_b._ With spores in receptacles or sporangia MYXOGASTRES

Sub-Cla.s.s PHYTOMYXINae _Schroeter_

1889. _Phytomyxinae Schroeter, 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 .

I. PLASMODIOPHORA BRa.s.sICae _Woronin_.

1879. _Plasmodiophora bra.s.sicae_ 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-Cla.s.s EXOSPOREae _Rost._

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

Spores developed, superficially, outside the fructification, which consists of sporoph.o.r.es, 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 amoeboid to blend into genuine plasmodia. At maturity the plasmodium gives rise to numerous minute divisions, each of which may lengthen in a direction perpendicular to the surface and bear a spore at the tip.

The h.o.m.ologies between the structures just described and the fructification of the ordinary slime-mould are somewhat obscure, if indeed any really exist. Are these minute reproductive bodies spores?--their behavior on germination is unique; are they sporangia?--the arrested development they exhibit is none the less puzzling. Perhaps the sporiferous pillars represent incipient stipes, the spores the uncombined fragments of what might otherwise have coalesced at the summit of the pillar to form a true sporangium.[16]

Several species have been recognized, all referable probably to one or two, or at most, four forms. That universally recognized alike in the literature of the past and in recent studies is,--

1. CERATIOMYXA FRUTICULOSA (_Muell._) _Macbr._

PLATE I., Figs. 7 and 7 _a_.

1729. _Puccinia ramosa, bifurcata_, etc. Micheli, p. 213, Tab. 92, Fig. 2.

1775. _Byssus fruticulosa_ Muller, in _Fl. Dan._, t. 718, Fig. 2.

1778. _Tremella hydnoidea_ Jacquin, _Misc._, Vol. I., t. 16.

1783. _Clavaria puccinia_ Batsch, _Elench. Fung._, p. 139, Fig. 19.

1791. _Puccinia byssoides_ Gmelin, _Syst. Naturae_, p. 1462.

1791. _Clavaria byssoides_ Bulliard, _Champ. de la France_, t. 415, Fig. 2.

1794. _Isaria mucida_ Pers., Romer, _N. Mag. Bot._, I., p. 121.

1801. _Isaria mucida_ Pers., _Syn. Meth._, p. 688.

1805. _Ceratium hydnoides_ Alb. & Schw., _Consp. Fung._, p. 258.

1811. _Ceratiomyxa porioides_ (A. & S.) Schroet., _Mycet._, p. 26, _var._ 1829. _Ceratium hydnoides_ Fries, _Syst. Myc._, III., p. 294.

1872. _Ceratium hydnoides_ Wor. & Fam., _Mem. Acad. Imp._, Petersburg.

1887. _Ceratium hydnoides_ DeBary, _Comp. Morph. Fung._, p. 432.

1889. _Ceratiomyxa mucida_ Schroeter, _Engl. u. Prantl Nat. Pflanz._, I., i., p. 16.

1893. _Ceratiomyxa mucida_, Pers., Macbr., _Bull. Nat. Hist. Iowa_, II., p. 114.

1894. _Ceratiomyxa mucida_ Schroet., Lister, _Mycetozoa_, p. 25.

Plasmodium in rotten wood, white or nearly transparent; when fruiting, forming on the substratum mould-like patches composed of the minute sporiferous pillars, generally in cl.u.s.ters of three or more together; spores white, ovoid, or ellipsoidal, smooth, 10-126 .

Very common, occurring in summer on shaded rotten logs, especially after warm showers and in sultry weather. Easily distinguishable from all similar moulds by the absence of mycelium or of anything like a hypha. In Europe the plant seems to be in autumn exceedingly common.

Micheli not only described the form but figured it, nearly two hundred years ago. Micheli's figure is good, as is that of Mueller, _Fl. Dan._, l. c. Mueller referred the species to a Linnean genus _Byssus_, which seems to have included Algae rather than anything else, if one can determine its limits at all. The same thing is true of _Tremella_; but this name is now otherwise applied, as are all the other generic names down to _Ceratium_, Alb. & Schw. But this had been by Schrank preoccupied, 1793. See the reference above for 1889. As for specific name, there seems no reason to depart from the rule of priority, since Mueller's work is determinative.

_Ceratiomyxa arbuscula_, Berk. & Br., apparently a form of this, is cited from Toronto by Miss Currie. Ma.s.see gives it recognition; Lister as varietal. The sporoph.o.r.es are inclined to be simple, stipitate and dendroid.

_C. filiforme_ of the English authors latest named is a wonderful thing and deserves a paragraph here, if not recognition as a distinct species.

It occurs rarely; but once it appears, attracts attention. As in the historic species, the sporifers are white, stand more or less erect, but are every way finer and larger. Each individual sporifer rises like a stiff stem, as of white thread, 2-3 mm. high; at top a tuft of fruiting branchlets, more or less distinct. All taken together, we have a dense mat completely concealing the substratum and spreading out sometimes over an area of surprising extent, several centimetres square.

Common everywhere in summer on decaying sticks and wood of every description, especially in wet places. Alaska to Nicaragua, and probably around the world.

2. CERATIOMYXA PORIOIDES (_Alb. & Schw._) _Schroeter._

1805. _Ceratium porioides_ Alb. & Schw., _Consp. Fung._, p. 359.

1829. _Ceratium porioides_ Fries, _Syst. Myc._, III., p. 295.

1873. _Ceratium porioides_ Fam. & Wor. _Acad. Imp._, XX., 3, p. 5.

1889. _Ceratiomyxa porioides_ Schroet., _Engl. u. Prantl_, I., i., p. 16.

1894. _Ceratiomyxa mucida_ Schroet. var. _porioides_ Lister, _Mycetozoa_, p. 26.

1899. _Ceratiomyxa porioides_ Alb. & Schw. (Schroet.), Macbr., _N.

A. S._, p. 19.

1911. _Ceratiomyxa porioides_ Alb. & Schw., Schroet., _List.

Mycet._, p. 26, _var._

Entire fructification confluent forming a mucilaginous ma.s.s, porose.

Pores ample, angulate, at length radiate-dentate. Spores as in the preceding. Plasmodium yellow.

Of these two species Fries remarks: "... Duae sunt distinctissimae, inter has vero longa formarum intermediarum series." Famintzin and Woronin not only concur, but consider it were more fitting to place the present species in a distinct genus, as _Polyporus_ is set off from _Hydnum_. A species based upon the color of the vegetative phase only, unconfirmed by any subsequent differential character in the fruit would seem somewhat hazardous. The color of the plasmodium is incident probably to varied nutrient environment. Pores, however, are usually in evidence.

Iowa, Tennessee, Missouri, etc.; probably common everywhere.

Sub-Cla.s.s MYXOGASTRES (_Fries_) _Macbr._