The embryology ofStegnospermataceae,with a discussion on its status,affinities and systematic position

The embryology ofStegnosperma halimifolium andS. watsonii has been studied in detail. The tapetum is of the secretory type and its cells become multinucleate. Simultaneous cytokinesis in the pollen mother cells follows meiosis. The ripe pollen grains are 3-celled. The ovule is crassinucellate, bitegmic and amphitropous, with the micropyle formed by the inner integument alone. The female archesporium is one celled, and the parietal tissue 3–5 layered. The embryo sac development conforms to thePolygonum type. A central strand, 6 or 7 cells thick, differentiates inside the nucellus and extends from the base of the embryo sac to the chalazal region. The endosperm is nuclear. The embryogeny conforms to the Caryophyllad type. The seed coat is formed by the outer epidermis of the outer integument and the inner epidermis of the inner integument. Based on this evidence and other data, the status of the genus as an independent family,Stegnospermataceae (Stegnospermaceae) is confirmed. Apparently, it forms a connecting link betweenPhytolaccaceae andCaryophyllaceae.     

Development of ovule,embryo sac,and endosperm in Dipterostemon and Dichelostemma (Alliaceae) relative to taxonomy

Dipterostemon capitatus and all species of Dichelostemma have the following characters in common: the ovule is anatropous and bitegmic; the nucellar epidermis is penetrated by the embryo sac; the remaining chalazal part of the nucellus expands, partly due to periclinal divisions in its epidermis; the micropyle is formed by the inner integument only; parietal cells are present; the embryo sac develops according to the Polygonum type; the endosperm is nuclear; after fertilization, the cells of the inner integument enlarge greatly. One difference between the genera is that the inner integument is two cells thick in Dipterostemon, but five to seven cells thick in all Dichelostemma species. In Dipterostemon, embryogenesis is of the Asterad type, and the formation of walls in the endosperm occurs much as in wheat. The absence of variation in embryological characters among the species of Dichelostemma strongly supports the view that these species all belong in one genus, despite differences in gross morphology. Dichelostemma is very closely related to Brodiaea, since species of these two genera show identical embryology. Dipterostemon must be retained as a genus because a deviating inner integument adds to uniqueness in gross morphology. Dipterostemon, Dichelostemma, and Brodiaea, are embryologically quite different from Triteleia. Neither Dipterostemon nor Dichelostemma show any close affinity with Allium.     

Ephemeral and non-ephemeral structures during seed development in two Cytisus species (Papilionoideae,Leguminosae)

Abstract

Seed formation involves not only the embryo and endosperm development, but also the formation of a series of either ephemeral or non-ephemeral structures. In this article, we study several of those structures in Cytisus multiflorus and Cytisus striatus. The endosperm development is first nuclear and later cellular, except for the chalazal area, whose development is always nuclear. It generates, in the early developmental stages, a sac-like haustorium. As the seed develops, two structures seem to be closely related to nutrient mobilization to the embryo sac: on the one hand, a group of cells and a channel, located in the chalazal area and closely related between them and to the endosperm haustorium, which could be interpreted as a hypostase and on the other hand, an endothelium, derived from the inner integument, which later degenerates leaving no trace in the mature seed. All of these structures would be associated with the directionality of assimilates from ovule tissues to embryo sac. In mature seed and surrounding the embryo appears a unicellular layer of cells rich in proteins (aleurone layer), which is the origin of the outermost layer of the cellular endosperm. The seed coat is made up only of the outer integument.     

Embryology ofCrocus thomasii (Iridaceae)

The embryology ofCrocus thomasii is described. Male meiosis is of simultaneous type, and gives rise to starchy microspores which develop into lipoid pollen grains; these are two-celled and show a spinulate acolpate, abaculate exine lacking apertures. The tapetum is glandular and its cells become bi- or sometimes multinucleate. The ovule is anatropous and bitegmic; the inner integument forms the micropyle. Megasporogenesis is heteropolar with starch accumulation in the functional chalazal megaspore. Embryo sac development conforms to thePolygonum type. The endosperm development is nuclear. The embryo develops according to the Caryophyllad type. In the ripe seed it is differentiated and enveloped by a starchy cellular endosperm. The embryological characters observed strongly favour a close relation betweenC. thomasii andC. sativus.     

