The North American Slime-Moulds Part 38

1753. _Stemonitis_ Gleditsch, in part, _Meth. Fung._, p. 140.

1873. _Stemonitis_ (Gleditsch) Rost., _Versuch_, p. 7.

Sporangia distinct, though often closely aggregate, cylindric, stipitate; columella prominent; capillitium well developed by repeated lateral and apical branching of the columella, at length a.s.suming at the surface the form of a distinct net which supports an evanescent peridium.

The genus is marked by its surface-net supported at the tips of the dichotomously branched divisions of the columella. Over the net is spread, theoretically at least, the peridial film supported by very short points projecting from the net,--the peridial processes; the peridium, however, is seldom seen; in some cases, certainly, is never developed. Rostafinski first defined the genus as employed by recent writers. Gleditsch simply renamed Micheli's _Clathroidastrum_; all writers subsequent included species of other genera.

The taxonomy of this genus is of the most difficult. Macroscopic, defining characters are few, and even these sometimes uncertain.

Microscopic distinctions also tend to be illusive, variable in such fas.h.i.+on that often at the critical point the most exact description fails. All that may be done at present is to recognize two or three definite types and then cautiously differentiate among these with the light we have, until more general study of the group brings to service a wider range of observation with more comprehensive record on which judgment may better be sustained.

We have before us many and beautiful forms of this genus yet unstudied.

Some of these doubtless have already found place in our growing taxonomic literature; some apparently undescribed; all to wait wider leisure or perhaps a younger hand.

The entire life-history of every form is none too much if we would set out with any hope of accuracy the genetic relations.h.i.+ps for which taxonomy stands. Recently European students are making the color of the plasmodium a basis for species-discrimination, which is good so far. But plasmodic characters are at present unserviceable generally, for two reasons; they vary in the same species; and unfortunately, when most needed, they are unknown and inaccessible. The student is generally confronted by forms mature, the plasmodic stage already past.

=Key to the Species of Stemonitis=

_A._ Sporangia connately united.

_a._ Spores verruculose 1. _S. confluens_

_b._ Spores reticulate 2. _S. trechispora_

_B._ Sporangia at maturity distinct.

_a._ Spore-ma.s.s grayish black.

1. Larger, 8-12 mm. spores distinctly reticulate or warted, but sometimes nearly smooth 3. _S. fusca_

2. Spores reticulate and spinulose.

i. Spores adherent, cl.u.s.tered 4. _S. uvifera_

ii. Sporangia very tall, 15-20 mm., rigid 5. _S. dictyospora_

iii. Sporangia short, jet- or violet-black 6. _S. nigrescens_

_b._ Spore-ma.s.s rich brown.

1. Columella central.

i. Sporangia shorter, 5-6 mm., spores banded 7. _S. virginiensis_

ii. Sporangia 8-10 mm.; spores verruculose 8. _S. webberi_

iii. Sporangia tall, 15-20 mm. or more 9. _S. splendens_

2. Columella eccentric, sporangium in cross-section, angular 10. _S. fenestrata_

_c._ Spore-ma.s.s ferruginous; sporangia in tufts.

1. Spores smooth or nearly so.

i. Sporangia pale, small, 3-5 mm., crowded, stipe unpolished 11. _S. smithii_

ii. Sporangia ferruginous; columella regular 12. _S. axifera_

iii. Sporangia ferruginous; columella proliferate just below the apex 13. _S. flavogenita_

iv. Sporangia, spore-ma.s.s, dusky-purplish or brown.

O On dead wood.

o Scattered, apex blunt 14. _S. pallida_

oo Cl.u.s.tered, ac.u.minate 15. _S. carolinensis_

OO On living leaves, preferably, spore-ma.s.s brown 16. _S. herbatica_

1. STEMONITIS CONFLUENS _Cooke & Ellis._

PLATE XI., Figs. 4, 4 _a_, 5.

1876. _Stemonitis confluens_ Cke. & Ell., _Grev._, V., p. 51.

1894. _Stemonitis splendens var. confluens_ Lister, _Mycet._, p. 112.

1899. _Stemonitis confluens_ Cke. & Ell., Macbr., _N. A. S._, p. 114.

1911. _Stemonitis confluens_ Cke. & Ellis, List., _Mycet., 2nd ed._, p. 147.

"Sporangia fasciculate, confluent on a persistent hypothallus, dark fuscous; peridia very fugacious; stipes united at the base, erect, furcate; spores large, brown, globose. On oak bark.

"The stems are branched in a furcate manner and confluent at the base, forming a compact tuft. The capillitium is membranaceous at the angles; spores very large compared with allied species, being 12 . The specimens were too fully matured for more satisfactory description."

Such is the original description of this unique and interesting species.

The sporangia occur in close-set tufts or cl.u.s.ters, are distinct, separate at their tips and bases only; perhaps not always at base. The capillitium rises by branching from the columella, rather more prolific than usual, and combines to form a distinct superficial net of large even meshes. From the outer arcs of the bounding net spring rather long acute processes which should support the peridium. This, however, is altogether rudimentary. In most places there is no sign of peridium at all, but here and there between contiguous sporangia opposite processes unite and at their point of union a tiny circular disk of the peridial membrane appears. At intervals, therefore, over the entire sporangium are seen these small brown disks, each about equalling in diameter the size of the average mesh. At other points the sporangia do not seem at all coalescent, but where the opposing processes do meet the union is perfect and the little disk seen edgewise looks like some delicate counter strung upon a wire.

The interest attaching to this in view of what has been said about _Amaurochaete_ and _Brefeldia_ is obvious.

Under the lens the spores and capillitium are concolorous, dark fuscous, the spores distinctly verruculose, about 12.5 .

The original gathering here described was from New Jersey; twenty years later Mr. Ellis was so fortunate as to find again fine specimens all on oak bark. The sporangia are quite small, only 3 mm. high, when blown out concolorous with the habitat.

2. STEMONITIS TRECHISPORA (_Berk._) _Torr._

PLATE XX., Figs. 11, 11 _a_, 11 _b_, 11 _c_.

1909. _Stemonitis fusca_ (Roth) Rost. var. _trechispora_ (Berk.), _Fl. Myxom._, Torrend, p. 141.