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MYCETOZOA (Myxomycetes, Schleimpilze)
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See also:MYCETOZOA (Myxomycetes, Schleimpilze) , in See also:zoology, a See also:group of organisms reproducing themselves by spores. These are produced in or on sporangia which are formed in the See also:air and the spores are distributed by the currents of air. They thus differ from other spore-bearing members of the See also:animal See also:kingdom (which produce their spores while immersed in See also:water or, in the See also:case of parasites, within the fluids of their hosts), and resemble the See also:Fungi and many of the See also:lower See also:green See also:plants. In relation with this See also:condition of their fructification the structures formed at the spore-bearing See also:stage to contain or support the spores See also:present a remarkable resemblance to the sporangia of certain See also:groups of Fungi, from which, however, the Mycetozoa are essentially different. Although the sporangial and some other phases have See also:long been known, and See also:Fries had enumerated 192 See also:species in 1829, the See also:main features of their See also:life-See also:history were first worked out in 1859–186o by de Bary (1 and 2). He showed that in the Mycetozoa the spore hatches out as a See also:mass of naked See also:protoplasm which almost immediately assumes a See also:free-See also:swimming flagellate See also:form (zoospore), that after multiplying by See also:division this passes into an amoeboid phase, and that from such amoebae the plasmodia arise, though the mode of their origin was not ascertained by him. The plasmodium of the Mycetozoa is a mass of See also:simple protoplasm, without a differentiated envelope and endowed with the See also:power of active locomotion. It penetrates the interstices of decaying See also:vegetable See also:matter, or, in the case of the species Badhamia utricularis, spreads as a film on the See also:surface of living fungi; it may grow almost indefinitely in See also:size, attaining under favourable conditions several feet in extent. It constitutes the dominant phase of the life-history. From the plasmodium the sporangia take their origin. It was Cienkowski who (in 1863) contributed the important fact that the plasmodia arise by the See also:fusion with one another of See also:numbers of individuals in the amoeboid phase—a mode of origin which is now generally recognized as an essential feature in the conception of a plasmodium, whether as occurring among the Mycetozoa or in other groups (7). De Bary clearly expressed the view that the life-history of the Mycetozoa shows them to belong not to the vegetable but to the animal kingdom. The individual sporangia of the Mycetozoa are, for the most See also:part, See also:minute structures, rarely attaining the size of a See also:mustard-See also:seed, though, in the composite form of aethalia, they may form cake-like masses an See also:inch or more across (fig. 21). They are found, stalked or sessile, in small clusters or distributed by the thousand over a wide See also:area many feet in See also:diameter, on the bark of decaying trees, on dead leaves or sticks, in See also:woods and shrubberies, among the stems of plants on wet See also:moors, and, generally, at the surface in localities where there is a substratum of decaying vegetable matter sufficiently moist to allow the plasmodium to live. Tan-heaps have long been known as a favourite See also:habitat of Fuligo septica, the plasmodia of which, emerging in See also:bright yellow masses at the surface See also:prior to the sporangial (in this case aethalial) phase, are known as " See also:flowers of tan." Thefilm-like, See also:expanded condition of the plasmodium, varying in See also:colour in different species and traversed by a network of vein-like channels (fig. 5), has long been known. The plasmodial stage was at one See also:time regarded as representing a distinct group of fungi, to which the generic name Mesenterica was applied. The species of Mycetozoa are widely distributed over the See also:world in temperate and tropical latitudes where there is sufficient moisture for them to grow, and they must be regarded as not inconsiderable agents in the disintegrating processes of nature, by which complex organic substances are decomposed into simpler and more See also:stable chemical groups. See also:Classification.