Fig. 6. Cytological analysis of pollen tube entry into feronia embryo sacs. (A,B) Semi-thin sections stained with Toluidine Blue. (C-F) Transmission electron micrographs of invaded feronia FG at 24 HAP. (A) The winding PT (pt) is covered by the dark staining remains of the synergid cell (sc). (B) PT invasion in mutant ovules is in most cases restricted to the synergid and does not enter the central cell (cc). (C) The PT enters the synergid and bifurcates (arrow) immediately after entry into the degenerated synergid (dsy). The egg cell membrane (arrowheads) appears to be intact and the secondary endosperm nucleus (sen) is present. (D) Adjacent but not successive section of the same sample as shown in C at higher magnification. The PT passes the filiform apparatus (fa) and enters the FG. Remains of the degenerated synergid surround the entering PT. (E) Branching (arrow) of the PT within the synergid. (F) The invading PT rearranges the micropylar area of the embryo sac, but the egg cell membrane appears to be intact (arrowheads). Scale bars: (A,B) 25 µm; (C-F) 5 µm.