Accumulation of smooth cisternae in the tapetal cells of Ulex europaeus L. (Papilionoideae).

In addition to the events occurring in the tapetal cells of most angiosperm species (cell wall lysis, endoplasmic reticulum development and sporopollenin deposition on the outer face of the cells) the tapetum of Ulex europaeus L. exhibits two characteristics. No orbicules, generally associated with the locular face of the secretory tapetum of angiosperms, are found, but some intracellular macro-orbicules are formed and then released in the anther loculus. The great diversity of reticular structures is emphasized by the presence of accumulations of smooth and flattened cisternae in the mature cells. Their similarity to those observed in the sieve elements of differentiating phloem suggests a possible functional interpretation in the light of the 'holocrine' behaviour of the tapetal cells.