Contributions to the resumption of growth in ecodormant buds of apple

The resumption of development in ecodormant buds in terms of establishing a functional vascular connection between the inflorescence primordia and spur tissues in apple trees was investigated. Differentiation of the xylem elements could be observed first in the pedicel of the flower primordium, in the middle of January. Much later (at the beginning of April) there were mature xylem vessels in the wall of the receptacle and, merely a procambial strand for the ovule primordium which was at this time an undifferentiated protrusion of meristematic cells, only. As for phenological development of buds incubated at a temperature of 20 °C, it was the slowest in buds sampled in January, faster in buds sampled in the middle of February and, buds from the middle of March responded very quickly. The function of temperatures needed both for xylem differentiation and for the flower primordium to achieve maturity is pointed out. The nature of frost damage in vessel elements, as well the relationship between chilling requirement and growth features of apple cultivars will be discussed.

Ontogenèse des canaux sécréteurs d'origine primaire dans le bourgeon de Pin maritime

In the bud of Pinus pinaster Ait., two resin ducts are formed at the base of each very young scale on each side of the procambial strand. They differentiate in the acropetal and basipetal directions as do the vascular tissues. During the basipetal differentiation, the resin ducts from each scale anastomose in a definite way: the left resin duct of each scale is connected with the right duct of the n – 8 scale rank and the right duct, with the left duct of the n – 5 scale rank. The resin canal system of the shoot is then constituted of only 13 resin ducts. The resin ducts of the maritime pine are formed on a schizolysigenous pattern: a schizogenous process induces the formation of the lumen; then a transitory stage with two secretory layers takes place before a lysigenous process which enhances the enlargement of the duct lumen. Observations were done using light and electron microscopy.

Floral development of Aponogeton natans and A. undulatus

The primordia of the floral appendages are initiated in an acropetal succession. Members of the same whorl appear nearly simultaneously. The gynoecial whorl and the two staminal whorls are trimerous, whereas the perianth consists only of two anteriolateral tepals. However, the posterior (adaxial) tepal may be present as an extremely reduced buttress whose growth becomes arrested immediately after its inception. If this somewhat questionable tepal rudiment is included we have a perfectly trimerous and tetracyclic flower with alternation of successive whorls. Subtending bracts of the flowers are completely missing in all developmental stages. While the tepal primordia are dorsiventral from their inception, the stamen and pistil (carpel) primordia originate as hemispherical mounds which become dorsiventral in subsequent stages of development. Each pistil (carpel) primordium becomes horseshoe shaped. As the margins grow up and contact they fuse postgenitally. No cross zone is formed. Placentation is submarginal. In A. natans eight ovules are formed and in A. undulatus only two arise; all ovules are bitegmic. The floral apices have a two-layered tunica up to the stage of pistil formation. The inception of all floral appendages (including the ovules) occurs by periclinal cell division in the second tunica layer. The third layer (corpus) may contribute to the formation of the stamens and pistils. Each appendage primordium receives only one procambial strand which begins to differentiate after the inception of the primordium. The questionable rudimentary tepal buttress lacks a procambial strand. Apparently it does not reach the developmental stage at which procambial induction occurs. From the point of view of floral development, the two species of Aponogeton differ drastically from members of the Alismatales studied so far. Among the Helobiae, the Aponogetonaceae appear to be most closely related to the Scheuchzeriaceae and the Juncaginaceae (Triglochinaceae).

Ovule and seed development in Pinus radiata: postmeiotic development, fertilization, and embryogeny

Development of ovule tissues in Pinus radiata after meiosis, fertilization, and embryogeny is comparable with that of other pines, but P. radiata takes longer to develop. Fertilization occurs 15 months after pollination and morphological embryo maturity is reached 5 months later. In ovules harvested in spring after meiosis, a curved band of small cells with dense cytoplasm extends from the chalazal end of the ovule to the vascular tissue of the ovuliferous scale. It is interpreted as a procambial strand, which in the next year, differentiates basipetally into elongated, thick-walled cells with degenerated nuclei.

Leaf development in Begonia hispida var. cucullifera with special reference to vascular organization

The leaf is initiated by periclinal divisions in the second cell layer of the apex. Early in development, it assumes an asymmetrical shape as a result of the non-median position of the apical meristematic region that forms the leaf tip. The other main lobes of the leaf are formed by two additional regions of growth to the side of the tip. In the second plastochron, primordia are initiated on the upper surface of the main ribs of the leaf and these often develop into large, leaf-like appendages. During the third plastochron, the leaf becomes covered by a dense layer of trichomes. Vascular development is well correlated with regions of growth. The median procambial strand extends diagonally into the skewed apical growth region and another strand branches from this and develops on the other side. Lateral procambial strands usually form in an abaxial to adaxial sequence in the petiole: one strand of the first pair to develop forms part of the median rib and the other forms a third main rib on the opposite side. After the initiation of primordia on the leaf surface, a 'ventral system' of procambia is developed supplying mainly the ventral rib surface and consequently the epiphyllous appendages. This consists of branches from the adaxial-most peripheral bundles in the petiole as well as a bundle in the centre. The vascular anatomy of the stem and nodal region is also described in relation to that of the leaf.

