Prec. Indian Acad. Sci,, Vol. 87 B, No. 2, February 1978, pp. 23-27, 9 Printed in India. The embryology of Ximenia americana L. K SANKARA RAO and G SHIVARAMIAH Department of Botany, St. Joseph's College, Bangalore 560 001 MS received 18 July 1977; revised 2 November 1977 Abstract. Olacaceae, Ximenia americana L.--Embryology. Anther tapetum glandu- lar. Endothecium fibrous. Cytokinesis in microsporocytes simultaneous. Pollen dimorphic, two-celled. Ovules ategmic, crassinucellar. Embryo sac Polygonum type, produces a haustorial caecum. A comparison with earlier investigations pre- sented. Keywords. Ximenia americana; embryology. 1. Introduction A perusal of the literature reveals that there are no adequate embryological data on the family Olacaceae except for the significant contributions by Fagerlind (1947), Shamanna (1954, 1961) and Agarwal (1961, 1963a, b). The present paper deals with aspects on the embryology of Ximenia americana L. 2. Materials and methods Flower buds at different stages of development were collected from Bannerghatta National Park, Bangalore, and fixed in FAA. Customary methods of dehydration and embedding were followed. Sections were cut at 8-12/zm and stained with Heidenhain's haematoxylin and counterstained with erythrosin. 3. Observations The creamy white flowers are 4--5-merous, actinomorphic, bisexual and hypogynous. Petals are hairy and reflexed. Stamens are twice as many as petals. Anthers are dithecous. Ovary is sessile and incompletely 3-4-celled each with one pendulous ovule (figures I-7). Anthers are tetrasporangiate. A transection of a young anther shows the epider- mis, endothecium, a middle layer and tapetum around the sporogenous tissue (figure 8). The tapetum is of the glandular type and its cells remain uninucleate throughout. The microsporocytes undergo simultaneous meiotic division and form tetrahedral or decussate microspore tetrads (figures 9 and 10). In the mature anther, the endothecial cells acquire fibrous thickening and the middle 23 24 K Sankara Rao and G Shivaramiah Figures 1-7. 1. L.S. of young flower bud. 2-7. L.S. of pistil showing ovular develop- ment (X 50). The embryology of Ximenia americana L. 25 Figures 8-21. 8. Transection of a young anther showing microsporocytes, tapetum, middle layer, endothecium and epidermis (X 1200). 9-10. Tetrahedral and decussate microspore tetrads (X 1600). 11. Portion of mature anther in transection showing fibrillar endothecium and two-celled pollen grains (X 1200). 12-13. Pollen grains (X 2000). 14-17. L.S. of young nucellus (X 1200) showing. 14. Hypodermal archesporial cell. 15. Multiple archesporium. 16. Megaspore mother cell. 17. Linear tetrad of megas- pores. 18-20. Stages in the progressive development of the embryo sac (X 1200). 21. Embryo sac with the haustorial diverticulum (X 900). 26 K Sankara Rao and G Shivaramiah layer is crushed (figure 11). Anther dehiscence is by longitudinal slits. The pollen grains are 2-celled when shed (figure 11). These are usually triangular with three germ pores, but occasionally, may be pentangular with 5 germ pores (figures 12 and 13). Pollen grains are dimorphie. Ovules are crassinucellar and ategmic (figures 1-7). The female archesporium consists of a single hypodermal cell (figure 14). In some ovules, 3--4 arehesporial cells differentiate in the nucellus (figure 15). However, one of these cells develops further. After giving rise to 2-3 cells of parietal tissue, the archesporial cell forms the conspicuous megaspore mother cell (figure 16). Meiotic division in the megaspore mother cell results in a linear tetrad of megaspores (figure 17). The chalazal megas- pore becomes functional while the other three degenerate. The nucleus of functional megaspore undergoes a first mitotic division and the two resulting nuclei move to opposite poles of the enlarging megaspore with a vacuole developing between them (figure 18). The 2-nucleate embryo sac enlarges while its nuclei by two successive free nuclear divisions give rise to an 8-nucleate embryo sac (figures 19 and 20). In an organised embryo sac, the egg-apparatus consists of a large median egg cell flanked by a pair of equally large synergids. The synergids develop