GUMMOSIS OF PRUNUS JAPONICA 309 



micro-sclerotia, fully exposed to the air, produce a chain of 

 two or three very large, colourless cells, and these in turn 

 bear numerous smaller, elliptical conidia. When mature the 

 conidia become free and reproduce themselves quickly by 

 gemmation. This condition of conidia formation corre- 

 sponds to the stage known as Dematium pullulans, De 

 Bary, and is the aerobic mode of reproduction of the 

 Cladosporium. 



Numerous pure cultures of the various phases described 

 above were made, and inoculations with the olive conidia 

 of the ordinary condition of Cladosporium, and also with 

 the conidia of the aerobic stage, produced the disease. 

 Inoculation with conidia of the anaerobic condition gave 

 no result. 



This is the first instance where gummosis has been 

 directly proved to be caused by a fungus. 



PREVENTIVE MEANS. Diseased branches should be 

 removed, or, better still, collar-pruning should be resorted 



Fig. 82. Cladosporium epiphyllum. i, portion of a branch of Prunus 

 japonica, bearing two masses of gum, half nat. size ; 2, Cladosporium, form 

 of fruit, x 250 ; 3, section of a portion of the periphery of a black gum- 

 mass, showing the hyphae of the Cladosporium, x 50 ; 4, dark-coloured 

 tips of hyphae from the periphery of a gum-mass, bearing large, thick- 

 walled, brown cells, x 250 ; 5, large thick- walled cells germinating in a 

 nutrient solution in the absence of air, and producing yeastlike cells, which 

 reproduce themselves by gemmation, x 250 ; 6, stray cells emitting a 

 germ-tube, seen in the material described under 5 ; 7, micro-sclerotia 

 germinating under conditions similar to those described under 5, and 

 producing similar conidia, X4oo; 8, large, brown, thick-walled cells 

 germinating in a nutrient solution, with free access of air, and producing 

 the form of fruit known as Dematium pulhilans, x 250 ; 9, conidia of the 

 Dematium increasing by germination, x 250; 10, fragments of sporophores 

 of Cladosporium producing a slender form of Dematium pullulans, x 250 ; 

 n, a form of Macrosporiiim often appearing on old canker-spots caused 

 by the Cladosporium : no genetic connection between the two could be 

 established, x 300 ; 12, spore of Macrosporiiim germinating, x 400. (From 

 Kew Bulletin. ) 



