DEVELOPMENTAL MORPHOLOGY OF THE ROOT OF SELAGINELLA KRAUSSIANA A. BR. AND SELAGINELLA WALLACEI HIERON.

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Abstract
The origin and development of the root in the isophyllous Selaginella wallacei and the anisophyllous S. kraussiana have been investigated, and the observations agree closely with those previously made by the authors on the isophyllous S. densa. In both species the root arises from an angle-meristem on the upper surface of the stem at the angle of each unequal terminal branching of the shoot. In its early development, the root meristem is not covered by a cap, but after a small amount of growth, a root cap is initiated as a result of the formation of distal segments by the apical cell and its immediate derivatives. Soon after cap formation has begun the root meristem undergoes terminal branching beneath the root cap, but there is a considerable delay before branching of the root is visible externally. In both of the species investigated, as previously in S. densa, no evidence for a rhizophore or for endogenous root origin could be found. These observations are discussed in the light of reports by previous workers in which similar structures are interpreted as rhizophores bearing endogenous roots.