InEpidendrum ibaguense, pollen is aggregated into pollinia as united masses. The present study demonstrates that the mechanism of pollen aggregation is built into the various stages of pollen development. It is suggested that the pollen are held together due to a combined effect of the following features: (1) the remains of the pollen mother cell wall, (2) the fibrillar material present within the callosic cell wall during meiosis and tetrad formation, (3) the persistence of some plasmodesmata from the PMC stage of pollen development, (4) incomplete cell wall formation within tetrads, and (5) little size increase of developing microspores
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