—The Mycetozoa, as here understood, fall into three main divisions. The Endosporeae, in which the spores are contained within sporangia, form together with the Exosporeae, which See also:bear their spores on the surface of sporophores, a natural group characterized by forming true plasmodia. They constitute the Euplasmodida. See also:Standing apart from them is the small group of the See also:mould-like Sorophora, in which the amoeboid individuals only come together immediately prior to spore-formation and do not completely fuse with one another. A number of other organisms living on vegetable and animal bodies, alive or dead, and leading an entirely aquatic life, are included by Zopf (31) under the Mycetozoa, as the " Monadina," in distinction from the " Eumycetozoa," consisting of the three groups above mentioned. The See also:alliance of some of these (e.g. Protomonas) with the Mycetozoa is probable, and was accepted by de Bary, but the relations of other Monadina are obscure, and appear to be at least as See also:close with the See also:Heliozoa (with which many have in fact been classed). The limits here adopted, following de Bary, include a group of organisms which, as shown by their life-history, belong to the animal stock, and yet alone among animals' they have acquired the See also:habit, widely found in the vegetable kingdom, of developing and distributing their spores in air. Class MYCETOZOA. Sub-class I.—EUPLASMODIDA 2 Division I. Endosporeae. See also:Cohort 1.—Amaurosporales. Sub-cohort I.—Calcarineae. See also:Order I. Physaraceae. Genera: Badhamia, Physarum, Physarella, Trichamphora, Erionema, Cienkowskia, Fuligo, Craterium, Leocar pus, Chondrioderma, Diachaea. Order 2. Didymiaceae. Genera: See also:Didymium, Spumaria, Lepidoderma. Sub-cohort 2.—Amaurochaetineae. Order 1. Stemonitaceae. Genera: Stemonitis, Comatricha, Ener- thenema, Echinostelium, Lamproderma, Clastoderma. Order 2. Amaurochaetaceae. Genera: Amaurochaete, Brefeldia. Cohort 2.—Lamprosporales. Sub-cohort I.—Anemineae. Order 1. Heterodermaceae. Genera: Lindbladia, Cribraria, Dictydium. Order 2. Licaeceae. Genera : Licea, Orcadella. Order 3. Tubulinaceae. Genera: Tubulina, Siphoptychium, Alwisia. Order 4. Reticulariaceae. Genera: Dictydiaethalium, Enteridium, Reticularia. Order 5. Lycogalaceae. Genus: Lycogala. Sub-cohort 2.—Calonemineae. Order 1. Trichiaceae. Genera: Trichia, Oligonema, Hemitrichia, Cornuvia. Order 2. Arcyriaceae. Genera: Arcyria, Lachnobolus, Perichaena. Order 3. Margaritaceae. Genera: See also:Margarita, Dianema, Prototrichia, Listerella. Division 2. Exosporeae. Order I. Ceratiomyxaceae. Genus: Ceratiomyxa. Sub-class 2.—SOROPHORA. Order 1. Guttulinaceae. Genera: Copromyxa, Guttulina, Gultulinopsis. Order 2. Dictyosteliaceae. Genera: Dictyostelium, Acrasis, Poly sphondylium. ' Bursulla, a member of Zopf's Monadina, likewise forms its spores in air. 2 The classification of the Euplasmodida here given is that of A. and G. See also:Lister (22), the outcome of a careful study of the group extending over more than twenty-five years. The writer of this See also:article desires to See also:express his indebtedness to the opportunities he has had of becoming See also:familiar with the See also:work of his See also:father, Mr A. Lister, F.R.S., whose views on the See also:affinities and life-history of the Mycetozoa he has endeavoured herein to summarize. LIFE-HISTORY OF THE MYCETOZOA EUPLASMODIDA Endosporeae. We may begin our survey of the life-history at the point where the spores, See also:borne on currents of air, have settled among wet decaying vegetable matter. Shrunken when dry, they rapidly absorb water and resume the spherical shape which is found in nearly all species. Each is surrounded by a spore See also:wall, sheltered by which the protoplasm, though losing moisture by drying, may remain alive for as many as four years. In several cases it has been found to give the chemical reaction of See also:cellulose. It is smooth or variously sculptured according to the species. Within the protoplasm may be seen the See also:nucleus, and one or more contractile vacuoles make their See also:appearance. After the spore has lain in water for a See also:period varying from a few See also:hours to a See also:day or two the wall bursts and the contained protoplasm slips out and lies free in the water as a minute colourless mass, presenting amoeboid movements (fig. c). It soon assumes an elongated piriform shape, and a flagellum is See also:developed at the narrow end, attaining a length equal to the See also:rest of the See also:body. The minute zoospore, thus equipped, swims away with a characteristic dancing See also:motion. The protoplasm is granular within but hyaline externally (fig. 1, d). The nucleus, lying at the end of the body where it tapers into the flagellum, is limited by a definite wall and contains a nuclear network and a nucleolus. It often presents the appearance of being See also:drawn out into a point towards the flagellum, and a See also:bell-like structure [first described by Plenge (27)j, staining more darkly than the rest of the protoplasm, extends from the See also:base of the flagellum and invests the nucleus (fig 2, a and c). The other end of the zoospore may be evenly rounded (fig. 1, d) or it may be produced into See also:short pseudo-podia (fig. i, e). By means of these a, the zoospore captures bacteria panicea, stained. contractile vacuole is also present In a and c the bell-like strut- near the See also:hind end. Considerable See also:ture Investing the nucleus is See also:movement may be observed among clearly seen. the granules of the interior, and in the large zoospores of Amaurochaete atra this may amount to an actual streaming, though