MILDEWS, RUSTS AND SMUTS 
7 
conidium being furnished with a wart or papilla. Finally 
the conidia in Peronospora produce a thread-like hypha, 
or germ-tube on germination, whereas in Plasmopara, the 
conidia produce zoospores on germination. 
KEY TO THE GENERA 
A . Planohlastae 
Conidial or asexual mode of reproduction gives origin to 
zoospores on germination. 
* Hyphae bearing conidia and sporangia, not clearly 
differentiated from the vegetative mycelium. Pythium. 
** Conidiophores short, but differentiated from the vegeta¬ 
tive mycelium. Conidia in chains . . . Cystopus. 
*** Conidiophores aerial, sharply differentiated from the 
vegetative mycelium. 
t Conidiophores simple (= unbranched). Tip of conidio- 
phore swollen and studded with a number of short 
processes, each of which bears a conidium. Basidiophora. 
If Conidiophores more or less branched. Conidia emerging 
through the stomata, elongated, simple or sparingly 
branched, upper portion with knots or swellings at 
intervals . Phytophthora. 
Conidiophores short, stout, with a few short branches, 
soon collapsing . Sclerospora. 
I Conidiophores elongated, much branched upwards, per¬ 
sistent . Plasmopara. 
B. Siphohlastae 
The asexual fruit, or conidia emit a thread-like mycelium 
or germ-tube on germination. 
Conidiophores much branched, tips of the ultimate branch- 
lets flattened into a saucer-shaped body, having a 
number of short projections on the edge, each of which 
bears a conidium . Bremia. 
Conidiophores much branched, the tips of the ultimate 
branchlets pointed, and bearing a conidium 
Peronospora. 
PYTHIUM, Pringsheim 
Mycelium simple or branched, colourless, zoosporangia 
terminal or interstitial, formed from the protoplasm and 
becoming furnished with a very delicate cell-wall, zoospores 
escaping through the ruptured wall, naked, that is, not 
protected by a cell-wall; oosphere containing only one 
