bluuebunny/crossref_metadata_2025 huggingface dataset:
WOOD ANATOMY OF ILLICIUM (ILLICIACEAE): PHYLOGENETIC, ECOLOGICAL, AND FUNCTIONAL INTERPRETATIONS
Authors: Carlquist Sherwin
Published: January 2018

Quantitative and qualitative features are reported for 23 collections of ten species of Illicium, sole genus of Illiciaceae. Vessel elements are long, thin‐walled, and angular; perforation plates are scalariform and range from long to moderately long; vessel‐ray pitting is scalariform to opposite. Tracheids bear fully bordered pits. Axial parenchyma is sparse, abaxial to vessels with some diffuse cells also present. Rays are both multiseriate and uniseriate; the former are lacking near the pith in some species. No erect sheathing cells are present on multiseriate rays, and procumbent cells become more abundant as stems increase in size. Four species from montane subequatorial highlands lack growth rings and helical sculpture in vessels; the remainder of Illicium species have these features. Notably narrow vessels and large numbers of vessels per sq. mm characterize the temperate species from northern limits for the genus, I. anisatum, I. floridanum, and I. parviflorum. Greater vessel density offers redundancy and greater safety and is correlated with greater frost and possibly greater fluctuation in moisture availability. These two ecological features are probably also related to the narrow vessel diameter, which may retard entry of air embolisms (lowered air entry values) in accord with the physiological considerations of Slatyer. Reduction of number of bars per perforation plate within Illicium is also correlated with the more northerly climates. An additional hypothesis for evolution of shorter vessel elements in dicotyledons is introduced: if, as claimed by Slatyer, air embolisms in vessels tend to stop at ends of vessel elements and thus do not disable entire vessels, shorter vessel elements would maximally localize air embolisms. Presence of helical sculpture and other forms of relief within vessels has been difficult to explain in conifers and dicotyledons; such features might help resist cavitations by increasing adhesion of water molecules to cell walls (hydration).
DEVELOPMENTAL MORPHOLOGY OF THE EMBRYO AND SEEDLING OF RHIZOPHORA MANGLE L. (RHIZOPHORACEAE)
Authors: Juncosa Adrian M.
Published: January 2018

The embryo of Rhizophora mangle L. is initially attached to the integument by a long multiseriate suspensor. Its basal cells lyse, and intrusive growth of the endosperm envelops the embryo, forces the micropyle open, and often carries the embryo out of the integument. Thus, “germination” is effected by growth of the endosperm rather than of the embryo. The surface of the endosperm differentiates into a layer of peculiar transfer cells. The cotyledonary body initiates as a toroidal primordium, which later becomes lobed; most of the free portions ultimately fuse. After “germination,” the axis of the viviparous seedling grows by a diffuse intercalary meristem below the cotyledonary node. Before seedling abscission, the shoot apex produces three pairs of leaves, the first of which aborts, leaving the rest of the plumule protected by their stipules. The (immersed) radicle apex is nearly inactive, but lateral roots arise early in seedling development; these are usually the first or only roots to grow during establishment. Ten provascular strands “differentiate” in the cotyledons; a hollow provascular cylinder develops in the hypocotyl. Initial vascular differentiation in the latter is of many alternate poles of xylem and phloem; later, de novo differentiation of metaxylem opposite the protophloem poles, and vice versa, produces collateral bundles. Xylem maturation is endarch over most of the length of the hypocotyl, but tangential and random series of metaxylem vessels occur in the radicle end.
STUDIES ON THE GERMINATION OF SEEDS OF THE ROOT PARASITES, ALECTRA VOGELII AND STRIGA GESNERIOIDES. II. DNA SYNTHESIS AND DEVELOPMENT OF THE QUIESCENT CENTER IN THE RADICLE
Authors: Raghavan V. , Okonkwo S. N. C.
Published: January 2018

DNA synthetic activity in the radicle meristem of embryos of germinating seeds of the obligate root parasites, Alectra vogelii and Striga gesnerioides was followed by autoradiography of 3H‐thymidine incorporation. Incorporation of 3H‐thymidine occurred in the nuclei of cells destined to form the vascular tissues, ground meristem and epidermis. An analysis of the distribution of labeled nuclei demonstrated the presence of a quiescent center of 2‐4 cells in the radicle at the beginning of seed germination, becoming more prominent at later stages of germination. During continued growth of the radicle which resulted in a reduction in size of the meristem, cells of the original quiescent center were activated to undergo DNA synthesis.
PLANT POPULATION GENETICS AND EVOLUTION
Authors: Hamrick J. L.
Published: January 2018

