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The Morphology and Embryology of Floerkea Prosepinacoides~Willd

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The Morphology and Embryology of Floerkea Prosepinacoides~Willd The Morphology and Embryology of Floerkea prosepinacoides~Willd. with a Discussion on the Systematic Position of the Family Limnanthaceae by P. MAHESHWARIand B. M. JoHRI* ReceivedJune 30, 1956 The family Limnanthaceae comprises two genera, Floerkea and Limnanthes. The embryology of Limnanthes douglasii has been studied by Stenar (1925), Eysel (1937), Fagerlind (1939) and Mason (1951) but without any agreement on several critical points. More recently Mathur (1956) has investigated L. douglasii and L. striata and concluded that the embryo sac is tetrasporic corresponding to the pseudomono- sporic, biphasic type' of Harling (1950). The earlier interpretation of Stenar and Eysel of an Adoxa type of development is not confirmed (see also Fagerlind, 1939). Mason (1952) has recently conducted a systematic study of the genus Limnanthes and "utilized the traditional morphological approach, as well as chromosome studies of hybridization as embodied in more recent taxonomic techniques." On Floerkea, a monotypic genus of North America, there is a general article by Russell (1919) and a short note by Johni & Maheshwari (1951) on its embryo sac and endosperm. The systematic position of the family Limnanthaceae has been a debated ques- tion. Brown (1933) recognized some common features with the hypogynous families but did not assign a definite place to it. Engler & Prantl (1897) placed it in the order Sapindales and Hutchinson (1926) in the Geraniales. As will be shown here, none of these assignments is satisfactory and porbably the family needs to be raised to an ordinal rank. Materials and methods While on tour in the U.S.A..in 1946, one of us (P.M.) fixed some material of the plant from Madison, Wisconsin. Additional material was obtained in 1952 from Dr. L. Farquharson (Bloomington, Indiana) and Dr. L. A. Kenoyer (West Michigan College), and in 1952 from Dr. M. Fulford (Cincinnati, Ohio) and Dr. C. T. Mason Jr. (Stanley, Wisconsin). To all these persons we offer our most grateful thanks. Buds flowers and fruits were prepared and imbedded in the usual way. Sections were cut at 6-15 microns and stained in iron-haematoxylin as well as safranin and * Departmentof Botany, Universityof Delhi,Delhi 8, India. 1) When only one of the four megasporenuclei contributesto the formationof the embryo sac, the developmentis pseudomonosporic.The term biphasicmeans that twopost-meiotic divisions occur beforethe organizationof the embryosac. Oct.-Nov. 1956 Bot. Mag. Tokyo, Vol. 69, Nos. 820-821 411 fast green. Both combinations gave good results. Dissections were also made of the endosperm at the globular stage of proembryo and stained with cotton blue in lactophenol. Morphology Floerkea proserpinacoides, popularly known as the `false mermaid weed', is a short-sized (about 10 cm. high) annual, marshy herb with pinnately dissected, simple, alternate leaves. Figs. 1-11. Floral morphology and anatomy. (a, androecium ; c, corolla ; d, stylar bund- les ; k, calyx ; o, ovary wall; ov, ovule; st, style ; v, ovular bundles). Fig. 1. L.s. flower at mature embryo sac stage ; the swollen portion of the filament on the right represents the basal gland. x 25. Figs. 2-8. Transection of a flower with tricarpellary gynoecium showing origin of vascular traces to various organs ; approximately at level marked in Fig. 1, but of a younger flower. x 39. Figs. 9-11. T. s. older flower (bicarpellary gynoecium), more or less at levels, 7, 8 and 11 indicated in Fig. 1. x 39. 412 植 物 学 雑 誌 第69巻 第820-821号 昭 和31年10-11月 The solitary axillary flowers possess three large, imbricate sepals and three contorted petals (Figs. 1, 8, 10, 11) ; rarely there may be four sepals. The sip stamens are arranged in two whorls, the outer alternating with the petals (Figs 7-10) and having conspicuous basal glands. The gynoecium is usually tricarpellars but sometimes bicarpellary, with a gynobasic style (Figs. 1, 8, 10). The ovaries alternate with the petals, and each has a single basal-parietal ovule (Figs. 1, 8, 10) The vascular supply of the flower is shown in Figs. 1-11. There are three bundles at the upper end of the pedicel (Fig. 2), alternating with which arise the three traces (k1, k2, k3) to the sepals (Fig. 3). The traces to the petals (c1, c2 c3) alternate with those of the sepals (Fig. 4). Further up each sepal shows one median and two lateral bundles, while the petal traces proceed undivided (Fig. 11) Next are the six staminal traces (al-a6) which arise at about the same level (Fig. 5) The remaining bundles of the central ring supply the gynoecium. One bundle enters each ovule, curves round and branches, the ramifications continuing up tc the integument (Figs. 1, 7-10). Bundles alternating with the ovular supply enter the style (Figs. 6-8, 9, 10) and bifurcate in the region of the stigma (Fig. 11). A* in LininnnT e s (5aimders_ 192R~ _ the ov a rv wall i s devoid of any vascular sunnly. Figs. 12-25. Microsporogeneis and male gametophyte. Figs. 12, 13. Portions of anther lobes at tetrad and uninucleate pollen grain stage respectively. x 434. Figs. 14, 15. Micro- spore mother cells, Meiosis I and II. x 1585. Fig. 16. Cytokinesis by furrowing. x 1585. Fig. 17. Decussate tetrad. x 1585. Fig. 18. Uninucleate pollen grain. x 1585. Fig. 19. Division of microspore nucleus, x 1585. Figs. 20--23. Two-celled pollen grains. x 1585. Fig. 24. Outline diagram for Fig. 25. x 50. Fig. 25. Portion of anther lobe marked in Fig. 24, to show region of dehiscence. x 434. Oct.