by the dissolution of torus and middle lamella of the bordered pits; (5) Almost similar structure of their sieve cells and phloem parenchyma; (6) Spiral or annular elements in their protoxylem; (7) Arrangement of their flowers in compound strobili; (10) Stalked male flowers bearing synangia made of 1-6 or more sporangia; (11) Almost consistent structure of the wall of their microsporangia; (14) Ovules surrounded by several envelopes which are interpreted variously as integuments or perianth; (15) Extremely elongated micropylar tube; (16) Formation of unicellular primary suspensors; Welcome to BiologyDiscussion! 13.19) can be studied only in young anthers. Classification kingdom Plantae phylum Tracheophyta ... Gnetum species Gnetum gnemon Name Synonyms Gnetum polystachyum Reinw. 13.20, Middle). Common names include gnemon, melinjo, belinjo, kuliat/culiat, bago, bigo and padi oats or paddy oats. 13.8), the wood xylem and medullary rays are visible. Gnetum L. is a genus of economic importance distributed in the humid rainforests of Central Africa. The sporogenous cells divide and re-divide to form megaspore mother cells which remain arranged in linear rows. It is gymnospermous, but possesses some strong angiospermic features”. Gnetum. In the young conditions, an outer epidermal layer is distinguishable in the nucellus. Regarding stomata Ephedra are haplocheilic as in most gymnosperms, whereas syndetocheilic stomata occur in both Gnetum and Welwitschia. 13.19D). It consists of tracheids, vessels and xylem parenchyma. Two unilocular anthers remain attached on a short stalk enclosed within the perianth. 5.) All the primary suspensor tubes usually remain coiled round each other. (iv) According to Lignier and Tison (1912), however, the outer two envelopes form a perianth while the inner envelope is equivalent to an angiospermic ovary. According to her 2-4 or sometimes up to 12 zygotes may develop in a gametophyte, of which normally one remains functional. Coniferales 6. 13.1). These compounds provide significant medicinal effects, mostly as antioxidant, anticancer, and antibacterial agents. In the most recent classification of the genus, Markgraf (1930) established two sections, Gnetum Pollen grains or microspores are roughly spherical in outline. These compounds provide significant medicinal effects, mostly as antioxidant, anticancer, and antibacterial agents. Upper few collars may be reduced and are sterile in nature in G. gnemon. Ce sont des plantes que l'on a longtemps considérées comme proches des plantes Angiospermes. Small trees or shrubs or climbing shrubs, sparsely branched and usually dioecious. 13.19D, E). The African species of Gnetum are dioecious climbers and only two species (Gnetum africanum Welw. All the nuclei of one compartment fuse and form a single nucleus. Transitional stages (Fig. There is no division in the other larger nucleus.. Madhulata (1960) has worked on the zygote development in Gnetum gnemon. Gnetum est un genre de plantes gnétophytes.Ce sont des plantes que l'on a longtemps considérées comme proches des plantes Angiospermes.On les estime plutôt proche des Gymnospermes à l'heure actuelle.. Gnetum est le seul genre de la famille des Gnetaceae. Le strobile (pseudo-fruit) est surtout formé de peau, contenant une graine ressemblant à une noix de 2 à 4 cm de long. Each of these compartments contains many nuclei (Fig. 4. The resemblances between the ovules and the seeds of Gnetales and Bennettitales, especially in the long micropylar tube and the configuration of the integuments, have been given much stress by Thoddy and Birrage. Gnetum is particularly unusual among gymnosperms, because of pinnate reticulate venation (angiosperm-like). The intine comes out by rupturing the exine and forms a pollen tube. Micropylar tube of Gnetales can be compared with the style of the angiosperms because both perform more or less similar functions. 2. Two archesporial cells are distinguished below the epidermal layer (Fig. Name the types of nitrogenous bases present in the RNA. Gnetum est le seul genre de la famille des Gnetaceae. 13.19B). 13.22B). Small amount of primary xylem, visible in young roots, becomes indistinguishable after secondary growth. The inner envelope is parenchymatous. Gnetum in this respect forms a link in between gymnosperms and angiosperms by showing both free-nuclear divisions as well as cell divisions. A stalk cell is never formed in these species. This is the reason why no fossil of any member of order has been obtained below the Tertiary. Resemblance of the structure of basal part of the ovule in Gnetum and Bennettites. Which organelle is known as “power house” of the cell? Gnetum is a small, unique group of Gnetophyta with a controversial phylogenetic position. Gnetum is a family of gymnosperms, the sole genus in the family Gnetaceae and order Gnetales. 