This paper reviews recent developments in plant population genetics and evolution. Topics discussed include: 1) levels of genetic variation within and among populations; 2) gene flow; 3) mating systems; 4) selection and adaptation; and 5) the genetic structure of natural populations. The current status of each topic is briefly reviewed and suggestions are made of areas where additional research is needed.
ULTRASTRUCTURE OF THE LICHEN COENOGONIUM INTERPLEXUM NYL.
Authors: Meier Judy L. , Chapman Russell L.
Published: January 2018

Coenogonium interplexum Nyl. is a green to yellow‐orange filamentous lichen commonly found on tree bark, rocks, and soil. The mycobiont is the ascomycetous fungus Coenogonium. The ultrastructure of the lichenized phycobiont, Trentepohlia, closely resembles that of the non‐lichenized form, a filamentous subaerial green alga. The mycobiont has a typical fungal ultrastructure, and the cell wall sometimes appears thinner at points of contact with the phycobiont wall. Several branched fungal hyphae are usually randomly arranged around a Trentepohlia filament, and may in some cases completely ensheath the alga. Although no haustoria were observed, this relationship may still be termed a lichen since there is some modification of the alga and the lichen is structurally distinct from the two symbionts.
THE PRIMARY THICKENING MERISTEM: DEFINITION AND FUNCTION IN MONOCOTYLEDONS
Authors: DeMason D. A.
Published: January 2018

The PTM should be defined as a diffuse primary meristem which decreases in cross‐sectional extent (i.e., becomes a thinner‐walled cylinder) in a basipetal direction. It is associated with extensive anticlinal cell files and consists of cell initials that divide predominantly in periclinal planes. This meristem occurs typically in monocotyledons, especially those with thick, compact stems in species with rosette shoot axes. The PTM is also associated with a wide crown, so that the apical meristem is either slightly above the level of youngest leaf primordia, at approximately the same level as the leaf primordia, or distinctly sunken below surrounding stem tissue and the youngest leaf primordia. The location is dependent on the extent of primary thickening growth occurring in a particular species. A meristem associated with primary thickening of other plant groups should not be called a primary thickening meristem unless all of the above characteristics are shown to be associated with the meristem being examined. The primary thickening meristem is responsible for primary thickening of a stem axis. Its ontogenetic relationship with the STM needs further investigation. Extensive primary stem thickening has been observed in non‐monocotyledons (ferns, lycopods, cycads, and dictyledons). Some of these organisms appear to undergo primary thickening from a PTM in a similar process as that which occurs in monocotyledons. Further research is necessary to establish the mechanisms of primary thickening in these cases.
THE DEVELOPMENTAL BASIS OF ANISOPHYLLY IN SELAGINELLA MARTENSII. II. HISTOGENESIS
Authors: Dengler Nancy G.
Published: January 2018

The anisophyllous shoots of Selaginella martensii are characterized by opposite pairs of dorsal and ventral leaves which differ in size and form. This paper documents the processes of histogenesis for each leaf type and shows that both leaf types show a strong basipetal gradient of tissue maturation as indicated by cell size, distribution of cell division, cell vacuolation, intercellular space formation and stomatal differentiation. These processes are complete at an earlier stage of development in dorsal leaves (P7–8) than for ventral leaves (P12, 13). Measurement of cell number in the uppermost dermal layer indicate that cell divisions occur at a greater rate during ventral leaf development and observations of mitotic figures indicate that cell division occurs over a slightly longer time period in ventral leaves (through P6) as compared with dorsal leaves (through P5). While the morphological and histological differences that occur between the mature ventral and dorsal leaves begin to appear at or shortly after leaf inception, the general pattern of histogenesis of both types of leaf is similar. Histologically the dorsal leaf is primarily distinguished by a precocious maturation of tissues.
SEASONAL PATTERNS IN RECOVERABLE UNDERGROUND RESERVES IN SPARTINA ALTERNIFLORA LOISEL.
Authors: Gallagher John L.
Published: January 2018

