Gone and ovule ontogeny in Phyllocladus (Podocarpaceae)

TOMLINSON, P. B., TAKASO, T. & RATTENBURY, J. A., 1989. Cone and ovule ontogeny in Phyllocladus (Podocarpaceae). Cones are borne directly on phylloclades, usually in the position of basal segments or as segment appendages. Each cone consists of a series of spirally arranged bracts, of which the middle bracts each subtend a single, sessile ovule. There is no ovuliferous scale. Ovules arise as ovoid outgrowths; integument development involves periclinal divisions of hypodermal cells with the integument becoming bilobed and extended laterally. The mature ovule is flask-shaped. The integument includes an extensive middle region bounded by an inner and outer epidermis; the outer hypodermis is differentiated as two contrasted cell layers. An aril differentiates late by periclinal divisions of the outer hypodermal cells at the base of the ovule. The three outermost layers of the integument become differentiated in the mature seed as an epidermis, with thick, cutinized outer tangential walls, an outer hypodermal tanniniferous layer and a sclerotic inner layer. Each ovule is vascularized by two strands that diverge from the axial bundles delimiting the gap left by the departing bract trace.     

砂仁种子的解剖学和组织化学研究

砂仁种子包括假种皮、种皮、外胚乳、内胚乳与胚。假种皮由内表皮、外表皮及其间的６－９层薄壁细胞组成。种皮分为外种皮、中种皮与内种皮。外种皮由１层表皮细胞构成,其壁增厚并略木质化。中种皮包括各含１层细胞的下层皮和半透明细胞层与含３－５层细胞的色素层;下皮层与色素层细胞均含有红综色素,后者的壁呈网状增厚。内种皮由１层内切向壁与径向壁非常增厚的石细胞构成。种皮表面具有许多疣状突起,它们是体积较小的表皮细胞     

A Developmental Study of Silicification in the Trichomes and Associated Epidermal Structures of the Inflorescence Bracts of the Grass, Phalaris canariensis L

Silicon accumulation is greatest in the abaxial epidermis ofthe inflorescence bracts of Phalaris canariensis L. It occursinitially in glumes 1 week before emergence, at low levels inthe trichomes and long cells, but at high levels in the papillae.Accumulation in long cells remains low throughout, althoughit increases with time. Papillae and prickle hair silicon countsconsiderably exceed values for other epidermal structures. Siliconis also deposited in glume macrohairs before emergence, andat maturity reaches intermediate levels. Little silicon is present in the macrohairs and long cells ofthe abaxial epidermis of the fertile lemma prior to emergence.After emergence, however, silicon is rapidly accumulated inthese structures, and at maturity they have the highest siliconlevels of all the mature bract tissues. Silicon accumulation in the lemma lags behind that of the glumeuntil emergence, when it increases more rapidly, and by maturityexceeds that of the glume in macrohairs and long cells. Thesignificance of the results is discussed in relation to wallthickening, bract anatomy and panicle emergence. Phalaris canariensis, L, canary grass, inflorescence bracts, silicification, trichome, glume, lemma     

Electron-probe Microanalysis Studies of Silica Distribution in Barley (Hordeum sativum L.)

Silicon occurence has been investigated by means of epidermalpeels, cryostat, and ultrathin sections of the internode, nodes,leaves, inflorescence bracts, and caryopsis of Hordeum sativumL. (cultivar Deba Abed) using the electron probe microanalyser.Analyses were made on growth stages during ear emergence andat maturity. The results indicate that silicon is present inthe internode with the highest concentration associated withthe opaline deposits. Detectable quantities are also found inthe outer tangential walls of the long cells, in the walls ofstomata, the sclerenchyma, and all vascular bundle regions.In mature upper internodes, silicifiation is confined to theupper third region, but this limit extends closer to the basalmeristem with increasing age of internode. The nodes have agreater concentration in the radial than in outer tangentialwalls. Heavy deposits are found in the leaves but with considerablevariation between blade and sheath, abaxial and adaxial surfaces,and the leaf position. The flag leaf contained the highest accumulations. In the inflorescence bracts (lemma and palea), silicon is detectableonly in the abaxial epidermis and hypodermis. Awns are alsoheavily silicified with the highest concentrations in the sclerenchymaand trichomes.     