中国特有河口异叶苣苔（苦苣苔科）胚胎学研究

对河口异叶苣苔的胚胎学观察旨在为该属的系统学研究提供参考。该种的花药药壁由表皮、药室内壁、中岐和绒层４层细胞组成。２－３－核细胞在绒毡层频繁出现。胚珠属倒生,单珠被和薄珠心。胚囊发育属蓼型。该种胚囊发中的双大孢子母细胞现象,分别为并列和前后排列型。前者发育至双并列四分体,后者发育到呈棱形的４个大孢子。胚乳的发育属细胞型。并在合点端和珠也端分别具有吸器。珠孔吸器发育早期为单核、２－细胞、后期为两核、２－细胞或单核、４－细胞,有时为多细胞,并在发育过程中向外伸长形成外珠孔。合点吸器为两核。由于合点吸器和珠孔吸器的活动,位于珠被最外层细胞的珠和被绒毡层之间的２－３层细胞逐渐解体和被吸收,胚的发生和发育属柳叶菜型,在胚的发育过程中,胚乳几乎被吸收耗尽,仅利下一层胚乳细胞紧贴内种皮,成熟种子的种皮由珠被最外层细胞和珠被绒毡层发育而来,本文对河口异叶苣苔的胚胎发育过程员苦苣苔科其它类群进行了广泛的比较和讨论。     

Embryology and probable relationships of Eriospermum (Eriospermaceae)

Three South African species of the African genus Eriospermum Jacq ., which makes up Eriospermaceae Endl., have been studied in connection with the project "Families of Vascular Plants", partly to establish the phylogenetic relationships of the family. The embryology is unusual in several features reflecting the advanced character of the genus in this respect. The following features are the most important: the tapetum is secretory; microsporogenesis is successive; the ovules are anatropous and crassinu-cellate; the primary archesporial cell cuts off a parietal cell; the embryo sac formation is of the Polygonum type; endosperm formation is nuclear, but the endosperm is soon consumed, nucellus cells bordering on the sides of the chalazal half of the embryo sac divide to form a perispermal sheath around the embryo; embryo formation follows the Nicotiana variation of the Solanad type; the embryo of the mature seed is large and cylindrical-obconical, reaches above the perisperm. The seed coat is formed by both the outer and the inner integuments, both 2-layered; the epidermal cells of the test a grow out into long trichomes. The embryology and seed shape of Eriospermum is compared to those in Cyanastrum, Walleria , and genera of Tecophilaeaceae and some other families as far as details in these are known.     

Development of ovule, embryo sac, and endosperm in Triteleia (Themidaceae) relative to taxonomy

Six of 14 species of Triteleia were studied. All possess septal nectaries, raphides in the ovary wall, an anatropous and crassinucellate ovule with a micropyle formed by the inner integument only, and parietal cells. A short and thick nucellus, which is not penetrated by the embryo sac, has a one-layered apical epidermis and thickens from its subepidermal layer. The permanently two-layered inner integument is made up of normal, i.e., not greatly enlarged, cells. The embryo sac is of the Polygonum type, and the endosperm is of the helobial type. Embryo development is of the Asterad type in Triteleia laxa and T. ixioides. From an embryological point of view, Triteleia is closely related to Muilla maritima because the two taxa are alike in all characteristics, except for the number of layers in the apical nucellar epidermis. Triteleia is only distantly related to Dipterostemon, Dichelostemma, and Brodiaea, judging from the numerous differences in embryology. Both Triteleia and Muilla maritima are embryologically more primitive than the Dipterostemon-Dichelostemma-Brodiaea group. Embryologically, the Themidaceae are more similar to the Hyacinthaceae than to Allium. However, all embryological similarities with Hyacinthaceae are in plesiomorphic characters.     