filiform apparatus. The polar nuclei are conspicuously large. The three antipodals degenerate soon after their organisation into cells (figure 20). In some ovules, the embryo sac develops a lateral caecum which eventually grows into a diverticulum and elongates enormously parallel to the embryo sac within the nucellus (figures 7 and 21). The egg apparatus and the antipodal cells are organised inside the diverticulum while the polars remain within the embryo sac proper (figure 21). Antipodal cells in these embryo sacs with haustorial growth remain persistent for a longer period. Starch grains are seen to accumulate in the cytoplasm around the antipodals. Antipodal cells are stacked one above the other in the chalazal end of the diverticulum. One of these cells elongates considerably, probably serving as a haustorium. 4. Discussion The anther structure, morphology of the ovule and the development of female gametophyte in Olacaceae are varied and interesting. The structure of the anther in Ximenia americana differs from that found in other investigated members of the family (Agarwal 1963a; Shamanna 1954, 1961). The number of middle layers is 2 or 3 in the other members whereas in X. americana, it is 1. In Strombosia ceylanica, the endothecium is 2-1ayered at places and in Olax fibrous thickenings appear in some cells of the adjoining middle layer (Agarwal 1961, 1963a). But in X. americana the fibrous endothecium remains single-layered throughout. Tapetal cells are uninucleate in most members of the family including X. americana, the only exceptions being Olax with multinucleate condition. The pollen grains are tri- angular with 3 germ pores in most of the members. Occasionally, they are squarish with 4 germ pores in Strombosia ceylanica (Agarwal 1961). In X. americana they are tri- and pentangular with 3 and 5 germ pores respectively. Pollen grains of two different sizes within the same anther loculus are observed in this genus. Pollen dimorphism has not yet been observed in any other member of Olacaceae. Pollen grains at the time of shedding are 3-celled in Olax scandens and Olax wightiana The embryology of Ximenia americana L. 27 and 2-celled in S. ceylanica and Olax stricta (Agarwal 1963) and X. americana (present report). Ovules of Coula edulis, Heisteria cyanocarpa, Macrotheca elaeocarpa, Minquartia guianensis and Octoknema are bitegmic. In Anacolosa frutescens, Olax stricta, Olax wightiana, Strombosia ceylanica and Tetrastylidium janeirense, they are unitegmic. In Olax imbricata, the distinction between the nucellus and the integument is not marked. Ovules of Liriosma acuta, Ptychopetalum petiolatum and X. americana are without integument. Crassinucellate as well as tenuinucellate ovules are observed in the family. Thus, Olacaceae displays ovules which are structurally simple to complex types. Fagedind (1948) considers the tenuinuceUate and ategmic ovules in the family as a derived condition, resulting through a reduction in their complexity. A critical study of ovules in other uninvestigated members of the family may provide further information to elucidate their phylogeny. Another interesting feature in Olacaceae is the development of female gametophyte. Both Polygonum and Allium types are represented. It is remarkable that these two types of development are noticed among the species of the same genus; Olax wightiana shows the Allium type while all other investigated species of Olax show the Polygonum type of development. The mature embryo sac remains confined to the ovule in Anacolosa frutescens, Octoknema and S. ceylanica. But in Chaunochiton kappleri, Olax imbricata, Olax scandens and Olax wightiana the micropylar end of the embryo sac grows out of the ovule towards the stylar canal. In X. americana, a haustorial caecum arises from the embryo sac laterally and develops into a diverticulum. A similar haustorial growth extending as far as the placenta is noticed in Olax stricta. Starch grains are present in the embryo sac of X. americana as also in S. ceylanica. Acknowledgement The authors are grateful to the Principal, St. Joseph's College, Bangalore for the facilities and encouragement. 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