Wormald. — ‘ Brown Rot ’ Diseases of Fruit Trees . 369 
(c) Sources of Infection on Plum Trees. 
It is only during years of abnormal weather conditions, such as 
obtained in the spring of 1918, that heavy losses are produced on sweet 
cherries by the Brown Rot fungi. The plum tree, however, proves generally 
to be more susceptible, and each year extensive damage to the crop is 
reported. Monilia fructigena appears to be confined to the fruit, and 
persists from year to year, so far as is at present known, only on the 
mummied fruit, in this country. M. cinerea , on the other hand, not only 
attacks the fruit, but also the flowers, leaves, young shoots, and branches, 
thus not only directly reducing the cropping powers of the tree, but 
providing numerous sources of infection for the developing fruit. 
From observations made at Wye it was found that at the time the 
fruit is about half grown, pustules of M. cinerea may be found on 
(1) mummied fruit, the result of infection during the previous year ; 
(2) flowers killed in the spring of the current year ; 
(3) newly-attacked leaves on the vegetative shoots of the current 
year ; 
(4) vegetative shoots killed during the previous year ; 
(5) cankers formed the previous year on the branches. 
The ‘ Wither Tip ’ condition may occur also on the ‘suckers’ at the 
base of the trees, and on those shoots growing out from the stumps of 
trees cut down ; these serve as sources of infection which may easily escape 
observation. 
(d) An Epidemic Outbreak of a ‘ Blossom Wilt ’ of Plum and 
Cherry Trees in 1918. 
In 1918 the yields of the plum and cherry crops were far below the 
average. From investigations made in Kent it appeared that the failure 
was largely due to Monilia cinerea aided by weather conditions particularly 
favourable for the dissemination and development of the fungus during the 
period when the trees were in bloom, the atmosphere being almost con- 
tinually saturated with moisture for about a week. The following factors 
contributed in inducing the epidemic outbreak of the disease : 
(1) The low temperature retarded the development of the flowers, 
which on opening remained receptive and liable to infection for a relatively 
long period ; this was partly owing to the fact that the cold wet weather 
decreased the activities of pollinating insects. 
(2) The successive expanding of the flowers extended over a period 
long enough for those primarily infected to produce pustules of conidia 
during the time that later flowers were in progress of opening ; these 
flowers which expanded towards the end of the flowering period were 
