Sieve-element ultrastructure in Platycerium bifurcatum and some other polypodiaceous ferns: The refractive spherules.

Sieve elements of various ages of Platycerium bifurcatum (Cav.) C. Chr. and Phlebodium aureum (L.) J. Sm. and older ones of Polypodium schraderi Mett. and Microgramma lycopodioides (L.) Copel. were examined with the electron microscope. Evidence was obtained which implicated the Golgi apparatus with the formation of refractive spherules in Platycerium and Phlebodium. In all four species the delimiting membranes of the refractive spherules eventually fuse with the plasmalemma in mature sieve elements, and the material comprising the spherules is liberated into the region of the wall.