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 mu in diameter; spores minutely warted, 7-9 mu, 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 identity 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 mu.

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.

3. DIDYMIUM WILCZEKII _Meylan_.

1908. _Didymium wilczekii_ Meyl., _Bull. Soc. Vaud. Sci. Nat._, XLIV., p. 290. 1911. _Didymium wilczekii_ Meyl., List., _Mycetozoa, 2nd ed._, p. 134.

Plasmodiocarpous, dehiscing irregularly, columella scant; capillitium abundant, the threads brown, anastomosing, forming an elastic net; spores purple-brown, minutely spinulose, 10-12 mu.

Resembling plasmodiocarpous forms of _D. squamulosum_, a montane var.; small and delicate, our specimen about 16 x 6 mm. Evidently not common; collected but once by Professor Bethel at an altitude of 11,000 feet, Rocky Mountains of Colorado.

Reported in Switzerland and Sweden.

In certain Swiss gatherings made in 1913 Miss Lister finds capillitial threads with _spiral_ taeniae as in _Trichia_! (_Jour. of Bot._, Apr. 1914.) The threads in our specimen are roughened, somewhat as in _D. squamulosum_, though less strongly; the spores are nearly smooth, fuliginous at first, paler and violaceous when saturate.

4. DIDYMIUM FULVUM _Sturgis._

1917. _Didymium fulvum_ Sturgis, _Mycologia_, IX., p. 37.

Sporangia gregarious, sessile, elongate or forming curved plasmodiocarps, sometimes confluent, rarely sub-globose, concave beneath, pale-raw-umber in color, 0.5-0.8 mm. in diameter, occasionally seated on a concolorous, membranous, lime-encrusted hypothallus which may form pseudo-stalks; sporangium wall membranous, stained with yellow blotches, thickly sprinkled with clusters of large acicular crystals of pale-yellowish lime; columella very much flattened or obsolete; capillitium an abundant network of delicate, almost straight or flexuose, pale-purple or nearly hyaline threads, frequently with dark, calyciform thickenings as in _Mucilago_, and occasionally showing fusiform, crystalline blisters; spores dark-purplish-brown, coarsely tuberculate, the tubercles usually arranged in curved lines, paler and smoother on one side, 12.5 to 14.5 mu. Colorado.

5. DIDYMIUM CRUSTACEUM _Fr._

1829. _Didymium crustaceum_ Fr., _Syst. Myc._, III., p. 124.

Sporangia closely aggregated, globose, or by compression deformed, sessile, snow-white, by virtue of the remarkably developed covering of calcareous crystals by which each sporangium is surrounded as if to form a crust, the peridium membranous, colorless, usually shrunken above and depressed; columella pale, small, or obsolete; hypothallus scant or vanishing; capillitium of rather stout violaceous threads seldom branched except at the tips, where they are pale and often bifid, or more than once dichotomously divided; spores strongly warted, globose, violet-brown, 10-13 mu.

This species has in some ways all the outward seeming of a diderma, but cannot be referred to that genus because of the crystalline character of its crust. This is a very marked structure; loosely built up of very large crystals, it is necessarily extremely frail, nevertheless persists, arching over at a considerable distance above the peridium proper. Sometimes, however, caducous, evanescent.

The sporangia are said to be sometimes stipitate. This feature does not appear in any of the material before us. Lister in _Mycetozoa_ Pl. XL., _c._ draws the capillitium much more delicate than it appears in our specimens. The hypothallus is sometimes noticeable under some of the sporangia where closely crowded, but is not a constant feature.

Rostafinski (by typographical error?) confused in the _Monograph_, pp. 164, 165, this species with Persoon's _Physarum confluens_. In the _Appendix_ he substitutes the Friesian nomenclature. Persoon's description of his species is insufficient, and throws no light on the problem whatever.

Rare. Iowa; Black Hills, South Dakota. Reported common in Europe. Canada; Vancouver Island to the St. Lawrence.

6. DIDYMIUM SQUAMULOSUM (_Alb. & Schw._) _Fries._

1805. _Diderma squamulosum_ Alb. & Schw., _Consp. Fung._, p. 88. 1816. _Didymium effusum_ Link, _Diss._, II., p. 42. 1829. _Didymium squamulosum_ (Alb. & Schw.), Fries, _Syst. Myc._, III., p. 118. 1875. _Didymium effusum_ (Link) Rost., _Mon._, p. 163. 1894. _Didymium effusum_ (Link) List., _Mycetozoa_, p. 99.

