Development of the echinate pollen wall inFarfugium japonicum (Compositae: Senecioneae)

Development of the echinate pollen grains inFarfugium (Compositae: Senecioneae) has been studied by a combination of transmission electron microscopy and field emission scanning electron microscopy with a freeze fractured method. The inner surface of the callose wall surrounding each microspore does not possess an echinate pattern before primexine deposition begins. The primexine formation coincides with the initiation of spines. The freeze fractured primexine shows probacula which form transverse rods. The developing exine has an inner spongy substructure. The endexine is formed by the accumulation of the electron dense lamellae with white lines after the dissolution of the callose wall. In the present study, it is confirmed that the developmental process of pollen formation revealed in the field emission scanning electron microscope is consistent with the results obtained using the transmission electron microscope.