I7<) ^l Blossom WiJf and Canker of ApjtJe Trees 



induce them to germinate ; attempts by the present writer to obtain 

 germ tubes from these sporidia have also failed. 



Of sterilised media the most suitable for the development of conidia 

 has hitherto proved to be steamed potato, and in diagnosing a fresh 

 strain this is at present always used. Roux's tubes are found useful 

 for these cultures though ordinary wide test tubes are also employed. 

 Vigorously growing mycelium transferred from an agar plate will reach 

 the edge of the potato in four days and tufts of conidia are produced 

 within a week. Measurements of conidia from potato cultures were 

 taken when the cultures Avere 6-8 days old ; if left for a longer period 

 the conidia, particularly those of the canker strains, became overgrown 

 by hyphae probably from their own germ tubes. The conidial tufts 

 of M. fructigena in these cultures are yellow in colour and usually form 

 distinct continuous raised zones towards the upper end of the potato, 

 while those of the canker strains were smaller, scattered, more diffuse, 

 and grey in colour. 



An examination of the Monilia.s found on the stone-fruit trees 

 {Prunus spp.) in this country led to the discovery that there are (in 

 addition to M. fructigena which occurs frequently on the plum and 

 sweet cherry) two forms both of which may be referred to ill. cinerea, 

 though they differ from one another culturally, and one of these appears 

 to be identical with that form which causes the destruction of the apple 

 blossom. The latter when growing as plate-cultures on prune juice 

 agar is at first hyaline, but, when growth has extended for about 2 cm. 

 from the point of inoculation, a circular band appears, olive green to 

 dark brown in colour, approximately at I cm. from the centre, and 

 later other brown zones develop. This brown coloration is more 

 intense when the fungus is grown as agar slant cultures and appears 

 to be favoured by the depth of the medium, for the brown zone first 

 appears as a curved transverse band on the lower (deeper) side of the 

 point of inoculation. The colour becomes darker and more general 

 with the age of the culture which eventually is almost black throughout. 

 Strains which also become brown on this medium have been obtained 

 from the stone-fruit but whether any of these are able to infect the 

 apple flower has not yet been determined. 



Other strains, obtained from plums and sweet cherries, remain 

 hyaline both in plate and tube cultures of prune-juice agar. Of two 

 strains obtained by isolating conidia from a damson, one retained the 

 hyaline appearance, the other produced a dark brown band when the 

 two were grown side by side on the same plate. 