Embryology of the dioecious Woonyoungia septentrionalis (Magnoliaceae)

The embryological characteristics and ovular integument development of the dioecious species Woonyoungia septentrionalis (Dandy) Law (Magnoliaceae), which are poorly understood, were investigated under laser scanning confocal microscope (LSCM) and light microscope (LM). The embryological characteristics conform to most of the previously studied species in Magnoliaceae. The anther has 4 microsporangia, and the anther wall develops according to the dicotyledonous type. Cytokinesis at meiosis of the microspore mother cells follows a modified simultaneous type, giving rise to isobilateral or decussate tetrads, and a cell plate is absent, but a membrane was observed. Mature pollen grains are 2‐cellular and have high germination rates. The ovule is anatropous, crassinucellate and bitegmic, and meiotic result in linear tetrads of megaspores, the one at the chalazal end functions directly as an embryo‐sac cell. The development of the embryo sac is of the Polygonum‐type and endosperm formation is of the nuclear type. The outer integument of the ovule differentiates into an outer fleshy and an inner stony layer while the inner integument is reduced to a tanniniferous layer. The normal embryological development, high germination rates of pollen and high seed set indicate that the primary reason for the decline of the species is not to be found in these developmental processes.     

Embryology and fruit development in four species of Pistacia L. (Anacardiaceae)

Pistacia atlantica, P. palaestina, P. lentiscus and P. saportae , were found to have great similarity in their embryology and fruit development. The anatropous, pendulous and crassinucellate ovule was initially unitegmic; later, the integument split close to the micropyle, forming a partial second integument. After anthesis there was a development of a hypostase and an obturator. The development of the Polygonum-type embryo sac followed division of a megaspore mother cell, giving a tetrad or triad of megaspores. The functional megaspore was the chalazal one. The ovary developed into a mature pericarp after anthesis, even when pollination was prevented, and before the zygote divided. Therefore, the fruit can be parthenocarpic. The ovule started to grow after initiation of embryo development until it filled the cavity within the pericarp. The zygotes were dormant for 4–18 weeks after pollination. In P. saportae reproduction became arrested during the development of the embryo sac; only very few abnormal embryos were found. No fixed pattern of embryo development could be discerned. The endosperm was initially nuclear, becoming cellular when the embryo started to develop. The seed coat was derived from the integument and the remnants of the nucellus.     

Functional Anatomy of the Ovule in Broad Bean (Vicia faba L.): Ultrastructural Seed Development and Nutrient Pathways

Ovules of broad bean (Vicia faba L.) were studied to discloseultrastructural features, which can facilitate nutrient transportto the embryo sac from 10 d after pollination (DAP) to the matureseed. Fertilization occurs during the first 24 h after pollination.The endosperm is a coenocyte, which is eventually consumed bythe embryo. By 10 DAP the inner integument is degraded and theouter integument adjoins the embryo sac boundary. The heart-shapedembryo approaches the embryo sac boundary at two sites, whichhere are named contact zones. Small integument cells in theneighbourhood of the first formed contact zones become separatedby prominent intercellular spaces. A heterogenous scatteringmaterial, probably representing secretion products accumulatesin these spaces. By 14-16 DAP the integument exudate disappears,and the suspensor degenerates. As the contact zones increasein size, wall ingrowths form a bridging network in the narrowspace between the embryo sac boundary and the extra-embryonicpart of the endosperm wall. The epidermal cells of the embryoseparate adjacent to these zones, and develop conspicuous wallingrowths. At 20 DAP vacuoles showing various stages in formationof protein bodies appear in the cells of the embryo.Copyright1994, 1999 Academic Press Vicia faba, broad beans, ovule, seed, nutrient transport     

