Formation of pollen in the anther of Lilium. 1. Development of the pollen wall

The ultrastructural changes during the microsporogenesis and gametogenesis in Lilium are studied in relation to the surrounding tissues. In this article the development of the microspore and pollen wall is presented. In relation to the increase in pollen volume the nexine is increased but this process is discontinuous. It is concluded that four periods of sporopollenin deposition can be distinguished. The mechanism of exine formation during the young microspore stage is the embedding of sporopollenin on a sexine matrix of polysaccharides, some proteins and osmophilic material. During this period the sporopollenin deposition on membrane-like lamellae takes place on both sides of the exine. During the vacuolated raicrospore stage globules, containing sporopollenin are deposited on the exine too. After mitosis the "Pollenkitt” also contributes in sporopollenin addition to the nexine and sexine. Folds of the plasma-membrane of the microspore are the origin of the membrane-like lamellae. The pollen storage consists mainly of starch, lipid granules and lipoprotein.