hroeter, Engl. u. Prantl._, I., i., pp. 1 and 5.

The parasitic Myxomycetes affecting plants include but few (four or
five) species, distributed among four genera. All are parasites in the
cells of particular hosts; their vegetative phase is plasmodial and
their spores are formed by the simultaneous breaking up of the
plasmodium into an indefinite number of independent cells. But a single
genus need here concern us,--

=Plasmodiophora= _Woronin_

1879. _Plasmodiophora_ Woronin, _Pringsh. Jahrb._, XI., p. 548.

Parasitic in the parenchymatous cells of the roots of living plants,
causing noticeable enlargement of the affected organ, producing at
length galls, knots, and various deformities and distortions. Spores
spherical, smooth, colorless, 16 mu.

I. PLASMODIOPHORA BRASSICAE _Woronin_.

1879. _Plasmodiophora brassicae_ Woronin, _op. cit._

This species, typical of forms so far reported in this country, infests
the roots of cabbages,[15] and produces a very serious disease of that
vegetable. In England the malady has long been known under the names
"clubbing," "fingers and toes," etc. The roots affected swell greatly,
and at length resemble sometimes the flexed fingers of the human hand;
hence the English name. As the disease progresses, the roots speedily
rot away, to the serious injury of the leaf-bearing portion of the
plant. In badly affected fields, sometimes one-half of the crop is
utterly destroyed. Careful search continued through several years has
not availed to bring this species to my personal acquaintance.

For a full account of the parasitism of this species and its
distribution in the United States see _Jour. Myc._, VII., p. 79; also
_Bull._ 66, Agric. Sta. of Vermont.

Sub-Class EXOSPOREAE _Rost._

1873._ Exosporeae_ Rostafinski, _Versuch_, p. 2.

Spores developed, superficially, outside the fructification, which
consists of sporophores, membranous, or slender and branching; spores
white, stalked. A single genus,--

=Ceratiomyxa= _Schroeter_

1889. _Ceratiomyxa_ Schroeter, _Engl. u. Prantl_, I., i., p. 16. For
further synonymy, see under first species.

Sporangia none; spores superficial, borne on erect papillae or pillars,
or even on the inside of minute depressions or pits; each spore
surmounting a delicate pedicel or stalk. The spores on germinating give
rise to amoeboid zoospores, which undergo repeated divisions, later
become ciliate, and at length again a