without the See also:rhythm characteristic of the plasmodial stage. Other shapes may be temporarily assumed by the zoospore. Attaching itself to an See also:object it may become amoeboid, either with (fig. 1,f) or without (fig. 2, c) the temporary retraction of the flagellum; or it may take an elongated slug-like shape and creep with the flagellum extended in front, with tactile and apparently exploratory movements. That the zoospores of many species of the Endosporeae feed on bacteria has been shown by A. Lister (18). New See also:light has recently been thrown on the matter by Pinoy (26), who has worked chiefly with Sorophora, in which, as shown below, the active phase of the life-history is passed I Figures 1, 4, and 11–22 are from the See also:British Museum See also:Guide to the British Mycetozoa. The other figures are from Lankester's See also:Treatise on Zoology, part t. Introduction and See also:Protozoa. Fascicle 1. Article Mycetozoa.mainly in the See also:state of isolated amoebae. Pinoy finds that the amoebae of this group live on particular species of bacteria, and that the presence of the latter is a necessary condition for the develop-' ment of the Sorophora, and even (as has been recognized by other workers) for the hatching of their spores. Pinoy's results indicate, though not so conclusively, that bacteria are likewise the essential See also:food of the Euplasmodida in the See also:early phases of their life-history. The zoospores do, however, ingest other solid bodies, e.g. See also:carmine granules (Saville See also:Kent, tg). The zoospores multiply by binary fission, the flagellum being withdrawn and the nucleus undergoing mitotic division, with the formation of a well-marked achromatic spindle (fig. 3). , It is probable that fission occurs more than once in the zoospore . stage; but there is not satisfactory See also:evidence to show how often it may be repeated? At this, as at other phases of the life-history, a resting stage may be assumed as the result of drying, but also from other and unknown causes. The flagel- lum is withdrawn and the protoplasm, becoming spherical, secretes a cyst wall. The organism thus passes into the condition of a microcyst, from which when dry it may be awakened to renewed activity by wetting. At the end of the zoospore stage the organism finally withdraws its flagellum and assumes the amoeboid shape. It is now known as an amoebula. The amoebulae become endowed, as was first recognized by Cienkowski, with mutual attraction, and on After A. Lister. See also:meeting fuse with one another. Fig. 4 represents a group of such amoebulae. Several have already See also:united to form a See also:common mass, to which others, still free, are See also:con-verging. The protoplasmic mass thus arising is the plasmodium. The fusion between the protoplasmic bodies of the amoebulae which unite to form it is See also:complete. Their nuclei may be traced for some time in the See also:young plasmodium and no fusion between them has been observed at this stage (20). As the plasmodium increases in size by the addition of amoebulae the task of following the See also:fate of the individual nuclei by See also:direct observation becomes impossible. The appearance of an active plasmodium of Badhamia utricularis, which, as we have seen, lives and feeds on certain fungi, is shown in fig. g. It consists of a film of protoplasm, of a bright yellow colour, varying in size up to a See also:foot or more in diameter. It is traversed by a network of branching and anastomosingchannels, which See also:divide up and are gradually lost as they approach the margin where the, protoplasm forms a See also:uniform and lobate border. Elsewhere the main trunks of the network may See also:lie free with little or no connecting film between them and their neighbours. The plasmodia of other species, which live in the interstices of decaying vegetable matter, are less easily observed, but on emerging on the surface prior to 2 Pinoy states (26) that the spores of Spumaria See also:alba, cultivated with bacteria on solid See also:media, See also:hatch out into amoebae, which under these conditions do not assume the flagellate stage. The See also:amoeba from a spore was observed to give rise by three successive divisions to eight amoebulae. After A. Lister. a, The unruptured spore. b, The protoplasmic contents of the spore emerging. It contains a nucleus with the (light) nucleolus, and a contractile vacuole (shaded). c, The same, free from the spore wall. d, Zoospore, with nucleus at the base of the flagellum, and contractile vacuole. e, A zoospore with pseudopodial processes at the posterior end, to one of which a bacillus adheres. Two See also:digestive vacuoles in the interior contain ingested bacilli. f, Amoeboid phase flagellum. with retracted a °yJb After A. Lister. spore formation they present an essentially similar appearance. There is, however, See also:great variety in the degree of concentration or expansion presented by plasmodia, in relation with food See also:supply, moisture and other circumstances. The plasmodia move slowly