A l>A\\-rA\V LEAF-SroT. 289 



Tlie mycelium measured 2'8 jx to- 3'8 ft. across, and appears 

 primarily intercellular. Evidently some enzyme which kills the 

 cells of the host is excreted by the fungus. The cells in the 

 region of the discoloured areas are much shrivelled up and col- 

 lapsed, and in section these areas appear thinner than the rest 

 of the leaf. 



As mentioned, the pycnidia are evident in the white areas on 

 the upper leaf surface as minute black dots. 



These pycnidia are at first sub-epidermal, and later becoane 

 .erumpent. They measure 80 jx to' 106 jx in diameter; have thin 

 walls, are globose in shape an<l contain numerous^ spores of the 

 fungus. 



The spores are hyaline, straight toi slightly curved, rounded 

 at both ends, and measure 4*4 // to rrQ fx by 1"5 p. to 1*8 jx. 



Their walls do not coloui' with Schulze's solution, but the 

 contents turn reddish brown when treated with iodine. Evidently 

 the contents consist largely of glycogen. 



The fungus grows well in culture media, though pyenidiai do 

 not appear to- be readily formed. In beer wort agar plates a woolly, 

 white to greyish growth developed within six days. Reverse of 

 petri-dish was coloured grey, and clumged to a dark brown. 

 Aerial hyphae measured 3*7 jx to 7'4 jx. Pycnidia were observed 

 after twelve days, and more abundantly along the sides of the 

 petri-dish, 66',5 /x to 183 jx in diameter, one to' two ostiolate. 

 Spores hyaline, with rounded ends 3" 7 jx to'5"5 /x by 1*9 jx. 



On oatmeal agar slants a woolly, white tO' greyish growth 

 occurred, which, where medium, glass and growth meet, is dark 

 neutral in colour. Directly on medn.im dense felt-like mass of 

 interwoven hvphae, dark in colour, occur. Pycnidia were not 

 found. 



On sterilised rice in tubes, a white woolly growth occurred, 

 which, where rice, growth and glass meet, is reddish brown to dark 

 neutral. Immediately aroimd individual kernels, growth was 

 densely matted and interwoven and brown in colour. Here the 

 septa are close together and the indivdual cells become swollen. 

 Hyphae 3*7 p. diameter or thicker in swo'Uen mass around kernels. 



On artificial media the hvphae wei'e usually rich in oil 

 globules. 



A paw-paw was ino'culated by inserting small pieces of the 

 mycelium from pure culture into punctures made in marked areas 

 on a paw-paw. On the same paw -paw similar areas were marked 

 and punctiu-ed but not inoculated. These latter served as controls. 

 After inoculation the paw-paw was. cO'vered with a bell jar and 

 left at room temperature. Five days after inoculation some of 

 the infected areas showed reddish brown depressions, and were 

 so'ft to the touch. Pycnidia had by this time formed in one of 

 the inoculated spots. The control punctures were normal. 



As in the leaf the pycnidia are here originally subepidermal. 

 They measure 66 // to' 120 /x in diameter, and are separate or a few 

 aggregated together. 



The economic importance of the fungus, responsible for leaf- 

 spot or " shot-hole," is that in attacked leaves the assimilating 



