MILDEWS, RUSTS AND SMUTS 
17 
mycelium under the outer coating of the seed. Grain from 
a diseased head were sown without any treatment; some 
did not germinate, and those that grew presented abnormal 
characters, and microscopic examination showed the 
presence of mycelium in the younger parts of the plants. 
The following appears to support this statement. Seed 
of Saccharum officinale, obtained from France, was sown 
in a plot adjoining the Jodrell Laboratory, Kew Gardens. 
Two of the resulting plants were infested with Sclerospora 
graminis, and two other plants were badly '' smutted 
with Ustilago sacchari. Neither of these fungi had pre¬ 
viously been recorded as occurring in Britain, so that direct 
infection from spores was out of the question, and it is 
practically certain that in both cases, the source of infec¬ 
tion was imported along with the seed. By such means 
diseases are conveyed, unconsciously, from one part of 
the world to another. 
Cugini, Lc. Statione sper. Agrar. Ital., 35, p. 46. 
Peglioni, Atti. Reale Acad. Lincei, 305, p. 509. 
PLASMOPARA, Schroet. 
Mycelium stout, irregular, furnished with globose or 
elliptical haustoria; conidiophores erect, solitary or in 
tufts, emerging through the stomata, sparingly branched, 
branches usually monopodially arranged, not truly forked, 
spreading; conidia elliptical, generally with a papilla 
or wart at the tip, colourless, producing zoospores on ger¬ 
mination ; oospores globose, coloured, wall thick. 
Forming delicate white films on living leaves, and along 
with other genera, are popularly known as moulds. 
KEY TO THE SPECIES 
pygmaea. Parasitic on members of the order Ranuncu- 
laceae. 
pusilla. On plants belonging to the order Geraniaceae. 
densa. On plants belonging to Scrophulariaceae. 
viticola. Growing on plants belonging to the Vine family. 
nivea. Growing on plants belonging to the order Um- 
belliferae. 
Igeranii, Berl. and De Toni. Conidia obovate, 24—28 
X 12—15 p ; oospore globose, 25—35 p diam. On 
plants belonging to Geraniaceae. Geranium rohertia 
num, etc.] 
[impatientis, Berl. Ellis and Everh. Conidia globose, 
12—14 p, diam. On Impatiens fulva.] 
c 
