Structural changes in the apex of the female strobilus and the initiation of the female reproductive organ (ovule) in Ephedra distachya L. and E. equisetina Bge

Histological changes in the apex of the female strobilus and the initiation of the reproductive organ (ovule) were investigated in two species of Ephedra. In contrast to the vegetative shoot apex, periclinal cell divisions take place frequently in the dermal layer of the apex of the female strobilus and of the ovule. These divisions in the former begin at the summit before the initiation of the ovule, or they begin at both the summit and peripheral region simultaneously with the ovular initiation. Two ovule primordia originate from the axils of the uppermost bracts by mitotic activity in the subdermal region, their outer part becoming two-layered as the result of regular periclinal divisions in the dermal cells. As compared with the ovule primordia, the residual shoot apex between the ovule primordia shows less periclinal cell divisions just before and after it becomes discernible. The occurrence of these divisions in the apex of the female strobilus and in the ovule primordia is compared with that in the male ones.