SOME HISTOCHEMICAL,ULTRASTRUCTURAL, AND NUTRITIONAL ASPECTS OF THE OVULE OF QUERCUS GAMBELII

Histochemical analyses of the ovule of Quercus gambelii show that the major food reserves (starch grains and lipids) are located almost exclusively within the outer integument. Vascular traces are present only within this integument which contains numerous, well-developed plasmodesmata. The inner integument is virtually devoid of any food reserves and has very few plasmodesmata. The ovule has a persistent chalazal extension of residual nucellar cells (called the postament) which projects into the embryo sac. Due to the above information and the fact that the synergids rarely contain starch and no plasmodesmata are present in the walls of any of the cells of the egg apparatus (Mogensen, 1972), it is concluded that the synergids play little or no role in embryo sac nutrition. Rather, it is proposed that the pathway of available food materials in the young ovule is from the outer integument to the chalaza and through the postament into the embryo sac.     

Campynemanthe (Campynemaceae): Morphology, microsporogenesis, early ovule ontogeny and relationships

Campynemanthe Baill. consists of three species endemic to New Caledonia. Two species are studied and compared. The tapetum is secretory with 2-nucleate tapetal cells. Microsprogenesis is successive, microspore tetrads are isobilateral and the pollen grains are free and inaperturate or have a weakly defined aperture. Placentation is axile with 3–4 ovules in each of the three locules. Ovules are anatropous and crassinucellate with the micropyle formed by the inner integument alone. The archesporial cell cuts off a parietal cell, which divides to form a parietal tissue. The nucellar epidermis divides periclinally at the nucellar apex to become 2-layered. The megaspore tetrad is T-shaped, in which the micropylar megaspore cells are separated by an oblique wall. The chalazal megaspore enlarges and apparently developes into a Polygonum-type embryo sac, but a mature embryo sac has not been seen. The ripe seeds are pale and non-phytomelaniferous. They have copious endosperm rich in fatty oils. The embryo is minute. These characters and gross morphological similarities support relationship with Campynema Labill., but there are also conspicuous differences. The two genera are considered related. They also closely approach genera of the variable family Melanthiaceae and there are reasons to include them in this family.     

黄顶菊的大孢子发生、雌配子体与胚胎发育

用常规石蜡制片对黄顶菊(Flaveria bidentis(L.) Kuntze)大孢子发生、雌配子体和胚胎的发育过程进行了观察.黄顶菊雌蕊柱头二裂,2心皮,1室,单胚珠,基生胎座,单珠被,薄珠心,倒生胚珠,具发达的珠被绒毡层.珠心表皮下分化出孢原细胞,孢原细胞直接发育为大孢子母细胞,大孢子母细胞减数分裂形成直列四分体...     

An anatomical study of ovary-to-cuke development in consistently low-producing trees of the ‘Fuerte’ avocado (Persea americana Mill.) with special reference to seed abortion

Summary Cukes develop from female-sterile, cryptically male flowers on consistently low-producing Fuerte trees. A hypostase that has, as yet, not been reported for the avocado, is present in the chalazal tissue of the mature ovule and aborting seed. This layer seems to play a role in the degeneration of the peripheral nucellar tissue and the non-development of the intercalary meristem of the pachychalaza. The ultimate cause of cuke formation, however, seemingly lies in the disturbance of the polarity of the primordial nucellar tissue. Additional megagametophytes and non-functional megaspores that develop in the nucellus effect the collapse of the chalazal region of the embryo sac. Degeneration of these gametophytes and megaspores causes the formation of nucellar cavities that isolate the embryo sac from the nutritive tissues and chalazal flow of nutrients. The micropylar region of the embryo sac contains a well-developed egg cell, synergids and central cell nucleus. An embryo and a limited amount of endosperm tissue are formed. Because the endosperm is starved of nutrients, the formation of this tissue is curtailed at an early stage, and embryo development ceases. A meristematic zone that initiates from the inner layers of the outer integument, directly opposite the place where the vascular supply to the chalaza terminates, causes abnormal growth in the outer integument. It is suggested that, due to the absence of meristematic activity in the chalazal region of the embryo sac and the non-developing pachychalaza, resources are redistributed towards the stronger sink, i.e. the outer integument. Consequently, this part of the seed coat proliferates, while the embryo sac and pachychalaza degenerate. In spite of the abortion of the seed, the pericarp of the cuke continues to develop, possibly because the pericarp of the avocado contains phytohormones.     

