Proembryo Development and Suspensor Elongation in Araucaria Juss

Abstract

Development of the proembryo and suspensor was studied in three species of Araucaria– A cunninghamii, A. bidwillii and A. heterophylla. In all species there are six synchronous free nuclear mitoses followed by wall formation. The subsequent internal division gives rise to a typical U.S.E. conifer proembryo. although the E group includes the conspicuous symmetrical cap, and the U cells are very ephemeral. During all divisions the proembryo is situated in the central region of the archegonium. The cells of the S group subsequently elongate to form the functional suspensor. Cleavage polyembryony does not occur although simple polyembryony is common. The proembryo of Araucaria is considered to have diverged at an early stage of evolution of the conifer proembryo, but to have subsequently undergone considerable specialization in a direction unrelated to evolutionary trends recognizable among other conifers.