The Ultrastructure and Analytical Microscopy of Silicon Deposition in the Aleurone Layer of the Caryopsis of Setaria italica (L.) Beauv.

Silicon deposition in the caryopsis of foxtail millet (Setariaitalica (L.) Beauv.) from Lin Xian, Northern China was investigatedusing transmission electron microscopy and energy dispersiveX-ray analysis. The highest silicon count rates were obtained from the pericarpand outer aleurone cell walls, and particularly from a granularelectron-opaque layer external to the outer aleurone cell wall.Silicon was not detected in tissues interior to the aleurone. A possible mechanism for silicon deposition in the caryopsisis suggested, and the results are discussed with respect tothe high incidence of oesophageal cancer in Lin Xian, NorthernChina. Setaria italica (L.) Beauv., foxtail millet, silicon deposition, alcurone layer, caryopsis, ultrastructure, X-ray analysis     

FINE STRUCTURE OF THE LARVAL ANURAN EPIDERMIS,WITH SPECIAL REFERENCE TO THE FIGURES OF EBERTH

Small pieces of skin from 8 cm long Rana clamitans larvae were fixed in OsO₄, washed, dehydrated, and embedded in a methacrylate mixture. Ultrathin sections were cut on a Porter-Blum ultramicrotome and were examined in an RCA electron microscope, type EMU 2D. The sections showed that aggregates of fibrous material in the cells of the inner layer of epidermal cells are identical in disposition and size with the classical figures of Eberth. It is conclusively shown that these figures do not arise from an aggregation of mitochondrial filaments. The tendency of the fibrils to concentrate on attachment points, or thickenings of the basal plasma membrane, is noted. It is also observed that numerous mitochondria are located in the distal region of the cells of the outer layer of epidermis in association with the secretory vacuoles. Microvilli are seen occasionally on the free surface of the skin. Cisternae are found only in the cells of the outer epidermal layer, while vesicular endoplasmic reticulum is found in the cells of both epidermal layers.     

The Distribution of Silicon Deposits in the Fronds of Pteridium aquilinum L.

The occurrence of silicon in mature fronds of Pteridium aquilinumwas investigated using light and scanning electron microscopyand X-ray micro analysis. The heaviest deposits were locatedin the outer tangential walls of the epidermis of the petiole,but the upper epidermal cells of the costal regions of the laminaealso accumulated small quantities. No discrete bodies were associatedwith these deposits. However, the mid-ribs of the laminae exhibitedsome long siliceous fibres associated with the luminae of thestrengthening tissues. The significance of these accumulationsin relation to deposition mechanisms and possible carcinogeniceffects are discussed. Pteridium aquilinum L., bracken, frond, microanalysis, silica     

THE DEVELOPMENT OF THE SEED OF ABUTILON THEOPHRASTI. II. SEED COAT

Winter , Dorothy M. (Iowa State U., Ames.) The development of the seed of Abutilon theophrasti. II. Seat coat. Amer. Jour. Bot. 47(3) : 157—162. Illus. 1960.–The integuments of Abutilon theophrasti Medic. undergo a rapid increase in size, predominantly by anticlinal cell divisions during the first 3 days after fertilization. Within 7 days, the outer epidermis of the inner integument becomes thick walled. At maturity this compact, lignified, and cutinized palisade layer accounts for more than half the thickness of the seed coat. During early growth, the palisade cells form a continuous layer in the micropylar region. In the chalazal region the palisade layer is discontinuous in a slit-shaped region, 60 × 740 microns. The shape of this discontinuity constitutes a major difference between dormant-seeded Abutilon and non-dormant Gossypium seeds. Exterior to the palisade layer is the outer integument which consists of a small-celled layer and a large-celled layer sparsely covered with unicellular, lignified hairs. Interior to the palisade is the thick mesophyll of the inner integument which is largely digested during seed growth and leaves only 2 pigmented cell layers in most regions at maturity. The inner epidermis is small-celled, pigmented and cutinized and adheres tightly to the endosperm. Seed coat impermeability increases with seed maturity. Even immature seeds will germinate, if scarified, indicating a lack of embryo dormancy.     