about over on in the substratum, concentrating in regions where food supply is abundant, and leaving those where it is exhausted. On examining under the See also:microscope a film which has spread over a See also:cover-slip, the channels are seen to be streams of rapidly moving granular protoplasm. This movement is rhythmic to See also:character, being directed alternately towards the margin of an advancing region of the plasmodium, and away from it. As a channel is watched the stream of granules is seen to become slower, and after a momentary pause to begin in the opposite direction. In an active plasmodium the duration of the flow in either direction varies from a minute and a See also:half to two minutes, though it is always longer when in the direction of the See also:general advance over the substratum. When the flow of the protoplasm is in this latter direction the border be-comes turgid, and lobes of hyaline protoplasm are seen (under a high magnification) to start forward, and soon to become filled with granular contents. When the flow is reversed, the margin becomes thin from the drainage away of its contents. A delicate hyaline layer invests the plasmodium, and is apparently less fluid than the material flowing in the channels. The phenomena of the rhythmic movement of the protoplasm are not inconsistent with the view that they result from alternating contraction and relaxation of the See also:outer layer in different regions of the plasmodium, but any dogmatic statement as to their See also:causation appears at present inadvisable. a, Part of a stained Plasmodium of Badhamia vtricularis. n, Nuclei. b, Nuclei, some in See also:process of simple (amitotic) division. c, Part of a Plasmodium in which the nuclei are in simultaneous mitotic division. df, Other stages in this process. Minute contractile vacuoles may be seen in great numbers in the thin parts of the plasmodium between the channels. In stained preparations nuclei, varying (in Badhamia utricularis) from 2.5 to 5 micrornillimeters in diameter, are found abundantly in the granular protoplasm (fig. 6, b). They contain a nuclear reticulum and one or more well-marked nucleoli. In any stained plasmodium some nuclei may be found, as shown in the figure b, which appear to be in some stage of simple (amitotic) division, and this is, presumably, the See also:chief mode in which the number of the nuclei keeps See also:pace with the rapidly growing plasmodium. There is, however, another mode of nuclear division in the plasmodium which has hitherto been observed in one recorded instance (19, p. 541), the mitotic (fig. 6, c f), and this appears to befall all the nuclei of a plasmodium simultaneously. What the relation of these two modes of nuclear division may be to the life-history is obscure.
That the amitotic is the usual mode of nuclear division is indicated by the very frequent occurrence of these apparently dividing nuclei and also by the following experiment. A plasmodium of Badhamia utricularis spreading over pieces of the fungus Auricularia was observed to increase in size about fourfold in fourteen hours, and during this time a small See also:sample was removed and stained every See also:quarter of an See also:hour. The later stainings showed no diminution in the number of nuclei in proportion to the protoplasm, and yet none of the sample showed any sign of mitotic division (20, p. 9). It would appear therefore that the mode of increase of the nuclei during this period was amitotic.
Prowazek (28) has recently referred to nuclear stages, similar to those here regarded as of amitotic division, but has interpreted them as nuclear fusions. He does not, however, discuss the mode of multiplication of nuclei in the plasmodium.
In the group of the Calcareae, granules of carbonate of See also:lime are abundant in the plasmodia, and in all Mycetozoa other granules of undetermined nature are present. The colour of plasmodia varies in different species, and may be yellow, See also: See also:Nutrition.—The plasmodium of Badhamia utricularis, advancing over the pilei of suitable fungi, feeds on the superficial layer dissolving the walls of the hyphae (17). The protoplasm may be seen to contain abundant See also:foreign bodies such as spores of fungi or sclerotium cysts (vide infra) which have been taken in and are undergoing digestion. It has been found experimentally (It) that pieces of coagulated proteids are likewise taken in and digested in vacuoles. On the other See also:hand it has been found that plasmodia will live, ultimately producing sporangia, in nutrient solutions (9).1 It would appear therefore that the nutrition of plasmodia is effected in part by the ingestion of solid foodstuffs, and in part by the absorption of material in See also:solution, and that there is great variety in the complexity of the substances which serve as their food. Sclerotium.—As the result of drought, the plasmodium, having become much denser by loss of water, passes into the sclerotial condition. See also:Drawing together into a , .~ thickish layer, the protoplasm divides m°l up into a number of distinct masses, ~'. • w.