attempted. But wherever in the present work a name has been changed, the name of the earlier author will be found in parenthesis, followed immediately by that of him who made the change, and in general, recent practice, especially as expressed in the rules of the various codes, has determined the puzzling questions of nomenclature.

In justification of the use of Myxomycetes as a general title it may be said that in this case prevalent usage is not inconsistent with a rational application of the rules of priority. The Friesian designation Myxogastres was applied by its author in 1829 to the endosporous slime-moulds as a section of gasteromycetous fungi. Four years later Link, perceiving more clearly the absolute distinctness of the group, substituted the name Myxomycetes. In the same year Wallroth adopted the same designation, but strangely confused the limitations of the group he named. Wallroth seems to have thought Myxomycetes a synonym for Gasteromycetes Fries. In 1858 DeBary applied the title Mycetozoa to a group which included the then lately discovered Acrasieae with the true slime-moulds, both endosporous and exosporous. For all except the Acrasieae DeBary retained the old appellation, Myxomycetes. Rostafinski adopted DeBary's general name, but changed its application. As it has been shown, since DeBary's time, that the Acrasieae[3] have no true plasmodium, and are therefore not properly, or at least not necessarily, associated with the slime-moulds, there appears no necessity for the term Mycetozoa, and the question lies between Myxogastres and Myxomycetes. Of these two names the former, as we have seen, has undoubted priority, but only as applied to the endosporous species. The same thing was true of Link's designation until DeBary redefined it, but having been taken up by DeBary, redefined and correctly applied, Myxomycetes (Link) DeBary must remain the undisputed title for all true slime-moulds, endosporous and exosporous alike.

In arranging the larger divisions of the group the scheme of Rostafinski has been somewhat modified in order to give expression to what the present author deems a more natural sequence of species. The highest expression of myxomycetan fructification is doubtless the isolated sporangium with its capillitium. This is reached by successive differentiations from the simple plasmodium. The æthalium may be esteemed in some instances a case of degeneration, in others of arrested development. In any event in the present arrangement, æthalioid forms are first disposed of, leaving the sporangiate species to follow from plasmodiocarpous as directly as may be.

The artificial keys herewith presented proceed on the same plan and are to be taken, as such keys always are, not as definitive in any case, but simply as an aid to help the student more speedily to reach a probably satisfactory description.

PREFACE TO THE SECOND EDITION

The first edition of this little book having been exhausted long ago, the writer in this second issue takes opportunity to correct sundry errata, typographical and other, and at the same time to incorporate such new information in reference to individual species and to the subject entire as the researches of more recent years may afford.

To Miss Gulielma Lister, of London, the writer expresses his sense of deep obligation for much assistance in settling difficult matters of nomenclature and identification; it will be found as a result that in most instances the same thing in the two volumes, English and American, appears under the same name. There are still differences; these result in most cases from different points of view, different estimates or emphasis of characteristics in these ever elusive objects.

To Professor Torrend, formerly of Lisbon, the writer is indebted for a set of European types, and to Professor Bethel, pathologist of Denver, for rich material from the fertile mountains of Colorado and California. To Professor Morton Peck, of Oregon, we are indebted for many notes of the color of plasmodia and for collections of Pacific coast forms. Mr. Bilgram, of Philadelphia, read the manuscript of the genus Physarum and has contributed many rare species. To Dr. Sturgis, of Massachusetts, we are indebted for material from both east and west.

The present volume is intended especially for American readers and is accordingly particularly devoted to a discussion of species so far reported on the western continent; nevertheless it has seemed wise to include a brief description of some other forms as well, and reference to many extra-limital species now generally recognized will be found here and there in connection with the more extended treatment of related American forms.

February twenty-eight, 1921.

BIBLIOGRAPHY

The following are the principal works consulted in the prosecution of the investigations here recorded:—