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.     

TRANSFER CELLS IN THE PLACENTAL PAD AND CARYOPSIS COAT OF PAPPOPHORUM SUBBULBOSUM ARECH. (POACEAE)

During caryopsis development the layers of the pericarp, integuments, and nucellus all contribute to the formation of the caryopsis coat. The coat consists of a layer of outer pericarp epidermal transfer cells, a collapsed and senescent layer of middle pericarp cells, and a discontinuous layer of inner pericarp epidermal transfer cells. The latter is not present across the placental pad. The integuments are present as a collapsed dense layer, the nucellus is discontinuous and cellular. The placental pad occurs at the ventral surface of the caryopsis, opposite the scutellum and coleorhiza. It consists of 15–20 collapsed cell layers, including the pigment strand and placental vascular bundle. From the inside several partially collapsed cell layers of the nucellar projection occur which contain transfer-cell walls. The middle dense layers, the pigment strand, consist of the middle pericarp remnant, plus the remains of the placental vascular bundle. The pericarp inner epidermis does not extend across the pad. The aleurone layer is a continuous uniseriate layer around the entire caryopsis except at the placental pad; here it is crushed and contains the remnant of a transfer-cell wall. The outer pericarp epidermis is a continuous layer of transfer cells across the pad. These cells contain membranous inclusions suggesting that they may be functional during germination.     

THE DEVELOPMENT OF THE SPOROCARP OF MARSILEA VESTITA

The tissues of the sporocarp of Marsilea vestita undergo profound changes during development. Early in development, the cells of the peripheral tissues, epidermis, hypodermis and layers of the transitional zone between the hypodermis and more internal tissues contain prominent vacuolar bodies. As development proceeds, these vacuolar bodies disappear. Prominent amyloplasts are found only in the guard cells and in the cells of the transitional zone. Later in development the cells of the hypodermis divide periclinally forming two layers which differentiate as macrosclereids. The cells of the outermost layer of the transitional zone differentiate as osteosclereids. Internally, the cells of the sorophore accumulate large amounts of mucilage in the central vacuoles. The peripheral cytoplasm ultimately degenerates leaving just hygroscopic mucilage. The mucilage carbohydrate contains the sugars, rhamnose and arabinose. In the young sorus, only the spore mother cells and the cells of the indusium contain amyloplasts. By the time of meiosis, there is a massive accumulation of starch in the receptacle, stalk and jacket but not in the tapetum of the sporangia. Late in development, the starch disappears and the mega- and microspores become coated with carbohydrate.     

Selective light transmittance of translucent bracts in the Himalayan giant glasshouse plant Rheum nobile Hook. f. & Thomson (Polygonaceae)

Translucent bract transmittance of ultraviolet (UV) to infrared (IR) radiation (between 320 and 800 nm) and leaf anatomy were examined in a glasshouse plant, Rheum nobile Hook. f. & Thomson (Polygonaceae) to assess the function of avoiding injury by UV radiation while keeping the inflorescence warm by photosynthetically active (PA) and IR radiation. Although the translucent bracts and rosulate leaves transmitted little UV radiation, the former always transmit more PA and IR radiation. Additionally, the bracts transmit much more scattered solar radiation than direct radiation. The bracts are also anatomically different from the rosulate leaves. They have two or three layers of mesophyll cells with neither palisade nor spongy parenchymatous cells; in addition, the uppermost layer of mesophyll and the epidermis stain easily, and both are thought to play a role in attenuating UV radiation. The leaf epidermis of many land plants has UV absorbing pigments such as flavonoids, which absorb almost all UV radiation. Thus the role of the bracts of R. nobile is to protect the reproductive organs by absorbing UV radiation and to keep them warm by transmitting PA and IR radiation. The bracts are believed to have adapted function and form to the environment, in particular, to the weather conditions of the eastern Himalaya.     

