On the Occurrence in Britain of the Ascigerous 
Stage of a ‘Brown Rot’ Fungus. 
BY 
H. WORMALD. 
(. Mycological Department , South-Eastern Agricultural College , Wye , Kent.) 
With Plates VI and VII. 
.THOUGH the Brown Rot diseases* of fruit trees have been under 
review for over a hundred years, and have attracted the attention 
of numerous workers because of their economic importance, the systematic 
relationship of the fungi concerned is still a debatable subject. This is 
chiefly owing to the fact that the ascigerous forms are met with compara- 
tively rarely, especially in Europe, with the result that observations and 
descriptions have been chiefly confined to the conidial ( Monilia ) forms. 
The variation in the morphological characters of these Monilias in response 
to changes in the environmental conditions has created apparent discrepan- 
cies in such descriptions and has led to some confusion. This variation 
is well shown by Monilia cinerea , Bon., the grey fungus commonly found on 
plums and cherries, particularly with respect to the size of its conidia ; thus 
the average size of the conidia produced on mummied fruit and dead twigs 
in winter is about 11-5x8/4, while those conidia which develop on recently 
infected fruit in summer average about 17 x 11 //. That such variation is a 
specific character has been established experimentally (10) by cultivating 
pure line strains (each derived from a single conidium) and comparing their 
morphological characters when grown under varied conditions in the 
laboratory and on fruit trees in the open. 
When Woronin (11), in 1888, published an account of the life-history of 
Sclerotinia Vaccinii , in which he showed that a Monilia found on the 
young shoots of the Cowberry, Vaccinium Vitis-Idaea , was the conidial 
form of a Sclerotinia which produced apothecia on the mummied fruit, 
it was surmised that the Brown Rot fungi Monilict fructigena and M. 
cinerea were also to be referred to that ascomycetous genus, and Schroter 
(8) in 1893 included them in his Krytogamen-Flora as Sclerotinia fructi- 
gena and 5 . cinerea , although the corresponding ascigerous forms had not 
then been discovered. In 1902, however, Norton ( 5 ) found apothecia 
[Annals of Botany, Vol. XXXV. No. CXXXVII. January, 1921.] 
