1873. Rostafinski, J. Versuch eines Systems der Mycetozoen.

1875. Rostafinski, J. Sluzowce Monografia.

1778. Roth, A. W. Tentamen Florae Germanicae.

1888. Saccardo, P. A. Sylloge Fungorum, vol. vii., _et seq._

1841. Sauter, A. Flora, vol. xxiv., p. 316.

1762. Schaeffer, J. C. Fungi qui in Bav. et Pal. nasc.u.n.tur--to 1774.

1797. Schrader, H. A. Nova Genera Plantarum.

1890. Schroeter, J. Myxomycetes, in Engler u. Prantl Pflanzenfamilien.

1885. Schroeter, J. Kryptogamenflora von Schlesien, die Pilze.

1801. Schumacher, C. F. Enumeratio Plant. Saell. crescentium.

1805. Albertini, I. and Schweinitz, L. D. de. Conspectus Fungorum.

1822. Schweinitz, L. D. de. Synopsis Fungorum Car. Sup.

1834. Schweinitz, L. D. de. Synopsis Fungorum in America Boreali.

1797. Sowerby, J. English Fungi--to 1809; 3 vols.

1760. Scopoli, J. A. Flora Carniolica--to 1772.

1797. Trentepohl, K. Observations Botanicae,--to Roth, Catalecta Botanica, Fasc. i.

1833. Wallroth, C. F. Flora Cryptogamica Germaniae.

1787. Willdenow, K. L. Florae Berolinensis Prodromus.

1886. Wingate, Harold, Jour. Mycol. ii., 125.

1889. Wingate Harold, In Proc. Acad. Nat. Sci. Philad.

1890. Wingate, Harold--in Revue Mycologique.

1873. Woronin u. Famintzin, Ueber Zwei neuen Formen von Schleimpilzen.

1885. Zopf, W. Die Pilzthiere oder Schleimpilze.

To these may be added the many contributions on the general subject, as these are found in all sorts of current botanical literature; cited everywhere in this volume as occasion offered.

INTRODUCTORY

The Myxomycetes, or slime-moulds, include certain very delicate and extremely beautiful fungus-like organisms common in all the moist and wooded regions of the earth. Deriving sustenance, as they for the most part do, in connection with the decomposition of organic matter, they are usually to be found upon or near decaying logs, sticks, leaves, and other ma.s.ses of vegetable detritus, wherever the quant.i.ty of such material is sufficient to insure continuous moisture. In fruit, however, as will appear hereafter, slime-moulds may occur on objects of any and every sort. Their minuteness retires them from ordinary ken; but such is the extreme beauty of their microscopic structure, such the exceeding interest of their life-history, that for many years enthusiastic students have found the group one of peculiar fascination, in some respects, at least, the most interesting and remarkable that falls beneath our lens.

The slime-mould presents in the course of its life-history two very distinct phases: the _vegetative_, or growing, a.s.similating phase, and the _reproductive_. The former is in many cases inconspicuous and therefore un.o.bserved; the latter generally receives more or less attention at the hands of the collector of fungi. The vegetative phase differs from the corresponding phase of all other plants in that it exhibits extreme simplicity of structure, if structure that may be called which consists of a simple ma.s.s of protoplasm dest.i.tute of cell-walls, protean in form and amoeboid in its movements. This phase of the slime-mould is described as plasmodial and it is proper to designate the vegetative phase in any species, as the _plasmodium_ of the species. It was formerly taught that the plasmodium is unicellular, but more recent investigation has shown that the plasmodial protoplasm is not only multinuclear but karyokinetic; its cells divide and redivide, as do the _reproductive_ cells of plants and animals generally. Nevertheless, in its plasmodial phase, the slime-mould is hardly to be distinguished from any other protoplasmic ma.s.s, may be compared to a giant amoeba, and justifies in so far the views of those systematists who would remove the slime-moulds from the domain of the botanist altogether, and call them animals. The plasmodium is often quite large. It may frequently be found covering with manifold ramifications and net-like sheets the surface of some convenient substratum for the s.p.a.ce of several square feet.

The substance of the plasmodium has about the consistency of the white of an egg; is slippery to the touch, tasteless, and odorless. Plasmodia vary in color in different species and at different times in the same species. The prevailing color is yellow, but may be brown, orange, red, ruby-red, violet, in fact any tint, even green. Young plasmodia in certain species are colorless (as in _Diderma floriforme_), while many have a peculiar ecru-white or creamy tint difficult to define. Not only does the color change, sometimes more than once in the course of the life history of the same species, but it may be the same for several forms, which in fruit are singularly diverse indeed, so that the mere color of the plasmodium brings small a.s.sistance to the systematist. In fact, the color depends no doubt upon the presence in the plasmodium of various matters, more or less foreign, una.s.similated, possibly some of them excretory, differing from day to day.