Sporangia, in typical forms, gregarious, globose or depressed-globose, gray or snow-white, stipitate; the peridium a thin iridescent membrane covered more or less richly with minute crystals of lime; the stipe when present, snow-white, fluted or channelled, stout, even; columella white, conspicuous; hypothallus usually small or obsolete; capillitium of delicate branching threads, usually colorless or pallid, sometimes with conspicuous calyciform thickenings; spores violaceous, minutely warted or spinulose, 8-10 mu.

This, one of the most beautiful species in the whole series, is remarkable for the variations which it presents in the fruiting phase. These range all the way from the simplest and plainest kind of a plasmodiocarp with only the most delicate frosting of calcareous crystals up through more or less confluent sessile sporangia to well-defined elegantly stipitate, globose fruits, where the lime is sometimes so abundant as to form deciduous flaky scales. The hypothallus, sometimes entirely wanting, is anon well developed, even continuous, venulose, from stipe to stipe. The capillitium varies much in abundance as in color; when scanty, it is colorless and in every way more delicate, when abundant, darker in color and sometimes with stronger thickenings.

_D. fuckelianum Rost._, as shown in _N. A. F._, 2090, and in some private collections, seems to be a rather stout phase of the present species; the stipe is more abundantly and deeply plicate, is sometimes tinged with brown, and the capillitium is darker colored and coarser than in what is here regarded as the type of the species; but withal the specimens certainly fail to meet the requirements of Rostafinski's elaborate description and figure, _Mon._, p. 161 and Fig. 154.

_D. effusum_ Link, probably stands for a sessile form of this species, but Link's brief description (1816) is antedated by the much better one of Albertini and Schweinitz, _l. c._

Generally distributed throughout the wooded regions of North America, from New England to Nicaragua, and from Canada to California. Not uncommon about stable-manure heaps, in flower beds, and on richly manured lands. July, August.

Nicaragua specimens not only show a continuous vein-like hypothallus, but have the peridia often confluent, the columellae in such cases confluent, the stipes distinct. Furthermore, the largest spores reach the limit of 12.5 mu, and perhaps the larger number range from 10-12.5 mu, and all are very rough. This corresponds with _D. macrospermum_ Rost., which is distinguished, says the author (_Mon._, p. 162, _opis_), "chiefly by the large and strongly spinulose spores." However, the same sporangium in our Central American specimens yield spores 9.5-12.5 mu, a remarkable range. So that _D. macrospermum_ on this side the ocean, at least, cannot be distinguished from _D. squamulosum_, as far as spores are concerned. A similar remark may be made relative to the form of the columella which Rostafinski, in his figures especially, would make diagnostic. The columella in the sporangia with largest and roughest spores is that of a perfectly normal _D. squamulosum_.

7. DIDYMIUM MELANOSPERMUM (_Pers._) _Macbr._

PLATE VII., Figs. 3, 3 _a._

1794. _Physarum melanospermum_ Pers., _Roem. N. Mag. Bot._, p. 89. 1797. _Didymium farinaceum_ Schrader, _Nov. Gen. Pl._, p. 26, t. 5, Fig. 6.

Sporangia gregarious, hemispheric, depressed, umbilicate below, stipitate or sessile; the peridium firm, dull brown in color, frosted with minute crystals of lime, breaking irregularly; stipe, when present, short, stout, dull black, opaque, arising from a broad base or hypothallus; columella large, prominent; dark-colored, rough above, concave below; capillitium of more or less sinuous, usually dark-colored threads, sparingly branched, and often with calyciform thickenings; spore-mass black, spores by transmitted light pale, purplish-gray, spinulose or rough, 10-12 mu.

A well-marked and common species, distinguished by its depressed sporangium and dark-colored, opaque stipe. The latter is usually very short, almost completely concealed in the concavity of the umbilicate sporangium. The columella is dark-colored, forming the floor of the peridial cavity.

Persoon first named this species as here. Later on, _Uster's Ann._, XV., 6, he substituted _villosum_ as a more appropriate specific name. Schrader rejects both names given by Persoon as unsuitable, and suggests _farinaceum_. Schrad., _op. cit._, p. 27.

