In Ceratium, the sole genus of Exosporea, the plasmodium first collects into a mass, and then grows up into a number of processes or conidio-phores. Mass and processes alike are formed of a watery jelly supporting a network of granular protoplasm. This network traverses the whole substance of the mass; it passes into the processes as they develope and in them is confined to a superficial layer. It is finally resolved into polyhedral cells. Each cell grows out into a stalked sphere, protected by a delicate membrane. The protoplasm is concentrated by degrees in the sphere, which is converted into a spore by the development of a special membrane. The spores are detached with ready ease from their stalks, and the supporting jelly dissolves as soon as it is function-less.
The plasmodium of the Endosporea gives origin to a single sporocyst, or by division to many. It gathers together, developes a superficial coat or membrane, and extrudes at the same time all foreign bodies, pigment and Calcium carbonate if present1. The resulting sporocyst has generally the shape of a sessile or stalked vesicle; in a few instances it is tubular, slightly branched, or even reticulate, and then frequently receives the name of plasmodiocarp. It is attached to whatever it rests upon by the dried mucoid envelope or hypothallus, which forms either a thin flat expansion, a ridge, or peduncle. The protoplasm, freed from whatever is foreign to it, is colourless, and from it are derived the capillitium and the chlamydo-spores. The former consists of either stereonemata or coelonemata - stereonemata, that is to say cords cylindrical or flattened, solid, or at the utmost traversed by a fine canal; coelonemata, or tubes with thin walls and wide cavities. Both structures consist of a cuticularised membrane, and the stereonemata of the Calcariaceae include pigment and Calcium carbonate.
As to the mode in which the capillitium is disposed, the stereonemata are either variously shaped thickenings of the walls of the sporocyst2, or they are branching strands crossing its cavity and attached by their ends to its walls; the coelonemata take one of three forms, tubes, or elaters, closed at their ends and lying free as in Trichiaceae, a narrow-meshed expansile reticulum with its ends attached to the walls of the sporocyst, as in most Arcyriaceae and the Perichaenaceae, or.a branched structure with the cavity of its constituent tubes varying in width from point to point, as in the Reticidaraceae and Lycogala among Arcyriaceae.
1In Didymium the Calcium carbonate dissolves, and reappears on the outer surface of the sporocyst as a crystalline deposit.
3De Bary does not apply the term capillitium to these thickenings.
The elaters are thickened spirally, the tubes of a reticulum by circular ridges, by spines, tubercles, or a network of lines. As soon as the capillitium is established, the nuclei of the protoplasm remaining multiply, the protoplasm itself segments, a portion to each nucleus, the nucleated portions become rounded, acquire a membrane, and so pass into chlamydo-spores.
The sporocyst is now fully formed. It has a membranous wall, single or double, of varying thickness, white, black, violet, red, yellow, brown, sometimes smooth, sometimes ornamented with ridges or tubercles. When it has a peduncle, that structure is also membranous, hollow, closed or open at its apex, empty, or filled with various descriptions of useless materials. A drying process sets in, and the sporocyst becomes brittle and breaks up in different ways. When the capillitium is a system of thickenings of the membrane of the sporocyst, it prevents the collapse of the latter; when it traverses its cavity, it not only affords strength, but there is reason to believe that it executes hygroscopic movements, aiding partly in the rupture of the walls, partly in the scattering of the spores. Such is the case to a very marked degree with the elaters, and the expansile tubular reticulum of the Arcyriaceae, etc. (supra).
The aethalium, or spore-forming mass, produced by the aggregation or coalescence of a number of plasmodia, is met with in thirteen genera only, belonging to different families of Endosporea. It takes various shapes, a disc, cake (Fuligo), ball, or a miniature bush. In Fuligo it may attain a great size, as much as I ft. long and I in. thick. Structurally it may consist of a number of prisms set side by side, of interwoven and anastomosing tubes (Fuligo), of branched stems, or finally the parts may so completely fuse as to show no trace of their complex structure. It is often naked, sometimes protected by a thin membrane, or in Fuligo and Lycogala by a cortex composed in the first-named of the dried hypothallus, and the collapsed superficial tubes filled with Calcium carbonate and yellow pigment, the protoplasm having withdrawn to the central tubes. The capillitium of an aethalium follows the type of the family to which it belongs.
