All authorities agree that the myxomycetes have no connection in the direction of upward development, "keinen Anschluss nach oben," if then their only relationship with other organisms is to be found at the bottom (centre) of the series only, it is purely a matter of indifference whether we say plant or animal, for at the only point where there is connection there is no distinction.
But why call them either animals or plants? Was Nature then so poor that forsooth only two lines of differentiation were at the beginning open for her effort? May we not rather believe that life"s tree may have risen at first in hundreds of tentative trunks of which two have become in the progress of the ages so far dominant as to entirely obscure less progressive types? The Myxomycetes are independent; all that we may attempt is to a.s.sert their near kinship with one or other of life"s great branches.
The cellulose of the slime-mould looks toward the world of plants. The aerial fructification and stipitate habit of the higher forms tends in the same direction. The disposition to attach themselves to some fixed base is a curious characteristic of plants, more p.r.o.nounced as we ascend the scale; but by no means lacking in many of the simplest, diatoms, filamentous algae, etc., and it is quite as reasonable to call a vorticella, or a stentor, by virtue of his stipitate form and habit, a plant as to call a slime-mould an animal because in one stage of its history it resembles an amoeba. The total life of an organism in any case must be taken into account.[11] At the outset plants and animals are alike; there is no doubt about it; they differ in the course of their life-histories. The plasmodium is the vegetative phase of the slime-mould. It needs no cell-walls of cellulose, no more than do the dividing cells of a lily-endosperm; both are nourished by organic food and resort to walls only as conditions change. The possession of walls is an indication of some maturity. In the slime-mould the a.s.sumption of walls is indeed delayed. Walls at length appear and when they do come they are like those of the lily; they are cellulose. The myxomycetes may be regarded as a section of the organic world in which the forces of heredity are at a maximum whatever those forces may be. Slime-moulds have in smallest degree responded to the stimulus of environment. They have, it is true, escaped the sea, the fresh waters in part, and become adapted to habitation on dry land, but nothing more. It is instructive to reflect that even in her most highly differentiated forms the channel which Nature elects for the transmissal of all that heredity may bestow, is naught else than a minute ma.s.s of naked protoplasm. Nature reverts, we say, to her most ancient and simple phases, and heredity is still consonant with apparent simplicity; apparent we say, for as becomes increasingly evident, nothing that lives is simple!
The fact is the Myxomycetes const.i.tute an exceedingly well-defined group, and the question of relationship in any direction need not much perplex the student. Least of all is the question to be settled by anybody"s dictum, which is apt to be positive inversely in proportion to the speaker"s acquaintance with the subject. No one test can be applied as a universal touchstone to separate plants from animals. Such is simply _pet.i.tio principii_. Nor is there any advantage at present apparent in attempts to a.s.sociate slime-moulds with other presumably related groups. Saville Kent"s effort to join them with the sponges was not happy, and Dr. Zopf"s a.s.sociation of the slime-moulds and monads appears forced, at best; for when it comes to the consideration of the former, their systematic and even morphological treatment, he is compelled to deal with them by themselves under headings such as "Eumycetozoen," "Hohere Pilzthiere," etc. One rather commends the discreetness of DeBary, whose painstaking investigations first called attention to the uncertain position of the group. After reviewing the results of all his labors DeBary does not quite relegate the slime-moulds to the zoologist for further consideration, but simply says:[12] "From naked amoeba, with which the Mycetozoa (=Myxomycetes) are connected in ascending line, the zoologists with reason derive the copiously and highly developed section of the sh.e.l.l-forming Rhizopoda.... And since there are sufficient grounds for placing the rhizopods outside the vegetable and in the animal kingdom, and this is undoubtedly the true position for the amoebae, which are their earlier and simpler forms, the Mycetozoa, which _may_ be directly derived from the same stem, are at least brought very near to the domain of zoology."
