'n Embriologiese studie van Suid-Afrikaanse melianthaceae

Abstract

The embryology of Bersama transvaalensis Turrill, Greyia sutherlandii Hook. & Harv. and Melianthus major L. was studied. In the phyllosporous taxa, G. sutherlandii and M. major the placentation of the ovules is parietaI, but the stachyosporous B. transvaalensis has basal ovules. The mature ovules of all three taxa are anatropous, bitegmic and crassinucellar. In G. sutherlandii the ovule curves in the funicular region, but in B. transvaalensis and M. major the anatropous position is reached by bending of the nucelli. The outer integument in G. sutherlandii is triseriate, but in B. transvaalensis and M. major it is multiscriatc. A multiseriate parietal tissue develops in all three taxa and a nucellar cap is present. Linear macrosporc tetrads are formed in M. major and B. transvaalensis. In the latter taxon, however, triads may also occur. In G. sutherlandii the macrospore tetrads are either linear, or T-shaped. A Polygonum type embryo sac develops from the chalazal macrospore. In M. major the young embryo sac contains seven nuclei only, as one of the chalazal nuclei fails to divide. The mature embryo sac of the latter taxon has no antipodals. In B. transvaalensis and M. major the secondary embryo sac nucleus is hypertrophic. The embryos of the three taxa conform to the Asterad type. The embryos of both B. transvaalensis and M. major lack suspensors and are therefore placed under the Penaea variation, while the suspended embryo of G. sutherlandii follows the Erodium variation. In both B. transvaalensis and M. major the basal cell divides longitudinally, resulting in a primitive globular tetrad. The tctracellular proembryo of C. sutherlandii, however, is T-shaped. An epiphysis initial takes part in the embryogeny of all three species. Both integuments participate in the development of the seed coat of G. sutherlandii. The outer epidermii develop into fibrous protective layers, while the other cell layers disappear or are crushed. The outer integument of B. transvaalensis and of M. major thickens during seed coat development. In the latter taxon the outer epidermis cells change into macrosclereids and a thick inner cuticular layer separates the cells of the nucellus and the inner integument. No such protective layer develops in the seed coat of B. transvaalensis. The endosperm of all three species is nuclear in origin. Insofar as it is possible to make a recommendation on the grounds of embryological data, it is suggested that Creyia should not be placed in the same family as Bersama and Melian thus, but that Greyia should be placed in one and Bersama and Melianthus in another family in the order Sapindales.