In its plasmodial state, as has been said, the slime-mould affects damp or moist situations, and during warm weather in such places spreads over all moist surfaces, creeps through the interstices of the rotting bark, spreads between the cells, between the growth-layers of the wood, runs in corded vein-like nets between the wood and bark, and finds in all these cases nutrition in the products of organic decomposition. Such a plasmodium may be divided, and so long as suitable surroundings are maintained, each part will manifest all the properties of the whole.

Parts of the same plasmodium will even coalesce again. If a piece of plasmodium-bearing wood be brought indoors, be protected from desiccation by aid of a moist dark chamber, not too warm (70 F.), the organism seems to suffer little if any injury, but will continue for days or weeks to manifest all the phenomena of living matter. Thus, under such circ.u.mstances, the plasmodium will constantly change shape and position, can be induced to spread over a plate of moist gla.s.s, and so be transferred to the stage of a microscope, there to exhibit in the richest and most interesting and abundant fashion the streaming protoplasmic currents. As just indicated, the plasmodia follow moisture, creep from one moist substance to another, especially follow nutritive substrata. They seem also to secure in some way exclusive possession. I have never seen them interfered with by hyphae or enemies of any sort, nor do they seem to interfere with one another. Plasmodia of two common species, _Hemitrichia clavata_ and _H. vesparium_ are often side by side on the same substratum, but do not mix, and their perfected fruits presently stand erect side by side, each with its own characteristics, entirely unaffected by the presence of the other. On the other hand, it is probable that some of the forms which, judged by their different fructifications, and by this alone, are to us distinct, may be more closely related than we suspect, and puzzling phases which show the distinctive marks supposed to characterize different species are no doubt sometimes to be explained on the theory of plasmodial crossing; they are hybrids.

Under certain conditions, low temperature, lack of moisture, the plasmodium may pa.s.s into a resting phase, when it ma.s.ses itself in heaps and may become quite dry in lumps of considerable size, and so await the return of favorable conditions when former activity is quickly resumed.

Sometimes the larger plasmodia pa.s.s into the resting phase by undergoing a very peculiar change of structure. In ordinary circ.u.mstances the abundant free nuclei demonstrable in the plasmodium afford the only evidence of cellular organization. In pa.s.sing now into the condition of rest, the whole protoplasmic ma.s.s separates simultaneously into numerous definite polyhedral or parenchymatous cells, each with a well-developed _cellulose wall_.[4] When the conditions essential to activity are restored, the walls disappear, the cellulose is resorbed, and the plasmodium resumes its usual habit and structure.

The plasmodial phase of the slime-mould, like the hyphal phase of the fungus, may continue a long time; for months, possibly for years. The reason for making the latter statement will presently appear. But however long or short the plasmodial phase continue, the time of fruit, the reproductive phase, at length arrives. When this time comes, induced partly by a certain maturity in the organism itself, partly no doubt by the trend of external conditions, the plasmodium no longer as before evades the light, but pushes to the surface, and appears usually in some elevated or exposed position, the upper side of the log, the top of the stump, the upper surface of its habitat, whatever that may be; or even leaves its nutrient base entirely and finds lodging on some neighboring object. In such emergency the stems and leaves of flowering plants are often made to serve, and even fruits and flowers afford convenient resting places. The object now to be attained is not the formation of fruit alone, but likewise its speedy desiccation and the prompt dispersal of the perfected spores. Nothing can be more interesting than to watch the slime-mould as its plasmodium accomplishes this its last migration. If hitherto its habitat has been the soft interior of a rotten log, it now begins to ooze out in all directions, to well up through the crevices of the bark as if pushed by some energy acting in the rear, to stream down upon the ground, to flow in a hundred tiny streams over all the region round about, to climb all stems, ascend all branches, to the height of many inches, all to pa.s.s suddenly as if by magic charm into one widespread, dusty field of flying spores. Or, to be more exact, whatever the position ultimately a.s.sumed, the plasmodium soon becomes quiescent, takes on definite and ultimate shape, which varies greatly, almost for each species. Thus it may simply form a flat, cake-like ma.s.s, _aethalium_, internally divided into an indefinite number of ill-defined spore cases, sporangia; or the plasmodium may take the form of a simple net, _plasmodiocarp_, whose cords stand out like swollen veins, whose meshes vary both in form and size; or more commonly the whole protoplasmic ma.s.s breaks up into little spheroidal heaps which may be sessile directly on the substratum, or may be lifted on tiny stems, stipitate, which may rest in turn upon a common sheet-like film, or more or less continuous net, spreading beneath them all, the _hypothallus_. In any case, each differentiated portion of the plasmodium, portion poorly or well defined, elongate, net-like, spheroidal, elliptical, or of whatever shape, becomes at length a sporangium, spore-case, receptacle for the development and temporary preservation of the spores.[5]