New England, Ohio, Missouri, Alabama, Iowa, Nebraska; Europe; probably cosmopolitan.

8. DIDYMIUM MINUS _Lister._

PLATE X., Figs. 4, 4 _a_, 4 _b_.

1892. _Didymium farinaceum_ Schr., var. _minus_, List., _Mycetozoa_, p. 97. 1896. _Didymium minus_ List., Morg., _Jour. Cin. Soc._, p. 61. 1899. _Didymium minus_ List., Macbr., _N. A. S._, p. 89.

Sporangia gregarious, depressed-globose, umbilicate below, whitish or gray, small, about 1/2 mm., stipitate; stipe erect, rather slender, black, faintly striate, about equal to the sporangium in the horizontal diameter; columella distinct, dark brown, globose or depressed-globose, attaining in some cases the centre, rough; capillitium delicate, almost colorless, radiating, sparsely branched; spores in mass dark brown, by transmitted light violet-tinted, minutely roughened, 8-10 mu.

Probably more common than the preceding, and generally mistaken for it. Distinguished by its smaller size, longer and more slender stem, and general trim, well-differentiated appearance. Certainly very near the preceding, of which Mr. Lister regards it as merely a variety. Professor Morgan thought it in this country the more common form.

New York, Ohio, Iowa; reported from Europe, Africa, South America.

9. DIDYMIUM CLAVUS (_Alb. & Schw._) _Rabenhorst._

1805. _Physarum clavus_ Alb. & Schw., _Consp. Fung._, p. 96. 1829. _Didymium melanopus_ Fries, _Syst. Myc._, III., p. 114. 1844. _Didymium clavus_ (Alb. & Schw.) Rabh., _Ger. Cr. Fl._, No. 2282. 1875. _Didymium clavus_ (Alb. & Schw.) Rost., _Mon._, p. 153. 1899. _Didymium clavus_ (Alb. & Schw.) Rabenh., Macbr., _N. A. S._, p. 90. 1911. _Didymium clavus_ Rost., List., _Mycet., 2nd ed._, p. 128.

Sporangia gregarious, pale gray, discoid or pileate, depressed, stipitate; the peridium dark-colored, frosted with calcareous crystals above, naked below; stipe short, slender, tapering upward, furrowed, arising from a hypothallus more or less distinct, black; columella obsolete; capillitium of delicate threads, pale or colorless, little branched; spores violaceous, pale, nearly smooth, 6-8 mu.

This species is well differentiated, easy of recognition by reason of its peculiar discoid sporangium, calcareous above, naked and black beneath. _D. neglectum_ Massee, reported from Philadelphia, is said to be a slender form of the present species. The figures of _D. clavus_ by Albertini and Schweinitz are excellent, as also the description.

Not common. Pennsylvania, Ohio, Iowa.

10. DIDYMIUM NIGRIPES (_Link_) _Fries._

PLATE VII., Figs. 2, 2 _a_, 2 _b_.

1809. _Physarum nigripes_ Link, _Obs. Diss._, I., p. 27. 1818. _Physarum microcarpon_ Fr., _Sym. Gast._, p. 23. 1829. _Didymium nigripes_ (Link) Fr., _Syst. Myc._, III., p. 119. 1875. _Didymium microcarpon_ (Fr.) Rost., _Mon._, p. 157. 1896. _Didymium microcarpon_ Fr., Morg., _Jour. Cin. Soc._, p. 61.

Sporangia gregarious, globose or hemispheric, umbilicate beneath, small, white, stipitate; the peridium smoky, covered with minute calcareous crystals; stipe slender, erect, black, opaque; hypothallus scutate, black; columella distinct, globose, black or dark brown; capillitium of delicate threads, pale brown or colorless, with occasional brown thickenings or nodes, sparingly branched; spores pale, violaceous by transmitted light, minutely warted, 6-8 mu.

This is _D. microcarpon_ Rost. Fries, _l. c._, acknowledges the priority of Link's appellation, and discards _microcarpon_. Rostafinski adopted _microcarpon_ simply because he thought it more appropriate. Fries describes the columella "none or black." It is doubtful whether we have the typical Friesian form on this continent. The fructification is in our specimens small, about .4 mm., and the spores, as noted by Morgan, small; otherwise the species is hardly more than a variety of the next. Under the name _D. nigripes_ Lister groups our Nos. 10, 11, 12. _N. A. F._, 1393, represents Dr. Rex's conception of the present species.

