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 circumstances, the plasmodium will constantly change shape and position, can be induced to spread over a plate of moist glass, 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 hyphæ 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 pass into a resting phase, when it masses 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 pass into the resting phase by undergoing a very peculiar change of structure. In ordinary circumstances the abundant free nuclei demonstrable in the plasmodium afford the only evidence of cellular organization. In passing now into the condition of rest, the whole protoplasmic mass 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 pass suddenly as if by magic charm into one widespread, dusty field of flying spores. Or, to be more exact, whatever the position ultimately assumed, 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 mass, 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 mass 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 classed with the gasteromycetous fungi, puff-balls, 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 homologous; analogous 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 analogous 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 µ, and reveal their surface characters only