DEVELOPMENTAL MORPHOLOGY OF THE ROOT OF SELAGINELLA MARTENSII SPRING

Abstract

The origin and development of the root of Selaginella martensii have been investigated. The roots arise from angle-meristems situated at each branching of the stem. A ventral angle-meristem is present at each forking, and at some forkings a corresponding dorsal angle-meristem is also present. As the root grows through its aerial length (several centimeters), the tip undergoes bifurcation and a root cap is lacking. When the tip nears the soil, a cap is formed by distal segmentation of cells in the apical meristem. Externally visible branching and root hair formation usually occur soon after a cap is formed. The observations of root development in S. martensii agree in general with observations previously made on S. densa, S. wallacei, and S. kraussiana. No evidence for a “rhizophore” or endogenous root initiation as described previously by others has been found. The results are discussed in the light of the concept of a “rhizophore” in Selaginella.