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286 286 植物研究雑誌第 63 巻第 8 号昭和 63 年 8 月

S. S. Kumar SOOD*: Embryology of Pecteilis sus αnn αe (Orchidaceae)

S.K. スード Pectei lz" s susannae の腔学的研究

Orchidaceae Orchidaceae Juss. have attracted the attention of several embryologists from time to time because of the interesting diversity in the development and organization zation of anther ，embryo sac and embryo. The publications of Schnarf (1931) ， Swamy (1949a ，b) ，Wirth & Withner (1959) ，Davis (1966) ，Veyret (1974) and Abe (1972) summarized the previous embryological works on the family. Em- bryologically bryologically the genus Pecteilis of tribe Orchideae is unknown; and this lacuna prompted me to take up the present investigation. Material Material and methods Buds ，:fl owers and fruits of Pecteilis susannae (し) Ra 五n. were collected from Syree forest in Shimla District during July to

September 1986 and 自xed in formalin-acetic-alcoho l. Conventional methods of microtomy were followed. Serial sections (7-12μm) were cut and stained with safranin ・fast green. Camera-lucida drawings were made at the bench leve l. The voucher specimen no. OD-25 is deposited in Herbarium of Himachal Pradesh University. University. Observations Microsporangium ， microsporogenesis and male gametophyte. A transverse section of anther shows four locules (Fig. 1A). In a young anther anther the microspore mother cells are surrounded by epidermis ， outer secondary parietal parietal Iayer (osp) and inner secondary parietal Iayer (isp) (Fig. 1B). The Iatter Iatter divides periclinally to produce a middle layer and tapetum (Fig. 1B). The osp directly forms endothecium. The fully formed anther wall comprises of of epidermis ，endothecium ， middle layer and gIandular tapetum (Fig. 1C). It s development foIIows the Monocotyledonous type. The cells of the tapetum are uninucleate uninucleate (Fig. 1E). At maturity the anther wall consists of epidermis and endothecium with fibrous thickenings whereas the middle Iayer and tapetum disorganize disorganize (Fig. 1D). Meiosis in the microspore mother cells is of the simuI- taneous taneous type (Fig. 1F -H). The microspore tetrads are decussate ， isobilateraI and tetrahedral (Fig. 1，1 一K) . The tetrads are held together to form small bundles ，massulae which at anthesis are 2-celled (Fig. 1D).

* Department of Biosciences ，Himachal Pradesh University ，Shimla 171 005 ，H.P. ， India.

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05mm G-I

05mm J

G E

4m!!!...--- K

H Fig. 2. Pecteilis susannae ， megasporangium ，megasporogenesis and female gametophyte (ant ， antipodals; antipodals; dms ，degenerated megaspores; e，egg; fm ， functional megaspore; ii ， inner integument; oi ，outer integum 巴nt; sn ，secondary nucleus; syg ， synergid). A. Longisection of ovular primordium with archesporial cel l. B ，C. Origin of integuments in young ovules. D. Mega- spore mother cel l. E. Dyad; the micropylar cell is small. F. Lin 巴ar megaspore tetrad with

degenerated upper two megaspores. G- I. Two- ，4 ・ and 8-nucleate embryo sacs. J. Mature embryo sac. K. Longisection of mature ovule which is anatropous ，bitegmic and tenuinucellate.

