5. Capillitium made up of more or less distinctly sculptured threads, parietal or free, simple, branched, or reticulate; spores commonly yellow V. TRICHIALES This sequence is meant to convey the idea that the presence of lime is indicative of differentiation less complete. That the plasmodium should at the outset eliminate, by refusing the unnecessary lime, is indicative of higher rank than that the lime should be carried until the last and then be crystallized out, or excreted by simple desiccation. The circumstance that the excreted lime may sometimes serve a protective purpose in the fruit, does not vitiate the general principle. In Series B the differentiation reaches a climax in the sculptured capillitium of the trichias. ORDER I =PHYSARALES= Spores violaceous-black. The capillitium usually delicate and thread-like; peridium and capillitium, one or other or both, more or less extensively surcharged with lime. Peridium simple or double. Fructification various. This order is recognizable by several characteristics, but is especially marked by the peculiar calcareous deposits which affect the capillitium or peridium, now one, now the other, more often both. As here defined, the order Physarales includes two distinct families; of the one _Physarum_, of the other _Didymium_, is type. =Key to the Families of the Order Physarales= _A._ Fructification often calcareous throughout; capillitium intricate _Physaraceae_ _B._ Calcareous deposits, when present, affecting the peridium only, or sometimes the stipe, in the typical genus plainly crystalline; capillitium simple _Didymiaceae_ A. PHYSARACEAE =Key to the Genera of the Physaraceae= _A._ Fructification aethalioid 1. _Fuligo_ _B._ Fructification plasmodiocarpous or of distinct sporangia. _a._ Peridium evidently calcareous. i. Capillitium calcareous throughout 2. _Badhamia_ ii. Capillitium largely hyaline. O Sporangia globose, etc.; dehiscence irregular 3. _Physarum_ OO Sporangia vasiform or more or less tubular + Dehiscence by a lid or more or less circumscissile 4. _Craterium_ ++ Dehiscence irregular, peridium introverted 5. _Physarella_ _b._ Peridium apparently limeless, at least outside. i. Plasmodiocarpous 6. _Cienkowskia_ ii. Sporangia distinct 7. _Leocarpus_ C. Extra-limital. _a._ Sporangia stipitate, saucer-shaped, following No. 3. _Trichamphora_