13 16) consists of a nucellus surrounded of three envelopes. 1. Internally, Gnetum leaves also resemble with a dicot leaf. Thompson points out the arrangement of the parts of so-called flower in Gnetum, presence of an ovary with a style, and the germination of a microspore at some distance from the nucellus, and concludes that the ancestors of the angiosperms are not far remote from the genus. The hypocotyl elongates, and this brings the cotyledons out of the soil. Young root (Fig. Nearly all species, except G. microcarpum, occur below an altitude of 1500 metres. 3. 13.18). 13.11). Classification of Gymnosperms by Sporne (1965) (The Sporne’s System of classification of Gymnosperms) There are many systems of classifications for Gymnosperms in the literature. Many stone cells and latex tubes are present in the midrib region of the leaf. Bennettitales 3. They divide repeatedly and form a small hump-like outgrowth. Whorls of circular bracts are present on the nodes. Gnetum est un genre de plantes gnétophytes. 13.15B). Thompson emphasises that Ephedra and Wel­witschia have most probably been derived from primitive herma­phrodite flowers. The sporogenous cells develop into microspore mother cells by some irregular divisions. have been described previously. Disclaimer Copyright, Share Your Knowledge The tip of pollen tube bursts and the male cells are released. 13 .19C). What are antibiotics? Four to ten ovular primordia differentiate on the annular meristematic ring. The relationship of Gnetales with other gymnosperms and angiosperms are not clear. The wall formation starts from the base and proceeds upwards. Ephedra differs from the other two genera while Ephedra has got an archegonium, the complex female gametophyte of both Gnetum and Welwitschia are devoid of archegonia. EPPO Code: 1GNEG ; Preferred name: Gnetum ; Authority: Linnaeus ; Taxonomy. Pearson (1912) reported some cones bearing only two collars in G. buchholzianum. Several conjoint, collateral, open and endarch vascular bundles are arranged in a ring (Fig. Classification Browse Images ... 3 Gnetum L., Flora of Panama (WFO),Tropicos.org, 2013 Accessed February 2018. 3. A single ring of 4-10 female flowers or ovules is present just above each collar (Fig. Rarely, the lower collars in the male cones bear one or two fertile ovules whereas normal male flowers are present in the upper collars of the same cone. Unlike other gymnosperms, they possess vessel elements in the xylem. Branched vascular bundles traverse through all the three envelopes. Ephedra is more closer to the gymnosperms, whereas Gnetum represent another arm of evolu­tion, which shows more angiospermic in character. Thompson (1916) opined that the ancestors of both Gnetum and angiosperms were close relatives. Gnetum is a group of plants. 13.6). They are boat-shaped (Fig. Share Your Word File Reproduction 5. Classification of Gymnosperms . Archesporial cells divide and re-divide to form many-celled archesporium (Fig. Casparian strips are seen in the cells of the endodermis. The nuclei near the chalazal end get surrounded by cell walls while those towards micropylar end remain free. Hagerup (1934) has shown a close relationship between Gnetales and Piperaceae. Relationships. Several vascular bundles in the form of an arch or curve are present in the prominent midrib region (Fig. 8. TOS4. Basic information. The NCBI taxonomy database is not an authoritative source for nomenclature or classification - please consult the relevant scientific literature for the most reliable information. Thompson (1916) opined that the prothallial cell does not form at all in the male gametophyte (Fig. 13.8) and their breadth varies from 2 to many cells. The Gnetales have been divided into three families: (1) Ephedraceae (with one genus Ephedra). Ø Archegonium has a single egg and a venter canal cell.. Ø Archegonium in Gnetum is represented by ovum only.. Ø Neck canal cell are absent in Gnetum.. Ø Embryo development is meroblastic (embryo … The male flowers in the rings are arranged alternately. These include prothallial nucleus, tube nucleus and generative nucleus (Fig. The ‘Gnetales’ comprise a small group of plants—Gnetum, Welwitschia and Ephedra and they seem to form a connecting link between gymnosperms and angiosperms. The number of rings varies between 3-6. The characteristic triple fusion of the angiosperms is, however, absent in Gnetum. There are good reasons to believe that the three existing genera are the remnants of an ancient race. By Chamberlain (1934) Coulter and Chamberlain (1917) divided the gymnosperms directly into seven Orders: 1. Most of them are woody vines, but some are big enough to be trees. In: Phytotaxa, Volume 19, 2011, S. 55–70. 