Not common. New York, Ohio, Iowa.

11. DIDYMIUM XANTHOPUS (_Ditmar_) _Fr._

PLATE XVI., Fig. 10.

1817. _Cionium xanthopus_ Ditmar, Sturm, _Deutsch. Fl._, III., p. 37, t. 43. 1829. _Didymium xanthopus_ (Dit.) Fr., _Syst. Myc._, III., p. 120. 1873. _Didymium proximum_ Berk. & C., _Grev._, II., p. 52. 1892. _Didymium microcarpon_ (Fr.) Rost., Macbr., _Bull. Lab. Nat. Hist. Iowa_, II., p. 146, in part. 1894. _Didymium nigripes_ Fr., List., _Mycetozoa_, p. 98, in part.

Sporangia gregarious, white, globose, slightly umbilicate, stipitate; the peridium thin, and nearly or quite colorless, frosted with crystals of lime; the stipe yellowish or yellowish brown, corneous, erect, subulate, slender; hypothallus none; columella pale or white, turbinate, globose or depressed-globose; capillitium of dull brown, or colorless threads more or less branched, always white at the tips; spores violaceous, nearly smooth, 7.5-8.5 mu.

This seems to be the most common form in the United States. It is distinguished from the preceding by the longer, more delicate, generally orange-yellow, stem with pale or white columella. The spores also average a shade larger. _N. A. F._, 412 and 2089, are illustrations of _D. xanthopus_. The columella in blown-out specimens is very striking, well confirming the diagnosis of Fries, "_valde prominens, globosa, stipitata, alba_." Berkeley makes the color of the capillitium diagnostic of _D. proximum_, but this feature is insufficient.

Eastern United States; common.

12. DIDYMIUM EXIMIUM _Peck._

PLATE XVI., Figs. 11, 11 _a_, 11 _b_.

1879. _Didymium eximium_ Peck, _Rep. N. Y. Mus._, XXXI., p. 41.

Sporangia scattered, dull grayish-yellow or gray, depressed-globose, umbilicate, minute, stipitate; the peridium comparatively thick, tenacious, especially persistent below, tawny or yellow; the stipe pale brown or orange, erect, even or slightly enlarged at base; hypothallus scant or none; columella prominent, more or less discoidal, rough, or spinulose, especially on the upper surface, yellow; capillitium not abundant, pale fuliginous, often branching and anastomosing so as to form a loose net; spores nearly smooth, dark violaceous by transmitted light, 8.5-9.5 mu.

The species differs from _D. xanthopus_ in several particulars,--in the much firmer, more persistent, and less calcareous peridium, in the more complex capillitium, in the darker and larger spores, and especially in the peculiar and prominent columella, which is not only rough, but even "sometimes spinulose even to the extent of long spicules penetrating to one-third the height of the sporangia." _N. A. F._, 2493.

As stated under No. 8, these last two species are called varieties only of _D. nigripes_. They are so retained in _Mycetozoa, 2nd ed._ Since, however, they are the usual presentation of the species in the United States, it seems wise to let them stand for the present, as here. They are quite distinguishable; _D. eximium_ especially well marked.

Apparently rare, it yet ranges from New York to eastern Iowa, in colonies rather large. Okoboji Lake;--fine!

13. DIDYMIUM TROCHUS _List._

1898. _Didymium trochus_ List., _Jour. Bot._, XXXVI., p. 164.

Sporangia plasmodiocarpous, hemispherical or turbinate, white, sessile or very short-stalked, cream-colored or white; peridium double, the outer shell-like, the inner membranaceous, more or less adherent to the outer, both caducous together, leaving the thickened base surrounding an expanded columella; stipe, when present, very short, stout; capillitium colorless, nearly simple; spores brownish-purple, strongly warted, 9-10 mu.

On decaying leaves, rotten cactus, yucca, etc., Monrovia, California; _Bethel_.

Reported from England on beds of leaves or straw; in Portugal Dr. Torrend finds it on or _in_ dead leaves of _Agave americana_! Evidently an American species, and belonging to arid regions; its occurrence in England surprising!

