The North American Slime-Moulds Part 57

95. The plasmodium is pale pink, soon becomes buff when exposed in fruiting, finally pallid or somewhat livid, and is outwardly changed into the stout, tough peridium. This consists of an intricate network of irregular gelatinous tubules enclosing within the meshes protoplasmic ma.s.ses of pretty uniform size, 60-100 . Outwardly the protoplasmic vesicles predominate; inwardly the gelatinous tubules, which are, in some instances at least, continued toward the centre of fructification to form the capillitium. The protoplasmic ma.s.ses referred to respond to ordinary stains, are often broken into numberless small cells corresponding in size and appearance to ordinary spores.

Not common. New England, Ohio, Iowa. Perhaps more abundant in the Mississippi valley; Canada.

3. LYCOGALA EXIGUUM _Morg._

1893. _Lycogala exiguum_ Morg., _Jour. Cin. Soc._, p. 8.

aethalia small, 2-5 mm. in diameter, gregarious, globose, dark brown or black, sessile, minutely scaly, irregularly dehiscent; the peridium thin, the vesicles comparatively few, in irregular patches which are more or less confluent; capillitium as in preceding species, the tubules slender and branching; spore-ma.s.s pale, ochraceous, spores by transmitted light colorless, almost smooth, 5-6 .

Found in the same situations as No. 1, and at the same season.

Recognizable by its _gregarious_ habit, not crowded nor superimposed, small size, and dusky color. The little spheres occur a dozen or more in a place, dark lead-colored, shading to black, opening rather regularly at the top. It looks like a depauperate _L. epidendrum_, but seems to be constantly collected.

Our specimens are from Ohio, Iowa, Missouri, Canada.

4. LYCOGALA CONIc.u.m _Pers._

1801. _Lycogala conica_ Pers., _Syn. Fung._, p. 159.

1875. _Dermodium conic.u.m_ (Pers.) Rost., _Mon._, p. 284.

aethalia scattered, sometimes two or three together, small 2-4 mm. high, conical, sessile, pallid, grayish brown, marked by obscure black reticulations, opening regularly at the somewhat ac.u.minate tip; peridium thin in structure, as in _L. epidendrum_, but more delicate; capillitium made up of abundant, slender, uniform threads almost smooth, simple, the free ends obtuse, taking origin in the cortex much as in the preceding species; spores in ma.s.s ochraceous, by transmitted light colorless, minutely warted or faintly reticulate, about 5 .

A very distinct and rare little species. Well described by Persoon, who also appears to have observed the plasmodium "_primo rubra_." The color of the mature form varies with age; at first somewhat purplish. Dr. Rex collected it in Pennsylvania; Mr. Morgan has it from Ohio; our specimens are from southeastern Missouri.

ORDER V

=TRICHIALES=

Fructification sporangial, rarely plasmodiocarpous, the sporangia stalked or sessile, gregarious or closely crowded, limeless throughout; the capillitium of definite threads, free or attached to the sporangial wall, isolated or combined into a net; spores generally some shade of yellow, never purple or black.

The distinguis.h.i.+ng feature in this order is found in the peculiar sculpture of the capillitial threads. This is suggested by the tubules of _Lycogala_, though probably the resemblance is superficial only. The individual threads, as in _Trichia_, are called elaters, from their probable efficiency in spore-dispersal.

As here limited, the order is coextensive with the _Calonemeae_ of Rostafinski, except that that includes in addition the genera _Prototrichia_ and _Dianema_. The course of differentiation may be a.s.sumed to start with _Dianema_, through the _Perichaenaceae_ to the _Arcyriaceae_ and again from the same starting-point through _Prototrichia_ to the _Trichiaceae_.

=Key to the Families of the Trichiales=

_A._ Capillitial threads transverse to the sporangial cavity, attached usually at each end, plain or only slightly roughened _Dianemaceae_

_B._ Capillitium plain, papillose, or spinulose, often scanty, not netted, the threads sometimes attached by one end to the sporangium wall _Perichaenaceae_

_C._ Capillitium a distinct net, usually attached below to the sporangial wall; sculpture various, not continuous spiral bands _Arcyriaceae_

_D._ Capillitial threads transverse, fascicled, attached at both ends, but sculptured by well defined spiral bands _Prototrichiaceae_

_E._ Capillitial threads typically free, sometimes more or less branched, forming a loose net attached below, characterized by definite spiral bands, or sometimes by scattered rings _Trichiaceae_

_A._ DIANEMACEae

=Key to the Genera of the Dianemaceae=

_A._ Capillitial threads attached at one end, or free 1. MARGARITA

_B._ Capillitial threads attached at each end 2. DIANEMA

=1. Margarita= _List._

1894. _Margarita_ Lister, _Mycet._, p. 203.

Sporangia sessile, the capillitium simple, hair-like, coiled.

1. MARGARITA METALLICA (_Berk. & Br._) _List._

PLATE XVII., Figs. 1, 1 _a_, 1 _b_.

1838. _Physarum metallic.u.m_ Berk. & Br., _Mag. Zool. & Bot._, I., p. 49.

Sporangia scattered or cl.u.s.tered, globose, or somewhat plasmodiocarpous, .5-1 mm., sessile, coppery iridescent, the peridium thin, opening above irregularly; capillitium of long flexuous, coiling, simple or little dividing threads, nearly smooth, with infrequent attachments to the peridial wall; spores in ma.s.s yellowish, transparent under the lens, delicately verruculose, 10-12 .

One of the handsomer species of the present group. So far a Pacific coast form. California, Oregon, Was.h.i.+ngton; reported from Chile.

=Dianema= _Rex_

1891. _Dianema harveyi_ Rex, _Proc. Phil. Acad._, p. 397.

Sporangia simple or plasmodiocarpous; capillitium composed of threads without characteristic thickenings running entirely across the sporangium attached both to the base and to the opposite wall, not joined to form a network.

=Key to Species of Dianema=

_A._ Sporangia distinct, iridescent 1. _D. harveyi_

_B._ Fructification more or less plasmodiocarpous, dull brown 2. _D. corticatum_

_C._ Sporangia, some of them stipitate 3. _D. andersoni_

1. DIANEMA HARVEYI _Rex._

PLATE XVI., Figs. 5 and 5 _b_.

1891. _Dianema harveyi_ Rex, _Proc. Phil. Acad._, p. 397.