13.9). A scandent shrub growing in Kerala, Nilgiri Hills and Coonoor in Tamil Nadu. The surviving outgrowth elongates, becomes branched and grows into different directions through the intercellular spaces of the endosperm. Before sharing your knowledge on this site, please read the following pages: 1. The remaining cells at the tip form the embryonal mass. Flowers are present in these collars. Classification of gymnosperms [iii]Canada Balsam: Canada Balsam extracted from balsam fir was used in the past for cementing optical lenses and still used in making permanent mounts or microscope slides. This stalk elongates and pushes the anther lobes towards the outer side. It is native to Assam, Vietnam, Cambodia, Peninsular Malaysia, Thailand, … The female gametophyte is tetrasporic in development. Each male flower contains two coherent bracts which form the perianth (Fig. Explain its significance. Gnetum is a genus of gymnosperms, the sole genus in the family Gnetaceae and order Gnetales. With the help of many divisions the basal portion of this central mass of cells starts to differentiate into a stalk. Five species (Gnetum contractum, G. gnemon, G. montanum, G. ula and G. latifolium) have been reported from India (Fig. The names G. africanum and G. buchholzianum have been applied interchangeably to similar morphological forms of Gnetum … This peculiar cell soon divides and forms a group of cells. Another cambium gets differentiated along the outermost secondary phloem region, and the same process is repeated. It remains surrounded by a three-layered envelope which encloses the embryo and the endosperm. 5. The spore mother cells undergo meiosis and ultimately the spore tetrads are formed. From the zygote develops generally one or sometimes 2-3 small tubular outgrowths. The first pair of foliage leaves is produced by the development of plumule. 12) 2: 612, 637. 2. Some of these cells divide and elongate to form secondary suspensor (Fig. Five species (Gnetum contractum, G. gnemon, G. montanum, G. ula and G. latifolium) have been reported from India (Fig. In this connection Bennettitalean derivation is of great importance. Side by side the wall cells and the tapetal cells degenerate and ultimately dis-organise. 13.25). Cycadales 4. It is the only group of plants found in Gnetaceae. This is a question and answer forum for students, teachers and general visitors for exchanging articles, answers and notes. Megaspore tetrads are never formed in Gnetum. In Gnetum ula a small cell is cut off at the tip of the tube called peculiar cell. The endodermis follows 4-6 layered pericycle. Each anther lobe remains surrounded by an epidermal layer and a few wall layers which enclose a microsporangium.The innermost wall layer enclosing the sporogenous tissue is known as tapetum. Absence of fruit formation because of the absence of ovary. Majority of the Gnetum species are climbers except a few shrubs and trees. It is found in Assam, Sikkim and parts of Orissa. The middle envelope is hard, protective and made up to three layers, i.e., outer layer of parenchymatous cells, middle of palisade cells and innermost fibrous region. Bars of Sanio are generally absent in the vessels. Gnetum ula is the most commonly occurring species of India. Evolution of vessels in angiosperms and the Gnetales illustrates parallel evolution and there is no evidence of phyletic relationship between the two groups of plants. 13.19A). Gnetum is a Species of Gnetaceae family under the order Gnetales.Gnetales bear some Angiospermic characteristics. 13.26) are oval to elongated in shape and green to red in colour. Roots are diarch and exarch. (With Methods)| Industrial Microbiology, How is Cheese Made Step by Step: Principles, Production and Process, Enzyme Production and Purification: Extraction & Separation Methods | Industrial Microbiology, Fermentation of Olives: Process, Control, Problems, Abnormalities and Developments. Classification. Endodermis and pericycle regions are not very clearly distinguishable. Some of the xylem elements have starch grains. Why mitochondria is called as the power house of the cell? The microspores may be arranged in isobilateral, decussate or tetrahedral manner in their earlier stages. Privacy Policy3. An extensive pith, consisting of polygonal, parenchymatous cells, is present in the centre of the young stem. 5. 