The North American Slime-Moulds / A Descriptive List of All Species of Myxomycetes Hitherto Reported from the Continent of North America, with Notes on Some Extra-Limital Species

by Thomas H. Macbride

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 fashion 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 relationships 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-mass 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, clustered			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-mass 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-mass 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-mass, dusky-purplish or brown.
				O On dead wood.
					o Scattered, apex blunt	14. S. pallida
					oo Clustered, acuminate	15. S. carolinensis
				OO On living leaves, preferably, spore-mass 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.