STUDIES OF SPHENOPHYLLUM SHOOTS: SPECIES DELIMITATION WITHIN THE TAXON SPHENOPHYLLUM

Structurally preserved ultimate vegetative shoots and attached foliage of Sphenophyllum multirame and two additional taxa from Upper and Middle Pennsylvanian coal balls are described. Shoot axes of all taxa are delimited by small cube-shaped epidermal cells and contain three isolated strands of protoxylem tracheids separated by undifferentiated procambial cells. Metaxylem maturation is delayed for some distance below the apical meristem. Branches originate from a single protoxylem strand and are contiguous with the subjacent leaf trace for a short distance. Sphenophyllum multirame is considered a valid taxon. It is suggested that shoot and foliar anatomical characteristics may form valid criteria for species delimitation within the genus, and S. reedae is delimited by such characteristics. An additional form is tentatively suggested as a possible new species. Anatomical similarities between 5. reedae and Peltastrobus reedae suggest that these taxa represent vegetative and reproductive structures of the same plant.     

The Morphology and Development of Cross Veins in the Leaves of Bread Wheat (Triticum aestivum L.)

In the leaves of bread wheat Triticum aestivum L. the longitudinalvascular bundles are linked by small transverse bundles Pairsof similar small vascular bundles also link the upper ends ofminor longitudinal bundles to their neighbours in a Y-shapedarrangement The cross-vein procambial strands arise from unexpanded cellsof one layer of the mesophyll tissue. Lines of these cells connectone longitudinal procambial strand to the next The procambialcells subsequently undergo two tangential divisions to producecells which differentiate to form the conducting and parenchymatouselements of the mature cross veins. Anomalous cross veins are sometimes found. possible modes oforigin of these anomalous cross veins are considered.     

ONTOGENY OF MAJOR VEINS IN THE LAMINA OF POPULUS DELTOIDES BARTR

The ontogeny of the major venation in the lamina of Populus deltoides Bartr. leaves was investigated in relation to the development of original procambial bundles, subsidiary bundles, and their derivatives. Serial sections and clearings were used to show that the midrib region is a composite structure consisting of several independent vascular bundles, each of which eventually diverges into the lamina to become a secondary vein. The sequence of events in the ontogeny of major secondary veins is: (1) an original procambial strand develops acropetally and becomes the precursor of the first vascular bundle of the midrib region of the lamina, (2) ground tissue at the forefront of acropetally developing subsidiary procambial bundles differentiates in a wavelike continuum; meristematic regions precede the acropetally developing procambial bundles, (3) discrete subsidiary bundles differentiate in the meristematic regions as they advance acropetally, (4) subsidiary bundles diverge obliquely in the lamina margin giving rise to the secondary veins in a basipetal fashion, and (5) subsequent differentiation and maturation of the secondary veins occurs within the lamina. The original procambial bundles and first-formed subsidiary bundles become the secondary veins of the uppermost portions of the lamina, the next-formed subsidiary bundles become the secondary veins of the middle portions of the lamina, and the last-formed subsidiary bundles become the secondary veins of the lowermost portion of the lamina.     

QUANTITATIVE STUDIES OF PINNULE DEVELOPMENT IN THE FERNS ADIANTUM RADDIANUM AND CHEILANTHES VIRIDIS

Pinnule development was investigated in two fern species, Adiantum raddianum Presl cv. Decorum and Cheilanthes viridis (Forsk.) Swartz, by using clearings to facilitate the recording of mitotic divisions. Both species were found to possess a marginal meristem. This meristem consists of both a marginal row of large initials and a submarginal meristematic zone. The marginal meristem in these ferns is responsible for establishing the layers of the lamina, providing new cells which by enlargement will expand the pinnule, establishing general pinnule form, initiating the procambial stands, and forming the false indusia. The cells of the submarginal meristem were found to divide parallel to the pinnule margin more frequently if they were to become ground tissue, while dividing perpendicular to the margin more frequently if they were to become procambial. Details of vein dichotomies were also studied. Perimeter expansion was found to be associated with dichotomy of the veins, and venation pattern was found to be correlated with leaf form. The marginal meristem is active from the time of pinnule initiation until the pinnule reaches about 50% of its final length or width. Leaf development in leptosporangiate ferns resembles the traditional concept of development in angiosperms somewhat more than it does the more recent concepts. It is clear, though, that there is not a high degree of convergence in the marginal growth of fern and angiosperm leaves.     

