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. PHYSARACEÆ
Key to the Genera of the Physaraceæ