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Megasporangium. Numerous ovular primordia arise as small protuberances from the forked parietal placentae. Each primordium consists of an axial row of of cells surrounded by a layer of epidermal cells (Fig. 2A). The inner integument initial arises from the epidermal layer of ovular primordium (Fig. 2B). It It consists of two ，enlarged ，adjacent ，dermal cells which by periclinal and anticlinal anticlinal divisions form the two cells thick inner integument (Fig. 2C ， D). The micropyle is formed by the inner integument (Fig. 2K). The outer integument primordium is initiated a little later than the inner one. It di 百erentiates and develops exactly like that of the inner integument primordium (Fig. 2C ， D). The mature ovule is anatropous ， bitegmic and tenuinucellate (Fig. 2K). Megasporogenesis and female gametophyte. The hypodermal archesporial cell cell directly functions as the megaspore mother cell (Fig. 2A ， D). It enlarges and undergoes two meiotic divisions forming first a dyad and later a linear tetrad tetrad of megaspores (Fig. 2D-F). The chalazal megaspore is functional (Fig. 2F) 2F) and undergoes three successive mitotic divisions to form an 8-nucleate embryo sac (Fig. 2G-I). The mature embryo sac consists of an egg apparatus ，a secondary nucleus and three antipodal cells (Fig. 2J). Endosperm and embryo. The primary endosperm nucleus does not undergo any division but degenerates (Fig. 3A-E). The zygote (Fig. 3A) divides transversely versely resu1ting in a basa1 cell (cb) and a terminal cell (ca) (Fig. 3B). The former divides transversely producing a middle cell (m) and a suspensor initia1 cell cell (ci). The 1atter divides 10ngitudinally resulting in a T-shaped ， 4-celled proembryo (Fig. 8C ， D). The two cells of ca undergo a longitudinal division ， at at right ang1es to the 五rst ，forming a quadrant which divides transversely in an octant of two tiers 1 and l' (Fig. 3F ， G). Transverse division occurs in the cells cells m and ci resul ting in a linear row of four to six cells (Fig. 3E- H) . The cells cells d' and d" which are derived from m ， take part in the organization of the mature embryo (Fig. 3G 一K). Further divisions in the different embryonic tiers 1，1' ， d' and d" are irregular which result ，自 rst in a globu1ar proembryo and then then an undi 百erentiated mature embryo (Fig. 31 一K) . The suspensor is made up of 4-5 cells (Fig. 3H) ，and it collapses during maturation of the embryo. Seed and seed coat. Each seed contains an embryo surrounded by seed coat (Fig. (Fig. 3L). Both the layers of tegmen and the inner layer of testa degenerate after after fertilization. The cells of the outer layer of testa lose their protoplasts ，

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Fig. Fig. 3. Pecteilis susannae ，endosperm and embryogeny (dant ，degenerated antipodals; dpen ，degenerated primary endosperm nucleus; pen ，primary endosperm nucleus; z， zygote). A. Zygote ，

primary endosperm nucleus and degenerated antipodals. B ，C. Two- and 3・celled proembryos. D. Four-celled ，T-shaped proembryonal tetrad. E. Four-celled proembryo; note the transversely divided middle and vertically divided terminal cells; and degenerated primary endosperm nucleus. F-J. F-J. Stages leading to the formation of globular proembryo. K. Mature embryo. L. Surface view of mature seed with embryo.

-26 ー August 1988 Journ. Jap 、 Bo t. Vo l. 63 No. 8 291 become transparent and form a 1-1ayered seed coat. Discussion Discussion The anther wall of P. susann αe is 4-1ayers thick and its development corresponds to the Monocotyledonous type of Davis (1966). Swamy (1949a) (1949a) stated that in the mature anthers of orchids the epidermis disorganizes and the endothecium forms the conspicuous laye r. On the contrary ， it persists in in P. susannae as in most other orchids ，Arundina g γaminifolia ，CypriPedium cordigerum ，Haben α ria edgeworthii ，H. elisabethae ，H. galeandra ，Herminium angustifolium ， Microstylis cylindrostachya ， Neottia listeroides ，Satyrium nepalense ense and Spathoglottis plicata (Mohana Rao & Sood 1979 ，Prakash & Lee-Lee 1973 ，Rao 1967 ，Sood 1984 ，1985a ，b ，1986 ，Sood & Mohana Rao 1986). It appears that that the view of Swamy (1949a) is incorrect. Development of the female gametophyte conforms to the Polygonum type of of Maheshwari (1950). The phenomenon of 'strike' ，a feature peculiar to many orchids orchids (Abe 1972 ，Poddubnaya-Arnoldi 1967) is absent in the present species. Li ke most other Orchidaceous taxa ， the cells of nucellar epidermis and inner integument do not show any enlargement and their cells degenerate in the de- veloping veloping seeds. The mature embryo is constructed from the derivatives of tiers 1，1' ， d' and d". d". Its development conforms to the Group ‘ B' (Onagrad type) of Swamy (1949b). (1949b). A unique feature in the embryogeny of Pecteilis susannae is the participation participation of middle cell both in the organization of suspensor and embryo. The mature embryo is undi 百erentiated as in most other orchids investigated so far far (see Veyret 1974).

