222 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



PARASITIC ROSE CANKER. 

 A New Disease in Roses. • 

 By H. T. Giissow, F.R.M.S., F.R.H.S. 



Specimens of rose twigs showing signs of an obscure injury, said to be 

 spreading, were recently received from Larne, Co. Antrim. The twigs 

 were of various ages. The sender stated that the disease appeared in his 

 Hybrid Tea Roses about two years ago, and is now spreading to the 

 Wichuraianas. As the first specimens were rather dry and therefore 

 unsuitable for the further study of the injury, new ones were requested 

 and a well-chosen series of diseased twigs was obtained, together with 

 some additional notes on the behaviour of the disease. These notes, 

 which are very instructive, are given below : — 



" The disease starts first on the one-year-old wood. Leaves are not 

 affected, some specimens bearing leaves this season." 



" The plants are about four years old. A specimen Robert Craig has 

 been affected for about two years. The varieties most affected are Ards 

 Rover, Crimson Rambler, Robert Craig, and almost all the Wichuraianas. 

 The disease is more noticeable in wet weather, and spreads to neighbour- 

 ing plants, especially Wichuraianas." 



Unfortunately this disease, like many others, is not readily noticed 

 until far advanced, but it is to be hoped that this report will enable the 

 observant rose-grower to recognize it in its beginning and thus be able 

 to effect a cure. 



The accompanying photograph (fig. 33) shows the appearance of the 

 shoots when the disease has reached an advanced stage. These show 

 deep fissures covered with an abnormal growth, which have the 

 appearance of " canker " spots. The bark has burst and for some reason 

 or other the wound has not healed normally, but the callus has continued 

 to grow until badly " cankered " spots result. The single first specimen 

 received agreed exactly in appearance with some illustrations in a paper 

 by Professor Sorauer on Rose Canker (Zeitschrift f. Pflanzenkrank- 

 heitcn, XVII. pp. 22-32 Plate II. 1907). This author, in dealing with 

 a " K< se Canker," attributes the canker spots to frost injury. He de- 

 scribes the injury exceedingly well, but he owns that he failed to produce 

 the characteristic " development of outgrowing cells " (luxuriierende 

 Kberwallungen, p. 27) by exposure of rose trees to artificial frost. He 

 seeks to explain this failure by stating that he " probably had not chosen 

 the right time for his experiments." I will return to this statement of 

 Sorauer's later on, but will first deal with the development of the disease 

 from Die evidence of the specimens sent me. 



The older twigs were all more or less badly cankered. Those that 

 bowed less nui ked iigns ol injury, in I lie form of only a small outgrowth 

 of cells protruding from underneath the split bark, at the same time 

 showed that the cracks were surrounded by plainly diseased tissues of a 