The development and ultrastructure of the testa and tracheid bar inErythrina lysistemon Hutch. (Leguminosae: Papilionoideae)

Summary The development of the testa was studied inErythrina lysistemon using both light and electron microscopy. Cells of the outer epidermis of the outer integument divide anticlinally and undergo radial elongation to form a palisade layer. The outer tangential walls are thickened at an early stage, and deposition of fluted thickenings on the radial walls occurs at maturity. Palisade cells in the hilar region differentiate from sub-funicular tissue, and at maturity the outer ends of the cells undergo extensive deposition of secondary walls and associated lignification. The light line occurs at the junction between the outer, thickened portions of the cells and the inner, less thickened portions. An electron-translucent (suberised) cap develops in the outer tangential walls of the palisade cells at a late stage. Microtubules and dictyosomes are closely associated with the developing thickenings in palisade and tracheid bar, and the microtubules run parallel to the wall microfibrils. Differentiation of the tracheid bar coincides with final secondary wall deposition and lignification in the hilar palisade. The cells of the tracheid bar are dead at maturity, but are surrounded by sheaths of elongate parenchyma.     

Patterns of cell elongation in the determination of the final shape in galls of Baccharopelma dracunculifoliae (Psyllidae) on Baccharis dracunculifolia DC (Asteraceae)

Cell redifferentiation, division, and elongation are recurrent processes, which occur during gall development, and are dependent on the cellulose microfibrils reorientation. We hypothesized that changes in the microfibrils orientation from non-galled tissues to galled ones occur and determine the final gall shape. This determination is caused by a new tissue zonation, its hyperplasia, and relative cell hypertrophy. The impact of the insect’s activity on these patterns of cell development was herein tested in Baccharopelma dracunculifoliae—Baccharis dracunculifolia system. In this system, the microfibrils are oriented perpendicularly to the longest cell axis in elongated cells and randomly in isodiametric ones, either in non-galled or in galled tissues. The isodiametric cells of the abaxial epidermis in non-galled tissues divided and elongated periclinally, forming the outer gall epidermis. The anticlinally elongated cells of the abaxial palisade layer and the isodiametric cells of the spongy parenchyma originated the gall outer cortex with hypertrophied and periclinally elongated cells. The anticlinally elongated cells of the adaxial palisade layer originated the inner cortex with hypertrophied and periclinally elongated cells in young and mature galls and isodiametric cells in senescent galls. The isodiametric cells of the adaxial epidermis elongated periclinally in the inner gall epidermis. The current investigation demonstrates the role of cellulose microfibril reorientation for gall development. Once many factors other than this reorientation act on gall development, it should be interesting to check the possible relationship of the new cell elongation patterns with the pectic composition of the cell walls.     

STRUCTURE OF THE PEAR LEAF CUTICLE WITH SPECIAL REFERENCE TO CUTICULAR PENETRATION

Study of the pear leaf cuticle (Pyrus communis L. ‘Bartlett‘), in both intact and enzymatically isolated forms, has revealed that the cuticular membrane is separated from the underlying epidermal cell wall by a layer of pectic substances which extend into but not through the membrane. A layer of embedded birefringent waxes occurs towards the outer surface of the cuticular membrane. Platelet-like epicuticular waxes are deposited on the outer surface. The upper cuticular membrane is astomatous. The lower epidermis is stomatous, and the outer cuticular membrane is continuous with that lining the substomatal cavity. The lower cuticular membrane is also generally thicker than the upper, and both the upper and lower cuticular membranes are thicker over veinal than over mesophyll tissue. The birefringence frequently is discontinuous over anticlinal walls and over veinal tissue. The lower cuticle appears to contain fewer embedded waxes (as indexed by birefringence) than the upper. Enzymatic isolation of the cuticular membrane from the underlying tissues does not appear to cause any discernible change in structure as viewed with a light microscope. These findings are discussed in light of current knowledge concerning penetration of foliar applied substances into the leaf.     

