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JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



reference is made to celery at Winiborne, Dorset, " suffering from a 

 bad attack of the fungus Septoria petroselhii var. apii B. & C.,"'^ and in 

 voL xvi. p. 1010, the following occurs: " A celery-leaf disease caused 

 by a parasitic fungus called Septoria petroselini Desm. has been long 

 known in tliis country and on the Continent. In this instance the leaf 

 becomes studded wuth numerous small, irregularly angular, brown 

 spots, each bearmg a few very minute black points or perithecia, con- 

 taining myriads of very slender needle-shaped spores. As a rule, when 

 the fungus attacks celery an epidemic results, due to the rapid produc- 

 tion and dispersal of spores." 



The available evidence scarcely seems to justify the statement in the 

 foregoing quotation that this disease " has been long known in this 

 country. " It really appears to be of comparatively recent introduction, 

 and to be spreading far and rapidly each year. Furthermore, it appears 

 to be spreading on cultivated celery, and not by attacking wild celery, 

 for, as already pointed out, there are no records of the occurrence of the 

 fungus upon wild celery. It must, however, be confessed that our 

 knowledge of the occurrence and distribution of these minute fungi upon 

 wild plants is very incomplete. It would be a useful and interesting 

 piece of work for anyone with the requisite technical knowledge and 

 leisure to ascertain precisely to what extent the fungi which attack our 

 cultivated plants will infect their wild allies, and vice versa. Micro- 

 scopical examination alone is unfortunately not to be relied upon, and 

 may actually be misleading, for we have to reckon with two very 

 curious phenomena in the physiology of fungi — polymorphism, and the 

 perhaps even more strange case where morphologically similar fungi 

 are restricted in their range of infective capacity, and cannot indis- 

 criminately attack any variety even of one species. Only carefully 

 conducted and controlled cultural and infection experiments are likely 

 to give reliable evidence. 



In his latest book of plant diseases, Mas see! devotes considerably 

 more space to this disease than in the earlier publication (Lc), which 

 may perhaps be looked upon as an indication that his experience is 

 similar to our own, that the disease is spreading rapidly. Dr. G. H. 

 Pethybridge informs me that the disease has lately greatly increased 

 in Ireland. 



The manner in which plant diseases of this type spread from 

 place to place, and from country to country, often though separated 

 by wide seas, is a problem that frequently presents great difficulties 

 in its solution, and this is no exception. Two or three possible 

 ways of distribution from place to place suggest themselves, espe- 

 cially the throwing of diseased plants and leaves, perhaps brought 

 from another place, on the rubbish heap, whence they reach the garden. 

 Most mycologists are of opinion that the spores contained in these 

 pieces of diseased foliage, &c., form the source of infection in the 

 succeeding season, for when once the disease occurs in a garden, it 



* There is a specimen from Wimborne in the Kew Herbariimi. 



t Massee, G., Diseases of Cultivated Plants and Trees (1910), p. 425. 



