c. The considerations just mentioned may, indeed do, sometimes act as a handicap to the American student, for the simple reason that he comes later to the field of time. He must naturally defer to the decision of men in Europe who are supposedly familiar with original types. An American specimen is presumably the same as one occurring elsewhere in similar latitude and environment. It becomes evident after while that only in certain instances is this undoubtedly the fact. The flora of the American continent has been sufficiently disjoined in space and time from Europe to permit extensive differentiation even in these minor forms, so that we have indeed in the groups we study many species, some genera, definitely autochthonous, more it is believed than are now suspected. An attempt to bring a specimen under the terms of a species described in Western Europe is not seldom an error. It becomes evident, as we go forward, that in eastern North America there are forms not only not described in European literature, but really not, part of European flora, not even adventitiously. d. Many of the more minute species with which this volume has to do are very elusive, very difficult; for one reason,--perhaps in itself sufficient,--because of their minuteness, and consequent apparent paucity. They may be common, but none the less seldom seen. The comatrichas afford an illustration. There are several very small species. _C. pulchella_, _C. laxa_, _C. ellisii_ may be mentioned. _C. pulchella_ has been studied nearly a hundred years and has a synonymy accordingly. In 1875 Rostafinski in the material, and among the descriptions, thought he recognized two distinct forms, and went on to give them names; the first in honor of Persoon, _C. persoonii_, should show an ovate or ovate-cylindric outline with acuminate tip; the second should be truncate and represent a type first described by Berkeley under a name given by Babington, _C. pulchella_. Berkeley's drawing shows a sporangium with tip acuminate! Lilac or violaceous tints attracted attention in the spores of _C. persoonii_ only; in _C. pulchella_ all is ferruginous. Curtis is especially commended for noticing the fact in describing _S. tenerrima_, here included as we see. _Comatricha gracilis_ Wing. is slender, cylindric and has small spores hardly reaching 6 mu; should perhaps be now set out as a separate species; it is evidently purely an American phase. Our figures, Plate XII., 16 and 16 _a_, 18 and 18 _a_, show _C. pulchella_ and _C. gracilis_, respectively, extremes. Plate XIII., 4, shows an ovate form not very unusual. This and _C. gracilis_ occur on living leaves. _C. ellisii_ is another of this minor series, very constant in its delicate beauty, but approaches _C. nigra_ rather than the others here discussed.