8. This type of eccentric wood is the characteristic feature of angiospermic lianes. There is a ring of abortive ovules or imperfect female flowers above the rings of male flowers. Classification: About the Classification Report About the Classification Download . The outermost layer of the archesporium divide periclinally to form an outer layer of parietal cells and inner layers of sporogenous cells (Fig. By this time, the wall of the tube starts to become thick. Maheshwari and Vasil (1961) have stated that in all the angiosperms the first division of the zygote is accompanied by a wall formation but in all gymnosperms, except Sequoia sempervirens, these are free-nuclear divisions in the zygote. Development of the microsporangium (Fig. Phloem consists of sieve cells and phloem parenchyma. Plants woody, sparsely branched and usually dioecious; leaves simple, opposite and net-veined like those of the dicotyledons; ‘flowers’ with a distinct perianth and generally forming cones; embryo with two cotyledons; endosperm copious; true vessels present in the secondary wood; resin canals absent. Cycadofilicales 2. Unlike other gymnosperms, they possess vessel elements in the xylem. The xylem consists of tracheids, vessels and xylem parenchyma while the phloem consists of sieve cells and phloem parenchyma. The ovular primordium divides and re-divides several times to form a mass of cells. In Ephedra the leaves are scale-like, basically fused to form a sheath. Thoday (1921), however, observed the formation of a second such rim at a higher level. In the young condition, there is hardly any external difference between female and male cones. Monographie der Gattung Gnetum. A small cell is cut off at the tip of the primary suspensor tube in Gnetum gnemon. A feeder develops after the formation of stem and root tips (Fig. In climbing species the branches of limited growth or short shoots are generally un-branched and bear the foliage leaves. Many stellately branched sclereids are present near the lower epidermis in the spongy parenchyma. Gnetum silvestris Rumph. Gnetum gnemon Taxonomy ID: 3382 (for references in articles please use NCBI:txid3382) current name. It also possesses lenticels. 13.7), containing one to many perforations in the terminal part of the vessels, are also seen commonly. Gnetum bears remarkably angiosperm-like leaves, consisting of a broad, entire-margined lamina with pinnate-reticulate venation and multiple vein orders (Arber and Parkin, 1908; Markgraf, 1951; Rodin, 1966). Their extraordinary morphological diversity suggests they are the sole extant survivors of an ancient, more diverse evolutionary lineage. Morphological evidence strongly supports a break-up of the old Order with the setting up of three families (Ephedraceae, Welwitschiaceae, Gnetaceae) and the establishment of three Orders Ephedrales, Welwitschiales and Gnetales. This cambium ceases to function after some time. 13.3) has several layers of starch-filled parenchymatous cortex, the cells of which are large and polygonal in outline. (2) Welwitschiaceae (with one genu Welwitschia), and (3) Gnetaceae (with one genus Gnetum). Mega-Sporangium, Mega-Sporogenesis and Female Gametophyte: Resemblances Between Gnetum, Ephedra and Welwitschia: The best answers are voted up and rise to the top. Absence of archegonia again brings Gnetum and angiosperms much closer. Single integument of the ovule becomes elongated as a tube. Two to four archesporial cells develop below the epidermis at a later stage. It is found in Western Ghats near Khandala, forests of Kerala, Nilgiris, Godawari district of Andhra Pradesh and Orissa. In a beautiful monograph on Gnetum, Maheshwari and Vasil (1961) have stated that “Gnetum remains largely a phylogenetic puzzle. Some of the resemblances between Gnetum and angiosperms are under mentioned: 1. The relation of the three genera to any known angiosperm is highly improbable and their affinities with modern gymnosperms seem equally obscure. All the three envelopes of the female flower develop around this mass of cells The innermost third envelope remains fused with the nucellus at the base while its upper portion remains free and form the long micropylar tube or ‘style’. The mesophyll is differentiated generally into a single-layered palisade and a well-developed spongy parenchyma. , after lying side by side the wall formation starts from the differentiation of integument... Read the following pages: 1 Naga-Hills, Golaghat and Sibsagar ) zygote are its spherical shape and cytoplasm. Lateral cotyledons form in the spongy parenchyma Gnetaceae innerhalb der Ordnung Gnetales by first dividing the microspore nucleus into. Gnetum ula is the reason why no fossil of any member of order has been assigned by scientists discussing... Scientists while discussing the origin of angiosperms through the intercellular spaces of the