THE ANATOMY OF TUMORS INDUCED ON CITRUS BY CITRUS VEIN-ENATION VIRUS

Citrus vein-enation virus-induced tumors on leaves, thorns, stems, and roots of Citrus auranti-folia (Christm.) Swingle and C. jambhiri Lush. were investigated. Leaf vein tumors are initiated as cytological abnormalities of phloem fiber primordial cells adjacent to protophloem sieve tubes. The tumors then enlarge through hyperplasia of the affected fiber primordia. The mesophyll and epidermal tissues on the abaxial side of affected veins divide less prolifically and contribute to the tumor mass. Leaf vein tumors are determinate, like the protophloem where they originate, and cease enlarging as the leaf matures. Most thorn tumors are initiated in fiber primordia and develop similarly to vein tumors. Stem tumors and some thorn tumors develop from affected cells of the procambial tissue that lies between the metaxylem and metaphloem of vascular bundles. The cambium which differentiates in these areas is composed of affected cells and produces large amounts of abnormal xylem tissue. The resulting woody tumors are indeterminate like the cambium and secondary xylem.     

IDENTIFICATION OF PROCAMBIUM IN THE PRIMARY ROOT OF TRIFOLIUM PRATENSE (FABACEAE)

Histochemical and morphometric analyses were used to identify and define an early stage of procambial differentiation in 1.5–2.0-cm-long (48 hr after germination) primary roots of Trifolium pratense L. Esterase activity was used as a histochemical marker for early differentiation of procambium. Morphometric analysis of cell length and width as a function of distance from the root cap junction was performed on the same tissue using brightfield and Nomarski DIC optics. This combination of techniques allowed the identification of esterase activity in both the cell wall and cytoplasm and permitted the determination of the exact location, size, and shape of the histochemically stained cells within the apex. Esterase activity identified the proendodermis and procambial cylinder (six to seven cells in diameter) two to three cells proximal to the root cap junction. In this system, esterase activity proved to be an earlier marker for procambial differentiation than morphometric or cytological changes. It is suggested that these techniques will be useful in characterizing procambial pattern development in more complex shoot systems.     

ONTOGENY OF THE CLOSED DICHOTOMOUS VENATION OF REGNELLIDIUM

Pray , Thomas R. (U. South. California, Los Angeles.) Ontogeny of the closed dichotomous venation of Regnellidium . Amer. Jour. Bot. 49(5): 464–472. Illus. 1962.—The venation of the pinna of Regnellidium consists of a flabellate series of dichotomizing vascular strands, branches of a single pinna trace. At the laminal margin, the entire venation is closed by a marginal vein. The development of the pinna was investigated primarily by means of paradermal sections. During early development, the organization of the marginal meristem and its derivatives is very similar to that previously described for Nephrolepis. The arrangement of cells in the embryonic pinna is predisposed for the differentiation of dichotomizing procambial strands. During the final phases of pinna development, the marginal meristem is altered in such a manner as to result in a submarginal band of elongated cells which differentiates a marginal procambial strand connecting the tips of the dichotomizing veins. Relatively late in pinna ontogeny and after the entire procambial venation pattern has been delimited, the marginal meristem becomes inactive. The possible correlation between extended marginal growth and dichotomizing veins is discussed.     

Ontogeny of embryogenic callus in Medicago truncatula: the fate of the pluripotent and totipotent stem cells

Background and Aims

Understanding the fate and dynamics of cells during callus formation is essential to understanding totipotency and the mechanisms of somatic embryogenesis. Here, the fate of leaf explant cells during the development of embryogenic callus was investigated in the model legume Medicago truncatula.

Methods

Callus development was examined from cultured leaf explants of the highly regenerable genotype Jemalong 2HA (2HA) and from mesophyll protoplasts of 2HA and wild-type Jemalong. Callus development was studied by histology, manipulation of the culture system, detection of early production of reactive oxygen species and visualization of SERK1 (SOMATIC EMBRYO RECEPTOR KINASE1) gene expression.

Key Results

Callus formation in leaf explants initiates at the cut surface and within veins of the explant. The ontogeny of callus development is dominated by the division and differentiation of cells derived from pluripotent procambial cells and from dedifferentiated mesophyll cells. Procambium-derived cells differentiated into vascular tissue and rarely formed somatic embryos, whereas dedifferentiated mesophyll cells were competent to form somatic embryos. Interestingly, explants incubated adaxial-side down had substantially less cell proliferation associated with veins yet produced similar numbers of somatic embryos to explants incubated abaxial-side down. Somatic embryos mostly formed on the explant surface originally in contact with the medium, while in protoplast microcalli, somatic embryos only fully developed once at the surface of the callus. Mesophyll protoplasts of 2HA formed embryogenic callus while Jemalong mesophyll protoplasts produced callus rich in vasculature.

