CLADOSPORIUM 473 



commonly called 'gumming.' Stout branches are most 

 frequently attacked, the disease first showing under the form 

 of tear-like drops of almost colourless gum oozing from the 

 branches. The drops are solitary or crowded, and rapidly 

 increase in size, eventually forming nodulose lumps varying 

 in size from a marble to that of a walnut. During damp 

 weather the masses are soft and gelatinous, with just sufficient 

 consistency to hold together, whereas in dry weather they 

 shrink considerably and become horny. The small, colourless 

 masses of gum gradually change to grey, then black, as they 

 increase in size, the discoloration being due to an enormous 

 mass of dark-coloured chlamydospores of the Cladosporium 

 developed near the periphery of the mass of gum. The 

 primary extrusion of gum is entirely due to the action of the 

 fungus, which acts as a wound-parasite, entering the tissues 

 through small wounds in the bark, broken branches, and 

 more especially where leaf-buds or flower-buds have been 

 broken off by birds. An olive patch of Cladosporium first 

 appears at such injured points, and when the mycelium of 

 the fungus has passed into the tissues, gumming begins, 

 and the fungus grows into the gum mass and forms chlamydo- 

 spores and microsclerotia. The whole mass of gum is even- 

 tually dissolved and drips to the ground, carrying the various 

 forms of reproductive bodies of the fungus along with it, 

 where they remain until the following season, when they again 

 infect the plant. Repeated experiments, made by placing 

 Cladosporium spores in small wounds, caused the gumming. 



Conidiophores in tufts, erect, becoming flaccid, branched, 

 pale olive ; conidia abundant, blackish-olive in the mass, 

 continuous or i-septate, produced in short chains, pale 

 olive, 10-12 X4-6 p. 



FIG. 141. Cladosporium epiphyllum. i, Prunus branch with two masses 

 of gum ; 2, Cladosporium form of fruit ; 3, section of periphery of a gum- 

 mass, showing hyphae and chlamydospores of the fungus ; 4, dark-coloured 

 hyphae bearing large chlamydospores, from periphery of gum-mass ; 5, 

 chlamydospores germinating in a nutrient solution in the absence of air, and 

 producing yeast-like cells which reproduce themselves by gemmation ; 6, 

 stray cells emitting germ-tubes, from preceding culture ; 7, microsclerotia 

 germinating under same conditions as No. 5 ; 8, chlamydospores germina- 

 ting in air, and producing the form known as Dematium pullulans ; 9, conidia 

 of Dematium increasing by budding ; 10, fragments of sporophores of 

 Cladosporium producing a slender form of Dematium pullulans or Hormo- 

 dendron \ n, a Macrosporium often present on old canker spots caused by 

 the Cladosporium ; 12, Macrosporium spore germinating. No genetic con- 

 nection between the Macrosporium and the Cladosporium could be established. 

 Fig. i reduced ; remainder highly mag. (From Kew Bulletin. ) 



