FUNGOID PESTS OF CULTIVATED PLANTS. 95 



small bits of earth, but by placing the Potatos in water these bodies 

 become black and quite conspicuous. Many of them adhere very firmly. 

 The hyphae spread through the soil in various directions ; hence a single 

 diseased Potato may be the means of infecting an area of considerable 

 size. 



Plants which are attacked when young, if not killed outright, are 

 often dwarfed and frequently die long before tbe close of the season. 

 The parts below ground are thoroughly infected with the Bkizoctonia. 

 In some cases the disease attacks the plant just below the surface of the 

 ground, and under favourable conditions a stem rot called " Collar Rot" 

 or "Black Eing " is produced. When the attacks on the stem are not so 

 severe as to cause death the injuries may prevent the assimilated food 

 from being stored in the subterranean portion of the plant, large tops are 

 produced, and green tubers often form in the axils of the leaves (see 

 also Journ. B.H.S. xxvii. p. 1182 ; xxviii. 1904, p. 695 ; xxix. 1905, p. 870). 



Potato Bacteriosis. 



This has been described as occurring in Germany under the name of 

 Bacillus pliytophthorus, App. 



Dent. Botan. Gescl. 1902, p. 128; Journ. B.H.S. xxvii., p. 1181; 

 xxix. 1904, p. 145. 



We do not apprehend any danger to Potatos from the fungus described 

 under the name of Phycomyces splendens, for surely it can only be a 

 veritable saprophyte (see Garcl. Chron. June 26, 1886, p. 824). 



Potato Spot Mould. 



There has been some consternation in Europe upon the appear- 

 ance of a black mould (Cercospora concors) on living Potato leaves, but 

 it has not been heard of in Britain. 



Potato Macrospokium, or Leaf Curl. 



Two species of Macrosporlum have been described as affecting the 

 leaves of plants of the Potato family, but one of these is decidedly a 

 saprophyte and only occurs on dead leaves. The other (Macrosporium 

 Cookei) attacks the living leaves of Potato in this country, and of 

 Lycopersicum esculent um (Solatium Lycopcrsicum), in America, and has 

 large conidia (60-70 + 10 /<) with from four to six transverse septa. 

 The latter is not yet recorded as occurring in Europe. (Garcl. Chron. 

 Sept. 23, 1905, p. 230.) 



Tomato Leaf Mould. 



Cladosporium fulvum (Cooke), PL VIII. fig. 120. 



This mould first made its appearance on leaves of the Tomato in the 

 United States, and was described in 1883 from specimens received from 

 South Carolina, since which time it has not only spread in America, but 

 made its appearance in England, where it was first recorded in 1887. 



Brown felted spots of irregular size appear on the under surface of 



