H. WOIIMALD 17o 



but, to the time of writing, only on the fruit and not on the flowers or 

 twigs ^. 



The blossom- wilt Monilia, as it occurs on the twigs, fruiting spurs 

 and cankers of the apple tree in winter and spring, has pustules generally 

 smaller (but they may reach a diameter of 1-5 mm.) and grey in colour 

 rather than yellow, though when very powdery they may become some- 

 what ochraceous and are then easily mistaken for M. fructigena, while 

 the conidia are much smaller, being usually 10-12 /x in length and 

 rarely exceeding 14/x. AVhen, as occasionally happens, it occurs on 

 young apples in summer the dimensions of the conidia are greater and 

 this again may lead to some confusion. 



The two species grow vigorously on suitable sterilised culture media 

 and the utilisation of this property will probably afford a ready and 

 more definite means of identifying them, particularly as cultural methods 

 can be employed when the fungi are in the condition of sterile mycelium 

 only. Differences in habit of growth and development of conidia dis- 

 tinguish them when growing on two easily prepared media, viz., prune- 

 juice agar and steamed potato. 



The medium generally used by the writer to obtain mycelial growth 

 is a decoction of prunes (1 % stoned prunes) containing 1-5 or 2 % agar- 

 agar. M. fructigena produced, on plate cultures of this medium, a flat 

 disc of mycelium, circular in outline and growing out regularly to the 

 edge of the plate with a margin laciniate or almost entire. The growth 

 of the blossom- wilt Monilia at first resembles that of M. fructigena but 

 soon shows a tendency to become lobed, the lobes being deltoid or 

 flabelliform with narrow sinuses between them ; a characteristic feature 

 of these cultures is for growth to be arrested at about mid-way between 

 the centre and the edge of the plate and fresh growth commences as 

 flabelliform radiations from between the lobes. This condition has 

 not been observed in cultures of M. fructigena. 



Neither species produces conidia on the prune- juice agar medium 

 although both give rise to numerous clusters of minute spore-like bodies 

 produced in radiating chains which in the earlier stages of development 

 resemble the fructifications of a Penicillium but later become dense 

 irregular clusters. These "sporidia" were observed on M. fructigena 

 by Humphrey (11) who states that they germinate and produce mycelium. 

 Woronin figures them for M. fructigena and M. cinerea but failed to 



^ Since the present paper was sent to the press evidence has been obtained which 

 suggests that M. fructigena may extend from the infected f mit into the branches and 

 form cankers, in the case of certain varieties of soft-wooded apple trees (e.g. James 

 Grieve) ; thi- point is being investigated. 



12—2 