Notwithstanding all the controversy in regard to the matter, the study of the slime-moulds still rests chiefly with the botanists. A simple phylogenetic scheme for thallophytes is offered in the Strasburger text as follows:--
THALLOPHYTA
1. SCHIZOPHYTA BACTERIA CYANOPHYCEae
2. FLAGELLATA { MYXOMYCETES { PERIDINEae _a_ { CONJUGATae { HETEROCONTae
{ CHLOROPHYCEae _b_ { CHARACEae
3. RHODOPHYCEae
4. FUNGI
About 500 species of slime-moulds have been described. Saccardo enumerates 443, inclusive of those denominated doubtful or less perfectly known. These 443 species are distributed among 47 genera, of which 15 are represented by but a single species each,--monotypic. In the United States there have been recognized about 300 species. Of those here described, some are almost world-wide in their distribution, others are limited to comparatively narrow boundaries. The greater number occur in the temperate regions of the earth, although many are reported from the tropics, and some even from the arctic zone. Schroeter found _Physarum cinereum_ at North Cape. Our Iowa forms are much more numerous in the eastern, that is, the wooded regions of the state. _Physarum cinereum_ has however been taken on the untouched prairie, and on the western deserts, as also _Physarum contextum_ on the decaying stem of _Calamagrostis_, far from forest.
As to the economic importance of our myxomycetes, there is no long chapter to write. Fries says: "Usu in vita communi parum admodum sese commendant, sed in oeconomia naturae certe non spernendi. Multa insectorum genera ex eorum sporidiis unica capiunt nutrimenta." However this may be, there is one species which has come to light since Fries"s day which is the source of no inconsiderable mischief to the agriculturist. _Plasmodiophora bra.s.sicae_ occasions the disease known as "club-root" in cabbage, and has been often made the subject of discussion in our agricultural and botanical journals.[13] Aside from the injurious tendencies, possible or real, of the forms mentioned, I know not that all other slime-moulds of all the world, taken all together, affect in any slightest measure the hap or fortune of man or nation. And yet, if in the economic relations of things, man"s intellectual life is to be considered, then surely come the uncertain myxos, with their fascinating problems proffered still in forms of unapproachable delicacy and beauty, not without inspiration.
COLLECTION AND CARE OF SLIME-MOULD MATERIAL
On this subject a word may here be appropriate. As just now intimated, specimens may be taken at the appropriate season in almost any or every locality. Beginning with the latter part of May or first of June, in the Northern states, plasmodia are to be found everywhere on piles of organic refuse: in the woods, especially about fallen and rotting logs, undisturbed piles of leaves, beds of moss, stumps, by the seeping edge of melting snow on mountain sides, by sedgy drain or swamp, nor less in the open field where piles of straw or herbaceous matter of any sort sinks in undisturbed decay. Within fifty years tree-planting in all the prairie states has greatly extended the range of many more definitely woodland species, so that species of _Stemonitis_, for instance, are common in the groves on farms far into Nebraska and Dakota. In any locality the plasmodia pa.s.s rapidly to fruit, but not infrequently a plasmodium in June will be succeeded in the same place by others of the same species, on and on, until the cold of approaching winter checks all vital phenomena. The process of fruiting should be watched as far as possible, and for herbarium material, allowed to pa.s.s to perfection in the field.
Specimens collected should be placed immediately in boxes in such a way as to suffer no injury in transport; beautiful material is often ruined by lack of care on the part of the collector. Once at the herbarium, specimens may be mounted by gluing the supporting material to the bottom of a small box. Boxes of uniform size and depth may be secured for the purpose. Some collectors prefer to fasten the specimen to a piece of stiff paper, of a size to be pressed into the box snugly, but which may be removed at pleasure. Every pains must in any case be taken to exclude insects. Against such depredators occasional baking of the boxes on the steam radiator in winter is found to be an efficient remedy.
For simple microscopic examination it will be found convenient to first wet the material with alcohol on the slide, then with a weak solution of pota.s.sic hydrate, to cause the spores and other structures to a.s.sume proper plumpness. A little glycerine may be added or run under the cover if it is desired to preserve the material for further or prolonged study. For permanent mounting nothing in most cases is better than glycerine jelly. As a preparation, the material should lie for some time in Hantsch"s fluid,[14] opportunity being given for evaporation of the alcohol and water. When the material shows the proper clearness and fulness, it may be mounted in jelly in the usual way. Kaiser"s formula gives beautiful results. After mounting, the preparation should be sealed with some good cement, as Hollis"s glue.
