PLANT DISEASES. WILD PLANTS AS A SOURCE OF DANGER. 939 



budding is often covered with the rust fungus, so that it is not surprising 

 if the resulting Roses also suffer ; a little care, therefore, in the selection of 

 the Briers, would avoid much annoyance later on. In early summer the 

 fungus causes orange masses on the leaves and shoots, but in autumn 

 these give place to black patches which, in the case of leaves, are chiefly 

 seen on the under surface. The black patches are formed of resting spores 

 which remain dormant till the spring and then germinate and reinfect 

 the plant ; hence the more of these diseased leaves that are destroyed 

 in October and November the less the chances of infection the following 

 season. 



The Rose Mildeiu (Sphcerothcca pannosa) is of general occurrence 

 wherever Roses are grown, and it is common also on the wild forms. 

 Sulphur is the usual remedy, and is useful if applied early. If a little 

 more common sense were sometimes used as well, however, the results 

 would be more satisfactory. For instance, where Roses are grown under 

 glass, sulphur is generally applied if mildew is present, though plants just 

 outside the greenhouse (especially if common sorts) are not given this 

 attention. A case of this kind came before us lately ; an old climbing 

 Rose immediately outside a greenhouse was vigorously supplying the 

 spores of the Rose mildew ; these spores were blown inside whenever the 

 ventilators were open ; the Roses inside were well powdered with sulphur, 

 whilst the one outside, which was doing most of the mischief, was left 

 alone. 



FRUIT-TREES.— Apple Canker (Nectria ditissima). This fungus 

 is so general on all sorts of trees and shrubs that its spores may be 

 regarded as always present in gardens. These spores can only obtain an 

 entrance into the plant through wounds and cuts ; hence avoid bruising 

 the branches of the trees in any way. When once an entrance has been 

 effected the mycelium is permanent. Diseased patches may be cut out 

 and the wounded surfaces tarred, though in many cases the fungus 

 makes too much headway before it is discovered to allow of this. All 

 useless trees and branches attacked by canker should be removed and 

 burnt. 



Broiun Mould of Fruit. — This is exceedingly common on Apples and 

 Pears, but most kinds of rosaceous fruits are attacked. The spores of 

 this fungus (Monilia fmctigena), like the preceding one, are very 

 abundant. Diseased fruits should be burnt, as infection the following 

 year depends on spores produced on them.* Useless fruit-trees of every 

 kind should be removed, as they only increase the spread of the disease. 

 (See Journal, xxvi. p. 738.) 



Plum-leaf Blister. — The foliage of Plum-trees is often seen to be 

 spotted with red blotches caused by the fungus Poly stigma rubrum. 

 When the blotches cover large areas the injury done is serious, as the 

 assimilatory surface of the leaf is reduced. In fighting this pest it should 

 be remembered that wild species of Prunus, specially Sloe, can harbour 

 the fungus ; diseased leaves should be burnt, as they contain the resting 

 spores for reinfection in the spring. 



* Recent investigations have shown that this parasite produces an ascophore stage 

 on mummified fruit two years old : and it is now referred to the group Pezizai and 

 known as Sclcrotinia fructigena (Trans. Acad. Sci. St. Louis, xii. p. 91, 1902). 