Conclusions

The ontogeny of embryogenic callus in M. truncatula relates to explant orientation and is driven by the dynamics of pluripotent procambial cells, which proliferate and differentiate into vasculature. The ontogeny is also related to de-differentiated mesophyll cells that acquire totipotency and form the majority of embryos. This contrasts with other species where totipotent embryo-forming initials mostly originate from procambial cells.Key words: Callus, dedifferentiation, leaf veins, Medicago truncatula, pluripotency, procambium, protoplasts, reactive oxygen species, SERK, somatic embryogenesis, stem cells, totipotency     

Foliar δ15 N patterns are dependent on seasonal and spatial variations as shown in lowland Scottish scrub

Summary

Patterns of foliar δ¹⁵ N can suggest testable hypotheses concerning N use among and within plant species. However, both spatial and time-series sampling is required to establish how the patterns vary within and among species. On a seasonal basis, foliar δ^l5 Nrankings may change among the species compared. When symbiotic N₂-fixers are among the plants sampled, N₂-fixation may be temporally disjunct from the near-0%c, expected foliar δ¹⁵ N, which is usually attributed to N₂-fixation, and the fates of previously fixed N may not be apparent from a net foliar δ¹⁵ N of either soil or plants.     

INITIAL VASCULARIZATION OF THE VEGETATIVE SHOOT OF ABIES CONCOLOR

Parke , Robert V. (Colorado State U., Fort Collins.) Initial vascularization of the vegetative shoot, of Abies concolor. Amer. Jour. Bot. 50(5): 464–469. Illus. 1963.—In the dormant winter bud, the future vascular system of the shoot exists as a rather ill-defined system of procambial strands, which extends acropetally from the scale traces through a plate of thick-walled, deeply staining cells, the crown, and into the axis and the numerous foliar primordia making up the telescoped shoot. Each foliar primordium receives a single procambial strand or leaf trace. The procambial strands differentiate acropetally. No differentiated vascular tissue was observed in the dormant shoot. As the shoot elongates in the spring, vascular differentiation progresses at a rapid rate. In the leaf traces, protophloem differentiates acropetally. The protoxylem, which appears first in the axial region of the trace, differentiates acropetally into the foliar primordium and basipetally into the stem. The first-formed phloem elements are short-lived. They are nucleate and without sieve areas. In the protoxylem, the first-formed tracheids are mostly of the annular or spiral-thickened type.     

Quantitative survey of sieve tube distribution in foliar terminal veins of ten dicot species

Quantitative data on sieve tubes in foliar terminal veins (vein endings) were added to the meager published information from only five dicot species. Correlations with other minor vein configurations were also explored. Leaf samples from ten species of dicots (Oxalis nelsonii, O. pes-capri, O. rubra, O. stricta [Oxalidaceae], Caesalpinia pulcherrima. Glycine max, Trifolium repens [Leguminosae], Ampelamus albidus [Asclepidaceae], Eupatorium rugosum [Asteraceae], and Polygonum convolvulus [Polygonaceae]) were selected for two quantitative procedures: 1) a survey of the arrangement of terminal veins and distribution of sieve tubes in terminal veins in 100 areoles per species using stained leaf clearings; and 2) a search for correlations of sieve tube distribution with number and branching patterns of terminal veins, and with sizes of areoles using image analysis. Two Oxalis species (O. pes-capri and O. stricta) had the smallest areoles and virtually no sieve tubes in any terminal vein. Polygonum convolvulus, at the other extreme, had sieve tubes extending to the tips of most terminal veins. The other species had various intermediate sieve tube configurations. The data indicate that species with few or no sieve tubes associated with their terminal veins, regardless of the number of terminal veins per areole, have smaller areoles. These results may have implications regarding the entry of leaf photosynthates into the vascular system.     