FOOTNOTES:
[4] DeBary, _Morphology and Biology of the Fungi,_ p. 428.
[5] See, however, _Ceratiomyxa_, p. 18, following.
[6] Harper in _Botanical Gazette_, Vol. x.x.x., p. 219.
[7] The following germination periods are furnished by Dr. Constantineanu (_Inaugural Dissertation ueber die Entwickelungsbedingungen der Myxomyceten_; Halle, 1907).
_Reticularia lycoperdon_ 30 to 60 min.
_Fuligo ovata_ 30 to 90 min.
_Stemonitis splendens_ 5 to 6 hrs.
_Perichaena depressa_ 5 to 8 hrs.
_Amaurochaete atra_ 6 to 10 hrs.
_Arcyria incarnata_ 8 to 10 hrs.
_Lycogala epidendrum_ to 60 hrs.
_Physarum didermoides_ 1 to 10 da.
_Dictydium cancellatum_ 1 to 20 da.
These records are for sowings in drop cultures, in distilled water, kept at temperature of 65-70 F. (18-20 C.).
Our own experiments have been made both with distilled water and tap-water with the advantage in favor of the latter. _Dictydium cancellatum_ germinates in tap-water at temperature 70-80 F. in 12-15 hours fresh from the field. _Fuligo ovata_ spores were all swarming in about one hour at the same temperature. Jahn (_Myxomycetenstudien; Ber.
der Deutschen Bot. Ges._ Bd. XXIII., p. 495) finds that the germination in some cases as _Stemonitis_ species, is hastened by wetting, then drying, then wetting again.
Pinoy thinks microbes aid in germination (_Bull. Soc. Myc. de France_ T.
XVIII.).
[8] The plasmodium in this case chances to be red, scarlet, etc.
[9] "Die Myxomyceten sind ebenso den Pilzen wie den echten Thieren verwandt."--Rostafinski; closing sentence of the _Versuch_, thesis for his doctorate at the University of Strasburg, 1873.
[10] _Botanical Gazette_, XVII., pp. 389, etc.; 1892.
[11] Researches of Olive, _Trans. Wis. Acad. Sci., Arts and Let._, XV., Pt. 2, p. 771, and of Jahn, _Ber. d. Deutsch Bot. Ges._ XXVI., p. 342, and XXIX., p. 231, demonstrate synapsis, and accordingly some form of alternation among the slime-moulds. From the protracted and painstaking investigation of the German author it appears that in _Didymium_ at least, and probably _Badhamia_ synapsis immediately precedes spore-formation as in _Ceratiomyxa_; that the amoeboid issue of the spores are haploid; the nuclei of the plasmodium, diploid; that the ordinary vegetative plasmodium is accordingly sporophytic. That is, the sporophytic phase is dominant, as in higher plants.
[12] Cf., 1884, _Ver. Morph. u. Biol. der Pilz. Mycet. u. Bact._, p.
478. Italics, in quotations, ours.
[13] See _Journal of Mycology_, Washington, D. C., Vol. VII., No. 2; also _Bulletin No. 66, Agric. Station of Vermont_. See also Bull. _33 Arizona Agric. Ex. Station_: An Inquiry into the Cause and Nature of Crown-Gall. J. W. Tuomey. Also _Bull. Torrey Bot. Club_, Vol. 21, p. 26, where it appears that club-root may attack crucifers generally.
Professor B. M. Duggar in _Fungous Diseases of Plants_, pp. 97-102, gives to club-root an ill.u.s.trated chapter.
[14]
Hantsch"s Fluid:-- Alcohol 90% three parts Water two parts Glycerine one part
THE NORTH AMERICAN SLIME-MOULDS
THE MYXOMYCETES (_Link_) _DeBary_
Chlorophyl-less organisms whose vegetative phase consists of a naked ma.s.s of multinuclear protoplasm, the _plasmodium_; reproduced by spores which are either free or more commonly enclosed in sporangia, and which on germinating produce ciliated or amoeboid zoospores, whose coalescence gives rise to the plasmodium.
The Myxomycetes are,--
_A._ _Parasites_, in the cells of living plants PHYTOMYXINae
_B._ _Saprophytes_, developed in connection with decaying vegetable matter:
_a._ With free spores EXOSPOREae