cells little globular suckers, by means
of which the fungus feeds.

The spores already mentioned are formed at the ends of crowded
filaments, that push up, and finally rupture the epidermis (Fig. 33,
_B_). They are formed by the ends of the filaments swelling up and
becoming constricted, so as to form an oval spore, which is then cut
off by a wall. The portion of the filament immediately below acts in
the same way, and the process is repeated until a chain of half a
dozen or more may be produced, the lowest one being always the last
formed. When ripe, the spores are separated by a thin neck, and
become very easily broken off.

In order to follow their germination it is only necessary to place a
few leaves with fresh patches of the fungus under a bell jar or
tumbler, inverted over a dish full of water, so as to keep the air
within saturated with moisture, but taking care to keep the leaves
out of the water. After about twenty-four hours, if some of the
spores are scraped off and mounted in water, they will germinate in
the course of an hour or so. The contents divide into about eight
parts, which escape from the top of the spore, which at this time
projects as a little papilla. On escaping, each mass of protoplasm
swims away as a zooespore, with two extremely delicate cilia. After a
short time it comes to rest, and, after developing a thin cell wall,
germinates by sending out one or two filaments (Fig. 33, _C_, _E_).

[Illustration: FIG. 33.--_A_, leaf of pig-weed (_Amarantus_), with
spots of white rust (_c_), one-half natural size. _B_, non-sexual
spores (conidia). _C_, the same germinating. _D_, zooespores. _E_,
germinating zooespores. _sp._ the spore. _F_, young. _G_, mature sexual
organs. In _G_, the tube may be seen connecting the antheridium
(_an._), with the egg cell (_o_). _H_, a ripe resting spore still
surrounded by the wall of the ooegonium. _I_, a part of a filament of
the fungus, showing its irregular form. All x 300.]

Under normal conditions the spores probably germinate when the
leaves are wet, and the filaments enter the plant through the
breathing pores on the lower surface of the leaves, and spread
rapidly through the intercellular spaces.

Later on, spores of a very different kind are produced. Unlike those
already studied, they are formed some distance below the epidermis,
and in order to study them satisfactorily, the fungus must be free