MILDEWS, RUSTS AND SMUTS 
35 
ultimate branchlets tapering to a point, unequal; conidia 
elliptical or broadly pear-shaped, 24—30 X 16—20 p, 
tinged lilac ; oospores unknown. 
Parasitic on leaves of plants belonging to the order 
Plantaginaceae, as Plantago lanceolata and P. major. 
ERYSIPHACEAE, Lev. 
Parasitic on phanerogamic plants ; vegetative mycelium 
colourless, superficial, that is, on the surface of t’.c host- 
plant, sending haustoria into the epidermal cells only 
(except in the genus Phyllactinia) ; mycelium septate, 
thin-walled, branched, interwoven to form a more or less 
evident superficial layer, which gives origin to erect chains 
of large, colourless conidia, or in some instances only a 
single conidium is present, supported on an erect conidio- 
phore ; perithecia originating from the superficial my¬ 
celium, sessile, indehiscent, at first colourless, gradually 
passing through yellow to dark brown or blackish when 
mature, the outer cells of the wall giving origin to out¬ 
growths called appendages, which may more or less re¬ 
semble the mycelium, or may assume definite and charac¬ 
teristic shapes ; asci one or several in a perithecium, usually 
more or less globose, more rarely C3dindrical, 2—8-spored ; 
spores I-celled, colourless, paraphyses absent. 
The most pronounced feature of the present group con¬ 
sists in the indehiscent perithecium, that is, there is no 
definite mouth or opening through which the spores escape 
at maturit^g consequently they are only liberated when 
the perithecial wall deca^^s, or becomes ruptured. Another 
constant feature is the presence of certain outgrowths from 
the wall of the perithecium, these sometimes are but little 
different in appearance from the ordinary mycelium spring¬ 
ing from the base of the perithecium ; in other instances, 
however, the appendages assume very definite and charac¬ 
teristic forms, which are of value in the determination of 
genera and species. In all the genera, with the exception 
of Phyllactinia and one species of Erysiphe, the superficial 
mycelium sends haustoria into the epidermal cells of the 
host-plant only, whereas in the last-named genus, the 
superficial mycelium sends hyphae through the stomata 
into the intercellular spaces of the leaf, these h^^phae send 
haustoria into the adjoining cells. 
All the species are true parasites, mostly forming deli¬ 
cate white mildewed patches on the leaves and other parts 
of living plants, and many prove very injurious to cultivated 
