EMBRYOLOGICAL STUDIES IN COMPOSITZE. BY H. MAHESWAm DEVI (Department of Botany, Andhra University, Waltair)

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1 EMBRYOLOGICAL STUDIES IN COMPOSITZE HI. Gerbera jamesonii Bolus BY H. MAHESWAm DEVI (Department of Botany, Andhra University, Waltair) Received October 24, 1956 (Communicated by Prof. ft. Venkateswarlu, F.A.SC.) INTRODUCTION THIS paper deals with Gerbera jamesonii Bolus belonging to the small tribe Mutisie~e, the embryology of which is little known. MATERIALS AND METHODS The material was obtained from plants cultivated in the Botanical Gardens of the Andhra University, Waltair. Either acetic-alcohol or formalin-acetic-alcohol was used as a fixative. Customary methods of dehydration and staining were followed. Sections were cut 8 to 12 microns thick and stained with Delafield's Ha~matoxylin. ORGANOGENY The sequence of development of the floral whorls in bisexual flowers is petals, stamens and sepals followed by gyno~cium. In female flowers also the same sequence is observed except that no stamens were developed. STRUCTURE AND DEVELOPMENT OF ANTHER AND POLLEN The structure and development of the anther and pollen in Gerbera jamesonii presents features similar to those described in Laun~a pinnatifida (Venkateswarlu and Maheswari Devi, 1955 a). The primary archesporium in each anther lobe consists of a row of eight to ten cells in longitudinal section and a single cell in transverse section (Figs.l and 2). In the structure of the anther, the epidermis is followed by two wall layers and a periplasmodial tapetum which surrounds the sporogenous tissue (Figs. 3 to 7). The sporogenous tissue is more extensive than in Laumea pinnatifida (Venkateswarlu and Maheswari Devi, 1955 a). In this respect and also in the structure and behaviour of the tapetal cells Gerbera jamesonii resembles Tagetes patula (Venkateswarlu and Maheswari Devi, 1955 b). Here also the parietal layers become crushed and disorganised during the development of the anther. The meiotic divisions in. the pollen mother cell take place in a simultaneous manner and cytokinesis is by furrowing (Fig. 8). Pollen tetrads are either bilateral or tetrahedral. 68

2 Embryological Studies in Compositoe 69 I I Tgrr-Fms Structure and development of anther and pollen. Fig. 1. T.S. of an antherhalfshowingprimaryarchesporinm. Fig. 2. L.S. of an anther lobe showing primary archesporium. Figs Anther lobes at various stages of development. Fig. 7. LS. anther lobe showing periplasmodial tapetum surrounding the pollen grains. Fig. 8. Tetranucleate pollen mother cell showing cytokinesis by furrowing. Fig. 9. One-nucleate pollen grain showing four germ pores. Fig. 10. Mature thre~-celled pollen grain. Figs. 1-3 and 7, 728; Figs. 4-6 and 8-10, 1,091.

3 70 H. MAI-mSWARI DEVI At the time of shedding the pollen grains are spherical and three-ceued. The surface of the exine shows minute projections. There are three germ pores in it (Fig. 10). Occasionally pollen grains with four germ pores (Fig. 9) also have been encountered as in Tagetes patula (Venkateswarlu and Maheswari Devi, 1955 b), Tridax procumbens and Blumea laeiniata (Banerjee, 1940 and 1942). No fibrous endothecium has been differentiated. The epidermis persists till maturity (Fig. 7). MEGASPOROGENESIS AND FEMALE GAMETOPHYTE The ovule, as in all Composit~e, is anatropous, unitegmic and" tenuinucellate. A single hypodermal archesporial cell is differentiated in the young ovule at about the time usually the integument is seen (Fig. 11). The archesporial cell enlarges and directly functions as the megaspore mother cell (Fig. 12). A linear tetrad of megaspores is formed (Fig. 13). Usually the chalazal megaspore becomes functional and an eight nucleate embryo-sac is formed according to the Polygonum type (Figs. 13, 15 and 16). In a few cases, however, both the micropylar and chalazal megaspores of the tetrad enlarge and "develop upto the four-nucleate stage (Figs. 14 and 17) and the two middle ones degenerate. One of the cases is sketched in Fig. 17. In this the four nuclei are not distributed to each pole in the usual manner. In it one nucleus each is situated at either pole and two in the middle of the embryo-sac. The cells of the nucellar epidermis become crushed by the growing embryo-sac and finally disappear by the time the eight-nucleate embryo-sac is formed. The innermost layer of the massive single integument becomes differentiated as the endothelium. In the eight-nucleate embryo-sac the organisation of the antipodal cells takes place earlier than those of the egg apparatus (Fig. 15). Usually only two antipodal cells are organised. About thirty embryo-sacs have been observed and all of them showed this condition. The number of nuclei in each of the antipodal cells varies from two to twelve. The antipodal cells persist upto the time the cotyledons become differentiated in the embryo. The synergids are hooked and the secondary embryo-sac nucleus is usually situated near the egg apparatus (Fig. 16). FERTILISATION, ENDOSPERM AND EMBRYO Fertilisation is porogamous. The pollen tube discharges its contents into one of the synergids as in Tagetes patula (Venkateswarlu and Maheswari Devi, 1955 b). Syngamy and triple fusion take place normally (Fig. 18). The pollen tube and the synergids degenerate and disappear some time after the first division of the endosperm pldmordium.

