4 
MILDEWS, RUSTS AND SMUTS 
borne on mycelium buried in the matrix or substance on 
which the fungus is growing. The sexual organs are well 
differentiated in both function and size. The antheridium 
or male organ is usually much smaller than the oogonium 
or female organ. In many instances the oogonium com¬ 
mences as the much swollen tip of a hypha, which increases 
in size until it becomes spherical; the antheridium appears 
as a more or less club-shaped branch, springing from the 
hypha bearing the oogonium and just below it. When 
oogonium and antheridium are replete with protoplasm, 
each is cut off by a transverse septum from the parent 
hypha. The greater portion of the protoplasm in the 
oogonium then contracts and forms a sphere called the 
oosphere. The antheridium now comes into contact with 
the wall of the oogonium, and at the point of contact 
emits a fertilisation-tuhe or slender outgrowth which pierces 
the wall of the oogonium, and increases in length until 
it reaches the oosphere. Through this tube the nucleus 
and a portion of the protoplasm of the antheridium passes 
into the oosphere and blends with the protoplasm of the 
latter. The nucleus of the oosphere and of the antheri¬ 
dium now coalesce—the act of fertilisation. After this 
process of fertilisation the oosphere is termed the oospore, 
and undergoes further changes, and finally develops a 
firm cell-wall of its own, within the wall of the oogonium. 
Usually after a period of rest the oospore germinates. 
Sometimes oogonia are produced interstitially, or in the 
length of a hypha except at the tip, and the antheridia 
may grow on the same hypha as the oogonia, or the antheri¬ 
dia may be borne on an adjacent independent hypha. 
With the exception of the genus Pythiuni, conidial forms 
of reproduction are highly developed in the Peronosporaceae, 
and in many instances form the most beautiful of micros¬ 
copic objects met with in the vegetable kingdom. Many 
of the diseases popularly called mildews, are caused by 
the conidial stage of members of the present family. 
PERONOSPORACEAE 
Conidial reproduction by conidia producing zoospores, 
which germinate at once on coming to rest, or the conidia 
develop a germ-tube capable of infecting a host-plant. 
Sexual reproduction by oogonia and antheridia. 
