CONTRIBUTIONS FROM THE WISLEY LABORATORY. 373 



Fischer de Waldheim, received from Kew with Spongospora solani, 

 Brunchorst, but could find no difference in size or structure of the 

 spore-balls of the two, and he believed that Sorosporium scabies should 

 be removed from the Ustilagineae — that it was really Spongospora 

 solani. Soon after the publication of Johnson's paper Massee* dis- 

 covered, upon investigating tubers affected with " corky scab," that 

 the organism which he had supposed to be a "smut" fungus was 

 actually a Myxomycete, agreeing with Beunchokst's description. 

 He accordingly abandoned the generic but retained the specific name 

 given by Berkeley, renaming the parasite Spongospora scabies. 



In the following year a further paper by Johnson! appeared 

 in the Scientific Proceedings of the Royal Dublin Society. 

 This author, in the course of a retrospective survey of the literature 

 relating to potato scab, now claimed to have traced still earlier sup- 

 posed records of the occurrence of Spongospora than that of Berkeley, 

 with the result that the discovery of the organism was attributed 

 to Wallroth, and the parasite was renamed again — this time 

 Spongospora subterranea (Wall.), Johnson. 



3. Symptoms of Tumour and Canker in Potato. 



Potato canker first manifests itself in the form of small cushions or 

 wart-like excrescences scattered here and there upon the surface of 

 the tubers. These appear singly or in groups or patches. This con- 

 dition was most strikingly shown by potatos of the variety * King 

 Edward VII.' grown in 1910; accordingly one of the plants was 

 selected and, after the removal of the foliage and several tubers, 

 photographed (fig. 96). A full-size illustration of one of the tubers 

 belonging to this plant is shown in fig. 99 a. 



In these early stages it is sometimes quite possible to mistake 

 one disease for the other, especially if the "eyes" are affected. 

 The development of several warts close together at the ' ' eye , ' ' caused 

 by Spongospora, may produce a deformation closely resembling the 

 i warty appearance presented by tubers when slightly attacked by 

 Chrysophlyctis. The tubers illustrated in figs. 99 c and 99 d are affected 

 with Spongospora and Chrysophlyctis respectively. It is perfectly 

 clear, however, that it would be impossible to determine the disease 

 correctly, in each case, without the aid of a microscopic examination. 

 The warty condition of the tuber in fig. 99 b is more characteristic of 

 Chrysophlyctis than of Spongospora. The Spongospora warts are 

 usually smooth and show a rounded contour (fig. 99 a); the Chryso- 

 phlyctis warts are generally rugose, with a broken surface, and possess 

 a very irregular contour (fig. 99 f). The disease .in each case is 

 generally easily recognizable if the whole plant be dug up and 

 examined. Difficulties of identification most frequently occur when a 

 'tew tubers are compared or examined away from the plant. 



* G. Masses, I.e., p. 592. 



t T. Johnson, Sci. Proc. Roy. Dublin Soc, xii. (n. s.), No. 14 (1909), p. 165. 



