MILDEWS, RUSTS AND SMUTS 
II 
lepigoni. Oospore wall minutely waited. Parasitic on 
plants belonging to the order Caryophyllaceae. 
[tilleae. Conidia globose-ovoid 20—24 X 20—21 
terminal one larger and with a thicker wall. Parasitic 
on plants belonging to the order Crassulaceae.] 
\hliti. Wall of oospore with a rather large network.] 
iragapogonis. Wall of oospore with a vague network 
and spinulose warts. Parasitic on Composite plants. 
Cystopus candidus, Lev. Sori snow-white or faintly 
tinged yellow, size variable, often forming large patches ; 
conidiophores somewhat club-shaped, conidia all alike in 
shape, white, subglobose, 10—18 (x diam. ; oospores 
globose, yellowish brown or sometimes dark brown, coarsely 
waited, the warts sometimes running into irregular, wavy 
ridges, 30—50 [x diam. 
A destructive parasite, most abundant on the weed 
called Shepherds’ purse {Capsella bursa-pastoris), but at¬ 
tacking nearly all plants belonging to the order Cruciferae ; 
also attacks the Caper {Capparis spinosa), and species of 
Alisma. 
The snow-white patches of the fungus are very conspicu¬ 
ous on the leaves, flowers and fruit of the Shepherds’ purse, 
the plant being usually much distorted. Among plants 
of economic importance, attacked by this fungus, are 
Horse-radish {Cochlearia armoracia) ; radish (Raphanus 
raphanistrum) ; cress {Lepidium sativum) wall-flower 
(Chieranthus cheiri). 
Infection only occurs during the seedling stage of the 
host, hence the disease does not spread amongst older plants. 
The conidia on germination produce zoospores, which even¬ 
tually germinate and enter into the tissues of seedlings 
through the stomata. 
The oospores are formed in the tissues of the host-plant, 
and after passing the winter in a resting condition, liberate 
enormous quantities of zoospores, which attack seedlings. 
The “ Kerguelen’s Land Cabbage ” {Pringlea antiscor- 
hutica) although exempt from the fungus in its native land, 
could not be kept in cultivation at Kew, owing to the at¬ 
tacks of this parasite. 
[Var. convolvuli, Berk. Differs from the typical form in 
having cuboid instead of subglobose conidia. 
Syn. Cystopus convolvulacearum, Otth. 
Parasitic on various species of Convolvulus in S. Africa 
and the United States.] 