Abundance of microtubules in preprophase bands of some Triticum species

Root tip procambial cells of Triticum speltoides, T. tauschii, T. turgidum and T. aestivum have been investigated ultrastructurally for the detection of preprophase microtubule bands (PMBs) and to estimate the number of microtubules comprising the bands. The species selected are phylogenetically related but differ in the ploidy level. It was found that all species develop well-defined PMBs prior to mitosis. Estimations of microtubule abundance in the PMBs was carried out in midpreprophase cells, a stage judged by a feature of the nucleus in which electron-transparent canals are formed around the initial condensations of the chromatin material and the nucleoli. Triticum speltoides bears the smaller average number of microtubules per PMB and T. aestivum the greater. The results indicate that the increase follows the upgrade of the number of chromosome sets. It is suggested that the average number of microtubules of PMBs is related to the ploidy level.Abbreviation PMB preprophase microtubule band     

Geobotanical studies on zinc deposit areas of Zawar mines,Udaipur

This study reveals disjunct distribution patterns of certain plant species on zinc-rich soils in the Zawar mines region near Udaipur. Ten plant species have high constancy and fidelity values on zinc-rich soils in comparison to normal soil. The plant community composed of these species has been named Impatiens balsamina-Triumfetta pentandra association. As Impatients balsamina is the most characteristic species on metal dumps, it can be considered as a local indicator for the metal zinc.Acknowledgements: The authors are grateful to the University Grants Commission of India, New Delhi for substantial financial assistance.     

ONTOGENY OF THE OPEN DICHOTOMOUS VENATION IN THE PINNA OF THE FERN NEPHROLEPIS

Pray , Thomas r . (U. South. California, Los Angeles.) Ontogeny of the open dichotomous venation in the pinna of the fern Nephrolepis. Amer. Jour. Bot. 47(5) : 319—328. Illus. 1960.–The venation of the pinna of Nephrolepis consists of a midvein and 2 lateral series of dichotomizing veins all of which terminate freely near the margins. The development of the pinna is analyzed with particular attention to the nature of the marginal meristem and the organization of the embryonic pinna as it appears in paradermal section. The arrangement of cells in pinna wings during the period of marginal growth displays a pattern which foreshadows the pattern of the mature venation. In contrast with the development of the leaves of angiosperms, marginal growth continues into a relatively late phase of pinna ontogeny and apparently is active throughout the phases of ontogeny concerned with blocking-out the pathways of procambial differentiation. Thus the pattern of venation appears to be correlated with the manner of activity of the marginal meristem and subsequent orientation of its derivatives. The theoretical aspects of the result of this investigation are discussed in relation to other studies of foliar venation ontogeny.     

Ectopic divisions in vascular and ground tissues of Arabidopsis thaliana result in distinct leaf venation defects

Leaf venation patterns vary considerably between species and between leaves within a species. A mechanism based on canalization of auxin transport has been suggested as the means by which plastic yet organized venation patterns are generated. This study assessed the plasticity of Arabidopsis thaliana leaf venation in response to ectopic ground or procambial cell divisions and auxin transport inhibition (ATI). Ectopic ground cell divisions resulted in vascular fragments between major veins, whereas ectopic procambial cell divisions resulted in additional, abnormal vessels along major veins, with more severely perturbed lines forming incomplete secondary and higher-order venation. These responses imply limited vascular plasticity in response to unscheduled cell divisions. Surprisingly, a combination of ectopic ground cell divisions and ATI resulted in massive vascular overgrowth. It is hypothesized that the vascular overproduction in auxin transport-inhibited wild-type leaves is limited by simultaneous differentiation of ground cells into mesophyll cells. Ectopic ground cell divisions may negate this effect by providing undifferentiated ground cells that respond to accumulated auxin by differentiation into vascular cells.     

Development of the Kranz structure during leaf growth in C4 Euphorbia maculate

The development of the Kranz structure was investigated in leaves of C₄ Euphorbia maculata using electron microscopy. Four leaf stages, i.e., primordial, immature, young, and mature, were examined, based on the photosynthetic tissue that surrounded the veins. The examination revealed how cells differentiated into distinct bundle sheath cells (BSCs) and mesophyll cells (MCs). Specialization of the BSCs was invariably associated with the development of the veins as well as the MCs. Precursors for BSC and MC were recognizable fairly early, at the immature stage, according to their position and differential enlargement Once these precursors were delimited from the procambial area, differentiation into each cell type occurred synchronously, in a coordinated manner. All cells enlarged as they were displaced from the Kranz precursor area, but the BSC precursors were initially larger and remained relatively larger than the other cell types throughout leaf development The developmental changes sharply distinguished BSCs from the adjacent MCs at the onset of Kranz formation and continued until maturity. Chloroplast enlargement also occurred during cell displacement, but the rate of enlargement was greater in BSCs, resulting in larger chloroplasts at later stages. However, no significant structural differences were detected among the chloroplasts of BSC and MC in the early stages. Most of the specialized features appeared at the young-leaf stage; structural dimorphism became prominent at the later stages. This enhanced development of the BSC chloroplasts was correlated with asymmetric distribution of cellular components. In addition, the BSC formed thin primary pit fields with numerous plasmodesmata. Peripheral reticulum was present, but generally was not conspicuous. We also discuss the characteristics of leaf anatomy and ultrastructure inE. maculata as they relate to the C₄ photosynthetic pathway.     

