CANKER OF THE APPLE TREE. 573 



Structure and Origin of Canker of the Apple 



Tree. 



By 

 James E. Blomfiel«1, IVI..4., ]TI.D.(Oxoii.)< 



With Plate 32. 



The object of the present corainunicatiou is to give an 

 account of the structure and origin of the tumours produced 

 on the apple by the woolly aphis, Schizoueura lanig-era. 



These tumours are familiar objects in many orchards, and 

 are well known to gardeners who call the disease " canker." 



My reason for investigating these tumours and their mode 

 of origin arose from the circumstance that in examining a 

 transverse section stained differentially in carmine and methyl 

 green there appeared to be a transition of the wood cells into 

 the tumour cells suggestive of a malignant process. The 

 literature of vegetable pathology, as far as I could gain access 

 to it, gave me no help in discovering the meaning of this 

 appearance. Prillieux had described the structure of the 

 tumour in 'Bull, de la Soc. Bot. de France,' 1875. His re- 

 searches ai-e quoted by Kiister in his 'Pathologische Pflauzen 

 Anatomic,' but this authority notes that the subject of 

 wood-galls requires more exact investigation. This book, 

 published in 1903, gives exhaustive references to previous 

 observations in vegetable pathology, and I think that I am 

 justified in concluding that there is no satisfactory account of 

 how these tumours originate. 