References

Abe ， K. 1972. Contributions to the embryology of the family Orchidaceae. VI I. A comparative study of the orchid embryo sac. Sc i. Rep. Tohoku Univ. 36: 179-20 1. Davis ， G. L. 1966. Systematic embryology of the Angiosperms. John Wiley and Sons ，New York. Maheshwari ， P. 1950. An to introduction the the embryology of angiosperms. Tata McGraw-hill ，New Delh i. Mohana Rao ， P. P. R. & S. K. Sood 1979. Embryology of Satyrium nepalense (Orchidaceae). Norw. J. Bot. 26: 285-294. Poddubnaya-Arnoldi ， V. A. 1967. Comparative embryology of the Orchidaceae. Phytomorphology 17: 312-320. Prakash ， N. & Aow Lee-Lee 1973. Life history of a common Malaysian orchid Spathoglottis

-27- 292 292 植物研究雑誌第 63 巻第 8 号昭和 63 年 8 月 plicata. plicata. Phytomorphology 23: 9-17. Rao ，A. N. 1967. Flower and seed development in Arundin αgr αminifolia. Phytomorphology 17: 291-300. Schnarf ， K. 193 1. Vergleichende Embryologie der Angiospermen. Gebruder Borntraeger ， Berlin. Berlin. Sood ， S. K. 1984. An embryological study of Neottia listeroides ，a saprophytic saprophytic orchid in lndia. J. Plant Anat. Morpho l. 1: 69-75. 一一 1985a. Occurrence of uninucleate tapetal cells in diandrous orchid Cy 戸riPedium cordigerum Don (Orchidaceae). lndian Bot. Cont r. 2: 65-66. 一一一 1985b. Gameto- phytes ，integument initiation and embryogeny in Microstylis cylindrostachya (Orchidaceae ， Epidendreae). Proc. lndian Acad. Sc i. (Plant Sci.) 95 (6) : 379- 387. 387. 一一一 1986. Gametogenesis ，integuments initiation and embryogeny in three three species of llabenari α(Orchidaceae ， Orchideae). Proc. lndian Acad. Sc i. (Plant (Plant Sc i.) 96 (6) : 487-494. 一一& P. R. Mohana Rao 1986. Development of male and female gametophytes in llerminium angustifolium Benth. (Orchi- daceae). daceae). Phytomorphology 36 (1 ， 2) : 11-15. Swamy B. G. L. 1949a. Embryo- logical logical studies in the Orchidaceae. 1. Gametophytes. Am. Mid l. Na t. 41 : 184- 20 1. 一一 1949b. Embryological studies in the Orchidaceae. 2. Embryogeny. Am. Midd l. Nat. 41: 202-232. Veyret ， Y. 1974. Development of the embryo and the young seedling stages of orchids. In Withner ， C. L. (ed.): The urchids-a scienti 自c survey. p.223-265. John Wiley and Sons ，New York. Wirth ， M. & C. L. Withner 1959. Embryology and development in the Orchidaceae. Jn Withner ， C. L. (ed.): The orchids-a scienti 五c survey. p. 155-188. Ronald press ，New York.

* * * * Pecteilis Pecteilis susannae (ラン科)の花粉，匹嚢，/fE乳，/fEの形成を観察した。/fEの壁は表皮組織と endothecium とから作られる。その下に 1 層の middle layer があり，花粉塊を頼粒状のタベタムが包む。匪珠は倒生，薄層珠心である。匹嚢形成はタデ形。匝乳の核は分裂せずに消失する。伍の本体は 2 細胞期の ca 細胞全体と cb 細胞の上部の d 層から分化する。種子の時には子葉の分化も組織の分化も起こらない。