Embryology of <Emphasis Type="Italic">Hemerocallis</Emphasis> L. and its systematic significance

The embryology of the genus Hemerocallis L. was studied to re-evaluate its current systematic position proposed by recent phylogenies based on molecular data. Using the improved carbol fuchsin–aniline blue staining method and conventional paraffin sectioning technique, we followed the development of anther and pollen grain, ovule and female gametophyte, and embryo and endosperm up to seed maturity. Our results showed that the (1) anther wall development is of the Monocot type, with a one cell-thick middle layer and a secretory tapetum, (2) microsporocytes cytokinesis is of the intermediate type, (3) microspore tetrads are tetragonal or decussate, (4) pollen grains are two-celled, (5) ovary is superior and trilocular, with axile placentas bearing two collateral ovules per locule, (6) ovules are anatropous, tenuinucellate, and bitegmic, with micropyle formed by the inner integument, (7) megaspore tetrads are linear, and only the chalazal one is functional, (8) embryo sac development is typically of Polygonum type, (9) embryogenesis is of Graminad type, and (10) endosperm development is of nuclear type. Overall, our study thus confirms that the embryological features of Hemerocallis support its exclusion from Liliaceae in Liliales, its inclusion in Asparagales, and its affinities with Asphodelaceae.     

Embryogenesis and seed development in Sinomanglietia glauca (Magnoliaceae)

The development of the floral bud, especially the ovule and seed coat, of Sinomanglietia glauca was observed. Floral buds were covered by eight to nine hypsophyll pieces. The hypsophyll nearest the tepal was closed completely and characterized by two arrays of densely stained cells with dense cytoplasm, which split longitudinally at flowering. The perianth consisted of 16 tepals arranged in three whorls. The gynoecium was composed of numerous apocarpous carpels; the ovule was anatropous with two integuments. Embryogenesis was of the Polygonum type, and the endosperm was nuclear. The inner integument degenerated during seed development. The seed of S. glauca had an endotestal seed coat comprised of a sclerotic layer derived from the inner adaxial epidermis of the outer integument and a sarcotesta derived mainly from the middle cells between the inner and outer epidermis of the outer integument. The embryo developed normally, so embryogenesis is not the cause of difficult regeneration.     

ANATOMY OF THE SEED OF CONVOLVULUS ARVENSIS

Sripleng , Aksorn , (Kasetsart U., Bangkok, Thailand), and Frank H. Smith . Anatomy of the seed of Convolvulus arvensis. Amer. Jour. Bot. 47(5) : 386—392. Illus. 1960.–The anatropous ovule has a small, ephemeral nucellus covered by a massive integument. Shortly after fertilization, a lateral pouch develops from the upper portion of the embryo sac toward the dorsal side of the ovule and then downward. This leaves a partial integumentary septum in the base of the seed. The cellular endosperm is mostly absorbed by the embryo. Two—6 cell layers persist on all sides of the seed except below the cotyledons on the dorsal side where larger amounts persist. Over most of the seed the dermatogen develops into an epidermis that consists in part of groups of thick-walled elongate cells that produce the papillose appearance of the mature seed. The cells beneath the dermatogen divide periclinally and form 2 layers. The outer layer undergoes anticlinal divisions and differentiates a subepidermal layer of small, rectangular, thick-walled cells that become lightly lignified and suberized. The cells of the inner layer undergo some anticinal and periclinal divisions, elongate and differentiate as palisade sclerenchyma. The inner layers of the integument consist of parenchyma cells that are crushed and partially absorbed at maturity. The pad on the basal end of the seed, between the hilum and micropyle, is derived from a multiple epidermis that is differentiated into several layers of rectangular cells and a layer of palisade sclerenchyma. The subepidermal and palisade layers found over other parts of the seed dip beneath the pad.     