As to the physiological relations of the Mycetozoa, it has been shown that they consume oxygen energetically, are repelled by light, attracted by a supply of food or by moisture, provided that the plasmodium is not ripe for sporulation, when it moves to drier spots. The Sorophora for the most part inhabit dung, one or two decaying vegetable matter; one of them, Dictyostelium mucoroides, has been grown in solutions of Hippuric acid and Potassium urate. The remaining Mycetozoa live in moist rotting wood, leaves, or other vegetable debris. It is stated that the spores, whether amoebulae or flagellulae, but especially the former, take up foreign bodies, e. g. Bacteria; so too the plasmodium ingulfs very various materials.
But it is not possible to say how far these foreign bodies are utilised as food. Fuligo is known to possess a peptic ferment, and all plasmodia one that dissolves cellulose or cuticularised membranes, e. g. those of macrocysts. It has been shown that they do not all react in the same way towards the same body, e. g. carmine, one taking it up and acting upon it, the other leaving it alone and not acting upon what few particles it does ingulf.
By De Bary, the greatest authority on the class, the Mycetozoa have long been placed outside the limits of the vegetable kingdom. Whatever resemblances they may possess to various fungi is, he insists, superficial, certain Chytrideae excepted; but the latter, according to De Bary, have no plasmodia. On the other hand their peculiarities may be found in various undoubted Protozoa. Supposing them to be saprophytic, so e. g. are some Flagellata under certain conditions (p. 842); fusion to form plasmodia recurs in some Proteomyxan Monadineae, as to the animal nature of which there can be no doubt; so too in the same group the formation of sporocysts and chlamydospores (p. 915); if the nature of the membrane of the sporocyst be objected on the score that it sometimes stains blue with Iodine and Sulphuric acid, indicating the presence of cellulose, similar membranes are met with in some Monadineae (note 2, p. 919), not to mention other Protozoa and animals higher in the scale. There can be little reasonable doubt that the members of the class are Rhizopoda, adapted to a sub-aerial and perhaps saprophytic life.
The Mycetozoa, as defined above, are termed by Zopf, quoted infra, Eu-mycetozoa; the Mycetozoa, as he uses the term, include also the Monadineae (p. 917). The classification of the Eumycetozoa-=-Mycetozoa, as given by Zopf, is as follows: I. Sorophora (=Acrasieae, van Tieghem): no flagellula phase; pseudo- or aggregation-plasmodia; the sporocyst replaced by a sorus. Copromyxa, Guttulina, Dictyostelium, Aerasis, Polyspondy/ium1.
II. Endosporea: a flagellula phase; true or fusion-plasmodia; spores formed in sporocysts; a capillitium.
(i) Peritricheae: capillitium peripheral (see p. 910 and note 2), formed by stereonemata.
(ii) Endotricheae: capillitium traversing the cavity of the sporocyst.
(a) Stereonemea: capillitium formed by stereonemata, e. g. Calcariaceae.
(b) Coelonemea: capillitium formed by coelonemata, e. g. Trichiaceae.
III. Exosporea: a flagellula phase; true or fusion-plasmodia; spores borne upon sporophores s. conidiophores (p. 910): Ceratium.
De Bary, Comparative Morphology, etc. of the Fungi, Mycetozoa and Bacteria, translated by Garnsey, Oxford, 1887, pp. 421-53; Zopf, Die Pilzthiere oder Schleimpilze, Encyclopaedic der Naturwissenschaften, Breslau, Handbuch des Botanik, iii. pt. 2, 1884.
1 The Protomyxomyces coprinarius of D. D. Cunningham, Q. J. M. xxi. 1881, which inhabits the intestinal canal and dung of various animals, is a Sorophoran.