192 On Diseases of Plum Trees 



(b) On raisin, grape juice, or plum agar media. 



Victoria (1). Medium blackened. Pycnidia black, 1-2 mm. dia- 

 meter covered with a light-grey mycelial felt (cf. Fig. 9). 



Victoria (3). No discoloration of medium. Hyphae hyaline at 

 first, dark later. Pycnidia as in (1). 



Prince of Wales (5). Colourless mycelium. No discoloration. 

 Pycnidia black, covered with grey felt. 



Pond's Seedling (6). White mycelium. No discoloration. Forma- 

 tion of aerial hyphae similar to those produced on gelatine. Large 

 white pycnidia, covered with a greenish felt (Fig. 10). 



(c) On potato agar media. 

 Victoria (1). Greenish-black coloration of medium. Large pycnidia. 



(d) On wheat flour agar media. 



Victoria (1). No discoloration. Cream-coloured, almost invisible, 

 mycelium. Grey-coloured large pycnidia. 



(e) On acid and alkaline media. 



By titration with normal acid or alkali, using phenol phthalein as 

 an indicator, a series of raisin agar tubes was obtained, containing 

 various concentrations of acid or alkali. It was found that the degrees 

 of acidity or alkalinity limiting the growth of these fungi were 10 per 

 cent, normal HC1 and 5 per cent, normal NaOH. 



Victoria (1). 10 per cent, normal HC1. Slow growth. No dis- 

 coloration of medium. 



5 per cent, normal HC1, neutral, and 5 per cent, normal NaOH. 

 Normal growth, with discoloration of medium. 



Pond's Seedling (6) and Prince of Wcdes (5). Normal growth at all 

 concentrations, within above limits. 



Formation of perithecia. 



Prolonged but fruitless attempts were made to induce perithecia! 

 formation in culture. These included growing the fungi on pure agar, 

 agar with a high concentration of nutrient material, acid and alkaline 

 media, and upon wood. Cultures were also kept (a) at 28° C. for three 

 months, (6) frozen, (c) exposed throughout the winter on the laboratory 

 roof, (d) in the dark; but with negative results. 