~~':~`:.-•each containing some to to 20 nuclei, <f,"Et:;.c.4; and a cyst wall is excreted See also:round each„: mass (fig. 7). The whole has now a f;.r hard brittle consistency. In this state r 4f'-,-''~ ....:w ,; the protoplasm will remain alive for ~a i Syr' ~s" t.4:r` two or three years. On the addition FIG. 7.—See also:Section of the of water the cyst walls are ruptured plasmodium of Badhamia and in part absorbed, their contents join together, and the active streaming utricularis when passing into condition of the plasmodium is re- the condition of sclerotium. sumed. It is to be noted, however, n, The nuclei contained in that the sclerotial condition may be the young sclerotial cysts. assumed under other conditions than dryness, and sclerotia may even be formed in water. The existence of the sclerotial stage affords a ready means of obtaining the plasmodium for experimental purposes. If a cultivation of the plasmodium of Badhamia utricularis on suitable fungi (Stereum, Auricularia) is allowed to become partially dry the plasmodium draws together and would, if drying were continued, pass into the sclerotial stage on the fungus. If now strips of wet blotting-See also:paper are placed so as to See also:touch the plasmodium, the latter, attracted by the moisture, crawls on the blotting-paper. If this is now removed and allowed to dry rapidly, the plasmodium passes into sclerotium on it.' By this means the plasmodium is removed from the partially disintegrated and decayed fungus on which it has been feeding, and a clean sclerotium is obtained, which, as above stated, remains alive for years (21, p. 7). An easy method for obtaining small plasmodia for microscopic examination is to scatter small fragments, scraped from a piece of the hard sclerotium, over cover-slips wetted with See also:rain-water and kept in a moist See also:atmosphere. In twelve to twenty-four hours small plasmodia will be seen spreading on the cover-slips and these may be mounted for observation. The plasmodial stage ends by the formation of the sporangia. The plasmodium withdraws from the interstices of the material among which it has fed, and emerges on the surface in a diffuse or concentrated mass. In the case of Badhamia utricularis it may with-draw from the fungus on which it has been feeding, or See also:change into sporangia on it. The mode of formation of the sporangia will be described in the case of Badhamia, some of the chief See also:differences in the process and in the structure of the sporangia in other forms being subsequently noticed. When the change to sporangia begins the protoplasm of the plasmodium becomes gradually massed in discrete rounded lobes, about a half to one millimeter in diameter and scattered in clusters over the area occupied by the plasmodium. The reticulum of channels of the plasmodium becomes meanwhile less and less marked. When the whole of the protoplasm is drawn in to the lobes, the circulation ceases. The lobes are the young sporangia. Meanwhile foreign bodies, taken in with the food, are ejected, and the protoplasm secretes on its outer surface a pellicle of mucoid, transparent substance which dries as the sporangia ripen. This invests the young sporangia, and as they rise above the substratum falls together at their bases forming the stalks; extended over the substratum it forms the hypothallus, and in contact with the rounded surface of the sporangium it forms the sporangium-wall. While the sporangium-wall is formed externally a secretion of r A solution which has thus been found favourable contains the following See also:mineral salts: KH2PO4, K2HPO4,MgSO4, KNOB, CA (NO3)2, a free See also:acid, and 5% of See also:dextrine. 2 If the plasmodium is slowly dried it is very See also:apt to pass into sporangia. similar material occurs along branching and anastomosing tracts through the protoplasm of the sporangium, giving rise to the capillitium. The greater part of the lime granules pass,out of the protoplasm and are deposited in the capillitium, which in the ripe sporangia of Badhamia is white and brittle with the contained lime (cf. fig. 8). In this genus some granules are found also in the sporangium-wall. Strasburger concludes that the sporangium-wall of Trichia is a modification of cellulose (29). It has been stated (16), but the observation requires See also:confirmation, that a fusion of the nuclei in pairs occurs early in the development of the sporangium. through a young Sporangium FIG. to.