DEVELOPMENT OF THE PHYTOMELANIN LAYER IN FRUITS OF AGERATUM CONYZOIDES (COMPOSITAE)

The development of the phytomelanin layer in the achenes of Ageratum conyzoides (Compositae, Eupatorieae) was studied using light and electron microscopy. At the level of the embryo sac, the young ovary wall contains an outer zone, consisting of an epidermis and two hypodermal layers, and an inner zone, consisting of developing fiber cells and 3–5 layers of parenchyma. A schizogenous space forms between the developing fibers and the inner hypodermis at about the time that the embryo sac is fully organized. At this stage, the developing fibers contain papilla which are outgrowths that connect the fibers to the inner hypodermal cells. After fertilization, phytomelanin accumulates on the cell walls lining this space. Subsequently, by the time the fruit matures, the phytomelanin fills the space completely and forms a solid, black layer. The surface of the inner hypodermis that faces the space forms a mold; the characteristic peglike projections of the mature phytomelanin layer develop by filling the invaginations between the hypodermal cells. During phytomelanin accumulation, abundant smooth endoplasmic reticulum is present in the hypodermis, especially in the outer layer. It is hypothesized that the precursors of the phytomelanin are synthesized in this endoplasmic reticulum and that these precursors migrate into the space where the phytomelanin is polymerized.     

REGENERATION OF THE SUNFLOWER CAPITULUM AFTER CYLINDRICAL WOUNDING OF THE RECEPTACLE

Using the young capitulum of Helianthus annuus L., a cylindrical plug of undifferentiated receptacle tissue, 1 mm in diameter, was isolated from lateral communication with the rest of the receptacle surface by a vertical circular wound cut, while retaining continuity with the subapical meristem. Within 24 hr, active cell division was induced at the inner and outer surfaces of the wound and in the receptacle epidermis bordering the wound edges, creating a rounded rim at the top of the wound. Within 3–6 days, floral initials, spaced 133–166 μm apart appeared on the flanks of both rims and later on the top of the plug and surrounding receptacle surface. The first formed initials developed into involucral bracts or ray florets and the later ones into disc florets which were organized into contact parastichies, the number of which did not conform with the Fibonacci series. The base of the plug developed into a stem-like structure completing the regeneration of a fully formed functional capitulum. This operation was demonstrated for two sunflower cultivars and occurred in both long and short daylengths.     

Seed coat development, anatomy and scanning electron microscopy of Harpagophytum procumbens (Devil's Claw), Pedaliaceae

Seed coat development of Harpagophytum procumbens (Devil's Claw) and the possible role of the mature seed coat in seed dormancy were studied by light microscopy (LM), transmission electron microscopy (TEM) and environmental scanning electron microscopy (ESEM). Very young ovules of H. procumbens have a single thick integument consisting of densely packed thin-walled parenchyma cells that are uniform in shape and size. During later developmental stages the parenchyma cells differentiate into 4 different zones. Zone 1 is the multi-layered inner epidermis of the single integument that eventually develops into a tough impenetrable covering that tightly encloses the embryo. The inner epidermis is delineated on the inside by a few layers of collapsed remnant endosperm cell wall layers and on the outside by remnant cell wall layers of zone 2, also called the middle layer. Together with the inner epidermis these remnant cell wall layers from collapsed cells may contribute towards seed coat impermeability. Zone 2 underneath the inner epidermis consists of large thin-walled parenchyma cells. Zone 3 is the sub-epidermal layers underneath the outer epidermis referred to as a hypodermis and zone 4 is the single outer seed coat epidermal layer. Both zones 3 and 4 develop unusual secondary wall thickenings. The primary cell walls of the outer epidermis and hypodermis disintegrated during the final stages of seed maturation, leaving only a scaffold of these secondary cell wall thickenings. In the mature seed coat the outer fibrillar seed coat consists of the outer epidermis and hypodermis and separates easily to reveal the dense, smooth inner epidermis of the seed coat. Outer epidermal and hypodermal wall thickenings develop over primary pit fields and arise from the deposition of secondary cell wall material in the form of alternative electron dense and electron lucent layers. ESEM studies showed that the outer epidermal and hypodermal seed coat layers are exceptionally hygroscopic. At 100% relative humidity within the ESEM chamber, drops of water readily condense on the seed surface and react in various ways with the seed coat components, resulting in the swelling and expansion of the wall thickenings. The flexible fibrous outer seed coat epidermis and hypodermis may enhance soil seed contact and retention of water, while the inner seed coat epidermis maintains structural and perhaps chemical seed dormancy due to the possible presence of inhibitors.     

