102 DISEASES OF CULTIVATED PLANTS 



As a rule only one resting-spore is present in a cell of the 

 host-plant, 40-70 /x. diam. 



For the reasons given above, I consider the fungus 

 causing black scab in potatoes to be a typical species of 

 Synchytrium t and quite distinct from the fungus indicated by 

 Schilberszky. 



The disease is now unfortunately fairly common in this 

 country, but its presence has only been recorded twice on the 

 continent in Germany. Curiously enough no record exists 

 of its occurrence in Hungary, the country from which Dr. 

 Schilberszky obtained his specimen of Chlorophlyctis endobio- 

 tica. 



The only methods that can be suggested for checking the 

 spread of the disease are of a preventive nature, and as these 

 are unfortunately mostly outside the range of what may be 

 expected of the potato-grower, or, for the matter of that, any 

 one else, the field is open for the stump-orator, whose energies 

 are expended in denouncing the powers that be for not 

 promptly suppressing all trace of the disease from the British 

 Empire. Difficulty No. i consists in the fact that a potato 

 used for ' seed ' may be so slightly infected that the disease 

 would not attract the attention even of an expert. If such a 

 potato is used for 'seed' a diseased crop will probably result, 

 at all events the land in which the crop grew will be infected. 

 Difficulty No. 2 turns on the fact that when land is once infected 

 it remains in a condition capable of imparting the disease to 

 potatoes after a period of five years, as proved by careful 

 experiments conducted at Kew. This infection is brought 

 about by the liberation of the resting-spores of the fungus 

 into the soil. When a potato becomes diseased the presence 

 of the fungus in the tissues enables other fungi and bacteria 

 to gain admission, and the tuber often rots and decays under 

 the combined influence of these various organisms before the 

 time for lifting the crop arrives. No amount of legislation 

 can prevent the rotting of such potatoes, and the consequent 

 liberation of resting-spores in the soil. It is an insult to any 

 potato-grower to caution him against using for ' seed ' potatoes 

 obviously attacked by black scab ; on the other hand, if he 

 uses ' seed ' so slightly attacked that he cannot see the disease, 

 he is not responsible for the result. The only suggestion 

 that can be offered is that of procuring * seed ' from a district 

 where the disease has not been notified. So far as is known, 

 the disease is confined to the potato, consequently when land 



