32 
SAPROPHYTES AND PARASITES 
on living oaks, and, according to Hartig, causes a deep red- 
brown decomposition of the wood. 
Dcedalea quevcina (Plate XXXII.) also attacks living oaks. 
Six leaf parasites are shown on Plate XIV. : 
Fig. i. Exobasidium vaccinii .—A true Basidiomycete nearly 
allied to Corticium. It forms orbicular swellings on living 
leaves of the whortleberry (Vactinium myrtillus), rarely on 
the leaf-stalks and stems. The flesh-coloured hymenium 
protrudes from the under surface of the leaf; the opposing 
upper surface is red or purple. 
Fig. 2. Rhytisma acerinum, an Ascomycete, causes the 
familiar black spots on sycamore and maple leaves. The 
ascophores mature in spring after the leaves have been lying 
on the ground throughout the winter. If a spore settles on 
a young leaf the hyphae enter the tissues, causing yellowish 
spots to appear in June. These change in July to pitch- 
black. The leaves on autumnal shoots remain free of 
disease, and do not fall so quickly as infected ones. This 
pest is checked by carefully sweeping up and burning dis¬ 
eased leaves. 
Fig. 3. Rhytisma punctatum superficially resembles the 
preceding, but the spot consists of closely crowded punctate, 
not continuous, spots. The black spots frequently seen on 
willows are caused by R. salicinum. 
Fig. 4. Ascomyces pruni * causes the young fruit of culti¬ 
vated plums, also bullace, sloe, and wild cherry, to become 
deformed and swollen, assuming the condition known as 
“pocket plums” or “bladder plums.” The mycelium is 
perennial, spreading in spring through the young shoots, its 
fruit appearing as a delicate whitish bloom in July. It does 
not spread backwards on a branch, hence may be arrested 
by hard pruning. 
Fig. 5. Ascomyces deformans causes the well-known leaf curl 
of peach and almond, now universally distributed and very 
* Ascomyces is synonymous with Exoascus. 