—Part of a section of Trichivaria, showing the through a Sporangium of Trichia mitotic division of the nuclei (n) See also:varia after the spores are formed. prior to spore formation. c, Capillitium See also:thread. At a later stage, after the capillitium is formed, the nuclei undergo a mitotic division which affects all the nuclei of a sporangium simultaneously. This was first described by Strasburger (29). While it 0 o 6 a, Sporangia. b, Capillitium threads, with frag- cluster of ment of the sporangium-wall attached, lime knots at the junctions and spores. is in progress the protoplasm of the sporangium divides, into successively smaller masses, until each daughter nucleus is the centre of a single mass of protoplasm.' These nucleated masses are the young In some genera such as Arcyria and Trichia (illustrated in See also:figs. 9 and to) the division of the protoplasm does not occur until the nuclei have undergone this division. The protoplasm then divides up about the daughter nuclei to form the spores.spores. A spore-wall is soon secreted and the sporangium has now resolved itself into a mass of spores, traversed by the strands of the capillitium and enclosed in a sporangium-wall, connected with the substratum by a stalk. As ripening proceeds, the wall becomes membranous and readily ruptures, and the dry spores may be carried abroad on the currents of air or washed out by rain. We may now See also:review some of the main differences in structure presented by the sporangia. They may be stalked or sessile (fig. 13). If the former, the stalk is usually, as in Badhamia utricularis, b, Capillitium and spores. the continuation of the sporangium-walls (figs. 11 and 1z), but in Stemonitis and its See also:allies (figs. 17 and 18) it is an axial structure. A central See also:columella may project into the interior of the sporangium, either in stalked (fig. 15) or sessile (fig. 13) forms. a, Sporangia. b, A Sporangium deprived of spores, showing the capillitium and remains of the sporangium-wall. The sporangium-wall may be most delicate and evanescent (fig. 17), or consist of a superficial network of threads (fig. 18), which in Dictydium (fig. 19) present a beautifully See also:regular arrangement. a, Group of Sporangia, nat. size. a, Group of Sporangia. b, A Sporangium after See also:dispersion b, Capillitium. of the spores. c, Spore. In Chondrioderma (fig. 13) the wall is See also:double, the inner layer being membranous, the outer thickly encrusted with lime granules. In Craterium the upper part of the sporangium-wall is lid-like and falls away, leaving the spores in an open See also:cup (fig. 14). 6 ceum. a, Group of three Sporangia. b, Capillitium, fragment of sporangium-wall and spores. b turn. a, Two Sporangia, in one the lid has fallen away. b, Capillitium with lime knots and spores. a, Sporangia. b, Capillitium spores. and a, Two Sporangia, one showing the columella and capillitium. b, Capillitium, fragment of sporangium-wall with carbonate of lime in crystals, and spores. disks of lime are seen attached to the sporangium-wall. a b a, Group of Sporangia (nat. size). b, Portion of columella and capil- litium, the latter branching to form a superficial network. The condition of the capillitium is very various. In the Calcarineae the lime may be generally distributed through it (fig. ir), or aggregated at the nodes of the network in " lime-knots " (figs. 12 and 14) or it may be absent from the capillitium altogether. The capillitium attains its highest development in the Calonemineae in which the threads, distinct (in which case they are known as elaters, figs. 9 and io) or united into a network (fig. 20), present regular thickenings in the form of See also:spiral bands or transverse bars. These threads, altering their shape with varying states of moisture, are efficient agents in distributing the spores. In another group, the Anemineae, the capillitium is absent altogether. The Didymiaceae are characterized by the fact that the lime, though present in a granular form in the plasmodium, is deposited on the sporangium-wall in the form of crystals, either in radiating groups (fig. 15) or in disks (fig. i6). In most Endosporeae the sporangia are See also:separate symmetrical bodies, but in many genera a form of fructification occurs in which a, Aethalium. a, Group of Plasmodiocarps. b, Capillitium threads (with b, A continuous Plasmodiocarp lime-knots) and two spores. c, Spores. the spores are produced in masses of more or less irregular outline, retaining in extreme cases much of the diffuse character of the plasmodium. With the spores they contain capillitium, but there are no traces of sporangial walls to be found in their interior. They are known as plasmodiocarps (fig. 22). They are characteristic of certain species, but in others they may be formed See also:side by side with separate sporangia from the same plasmodium. There is indeed no See also:sharp See also:line to be drawn between sporangia and plasmodiocarps. On the other hand, the crowded condition of the sporangia of some species forms a transition to the large See also:compound fructifications known as aethalta (fig. 21). These, either in their young stages or up to maturity, retain some evidence of their formation by a coalescence of sporangia, and in addition to the capillitium they are generally penetrated by the remains of the walls of the sporangia which have thus united. Fxosporeae. It will be convenient to begin our survey of the life-history of Ceratiomyxa, the single representative of the Exosporeae, at the stage at which the plasmodium emerges from the rotten See also:wood in which it has fed. At this stage it has been observed to spread as a film over a slide, and