10 
MILDEWS, RUSTS AND SMUTS 
disease, and the oospores have been erroneously considered 
as belonging to the last-named fungus. 
CYSTOPUS, L6v. 
Mycelium branched, running between the cells of the 
host-plant, and giving off small vesicular haustoria that 
penetrate the cells ; conidiophores simple, blunt, in dense 
clusters, each bearing at its tip a single chain of conidia ; 
conidia either all alike in form, and all producing zoospores, 
or the terminal conidium with a thicker membrane, sterile, 
or germinating by the emission of a germ-tube, the re¬ 
mainder of the conidia producing zoospores; the sori 
or clusters of conidia remain covered by the epidermis 
until the conidia are mature, when they burst through ; 
oogonium globose, wall thin ; antheridium club-shaped ; 
oospores globose, wall coloured, usually netted or warted. 
The oospores are formed in the tissues of the host-plant, 
and germinate the following season, producing zoospores. 
The genus is called Albugo by some authors. 
KEY TO THE SPECIES 
* Terminal conidium not differing from the rest in shape 
or size. 
f Wall of conidia everywhere of equal thickness, 
candidus, Parasitic on cruciferous plants. 
\hrasiliensis, Speg. Conidia compressed, front view 20 (x, 
side view 10—14 p. Parasitic on Composite plants.] 
[euphorhiae, Cke. and Mass. Conidia minutely warted. 
On Euphorbiaceous plants.] 
[tropicus, Lagerh. Conidia subglobose, 18—20 p ; oos¬ 
pore, with large, flattened warts. Parasitic on Pipera- 
ceous plants.] 
•ff Wall of conidia with a thickened equatorial zone, 
[convolvulacearum, Speg. Conidia cuboid, 16—20x12—15 
p. Parasitic on Convolvulaceous plants.] 
[solivae, Schroet. Conidia subglobose, 20—22 X 18—20 
p ; wall of oospore minutely netted. Parasitic on 
Composite plants.] 
** Terminal conidium differing from the rest in shape or 
■ size or both. 
f Wall of conidia everywhere of equal thickness, 
portulacae. Oospore wall netted, with a wart in the centre 
of each mesh of network. Parasitic on plants belonging 
to the order Chenopodiaceae. 
