A Study of Stelar Ultrastructure in the Heterosporous Water Fern Marsilea quadrifolia L

Sieve tube elements occur in the rhizomes and petioles of Marsileaquadrifolia. These are either thick walled with compound sieveplates in oblique end walls or thin walled with simple sieveplates in transverse end walls. Vessels are restricted to themetaxylem in the roots where the phloem contains sieve cellsonly. The sieve pores are invariably callose lined and as inother pteridophytes, excepting the Lycopsida, refractive spherulesare ubiquitous in the sieve elements of Marsilea. The luminaof the protoxylem tracheary elements in the rhizomes and petiolesare occluded by tyloses but probably remain functional in theroots. Pericycle cells backing on to the root protoxylem armspossess wall ingrowths. Transfer cells are however absent fromthe vascular tissue of the rhizomes and leaves. It is suggestedthat their presence in the root pericycle is related to theretrieval of ions from the xylem sap which may be particularlycritical in water plants. The incidence of transfer cells incryptogams appears to be far more sporadic than in angiosperms.The root endodermis of Marsilea possesses a casparian stripand abundant vacuolar tannin deposits. Plasmalemmasomes arenumerous adjacent to the pericycle transfer cells. vascular ultrastructure, Marsilea quadrifolia L, transfer cells, sieve tube elements, tyloses