14. DIDYMIUM ANNULATUM _Macbr. n. s._

PLATE XX., Figs. 4, 4 _a_.

Sporangia small, scattered, annulate, not only without columella but perforate when the stipe is broken, umbilicate above and below, grey, coated with crystalline frustules, opening irregularly about the periphery; stipe white, or pallid, fluted, tapering upward from a distinct hypothallus; capillitium scanty consisting of delicate, sparsely branching threads, the branchlets anastomosing more or less at length, attached to the peridial wall, radiating from the rim of the slightly depressed top of stipe, without special thickenings save at the insertion of the ramules a triangular enlargement is usual and of dark or pallid shade; spores smooth; however they show three or four spots on the hemisphere and other minute but variable markings; 9-10 mu. Seattle, Washington.

Differs from _D. nigripes_ in color of the stipes, capillitium, spore-diameter, etc.

15. DIDYMIUM DUBIUM _Rost._

1875. _Didymium dubium_ Rost., _Mon._, p. 152. 1892. _Didymium listeri_ Mass., _Mon._, p. 244. 1894. _Didymium dubium_ Rost., List., _Mycetozoa_, p. 95. 1911. _Didymium dubium_ Rost., List., _Mycetozoa, 2nd ed._, p. 126.

Fructification wholly plasmodiocarpous, snow-white, small, 2-6 mm., flat and thin; the outer wall double, membranous within, calcareous-crystalline without; columella none; capillitium simple of rather thick, vertical, brown threads, sparingly united laterally, and only occasionally furcate at the ends, especially above; spores minutely spinulescent, violaceous pale, 12-15 mu.

Massee thought English specimens out of harmony with the original description and gave them a new name. To refuse this, Lister enlarges the range of spore-measurements and disregards some of Rostafinski's specifications as to capillitium. Our specimens are as described.

Bohemia. England. Shores of Lake Okoboji, Iowa.

This is indeed a doubtful form. It differs from _D. difforme_ chiefly in that the outer calcareous shell is not smooth, but is covered with abundant loose crystals, frosted. The spores are paler but about the same size. The frosting may be incident to local climatic conditions at the time and place of desiccation.

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 coarse, flat, dichotomously branching threads, broader below; spores minutely warted, or almost smooth, dark brown, 12-14 mu.

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 mu.

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 mu thick and usually containing small crystalline masses of lime. Spores bright violet-brown, minutely and irregularly spinulose, 10-11.5 mu 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. XXXV., p. 209. 1902. _Didymium excelsum_ Jahn, _Ber. Deut. Bot. Ges._, XX., p. 275.

Sporangia clustered 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 mu.

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. Hoehnel, _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 mu.

Like _Lepidoderma tigrinum_, but has different calcic crystals.

Java and Ceylon.

=3. Diderma= _Persoon_

1794. _Diderma Persoon_, _Roem. 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_

2. Fructification of distinct sporangia.

_a._ Sporangia on a common hypothallus.

O Outer wall fragile, not widely remote from the inner 2. _D. spumarioides_

OO Inner wall lacking 3. _D. simplex_

OOO Outer wall crustaceous, porcelain-like.

i. Spores 8-10 4. _D. globosum_

ii. Spores 12-15 5. _D. crustaceum_

OOOO Outer wall firm, not crustaceous 6. _D. lyallii_

_b._ Sporangia isolated, or, at least, not on a common hypothallus, sessile.

O Outer wall porcellanous, roseate 7. _D. testaceum_

OO Outer wall white 8. _D. niveum_

OOO Outer wall ashen 9. _D. cinereum_

_c._ Sporangia stipitate 10. _D. hemisphericum_

_B._ Sub-Genus LEANGIUM

1. Sporangia generally sessile.

_a._ Inner peridium distinct.

O Membranous colorless, columella scant 11. _D. sauteri_

OO Colorless, columella prominent, red 12. _D. cor-rubrum_

OOO Outer ochraceous, inner yellow 13. _D. ochraceum_

_b._ Peridial layers inseparable.

O Peridium multifid; columella small or none 16. _D. trevelyani_

OO Peridium breaking into but few irregular lobes; columella prominent.

i. Peridium umber brown 14. _D. roanense_

ii. Peridium ashen 15. _D. radiatum_