=Key to the Species of Didymium=

1. Lime-crystals merely whitening the peridial wall.

A. Fructification plasmodiocarpous.

_a._ White.

O Capillitium with adherent vesicles 1. _D. complanatum_

OO Capillitium simple 2. _D. anellus_

OOO Capillitium much combined; spores 10-13 3. _D. wilczekii_

OOOO Capillitium crystal-bearing 18_a_. _D. anomalum_

_b._ Yellow or tawny 4. _D. fulvum_

B. Fructification normally of distinct sporangia.

_a._ Sporangia sessile or nearly so; outer calcareous wall conspicuously developed 5. _D. crustaceum_

_b._ Sporangia plainly stipitate.

i. Peridium much depressed; umbilicate below.

O Stipe white 6. _D. squamulosum_

OO Stipe black.

+ Larger, about 7.5-1 mm. 7. _D. melanospermum_

++ Small, about .5 mm. 8. _D. minus_

+++ Sporangia discoid 9. _D. clavus_

ii. Peridium small, globose.

O Stipe dark brown or black; columella dark, obsolete or none. 10. _D. nigripes_

OO Stipe generally paler, of various tints of brown, orange, etc.

+ Columella pale or white, nearly smooth 11. _D. xanthopus_

++ Columella, yellow, discoid, rough 12. _D. eximium_

iii. Peridium turbinate, columella hemispheric 13. _D. trochus_

iv. Peridium annulate 14. _D. annulatum_

2. Calcareous crystals forming a distinct crust.

A. Fructification wholly plasmodiocarpous 15. _D. dubium_

B. Sporangia ill-defined, sessile, plasmodiocarpous.

_a._ Spores generally nearly smooth 16. _D. difforme_

_b._ Spores very rough, obscurely banded 17. _D. quitense_

EXTRA-LIMITAL

_a._ Sporangia discoid, spores reticulate 18. _D. intermedium_

_b._ Stipe, columella, peridium, orange-brown 19. _D. leoninum_

1. DIDYMIUM COMPLANATUM (_Batsch_) _Rost._

PLATE XVI., Fig. 8.

1786. _Lycoperdon complanatum_ Batsch, _Elench. Fung._, I., p. 251.

1829. _Didymium serpula_ Fr., _Syst. Myc._, III., p. 126, Rost., _App._, p. 21.

1875. _Didymium complanatum_ (Batsch), Rost., _Mon._, p. 151.

1899. _Didymium complanatum_ (Batsch) R., Macbr., _N. A. S._, p. 85.

1911. _Didymium complanatum_ Rost., List., _Mycetozoa, 2nd ed._, p. 127.

Fructification plasmodiocarpous, creeping, flattened, vein-like, annulate or reticulate, the dark-colored peridium covered with white, but not numerous crystals; hypothallus none; columella none; capillitium much branched, violaceous threads combined to form a rather dense net which bears numerous, peculiar, rounded vesicles, yellowish in color, 30-50 in diameter; spores minutely warted, 7-9 , violaceous-brown.

The defining characteristics here are the curious supplementary vesicles. These are evidently plasmodic, embraced, shot-through, by all the neighboring capillitial threads, withal warted like a spore. They remind of the curious, belated, spore-like but giant cells found in stipes, as in arcyriaceous forms. With all the wealth of his prolix, poetic, metaphoric tongue, the Polish author gives them abundant consideration. In the _Mon._, Tab. IX., Figs. 166 and 180, he clearly shows the structure, although in the explanation of the plate he has strangely mixed this species with _D. crustaceum_ Fr. Under _D. serpula_ Fries may refer to the present species, although there is nothing in his description to determine the fact. The same thing may be said of the description and figures of Batsch. Rostafinski, in the _Monograph_, seems to have been satisfied as to the ident.i.ty of Batsch's materials: in the _Appendix_, he writes _D. serpula_, but gives no reason.

Rare. New York. England, France, Germany.

2. DIDYMIUM ANELLUS _Morgan._

PLATE XVIII., Fig. 7.

1894. _Didymium anellus_ Morgan, _Jour. Cin. Soc._, p. 64.

1899. _Didymium anellus_ Morg., Macbr., _N. A. S._, p. 85.

1911. _Didymium anellus_ Morg., Lister, _Mycetozoa, 2nd ed._, p. 134.

Plasmodiocarp in small rings or links, then confluent and elongated, irregularly connected together, bent and flexuous, resting on a thin venulose hypothallus, or sometimes globose, the peridium dark colored, with a thin layer of stellate crystals, irregularly ruptured; capillitium of slender, dark-colored threads, which extend from base to wall, more or less branched, and combined into a loose net; columella a thin layer of brown scales; spores globose, very minutely warted, violaceous, 8-9 .

This minute species resembles a poorly developed, or sessile, phase of _D. melanospermum_. Some of the sporangia (?) are spherical; such show a very short dark stalk. The columella is scant, and the spores are smaller than those of _D. melanospermum_.

Ohio. Reported more recently from Europe and Ceylon.