Floral development of Zannichellia palustris

What, at maturity, appears to be a bisexual flower in the axil of one of two subopposite leaves, is revealed as a fertile nodal complex with quite different organization. Three appendages develop at each nodal complex. The first girdles the stem and becomes at maturity a membranous sheath about the entire node. The second subtends the axillary meristem, which terminates as the staminate flower, and branches laterally as a renewal growth in the axil of a sterile appendage just below the stamen. The third appendage is subopposite the terminal meristem, which gives rise to the pistillate floral bud towards the staminate flower, and a renewal growth apex towards the appendage. This renewal growth apex repeats the entire pattern at almost a 90° shift to the right or left, depending on the shoot. The single stamen of the staminate flower develops as those studied in Potamogeton and Ruppia. The pistillate flower develops two carpel primordia, which become peltate before initiating a single ovule primordium on the adaxial portion (Querzone). The membranous envelope which covers the carpels at maturity is initiated at ovule inception, below one of the carpels. A peltate stigma differentiates on a short style and at maturity becomes broad and lobed. The renewal growth apex has a one-layered tunica. The membranous sheaths of the node and of the pistillate flower are primarily protodermal in origin, while the rest of the sterile and reproductive appendages arise through activity in subprotodermal cells. Procambial development is acropetal closely following primordial inception. Each organ (sterile or fertile) receives one procambial strand, except for the membranous sheath about the node and the one about the pistillate flower.

Floral development of Ruppia maritima var. maritima

A hyaline, unvascularized sheath envelops a portion of the inflorescence near maturity. Though resembling an appendage of the main axis, in early ontogeny it develops as a prophyll of the renewal growth apex below the inflorescence. Two flowers develop on the inflorescence axis, subopposite each other. Fertile appendages are initiated in an acropetal sequence on each floral bud. The first to form, in the median position, are the two stamens, the lower preceding the upper. Each stamen develops two bisporangiate thecae separated by a broad connective. A dorsiventral outgrowth is initiated slightly abaxially near the tip of the connective at the stage of theca differentiation. This outgrowth appears to be homologous with a similar outgrowth in Potamogeton densus, but not with the sterile appendages of the Potamogeton flower which, by some authors, have incorrectly been interpreted as connective outgrowths. Each carpel arises as a radial primordium which becomes peltate after its inception. One ovule is initiated at the adaxial portion (Querzone). The stigma becomes broad and flat, lobing at its margins. A slight outgrowth develops at the abaxial wall of the carpel. The floral apex has a two-layered tunica. The primordia of the stamens, carpels, and ovules arise by periclinal divisions in the second layer. Procambial development is acropetal following closely primordial inception. Each appendage, including the ovule, receives one procambial strand. The outgrowths of the connective and the carpel lack procambium.

Floral development of Butomus umbellatus

The primordia of the floral appendages appear in acropetal succession and develop in the order in which they appear. The primordia of each whorl of appendages are formed in a rapid sequence. After the inception of outer tepal primordia, the floral apex becomes triangular. On each angle, one inner tepal primordium together with the primordia of a pair of outer stamens and an inner stamen is formed. The triangularity of the floral apex might be interpreted as an indication of the formation of petal–stamen (CA) primordia as reported for Alisma and Hydrocleis. If this is the case, the primary pattern of organogenesis of the Butomus flower is trimerous and tetracyclic, i.e. one whorl of outer tepals, one complex of inner tepals and stamens, and two whorls of pistils. The floral apices have a two-layered tunica surrounding a central corpus. The initiating divisions in the formation of all floral appendages occur in the second tunica layer. In the case of stamen primordia, the outer corpus is also involved. Procambial development is acropetal. One procambial strand differentiates into each floral appendage shortly after its inception. Additional procambial strands are formed in the pedicel and the perianth and gynoecium. The relationships of Butomus to the Magnoliidae are discussed.

Floral development of Potamogeton densus

The floral appendages of Potamogeton densus are initiated in an acropetal sequence. The first primordia to be seen externally are those of the lateral tepals, though sectioning young floral buds (longitudinally, parallel to the inflorescence axis) reveals initial activity in the region of the lower median (abaxial) tepal and stamen at a time when the floral meristem is not yet clearly demarcated. The lateral (transversal) stamens are initiated simultaneously and unlike the median stamens each arises as two separate primordia. The upper median (adaxial) tepal and stamen develop late in relation to the other floral appendages, and in some specimens are completely absent. Rates of growth of the primordia vary greatly. Though the lower median tepal and stamen are initiated first, they grow slowly up to gynoecial inception, while the upper median tepal appears late in the developmental sequence but grows rapidly, soon overtaking the other tepal primordia. The four gynoecial primordia arise almost simultaneously, although variation in their sequence of inception occurs. The two-layered tunica of the floral apices gives rise to all floral appendages through periclinal divisions in the second layer. The third layer (corpus) is involved as well in the initiation of the stamen primordia. Procambial strands develop acropetally, lagging behind primordial initiation. The lateral stamens though initiating as two primordia each form a single, central procambial strand, which differentiates after growth between the two primordia of the thecae has occurred. A great amount of deviation from the normal tetramerous flower is found, including completely trimerous flowers, trimerous gynoecia with tetramerous perianth and androecium, and organs differentiating partially as tepals and partially as stamens.

Histology and ultrastructure of oat blue dwarf virus infected oats

The oat blue dwarf virus is a small spherical virus (28–30 nm) in diameter and is obligatorily transmitted by the aster leafhopper Macrosteles fascifrons Stål. The virus causes abnormalities in the phloem development of infected plants. Hyperplasia and limited hypertrophy of phloic procambium, in a given procambial strand, begin only after the maturation of the first protophloem sieve-tube element in that particular localized area. The majority of phloem elements produced in hyperplastic areas are parenchymatous, have truncated end walls, and lack sieve plates. Electron-microscopic observations substantiated the hypothesis that the virus was phloem-limited by revealing virus particles only in phloem elements. The greatest accumulation of virus particles was observed in the region between immature and fully vacuolated phloem elements, implicating virus synthesis in immature elements. Crystals of virus particles were often large enough to be seen by light microscopy.