Female gametophyte and pollen tube of Epilobium palustre L.

The monosporic, tetranucleate embryo sac of Epilobium palustre (Onagraceae) develops from the micropylar megaspore in a linear tetrad. In mononucleate embryo sacs a peculiar chromatic structure associated with a nucleolus appears in the nucleus. This structure seems to be formed by fibrillar material and is not visible in the subsequant stages of development. A large amount of rough ER cisternae occurs in the late mononucleate stage, during the binucleate stage their contents become optically dense. It the early tetranucleate stage the amount of ER is small, it increases again in the developing synergids and central cell. Numerous amyloplasts present in the mononucleate embryo sac loose their starch grains and some are transformed into cup-shaped plastids or proplastids. They are passed on to each of the embryo sac cells. The growth of the pollen tube ceases immediately after the penetration through the filiform apparatus of a synergid. At the apex of the tube a pore is formed. At the last stages of the penetration the apical part of the pollen tube becomes separated by a transverse partition from the distal part of the tube. The contents of the both parts differ in their internal structure. The distal part contains cytoplasm with numerous organoids, while the apical part is mainly filled with spherical bodies