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 title 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 masses.... Through the amoebæ 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 pass by gradations easy to the filamentous algæ, 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.

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 assert 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 pronounced 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 amœba. 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 assumption 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 mass 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 constitute 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 petitio principii. Nor is there any advantage at present apparent in attempts to associate slime-moulds with other presumably related groups. Saville Kent's effort to join them with the sponges was not happy, and Dr. Zopf's association 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," "Höhere 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 zoölogist for further consideration, but simply says:[12] "From naked amœba, with which the Mycetozoa (=Myxomycetes) are connected in ascending line, the zoölogists with reason derive the copiously and highly developed section of the shell-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 amœbæ, 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 zoölogy."

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