CYTOLOGICAL BASIS FOR A TETRASPORY IN CUPRESSUS SEMPERVIRENS L. MEGAGAMETOGENESIS AND ITS IMPLICATIONS IN GENETIC-STUDIES

The processes of megasporogenesis and early megagametogenesis were cyt ologically investigated in Cupressus sempervirens L. in order to eluci date, at the cellular level: the origin of the megagametophyte. After pollination, sporogenous tissue developed in the chalazal region of th e nucellus, but only one megaspore mother cell differentiated and divi ded meiotically without cell-wall formation. This led to the developme nt of a cell with four nuclei which directly functioned as a megaspore . The C. sempervirens megagametophyte is thus tetrasporic, in contrast to the majority of conifers where the megagametophyte is monosporic. The consequenses of this observation are discussed from a genetics poi nt of view.