-Nov. 1956 Bot. Mag. Tokyo, Vol. 69, Nos. 82O821 413 Microsporogenesis and male gametophyte Each microsporangium of the dithecous anther shows a group of hypodermal archesporial cells. An endothecium, two persistent middle layers and the glandular tapetum are derived from the primary parietal layer (Figs. 12, 13, 25). During reduction divisions the tapetal cells enlarge and become binucleate, but later the nuclei fuse (Figs. 12, 13). The inner tangential walls of the tapetal cells break down at the microspore stage (Fig. 13), and as the pollen grains mature the tapetum disorganizes. The reduction divisions are simultaneous, secondary spindles are laid down during Meiosis II, and cy tok inesis occurs by furrowing. Centripetal wedges formed by the special mucilaginous wall bring about quadripartition (Figs. 12, 14-16). The microspores are usually arranged tetrahedrally or in a decussate fashion (Figs. 16, 17) ; isobila teral tetrads also occur sometimes. The microspores enlarge and the wall differentiates into an exine and an intine (Fig. 18). In some of the microsporangia there is widespread degeneration of the microspores (Fig. 13). On division the nucleus gives rise to a small generative and a large vegetative nucleus separated by a membrane (Figs. 19, 20). As the latter soon dissolves, the generative cell moves into the cytoplasm of the vegetative cell where it acquires a lenticular shape (Figs. 21, 22). In some pollen grains the vegeta- tive nucleus had flattened and came to lie adjacent to the generative cell (Fig. 23). The mature pollen grains are rounded and 4-colporate, and the exine has warty projections (Figs. 20-23). During maturation of the anther, the partition walls between the adjacent micro- sporangia break down (Fig. 24), and dehiscence occurs by longitudinal slits along the junction of the pollen sacs. In this region the epidermal and endothecial cells are smaller and thin-walled. Further, the former lack tannin and the latter are devoid of fibrous thickenings (Fig. 25). The stamens of the outer whorl dehisce earlier than those of the inner. Ovule The ovule is un itegmic and tenuinucellate, and the integument makes its appea- rance almost simultaneously with the differentiation of the archesporium. The curvature of the ovule is very rapid so that by the time the first meiotic division is over, it becomes anatropous (Figs. 26, 27). Besides the epidermis, the nucellus comprises only one more layer of cells on the sides (Fig. 30). This layer is crushed during megasporogenesis and the epidermis meets the same fate soon after. The integument is massive and shows a conspicuous vascular supply (Figs. 1, 8, 10, 28). During its expansion the embryo sac consumes the adjacent cells of the integument (Figs. 42, 43). Mathur (1956) reports that in Limnanthes douglasii a few cells of the integu- 414 植 物 学 雑 誌 第69巻 第820-821号 昭 和31年10-11月 Figs. 26-43. Megasporogenesis and female gametophyte. Figs. 26-28. L , s. ovule3 at arche- sporial, 2-nucleate and mature embryo sac stage; Figs. 27 and 28 are outline diagrams for Figs. 31 and 42 respectively. x49. Fig. 29. Multicel led archesporium. x 801. Fig. 30. Megaspore mother cell, x 801. Figs. 31--37. Stages in developmet of embryo sac; explana- tion in text. x 801. Figs. 38-39. Abnormal gametophytes ; Fig. 38. x 801; Fig.39. x 528. Figs. 40, 41. Mature embryo sacs. x 528. Figs. 42, 43. Same, 1. s. portions of ovules; note the thickened integumentary cells at the micropylar end. x 316. Oct.-Nov. 1956 Bot. Mag. Tokyo, vol. 69, Nos. 820-821 415 ment at either end of the embryo sac become thick-welled. They have dense cytoplasm and appear to have a nutritive function. In F'loerkea proserpinacoides such thick-walled cells are distinguishable only at the micropylar end (Figs. 42, 43). Megasporogenesis and female gametophyte There is a group of hypodermal archesporial cells (Fig. 29) but only one of them functions. As it differentiates into the megaspore mother cell, prominent vacuoles appear at either pole (Fig. 30). The first meiotic division results in a markedly smaller nucleus which migrates to the chalazal end, and a larger one which stays on in the centre o f the cell (Fig.
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