to exhibit the network of channels and rhythmic flow of the protoplasm in a manner precisely similar to that seen in the Endosporeae (20, p. 10). It soon, however, draws together into compact masses, from the surface of which See also:finger-like or antler-like lobes grow upwards. Here too the secretion of a trans-See also:parent mucoid substance occurs, which is at first penetrated by the anastomosing strands of the protoplasm, but gradually the latter tends more and more to form a reticular and ultimately a nearly continuous superficial investment, covering the mucoid material. The latter eventually dries and forms the exceedingly delicate support of the spores or sporophore (fig 23, a). The investing proto- plasm, with its nuclei, having become arranged in an even layer, undergoes cleavage and thus forms a See also:pavement-like layer of protoplasmic masses, each occupied by a single nucleus (fig. 23, b). Each of these masses now grows out perpendicularly to the surface of the sporophore. As it does so an envelope is secreted, which, closing in about the base forms a slender stalk. The minute mass, borne on the stalk, becomes the See also:ellipsoid spore, surrounded by the spore-wall. In this manner the whole of the protoplasmic substance of the plasmodium is converted into spores, borne on supporting structures (stalks and sporophores), which are formed by secretion of the protoplasm. In the course of the development of which the See also:external features have now been traced nuclear changes occur of which accounts have been given by See also:Jahn (14) and by See also:Olive (24 and 25). Jahn has shown that prior to the cleavage of the protoplasm a mitotic division of the nuclei takes See also:place, the daughter nuclei of which are those occupying the protoplasmic masses seen in fig. 23 b .l After the spore has risen on its stalk two further mitotic divisions occur in rapid See also:succession, and the four-nucleated condition characteristic of the spore of Ceratiomyxa, is thus attained. The spores, on being brought into water, soon hatch (fig. 23, d), and the four nuclei contained in them undergo a mitotic division Meanwhile the protoplasm divides, at first into four, then into eight masses, and the latter acquire flagella, although for some time remaining connected with their See also:fellows (fig. 23, e-h). On separating each is a free zoospore. From observation of cultivations of zoospores the impression is that here, as in the Endosporeae, they multiply by binary division, though no exact observations of the process have been recorded. The zoospores lose their flagella and become amoebulae, but the fusion of the latter to form plasmodia has not been directly observed in Ceratiomyxa, although from See also:analogy with the Endosporeae it can hardly be doubted that such fusions occur. Sorophora. The Sorophora of Zopf (Acrasiae of See also:Van Tieghem) are a group of microscopic organisms inhabit- See also:ing the dung of herbivorous animals and other decaying vegetable matter. As Pinoy (26) has shown, the presence of a particular species of bacteria with the spores is necessary for their hatching and as the essential food of the amoebulae which emerge from them. There is no flagellate stage, and it is in the form of amoebulae, multiplying by fission, that the vegetative stage of the life-history is passed. At the end of this stage numbers of amoebulae draw together to form a " pseudo-plasmodium." This appears to be merely an See also:aggregation of amoebulae prior to spore formation. The outlines of the individual amoebulae are maintained, and there is no fusion between them, as in the formation of the plasmodium of the Euplasmodida. In some genera certain of the amoebulae constituting the pseudo-plasmodium are modified into a stalk (simple in Guttulina and Dictyostelium, branched in Polysphondylium, fig. 24, d), along which the other See also:units creep to encyst, and become spores at the end or ends of the stalk. In other cases (Copromyxa, fig. 24, a and b) the pseudo-plasmodium is transformed into a mass of encysted spores without the differentiation of supporting structures. It is not impossible that the Myxobacteriaceae of See also:Thaxter may, as that author suggests, be allied to the Sorophora (30). Review of the Life-Histories of the Mycetozoa.—The data for a comparison of the life-history of the Mycetozoa with those of other Protozoa in respect of nuclear changes are at present incomplete. i Jahn (14) described two mitotic divisions at this stage, but in " Myxomycetenstudien 7-Ceratiomyxa," Ber. deut. bot. Gesellsch. See also:xxvi. a (1908) he shows that only one mitotic division occurs in the maturing sporophore prior to cleavage. Olive gives a preliminary See also:account of- a fusion of nuclei prior to cleavage, but as he has not seen the mitotic division which certainly occurs at this stage his results cannot be accepted as secure. From Lankster's Treatise on Zoology; figs. a and c-h after A. Lister; fig. b after Famintzin and Woronin. a, Ripe sporophore. b, Maturing sporophore showing the development of the