40 
MILDEWS, RUSTS AND SMUTS 
Podosphaera leucotricha, Salmon. Mycelium on both 
surfaces of leaves, thin, broadly effused, persistent ; peri- 
thecia crowded, rarely scattered, 75—76 p diam. ; appen¬ 
dages of two kinds, one kind springing in a tuft from the 
top of the perithecium, few in number, coloured below, 
long, simple or sparingly forked near the tip ; the second 
kind springing from the base of the perithecium, brown, 
wavy, simple or vaguely branched ; ascus oblong or sub- 
globose, 55—70 X 44—50 p ; spores 22—26 x 12—14 [jl. 
Syn. Sphaerotheca leucotricha, Ellis and Everh. 
Sphaerotheca mali, Burr. 
Parasitic on species of Pyrus. This is a very destructive 
parasite to the apple (Pyrus malus), in many parts of the 
world, often attacking seedlings and young trees. In this 
country, however, it proves most injurious to full-grown 
apple trees, where its oidium condition covers the clusters 
of leaves at the tips of the twigs with a dense, white, powdery 
coat, which prevents the further growth in length of the 
shoot. I first found the perithecia in this country on the 
branches of some suckers of an apple tree at Mortlake. 
They have since been found on the leaves, and also’on the 
fruit, but are not generally sufficiently abundant to account 
for the widespread occurrence of the oidium stage every 
season, and it is believed that the mycelium of the fungus 
hibernates between the bud-scales, and gives rise to the 
white oidium condition of the fungus. The oidium or 
conidial stage of the fungus is known in this country as 
Oidium farinosum, Cooke. 
Podosphaera schlechtendalii, Lev. Occurring on both 
surfaces of the leaves, mycelium soon disappearing ; peri¬ 
thecia scattered, subglobose, 78—90 [ji diam. ; appendages 
5—12, unequal in length, 6—12 times as long as the dia¬ 
meter of the ascus, springing from the top of the perithe¬ 
cium, and forming a long, weak, wavy tuft, 2, rarely 3 
times forked at the tip, branchlets recurved, terminal ones 
knobbed ; ascus subglobose, 76—84 x 68—74 [x ; spores 
8, 23—28 X 13—15 [i- 
Parasitic on leaves of plants belonging to the order 
Salicaceae. Salix alba, and S. viminialis. 
There is no direct evidence of the occurrence of this 
species in this country. It has been found in France. 
SPHAEROTHECA, Lev. 
Perithecia subglobose, ascus solitary, containing 8 spores ; 
appendages not well differentiated from the mycelium. 