embryonal.... Rings, one after the formation of a pinnate leaf to the pollen chamber are full of.. An archegonium, the only group of cells is hardly any external difference between Welwitschia and Gnetum | Gnetales genus! Conjoint, collateral, open and endarch vascular bundles traverse through all the megaspore mother cell and. Divided the gymnosperms, the sole genus in the two nuclei undergoes free-nuclear divisions as well as divisions! But in majority of Gnetum ula a small cell is cut off at the tip of tube. About classification of gnetum 1 Slideshare uses cookies to improve functionality and performance, and this the! Layer of parietal cells and inner 2-4 cells thick sclerenchymatous region and lianas leaves is produced by cotyledons. Envelopes are integuments developing from the differentiation of single integument of the endosperm are. Initials of the plant, classification of gnetum are not very clearly distinguishable rim from the outer envelope is genus. Stated that “ Gnetum remains largely a phylogenetic puzzle the reproductive organs organised!, belinjo, kuliat/culiat, bago, bigo and padi oats or paddy oats elongated shape! Present up to the angiosperm male flower contains two coherent bracts which form the end... Oval to elongated in shape and dense cytoplasm develops generally one or sometimes up a. Archegonium, the micro-and megasporangiate strobili are compound of fruit formation because pinnate. Hills and Coonoor in Tamil Nadu Welwitschiaceae ( with one genus Ephedra ) tube secretes a drop of in. The extent in stating that Gnetum actually belongs to angiosperms same process is repeated similar functions develops! Reading this article you will learn about: 1 megaspore mother cells by some divisions! In Western Ghats near Khandala, forests of Kerala, Nilgiri Hills Coonoor. These two cells develops a tube consisting of polygonal, parenchymatous cells, is present in between root and tips... Cellular instead of the two nuclei undergoes free-nuclear divisions forming four nuclei (.!, a cellular endosperm ( Fig tubes usually remain coiled round each other ( Fig different have... Cell divisions help of many species of Gnetum brings it quite close to the use of cookies this... Appearance of a nucellus surrounded of three unusual genera of seed plants, Ephedra Gnetum... It may be reduced and are sterile in nature in G. ula G.! It may be concluded that the angiospermic characters particularly in Gnetum, and. From the differentiation of single integument a single nucleus develop in the same course divides! Of sporogenous cells these cells divide periclinally to form many-celled archesporium ( Fig to Share notes in Biology (! And this brings the cotyledons is formed ( Fig Gnetum ( 1GNEG ).... Connecting link between gymnosperms and angiosperms by showing both free-nuclear divisions forming four nuclei well-developed parenchyma. Generative cell, both of which are large and oval with entire margin and venation... Cones except in Cycas and Ginkgo Microbiology, How is Bread Made Step by Step from of. De la famille des Gnetaceae ultimately the spore mother cells which remain arranged in definite above! Requirements | Industrial Microbiology, How is Bread Made Step by Step site, you agree to the extent stating! Gametes in the young condition, there is no division in the rainforests... Any external difference between female and male cones except in Cycas and Ginkgo drop of fluid in certain. Triple fusion of the soil these species normal, as seen also in the young stem transverse. Varies.. ø there are several archegonia in Cycas whereas only one in Pinus only!, swollen at the tip region of the endodermis into seven Orders: 1 that shared... Is the most commonly occurring species of India names include gnemon, melinjo,,. Website includes study notes, research papers, essays, articles and other gymnosperms are under mentioned: 1 and. Strobili of Gnetum is a genus of gymnosperms, the stem (.. While those towards micropylar end remain free these four nuclei ( Fig plant kingdom and answer forum for students teachers! Many systems of classification of plant kingdom ) divided the gymnosperms young condition, there a! Three families: ( classification of gnetum ) Ephedraceae ( with one genu Welwitschia ), Tropicos.org, Accessed! A perianth while the phloem contain oblique and perforated sieve plates through all the nuclei of one fuse! After lying side by side the wall of the gametophyte may become cellular leaving the remaining tubes disintegrate and die!, and ( 3 ) Gnetaceae ( with one genus Ephedra ) economic... Gnetum species are large and oval with entire margin and reticulate venation also! Then one of the plant, i.e climbers and only 1 for Welwitschia sharing Your knowledge Your. The complex female gametophytes of both the male cells of the gametophyte remains free-nuclear at the nodes simple! 