16. DIDYMIUM DIFFORME _Duby._

1797. _Diderma difforme_ Pers. _Tentamen Disp. Meth._, p. 19.

1830. _Didymium difforme_ Duby., _Bot. Gall._, ii., p. 858.

1875. _Chondrioderma difforme_ Pers., Rost., _Mon._, p. 177.

1894. _Didymium difforme_ Duby., List., _Mycetozoa_, p. 94.

1899. _Diderma personii_ Macbr., _N. A. S._, p. 96.

1911. _Didymium difforme_ Duby., List., _Mycetozoa, 2nd ed._, p. 124.

Plasmodiocarpous, the smooth, white outer peridium separable from the thin, colorless or purplish inner layer; capillitium of rather coa.r.s.e, flat, dichotomously branching threads, broader below; spores minutely warted, or almost smooth, dark brown, 12-14 .

The white crust-like outer wall has more than once carried this species into _Diderma_. It is still doubtful whether we are here dealing with _Chondrioderma calcareum_ Rost. Miss Lister cites a variety, _S.

difforme comatum_, with more abundant capillitium which may represent Rostafinski's species.

Evidently rare in the United States; reported more common in Europe and eastward. In our specimens the crust-like outer peridium shows crystals on the broken edge only; the body of the object, as its outer surface seems to be amorphous.

17. DIDYMIUM QUITENSE (_Pat._) _Torr._

1895. _Chondrioderma quitense_ Pat., _Bull. Soc. Myc. Fr._, XI., p. 212.

1909. _Didymium quitense_ (Pat.) Torr., _Flor. Myxom._, p. 150.

1911. _Didymium quitense_ Torr., List., _Mycetozoa, 2nd ed._, p. 126.

1913. _Didymium quitense_ (Pat.) Torr., Sturg., _Myx._, Col. II., p. 446.

Sporangia more or less plasmodiocarpous, scattered, depressed, white; the outer peridium distinct, crust-like, remote from the thin membranous inner wall; columella undefined; capillitium brown, much branched, forming a network especially outwardly; spores very dark violaceous-brown, rough with a tendency to obscure reticulation; 12-14 .

This species is different from _D. difforme_ chiefly in the rougher and somewhat banded epispore. It is reported from Ecuador by Father Torrend, and from Colorado mountains by Dr. Sturgis to whose kindness I am indebted for the specimens here described. Evidently a high mountain species.

Colorado.

18_a_. DIDYMIUM ANOMALUM _Sturg._

PLATE XIX., Figs. 13 and 13 _a_.

1913. _Didymium anomalum_ Sturg. _Myxomycetes of Col._, II., p. 444

Sporangia in the form of very thin effused grey plasmodiocarps, 2-10 cm.

long, 1 mm. or less in thickness. Wall single or membranous, hyaline or yellowish, with rather scanty deposits of small, stellately crystalline or amorphous lime. Columella none. Capillitium consisting entirely of straight membranous, tubular, columns, extending from the base to the upper wall of the plasmodiocarp, 7-22 thick and usually containing small crystalline ma.s.ses of lime. Spores bright violet-brown, minutely and irregularly spinulose, 10-11.5 diam.

Hab. on the inner bark of Populus. Colorado Springs, Colo., July 1911.

Our specimens by the courtesy of Dr. Sturgis.

=EXTRA-LIMITAL=

18. DIDYMIUM INTERMEDIUM _Schroeter._

1896. _Didymium intermedium_ Schroet., _Hedwigia_, Vol. x.x.xV., p. 209.

1902. _Didymium excelsum_ Jahn, _Ber. Deut. Bot. Ges._, XX., p. 275.

Sporangia cl.u.s.tered or gregarious, discoidal and umbilicate below, or lobed or convolute, greyish white, stipitate; stipe pale yellow, tapering upwards, stuffed with lime crystals, expanding into the yellowish, discoidal, recurving columella; capillitium colorless, more or less branching; spores dark purple-brown, irregularly reticulate, 9-12 .

Differs from _D. squamulosum_ in the reticulate epispore. Brazil.

19. DIDYMIUM LEONINUM _Berk. & Br._

1873. _Didymium leoninum_ Berk. & Br., _Jour. Linn. Soc._, XIV., p. 83.

1876. _Lepidoderma tigrinum_ Rost., _App. to Mon._, p. 23.

1909. _Lepidodermopsis leoninus_ v. Hohnel, _Sitz. K. Ak. Wiss. Wien, Math. Nat. Ks._, CXVIII., 439.

Sporangia gregarious, sub-globose, covered more or less completely with white or yellowish deposits of crystalline lime, stipitate; stipes short, orange or brown, containing lime, enlarged to form the globose orange columella and often connected at base by a venulose hypothallus; capillitium of slender threads, anastomosing, colorless at the tips; spores violet-grey, minutely warted, 7-9 .

Like _Lepidoderma tigrinum_, but has different calcic crystals.

Java and Ceylon.

=3. Diderma= _Persoon_

1794. _Diderma Persoon_, _Rom. N. Mag. Bot._, I., p. 89.

1873. _Chondrioderma_ Rost. _Versuch_, p. 13, _Mon._, p. 167.

1894. _Chondrioderma_ Rost., List., _Mycetozoa_, p. 75.

1899. _Diderma Persoon_, Macbr., _N. A. S._, p. 92.

Sporangia plasmodiocarpous or distinct, sessile or stipitate; the peridium as a rule double, the outer wall generally calcareous with the lime granules globular, non-crystalline, the inner wall very delicate and often, in the mature fructification, remote from the outer; columella generally prominent.

The genus _Diderma_ is usually easy of recognition, by reason of its double wall, the outer, crustaceous, usually calcareous, and its limits remain substantially as originally set by Persoon. His definition is as follows:--

"Peridium ut plurimum duplex; exterius fragile; interius pellucens, subdistans. Columella magna, subrotunda. Fila parca latentia."--_Syn.

Meth. Fung._, p. 168.

Rostafinski changed the name of the genus to _Chondrioderma_ (_chondri_, cartilage), seemingly at De Bary's suggestion, and seems to have regarded Persoon's definition as applicable to those species only in which the wall is not only plainly double, but in which the two walls are as plainly remote from each other. More especially he esteemed a new generic name necessary, since he regarded several included species, as _D. spumarioides_, _D. michelii_, etc., monodermic.

Since it is doubtful whether any diderma is really monodermic, and since Persoon's definition in any case seems sufficiently elastic, we have seen no reason to discard the older name. Persoon's _Diderma_ when established, _l. c._, included _D. floriforme_. He made some confusion in his later work by admitting some physarums. This induced Schrader to throw all the didermas into his new genus, _Didymium_.

According to the nature of the sporangial wall, the species fall rather naturally into two sections:--

_A._ Outer sporangial wall distinctly calcareous, fragile; species generally sessile _Diderma_

_B._ Outer sporangial wall cartilaginous, the inner less distinct, or concrete with the outer; species oftener stipitate _Leangium_

_A._ Sub-Genus DIDERMA

1. Fructification wholly plasmodiocarpous 1. _D. effusum_