoens.' Climbing " sports " of the 

 first three exist, and these in turn are as susceptible as the types 

 from which they sprang. Other varieties, on the other hand, possess 

 a marked degree of resistance. Amongst such are 1 Laurent Carle,' 

 ' Edme Metz,' and 1 Princess Marie Mertchertsky.' Further, some of 

 the newer Tea Roses are rust-susceptible. As an example that superb 

 Rose ' Mrs. Foley Hobbs ' must suffice. Its pedigree is unknown to 

 me, and I can only hazard a guess that a Hybrid Tea carrying the 

 factor for susceptibility was one of its parents. 



The incidence of the rose mildew on the newer races of Roses 

 again points to the fact that immunity and susceptibility are trans- 

 ferable on cross-breeding. The new race of Wichuraiana Roses, which 

 have so altered the appearance of our rose gardens in the last few 

 years, gives almost convincing proof of the fact. These Wichuraianas 

 are descended from the species Rosa Wichuraiana crossed with 

 various Teas, Hybrid Teas, Hybrid Perpetuals, &c. The species itself 

 shows an intense degree of resistance to mildew, whilst this is not 

 necessarily true of the other parents. It is customary to speak of 

 the whole class as being mildew-proof, the hard, polished leaves being 

 supposed to be impenetrable by the fungus. As a matter of fact, 

 many are badly attacked during mildew years, and if one looks up 

 the pedigrees of these varieties one finds that susceptible forms have 

 been used in their up-building. 



' Rene" Andre,' for instance, is R. Wichuraiana x ' LTd6al,' 

 ' Diabolo ' is R. Wichuraiana x ' Xavier Olibo,' ' Leontine Gervais ' 

 R. Wichuraiana X ' Souvenir de Catherine Guillot.' 4 Dorothy Perkins ' 

 R. Wichuraiana x ' Mme. Gabriel Luizet ' ; whilst the latest comer, 

 ' Wich-Moss,' has inherited the habit and foliage of R. Wichura- 

 iana and the multitudinous prickles of the Moss Rose, together with 

 its susceptibility to mildew. 



The third disease, black spot, is at present far less common than 

 either rust or mildew, though it appears to be becoming more abun- 

 dant each season. It is, as a rule, common on the Persian Yellow 

 Rose. This variety crossed with ' Antoine Ducher ' gave the equally 

 susceptible ' Soleil d'Or,' which in turn " sported " the susceptible ' Soleil 

 d' Angers.' The former has been the starting-point of the new race 

 of Pernettiana Roses. It is early to speak of the incidence of black 

 spot on these, but one of the most widely grown, the 1 Lyon Rose,' 

 rarely fails to provide me with an outbreak of the disease. 



A vague recognition of similar facts has led plant-breeders to make 

 the attempt to transfer the feature of immunity definitely to varieties 

 good in other respects, but lacking it, with some measure of success. 



Orton and his colleagues,* for instance, have bred new varieties 

 of Cowpeas and Water-Melons resistant to a wilt-disease caused by the 

 * Orton, C.R. IVe, Con. Inter, de Gdnetique, p. 247. 