spores. c, Ripe spore. Instead of the single nucleus here indicated there should be four nuclei, as in d. d, Hatching spore. e-h, Stages in the development of the zoospores. From Lankester's Treatise on Zoology a and b after Fayod; c and d after Brefelti from Zopf. See also:tea, slightly magnified. c and d, Polysphondylium laceum. c, A young sorus, seen in See also:optical section. A mass of elongated amoebulae are grouped round the stalk, and others are ex-tended about the base. d, A sorus approaching maturity. See also:vie- At some stage or other we are led by analogy to expect that a division of nuclei would occur in which the number of chromosomes would be reduced by one half, that this would be followed by the formation of gametes, and that the nuclei of the latter would subsequently fuse in See also:karyogamy. It is clear that both in the Endosporeae and Exosporeae a mitotic division of nuclei immediately precedes spore-formation. This is regarded by Jahn as a reduction division. If this is the case, the zoospores or the amoebulae must in some way represent the gametes. The fusion of the latter to form plasmodia appears to offer a process comparable with the conjugation of gametes, but though the fusion of the protoplasm of the amoebulae has been often observed no fusion of their nuclei (karyogamy) has been found to accompany it. A fusion of nuclei has indeed been described as occurring in the plasmodium, or at stages in the development of the sporangia or sporophores, but in no case can the evidence be regarded as satisfactory.' Until we have clear evidence on this point the nuclear history of the mycetozoa must remain incomplete. Jahn's observation of the mitotic division of nuclei preceding spore-formation in Ceratiomyxa gives a fixed point See also:fog comparison of the Exosporeae with the Endosporeae. Starting from this division it seems clear that the spore of Ceratiomyxa is comparable with the spore of the Endosporeae except that the nucleus of the former has undergone two mitotic divisions. Vzen Ceratium hydnoides, A. and Sch., and C. porioides, A. and h.,a' Mem. de l'acad. See also:imp. d. sciences de St See also:Petersburg, See also:series 7, T. 20, No. 3 (1873). (11) M. See also:Greenwood and E. R. Saunders, " On the Role of Acid in Protozoan Digestion," Jour. of See also:Physiology, xvi. 441 (1894). (12) R. A. Harper, " See also:Cell and Nuclear Division in Fuligo varians," Botanical See also:Gazette, vol. 30, No. 4, p. 217 (19oo). (13) E. Jahn, " Myxomycetenstudien 3. Kernteilung u. Geisselbildung bei den Schwarmern von Stemonitis flaccida, Lister," Bericht d. deutschen botanischen Gesellschaft, Bd. 22 p. 84 (1904). (14) " Myxom,cetenstudien 6. Kernverschmelzungen and Reduktionsteilungen,' ibid. Bd. 25, p. 23 (1907). (15) W. Saville Kent, " The Myxomycetes or Mycetozoa; Animals or Plants?" Popular See also:Science Review, n.s., v. 97 (1881). (16) H. Kranzlin, " Zur Entwicklungsgeschichte der Sporangien bei den Trichien and Arcyrien," See also:Arch. f. Protistenkunde, Bd. ix. Heft. 1, p.170 (1907). (17) A. Lister, " Notes on the Plasmodium of Badhamia utricularis and Brefeldia See also:maxima," See also:Ann. of See also:Botany, vol. ii. No. 5 (1888). (18) " On the Ingestion of Food Material by the Swarm-Cells of the Mycetozoa," Journ. Linn. See also:Soc. (Bot) See also:xxv. 435 (1889). (19) " On the Division of Nuclei in the Mycetozoa," Journ. Linn. Soc. (Bot.) vol. See also:xxix. (1893). (20) " A Monograph of the Mycetozoa," British Museum See also:Catalogue (See also:London, 1894). (21) " Presidential Address to the British Mycological Society," Trans. Brit. Mycological Soc. (1906). (22) A. and G. Lister, " Synopsis of the Orders, Genera and Species of Mycetozoa," See also:Journal ofBotany, vol. xlv. (May 1907). (23) E. W. Olive, " Monograph of the Acrasiae," Proc. See also:Boston Soc. of Nat. History, vol. See also:xxx. No. 6 (1902). (24) " Evidences of Sexual See also:Reproduction in the Slime Moulds," Science, n.s., xxv. 256 (Feb. 1907). (25) " Cytological Studies in Ceratiomyxa, Trans. See also:Wisconsin Acad. of Sciences, Arts and Letters, vol. xv., pt. ii. p. 753 (Dec. 1907). (26) E. Pinoy, " Role See also:des bacteries dans le developpement de certains Myxomycetes." Ann. de l'institut See also:Pasteur, T. xxi. pp. 622 and 686 (1907). (27) H. Plenge, " Ueber See also:die Verbindungen zwischen Geissel u. See also:Kern bei den Schwarmerzellen d. Mycetozoen," Verh. d. naturhist.-med. Vereins zu See also:Heidelberg, N.F. Bd. vi. Heft 3 .(1899). (28) S. von Prowazek " Kernveranderungen in Myxomycetenplasmodien," Oesterreich. botan. Zeitschr. Bd. liv. p. 278 (1904). (29) E. Strasburger, " Zur Entwickelungsgeschichte d. Sporangien von Trichia failax," Botanische Zeitung (1884). (30) R. Thaxter, " On the Myxobacteriaceae, a new order of Schizomycetes," Botanical Gazette, xvii. 389 (1892). (31) W. Zopf, " Die Pilzthiere See also:oder Schleimpilze," Schenk's Handbuch der Botanik (1887). (J. J. Additional information and CommentsThere are no comments yet for this article.
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