五种红树植物叶片结构的比较研究

以木榄(Bruguiera gymnorrhiza)、桐花树(Aegiceras corniculatum)、拉关木(Laguncularia racemosa)、海芒果(Cerbera manghas)、杨叶肖槿(Thespesia populnea)五种红树植物为材料,采用常规石蜡切片法对它们的叶片横切面结构进行显微观察,比较真红树植物和半红树植物叶片结构的特点及变化规律,研究红树植物叶对盐浸环境的适应性。结果表明:除杨叶肖槿为异面叶、掌状网脉外;拉关木为等面叶、羽状脉,其它三种植物为异面叶、羽状网脉;五种材料具4级叶脉,3级、4级脉具明显维管束鞘。木榄、桐花树、拉关木、杨叶肖槿1级脉为半周韧无限维管束,海芒果1级脉为外韧无限维管束。五种材料叶肉具有分泌腔,除海芒果外,具有含晶体细胞;木榄、桐花树有内皮层,拉关木有贮水组织;桐花树、海芒果有含单宁细胞;桐花树、拉关木、杨叶肖槿有盐腺。这五种植物的叶片结构体现出不同植物对盐浸环境适应性的特征。相比较而言,真红树植物的特化结构较半红树植物多。     

ECTODESMATA AND FOLIAR ABSORPTION

Franke , Wolfgang . (U. Bonn, Germany.) Ectodesmata and foliar absorption. Amer. Jour. Bot. 48(8): 683–691. Illus. 1961.—Plasmodesmata, called ectodesmata, in the outer walls of epidermal cells, have been investigated. Their occurrence and distribution in the epidermis of leaves of Plantago major and Helxine soleirolii have been examined in connection with foliar absorption. Leaf structures such as guard-cells, conical hairs, anticlinal walls and the epidermal cells adjacent to the leaf veins have been shown consistently to contain large numbers of ectodesmata, while in neighboring cells ectodesmata may be low in number or lacking. The same areas also are known to be especially pervious to water and dissolved dyes applied to the surface of the leaf. From special investigations, it appears that certain solutions that form visible crystals and precipitates in the outer wall enter the epidermal cell wall in localized pathways. The localization of these bodies coincides with that of ectodesmata. Therefore, it is concluded that the ectodesmata may be the pathways for transport of substances from the outside to the interior of tissues and vice versa. Nutrients applied to the surface of leaves are thought to enter by the same pathways, i.e., the ectodesmata, as those in which the penetration can be visibly detected. Some phenomena of foliar absorption which confirm this theory are explained in connection with the presence of ectodesmata.     

Born migrators: Historical biogeography of the cosmopolitan family Cannabaceae

Dispersal scenarios have been favored over tectonic vicariance as an explanation for disjunct distributions in many plant taxa during the last two decades. However, this argument has been insufficiently addressed in cosmopolitan groups showing disjunct patterns in both the temperate and tropical regions. In this study, we used the Cannabaceae, an angiosperm family distributed in tropical and temperate regions of both the New World and the Old World, to explore the role of dispersal in shaping disjunct patterns and species diversification of cosmopolitan plants. We reconstructed the phylogenetic relationships of all 10 genera and 75 species of Cannabaceae (ca. 64.1% of recognized species) based on eight DNA regions. Based on fossil calibrations, we estimated the divergence times and net diversification rates. We further inferred the ancestral geographical ranges with several models and compared the fitness of different models. The Cannabaceae and most genera were strongly supported as monophyletic except for the Parasponia being embedded within the Trema. The Celtis were resolved into two strongly supported clades primarily corresponding to temperate and tropical regions. We inferred that the Cannabaceae originated at ca. 93 Ma, and that subsequent rampant and widespread dispersals shaped the intercontinentally disjunct distribution of the Cannabaceae. Dispersal coincides with adaptation to drier and colder climate in the Northern Hemisphere, or humid and warm climate in the tropical regions, followed by rapid species diversification. This study advances our understanding as to the formation of distribution patterns and species diversification of a plant family with tropical to temperate disjunct distributions.