Structure of Aerial and Subterranean Roots of Selaginella kraussiana a. br.

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Abstract
Early in ontogeny, aerial roots of S. kraussiana develop a root cap which is retained throughout the aerial growth phase. Mature cap cells have thick walls, particularly the outer tangential walls, which are also covered by a cuticle. Small dense nuclei, large vacuoles (many with osmiophilic deposits), plastids with few thylakoids, lipid deposits and poorly organized mitochondria characterize this cytoplasm. Starch is not present. Aerial roots bifurcate several times before reaching the soil, but all of the root apices are enclosed within a common root cap. Subterranean roots lose the rounded appearance of aerial roots, becoming tapered and more rootlike. The thick-walled root cap in aerial roots is lost upon entering the soil and is replaced by a new root cap for each root apex formed. The new root-cap cells are in various stages of degeneration, the outermost being constantly sloughed. There is no cuticle covering the outer tangential cell walls. Cap cells recently formed from the root apical initial have few small vacuoles, large nuclei, plastids with no or little starch, well-developed mitochondria and few lipid bodies. Meristematic cells derived from the root apical initial of both aerial and subterranean roots have numerous plasmodesmatal connections.