The surface of Trachelomonas was examined readily with SEM at magnifications up to X 20,000 in unfixed or fixed material. Cells were placed directly on specimen holders without washing, air dried, and coated with aluminum or gold. Clones of T. grandis, T. hispida var. coronata, and T. oblonga var. punctata and three species from a natural collection showed the following features: the lorica was punctate or solid, and the surface projections, when present, consisted of minute papillae (0.1 μm), larger, often globose papillae (up to 0.8 μm), and spines which tapered to a point or which had parallel sides and ended bluntly; spines appeared hollow or solid. Pringsheim's clone of T. oblonga var. punctata, which he described as a new spineless variety, possessed short tapering spines and globose papillae. Such observations suggest that a major problem in delimiting species may be in discovering the ornamentation potential of a clone. The discovery of new features of the lorica (e.g., minute papillae and hollow projections), the clarification of shapes of surface features, and, in general, the excellent resolution at 10 times the usable magnification of light microscopy dictate a reexamination of known species with SEM. We suggest that a SEM study of the variation in the lorica surface in clonal material will lead to a recognition of polymorphism and eventually to a clearer understanding of taxonomic entities described from natural collections.
© 1975 Botanical Society of America.