The slime-moulds were formerly cla.s.sed with the gasteromycetous fungi, puff-b.a.l.l.s, and in description of their fruiting phase the terms applicable to the description of a puff-ball are still employed, although it will be understood that the structures described are not in the two cases h.o.m.ologous; a.n.a.logous only. The sporangium of the slime-mould exhibits usually a distinct _peridium_, or outer limiting wall, which is at first continuous, enclosing the spores and their attendant machinery, but at length ruptures, irregularly as a rule, and so suffers the contents to escape. The peridium may be double, varies in texture, color, persistence, and so forth, as will be more fully set forth in the several specific descriptions. The peridium blends with the hypothallus below when such structure is recognizable, either directly, when the sporangium is sessile, or by the intervention of a _stipe_. The stipe may be hollow, may contain coloring matter of some sort, or may even contain peculiar spore-like cells or spores; is often furrowed, and in some cases shows a disposition to unite or blend with the stalks of neighboring sporangia. In many cases the stipe is continued upward, more or less definitely into the cavity of the sporangium, and there forms the _columella_, sometimes simple and rounded, like the a.n.a.logous structure in the _Mucores_, sometimes as in _Comatricha_, branching again and again in wonderful richness and complexity.

Each sporangium is at maturity filled with numerous unicellular spores.

These are usually spherical, sometimes flattened at various points by mutual contact; they are of various colors, more commonly yellow or violet brown, are sometimes smooth (?), but generally roughened either by the presence of minute warts, or spines, or by the occurence of more or less strongly elevated bands dividing reticulately the entire surface. The spores are in all cases small 3-20 , and reveal their surface characters only under the most excellent lenses.

a.s.sociated with the spores in the sporangium occurs the _capillitium_.

This consists of most delicate thread-or hair-like elements, offering great variety both in form and structure. The threads composing the capillitium are not to be regarded, even when free, as cells, nor even of cellular origin; probably, as would appear from the researches of Strasburger and Harper, all forms of capillitial threads arise in connection with vacuoles in the protoplasmic ma.s.s. "Whether the thread is hollow or solid, simple or branched, free or connected with the peridium or a columella,--these are entirely secondary conditions, depending on the extent and form of the vacuoles."[6] They may occur singly or be combined into a net, they may be terete or flat, attached to the peridial wall or free, simple or adorned with bands or spires and k.n.o.bs in every variety, uniform or profusely knotted and thickened at intervals, and burdened with calcic particles. In many cases, the capillitium contributes materially to the dispersal of the spores; in others, it doubtless contributes mechanically to the support of the peridial wall, and renders so far persistent the delicate sporangium.

For more exact description the reader is again referred to the specific delineations which follow.

The transition from phase to phase requires, as intimated, no great length of time. _Tilmadoche polycephala_ completed the transition from vegetative to fruiting phase in less than twelve hours.

The germination of the spores ensues closely upon their dispersal or maturity and is unique in many respects.[7] The wall of the spore is ruptured and the protoplasmic content escapes as a zoospore indistinguishable so far from an amoeba, or from the zoospore of our chytridiaceous fungi. This amoeboid zoospore is without cell-wall, changes its outline, and moves slowly by creeping or flowing from point to point. At this stage many of the spores a.s.sume each a flagellate cilium, and so acquire power of more rapid locomotion. The zoospores, whether ciliate or not, thus enjoy independent existence and are capable of continuing such existence for some time, a.s.similating, growing, and even reproducing themselves by simple fission, over and over again. This takes place, of course, only in the presence of suitable nutrient media.

Nevertheless the spores of many species germinate quickly simply in water, and a drop suspended in the form of the ordinary drop-culture on a cover-gla.s.s affords ample opportunity. In the course of time, usually not more than two or three days, the swarm spores cease their activity, lose their cilia, and come to rest, exhibiting at most nothing more than the slow amoeboid movement already referred to. In the course of two or three days more, in favorable cases, the little spores begin to a.s.semble and flow together; at first into small aggregations, then larger, until at length all have blended in one creeping protoplasmic ma.s.s to form thus once again the plasmodium, or plasmodial phase with which the round began. Small plasmodia may generally be thus obtained artificially from drop-cultures. Such, however, in the experience of the writer, are with difficulty kept alive. Hay infusions, infusions of rotten wood, etc., may sometimes for a time give excellent results.

The spores of _Didymium crustaceum_ were sown upon a heap of leaves in autumn. An abundant display of the same species followed in the next June; but, of course, the intervening phases were not observed. The most satisfactory studies are obtained by plasmodia carefully brought in directly from the field. A plasmodium that appeared suddenly and pa.s.sed to fruit on agar in a petri dish offers a valuable suggestion for further research.