ANATOMY AND ASPECTS OF DEVELOPMENT OF THE STAMINATE INFLORESCENCES AND FLORETS OF SEVEN SPECIES OF ALLOCASUARINA (CASUARINACEAE)

The morphology, ontogeny, and vascular anatomy of the staminate inflorescences and florets of seven species of Allocasuarina are described. The generally terminal but open-ended inflorescences occur on monoecious or staminate dioecious trees and consist of whorls of bracts, each subtending a sessile axillary floret. Each floret consists of one terminal stamen with a bilobed, tetrasporangiate anther enclosed typically by cuculliform appendages, commonly considered bracteoles, an inner median pair and an outer lateral pair. The mature stamen is exerted, the anther is basifixed and is extrorsely dehiscent. In early development of a male inflorescence very little internodal elongation occurs and enclosing cataphylls appear. The inflorescence apex is a low dome with a uniseriate tunica and a small group of central corpus cells. Bract primordia are initiated by periclinal divisions of C₁ followed by further divisions of the corpus and anticlinal divisions in the tunica. The bracts are epinastic and become gamophyllous except apically by cell divisions in both sides of each primordium. Stomata are restricted to the axis furrows and the abaxial tips of the bracts. The axillary florets arise in acropetal succession initiated by periclinal divisions in C₁ accompanied by anticlinal divisions in the tunica. The lateral floral appendages are also initiated by C₁ followed by anticlinal divisions in the tunica. They become adnate basally later with the subtending bract. The median sterile appendages are initiated in a manner similar to the initiation of the outer appendages. The stamen is initiated by divisions in the outer layers of the corpus and in the tunica, and then develops first by apical growth followed by intercalary growth. The vascular system of the inflorescence is identical to that of the vegetative stem. Each floret is supplied by a single bundle that has its source in a branch from each of the two traces supplying a bract. Six bundles arise from the floral bundle; four of these terminate in the base of the stamen and two form an amphicribal bundle that supplies the anther. Pollen is binucleate, 3- to 7-porate. The exine is tegillate.     

DEVELOPMENTAL CHANGES IN THE GOLGI-APPARATUS OF MAIZE ROOT CELLS

Whaley , W. Gordon (U. Texas, Austin), Joyce E. Kephart , and Hilton H. Mollenhauer . Developmental changes in the Golgi-apparatus of maize root cells. Amer. Jour. Bot. 46(10): 743–751. Illus. 1959.—Golgi-apparatus comparable to that of animal cells has been observed in electron micrographs of all cells of the maize root tips studied. The central structure consists of a “stack” of cisternae with the edges of which small vesicles are associated. In conspicuously vacuolating inner cortical cells the Golgi-apparatus resembles that of dividing cells. The possible roles of these vesicles are discussed. As the cells of the epidermis and outer cortical layer mature these vesicles tend to accumulate and increase in size. In necrotic rootcap cells these vesicles are not apparent and the Golgi-cisternae are hypertrophied.