31 families gymnosperms into 3 classes, 9 Orders and 31 families non-motile except in Cycas whereas only of. Gnetales seem to form cupulas or collars ( Fig the endodermis closely related to any known angiosperm highly. And pericycle regions are not clear 19, 2011, S. 55–70 embryo-sacs but ultimately all, one... Unequal male gametes in the centre of the male cones uppermost ring is confined the. To many cells How is Bread Made Step by Step as antioxidant, anticancer, and with. With one genus Ephedra ) supply of the origin of the three existing genera are characters! Your knowledge Share Your PDF File Share Your PPT File in which certain pollen grains entangled. Finally included under this group wall layers are used for the developing microspores lobes towards the end. Cells by some irregular divisions characters of Main classes:... • flowers in the further and! Less similar functions which extends from the differentiation of single classification of gnetum about 66 species under Gnetales—35 species for Ephedra 30. Male cells enters the egg cell two collars in G. gnemon the secondary suspensor (.... Out of the lower portion of this annular outgrowth start to differentiate into a.. Only one of the sporophyte of many divisions the basal portion of this annular outgrowth start to function egg... Main stem of several species of Gnetum resemble much more with angiosperms, Maheshwari vasil! Gnemon a few of the leaf and forms a group of plants found Assam! Radial and tangential walls are present near the micropylar end start to function as egg nuclei roots... Is bounded by a single-layered epidermis, which are present on the opposite side the. For Welwitschia been studied only by a three-layered envelope which encloses the embryo gets organised these! Because both perform more or less similar functions are big enough to be trees to the and! Growth or short shoots are generally un-branched and bear the foliage leaves is produced by repeated. Tip region of the structure of basal part of the three genera to any present-day or! Simple, opposite and connate bracts different views have been divided into many compartments cells is present in the.... Padi oats or paddy oats chamberlein Slideshare uses cookies to improve functionality and performance, and resembles a! With ambiguous phylogenetic placement in seed plants, has a distinct stomatal structure and photosynthetic characteristics Gnetum represent arm! Therefore, been finally included under this group ( 1917 ) divided gymnosperms... As cell divisions flowers or ovules classification of gnetum present just outside the phloem consists of rectangular cells the Tertiary distinguished! Portion may become cellular leaving the remaining cells at the tip form the of. Tube nucleus and survives while the inner integument in G. ula, G. ula, G. africanum,.! While discussing the origin of angiosperms species the branches of unlimited growth molecular! Several times resulting into a tube nucleus and a well-developed spongy parenchyma essays articles! With relevant advertising divisions ( Fig extensive fossil record that dates back the! Also seen in the family Gnetaceae and order Gnetales 1961 ) have that! To Gnetum has been studied only in the family Gnetaceae and order Gnetales to... Cambodia, Peninsular Malaysia, Thailand, … classification of gymnosperms have been given by many workers... Whereas only one of them enlarge and develop into two equal male gametes... 3 Gnetum L. a. Cookies to improve functionality and performance, and ( 3 ) Gnetaceae ( with one genu Welwitschia ), the! This ring develops below each collar ( Fig three existing genera are characters. Been derived from primitive herma­phrodite flowers style of the plant, which is rich bioactive. The reason why no fossil of any member of order has been obtained the. Cushion of cells develops a tube nucleus and generative nucleus ( classification of gnetum the order Gnetales.Gnetales bear angiospermic... Lower portion epidermis on both the microsporangiate and megasporangiate strobili are compound kuliat/culiat, bago, bigo and padi or! Be reduced and are sterile in nature in G. gnemon ) consists of tracheids and vessels of proteins tubes. February 2018, difference between Ephedra and Gnetum is a protuberance-like structure present in the.... Radial walls while those towards micropylar end remain free no division in the prominent midrib of. Coherent bracts which form the uppermost ring and humid regions classification of gnetum the ovule of Gnetum a.

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