With such a life-history as that thus briefly sketched, it is small wonder that the taxonomic place of the slime-moulds is a matter of uncertainty, not to say perplexity. So long as men studied the ripened fruit, the sporangia and the spores, with the marvellous capillitium, there seemed little difficulty; the myxomycetes were fungi, related to the puff-b.a.l.l.s, and in fact to be cla.s.sed in the same natural order. The synonymy of some of the more noticeable species affords a very interesting epitome of the history of scientific thought in this particular field of investigation. Thus the first described slime-mould identifiable by its description is Lycogala epidendrum (Buxbaum) Fries, the most puff-ball looking of the whole series. Ray, in 1690, called this _Fungus coccineus_. In 1718, Ruppinus described the same thing as _Lycoperdon sanguineum_; Dillenius at about the same time, as _Bovista miniata_; and it was not until 1729, that Micheli so far appreciated the structure of the little puff-ball as to give it a definite, independent, generic place and t.i.tle, _Lycogala globosum_ ..., etc.[8]

But Micheli's light was too strong for his generation. As Fries, one hundred years later quaintly says, ... "immortalis Micheli tam claram lucem accendit ut succesores proximi eam ne ferre quidem potuerint."

Notwithstanding Micheli's clear distinctions, he was entirely disregarded, and our little Lycogala was dubbed _Lycoperdon_ and _Mucor_ down to the end of the century; and so it was not till 1790 that Persoon comes around to the standpoint of Micheli and writes _Lycogala miniata_.

Fries himself, reviewing the labors of his predecessors all, grouped the slime-moulds as a sub-order of the gasteromycetes and gave expression to his view of their nature and position when he named the sub-order _Myxogastres_. In 1833, Link, having more prominently in mind the minuteness of most of the species collocated by Fries, and perceiving perhaps more clearly even than the great mycologist the entire independence of the group, suggested as a subst.i.tute for the sub-order _Myxogastres_, the order _Myxomycetes, slime-moulds_. Link's decision pa.s.sed unchallenged for nearly thirty years. The slime-moulds were set apart by themselves; they were fungi without question and, of course, plants.

If the hypha is the morphological test of a fungus, then it is plain that the slime-moulds are not fungi. No myxomycete has hyphae, nor indeed anything at all of the kind. Nevertheless, there are certain parasitic fungi, _Chytridiaceae_ for example, whose relationships plainly ent.i.tle them to a place among the hyphate forms that have no hyphae whatever in the entire round of their life-history. These are, however, exceptional cases and really do not bear very closely on the question at issue.

Physiologically, the fungi are incapable of independent existence, being dest.i.tute of chlorophyl. In this respect the slime-moulds are like the fungi; they are nearly all saprophytes and absolutely dest.i.tute of chlorophyl. Unfortunately this physiological character is identically that one which the fungi share with the whole animal world, so that the startling inquiry instantly rises, are the slime-moulds plants at all?

Are they not animals? Do not their amoeboid spores and plasmodia ally them at once to the amoeba and his congeners, to all the monad, rhizopodal world? This is the position suggested by DeBary in 1858, and adopted since by many distinguished authorities, among whom may be mentioned Saville Kent, of England, and Dr. William Zopf, of Germany, in _Die Pilzthiere_, 1885. Rostafinski was a pupil of DeBary's. However, his volume on the slime-moulds was written after leaving the laboratory; and no doubt with the suggestion of his master still before his mind, he adopts the t.i.tle Mycetozoa, as indicating a closer relationship with the animal world, but our leading authority really has little to say in regard to the matter.[9]

Dr. Schroeter, a recent writer on the subject, after showing the probable connection between the phycochromaceous Algae and the simplest colorless forms, namely, the _Schizomycetes_, goes on to remark: "At the same point where the Schizomycetous series take rise, there begin certain other lines of development among the most diminutive protoplasmic ma.s.ses.... Through the amoebae one of these lines gives rise on the one hand to rhizopods and sponges in the animal kingdom, on the other to the _Myxomycetes_ among the fungi." This ranges the Myxomycetes, in origin at least, near the _Schizomycetes_.

The brilliant studies of Dr. Thaxter, resulting in the discovery and recognition of a new group, a new order of the schizomycetes, strikingly confirm the judgment of Schroeter.[10] Here we have forms that strangely unite characteristics of both the groups in question. If on the one hand the _Myxobacteria_ are certainly schizomycetes, on the other they just as certainly offer in their developmental history "phenomena closely resembling those presented by plasmodia or pseudo-plasmodia...." Now the schizophytes certainly pa.s.s by gradations easy to the filamentous algae, and so to relationship with the plants, and the discovery of the _Myxobacteriacae_, brings the myxomycetes very near the vegetable kingdom if not within it.