Abstract
SUMMARY A morphological study was made with respect to the changes during microsporogenesis of Pinus sylvestris L. from prometaphase I until the tetrad stage. Described and discussed are the breakdown and rebuilding of the nuclear membrane, the mixing of karyoplasm and cytoplasm with the transfer of ribosomal material, the nuclear invaginations, the kinetochore and microtubuli. A decrease of starch in the plastids starts in interphase II. The mitochondria do not change. The “lipid-complex” appears in telophase II. Many vesicles are present in the cytoplasm during the cell divisions. Ribosomes are observed in all stages, polysomes become visible during interphase II and telophase II. Rough endoplasmic reticulum is absent. The Golgi body produces small and large vesicles and long flat cisternae, similar to smooth endoplasmic reticulum. These Golgi vesicles fuse and form the primary cell wall. The presence of the plasma membrane is postulated as necessary for the synthesis of callose. No difference has been found between the morphological events during callose wall formation and cellulose wall formation. A relation may exist between the callose wall formation and the polysomes and lipid granules and “lipid complex”, but a relation with smooth endoplasmic reticulum is not clear. During diplotene and early tetrad stage the formation of the callose wall proceeds in the same way.
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