The Embryology of Nyssa sinensis Oliv. (Nyssaceae)

The flower develops in March and blossoms in early May in Nanjing. The cytokinesis of microsporocytes is simultaneous and most tetrads are tetrahedral. The tapetum is secretory and the nuclei become polyploid at last. The style is solid and most ovaries are unilocular, rarely bilocular. The ovule is pendulous, anatropous and unitegmic. The nucellus is pseudocrassinucellate. An obturator formed by transmitting tissue covers the micropyle. The raphe vascular strand extends into the integument when it reaches the chalaza and on a whole keeps a “U” shape. The endothelium cell is uninucleate. In most cases no nucellar cap is formed. No hypostase is found below the embryo sac. The archesporium is one-celled. The embryo sac development conforms to the Polygonum or Allium types. The degeneration of the megaspores in the linear tetrad usually occurs from the chalazal toward the micropylar end. Two synergids persist during fertilization. Three antipodal cells are uninucleate and ephemeral. Two polar nuclei fuse at the time of fertilization. The fertilization type accords with porogamy. The syngamy is premitotic. The development of endosperm is cellular. The initial four successive divisions of the primary endosperm cell are transverse-verticaltransverse-transverse subsequently, giving rise to sixteen cells of the early endosperm. The mature embryo is straight and nearly as long as the endospermous seed. The cotyledons are more or less cordate at base. The seedoat is thin and composed of 5-11 layers of compressed cells. Neither embryo nor endosperm contain the alkaloid camptothecine. The major similarities of Nyssa sinensis to the American nyssas in embryology, which may be a counted as the generic features, are the polyploid tapetum cells, the unitegmic ovule with U-shaped vascular strand, the direct enlargement of the archesporial cell to produce the megasporocyte, the pseudocrassinucellus, the usual absence of the nucellar cap, the Polygonum or Allium type of the embryo sac development, the first degeneration of the metachalazal megaspore, the ephemeral antipodal cells, a single nucleolus in the nucleus ofthe primary endosperm cell, the more or less cordate base of the cotyledons.     

Development of megagametophyte, embryo, and seed in Senna corymbosa (Lam.) H.S. Irwin & Barneby (Leguminosae – Caesalpinioideae)

The main aspects of seed ontogeny in Senna corymbosa were studied by standard anatomical microtechniques for light microscope observations. The results revealed an ana-campylotropous, bitegmic, and crassinucelate mature ovule. A single archesporocyte developed by an archesporial cell enlargement from the subhypodermal multicellular archesporium. Meiosis originated linear or T-shaped megasporic tetrads. The functional megaspore was the chalazal one. Megagametophytic development conformed to the Polygonum type. Fertilization was porogamic. Endosperm development was free nuclear and conformed to a chalazal haustorium. Cellular endosperm was initiated from the micropylar end during the globular embryo stage. Embryogeny derived from a linear proembryonal tetrad. The mature embryo showed an oblique axis. The testa derived from the outer ovular integument. Nucellar and endosperm remnants, and the micropylar region of the inner ovular integument, persisted at embryo maturity. The absence of a pleurogram would be adaptative to wetland habitats. The taxonomic use of the mature embryo axis in the Cassieae and the phylogenetic employment of megasporic arrangements in Leguminosae needs some reinterpretation.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 153 , 169–179.