4 Embryological Studies in Compositae 71 I TExT-FIQs. II-20. Structure and development of the female gametophyte. Figs. 11 and 12. L.S. young ovule showing archesporial cell and megaspore mother cell respectively. Fig. 13. Two-nucleate embryo-sac with the upper three degenerating megaspores. Fig. 14. Megaspore tetrad with chalazal and micropylar megaspores developing further. Figs. 15 and 16. Young and mature embryo-sacs. Fig. 17. Two 4-nucleate embryo-sacs. The nuclei are arranged irregularly. Fig. 18. Part of embryo-sac showing syngamy and triple fusion. Fig. 19. Upper part of embryo-sac showing the zygote, degenerating synergids and pollen tube. Endosperm nucleus is in its first division. Fig. 20. L.S. embryo-sac with egg, cellular endosperm and persisting antipodal cells. Figs. 11 and 12, x339. Figs. 13, 14, 18 and 19, x485. Figs. 15 and 16, x242. Fig. 17, x388. Fig. 20,x172. The endosperm is ab initio nuclear and the primary endosperm nucleus divides earlier than the fertilised egg (Fig. 19). The first division of the primary endosperm nucleus is sometimes transverse and other times vertical. In this feature Gerbera jamesonii resembles Tagetes patula (Venkateswadu and Maheswari Devi, 1955b). In later stages the endosperm becomes cellular (Fig. 20). It is completely absorbed in the mature seed.

5 72 H. MAI-mSWAlU DEVI TEXT-FIGs Various stages in the development of the embryo, 728. ca and cb, apical and basal cells of the two-celled pro-embryo; q, Quadrants derived from ca; m and ci, upper and lower daughter cells arising out of the first division of cb; n, Upper daughter cell derived from ci; n', Lower daughter cell derived from ci; o and p, Upper and lower daughter cells of n'. The embryo development is closely similar to that in Tagetes patula (Venkateswarlu and Maheswari Devi, 1955 b) and is shown in Figs. 21 to 29

6 Embryological Studies in Compositte 73 and in the following schematic representation. It conforms to the Asterad type and keys out to the Senecio variation. ca... q Cotyledons and stem tip Fertilized egg ~ cb~ ~"... Entire hypocotyledonary region and plerome initials of root n..... Root tip, root cap and dermatogen of root p-suspensor SEED In a fully developed seed the endosperm and also the integument, except for one or two of the outermost layers of its cells, are consumed by the embryo and thus the latter comes to lie in close proximity to the pericarp as in Launa~a pinnatifida (Venkateswarlu and Maheswari Devi, 1955 a). SU~RY In bisexual flowers the organogeny follows the following sequence: petals, stamens, sepals and gynczcium and in the female flowers the sequence is the same but for the absence of the stamens. The anther shows the epidermis, two wall layers, periplasmodial type of tapetum and sporogenous tissue. No fibrous endothecium is differentiated. The epidermis persists in the mature anther and the wall layers and periplasmodial tapetum disappear. Meiotic divisions in pollen mother cell are simultaneous. Cytokinesis is by furrowing. The mature pollen gains are three-celled. The exine shows small projections on the surface and contains three germ pores. Occasionally pollen grains with four germ pores have been encountered. The ovule is unitegmic, tenuinuceuate and anatropous. The primary archesporiurn is one-celled. It directly functions as the megaspore mother cell. Usually the chalazal megaspore of the linear tetrad develops into the eight-nucleate embryo-sac. Fertilisation is porogamous. Endosperm is of nuclear type. It later becomes cellular. Embryo development conforms to the Asterad type and keys out to the Senecio variation. The mature seed contains the fully developed embryo within the pericarp separated by a thin membrane which represents the crushed remains of the outer portion of the integument.

7 74 H. MAHESWARI DEVI ACKNOWLEDGEMENTS My grateful thanks are due to Prof. J. Venkateswarlu for kirldly suggesting the problem and for critically going through the manuscript. I wish to express my sincere thanks also to Prof. Rev. Fr. H. Santapau for "kindly furnishing me with the correct specific name of the plant. Banerji, I. Venkateswarlu, J. and Maheswari Devi, H. REFERENCES.. "A contribution to the life-history of Tridax procumbens L.," Proc. Ind. Acad. Sci., 1940, 1, "A contribution to the life-history of Blumea laciniata L.," dour. Indian hot. Sot., 1942, 21, "Embryological studies in the Composita~. I. Laumea pinnatifida Cass.," Proc. Ind. Acad. Sci., 1955 a, 51, "Embryological studies in Composita~. II. Helenie~e," Proc. Nat. Inst. Sci. India, 1955/7, 21B(4), Printed at The Bangalore Press, Bangalore City, by C. Vasudeva Rao, Superintendent, and Published by The Indian Academy of Sciences, Bangalore.