Rhizoid Cell Differentiation in the Fern Gametophyte of Pteris vittata

A series of events in the differentiation of rhizoid cells in the gametophyte of Pteris vittata L. is described. Differential in vivo staining reactions make it possible to trace a sequence of stages from pre-mitotic nucleocytoplasmic staining (corona stage), through the events of mitosis, to formation of an internally segmented rhizoid cell which then grows out from the parent thallus cell. When the standard ribonuclease test is employed, basophilic protoplasmic staining due to pyronin is prevented in developmental stages up through early formation of the rhizoid cell. Staining in these stages is therefore assumed to be due to ribonucleic acid associated with protein synthesis. A new developmental phase starts just prior to the protrusion growth of this cell when an intensely pyroninophilic material appears at the membrane of the rhizoid cell nucleus and along cytoplasmic strands radiating to the peripheral regions of the cell. The staining of this newly synthesized material cannot be prevented by ribonuclease treatment, and it shows strong positive tests for protein and polysaccharide. As long as the rhizoid continues to grow, this material remains concentrated in the growing tip region. Material showing similar staining reactions is also found in the cells of the meristematic notch area. Although thallus cell walls do not stain, the rhizoid cell wall adsorbs basic stain, in some cases, metachromatically. Finally, it is suggested on the basis of observations reported here that the sometimes neglected role of the nucleus in theories of unequal cell division-differentiation should be re-examined.