Seasonal differences in recoverable underground reserves in stands of Spartina alterniflora Loisel. were measured in Georgia and Delaware. They indicate that by winter substantial reserves are stored in both northern and southern marshes. Cycles of the quantity of stored reserves have greater amplitudes than cycles of the concentration of storage compounds reported in the literature. Maximum concentrations apparently occur at the same time as maximum storage tissue volumes. Seasonal measurements and defoliation studies in Delaware indicate that reserves are nearly exhausted by spring growth and that at least ⅓ are not replenished until after seed filling in the fall. This pattern of nearly complete utilization of reserves in spring with late fall replenishment may have an advantage for herbaceous perennial plants which are part of detritus based food webs. A cycle where substantial reserves are retained for canopy regeneration after early summer defoliation would be advantageous where a grazing web was dominant.
OVULE AND EMBRYO DEVELOPMENT IN DORITIS PULCHERRIMA (ORCHIDACEAE)
Authors: Yasugi Saburo
Published: January 2018

The placental ridge began to proliferate 10 days after pollination. Megaspore mother cell underwent meiosis to form two dyads at first division. At 50 days two megaspores and generating dyad were formed by second division. The functional megaspore divided successively three times to form an eight‐nucleate embryo sac at 60 days. Double fertilization occurred forming the zygote and endosperm initial cell. However, the endosperm initial cell degenerate soon thereafter. The zygote divided to form a terminal cell, the middle cell and suspensor initial cell at 70 days. The terminal and middle cells successively divided to form a multi‐celled embryo up to 120 days after pollination. Histochemical study showed that the stainability of DNA, RNA and total proteins were almost constant during ovule and embryo development. Stainability of total carbohydrates decreased.
WATER USE AND SALT BALANCE IN THREE SALT MARSH SUCCULENTS
Authors: Antlfinger Ann E. , Dunn E. Lloyd
Published: January 2018

Water‐use characteristics and potential salt accumulation rates were studied in three halophytes, Salicornia virginica, Balis marítima and Borrichia frutescens, inhabiting a salinity gradient in the high marsh. Xylem pressure potential (ψρ), leaf osmotic potential (ψπ) and leaf relative water content were measured seasonally in the three species. Species growing on the high end of the salinity gradient developed more negative xylem pressure potentials compared to species growing at lower soil salinities. This trend was also observed for leaf osmotic potentials. Low mean leaf ψπ (below –15 to –36 bars) and high ash contents (0.27–0.48 g NaCl/g DW) indicated salt accumulation in transpiring tissues. However, calculations of potential salt accumulation, based on rates of transpiration and substrate salinity, suggest that some mechanism of salt exclusion at the roots may be operating.
WOOD ANATOMY OF BUBBIA (WINTERACEAE), WITH COMMENTS ON ORIGIN OF VESSELS IN DICOTYLEDONS
Authors: Carlquist Sherwin
Published: January 2018

Quantitative and qualitative features of wood anatomy are reported for ten collections of seven species of Bubbia. Variations on the basic plan for Winteraceae can be interpreted in terms of taxonomic and ecological distinctions. Tracheid length is correlated with plant size and habit: tracheids are shortest in shrubs. Tracheid wall thickness and ray cell wall thickness distinguish species. Ray cell procumbency and multiseriate ray width increase with age. Growth rings occur only in a species from stream margins. SEM studies reveal absence of a warty layer within tracheids. Helical thickenings are absent. Presence of these two features in Pseudowintera may be correlated with the cool temperate habitats of that genus. Overlap areas of tracheids in Bubbia show various degrees of scalariform pitting, ranging from none (B. semecarpoides) to abundant presence (B. balansae). Perforation‐like pits in tracheids of the latter prove, with SEM studies, to have pit membranes containing porosities less than 1 μm in diameter. Scalariform pitting on overlap areas is absent in earlier secondary xylem and increases during later secondary xylem. Scalariform lateral wall pitting can occur in abnormally wide tracheids formed after pauses in cambial activity. These facts show that primitive dicotyledon woods like those of Bubbia can activate genetic information for scalariform end wall patterns and lateral wall pitting such as primitive vessels show without the intervention of paedomorphosis. Paedomorphosis in dicotyledon woods is held still to apply only to special herbaceous and herblike growth forms, not to primarily woody plants. Progenesis (in xylem, loss of secondary xylem) is not held to be necessary to account for the scalariform patterns seen in tracheary elements of primitive dicotyledons. Reasons are given for rejection of the hypothesis that Winteraceae and other woody dicotyledons (Amborella, Sarcandra, Tetracentron, Trochodendron) are secondarily vesselless.
EFFECTS OF WATER STRESS, ABSCISIC ACID, AND GIBBERELLIC ACID ON FLOWER PRODUCTION AND DIFFERENTIATION IN THE CLEISTOGAMOUS SPECIES COLLOMIA GRANDIFLORA DOUGL. EX LINDL. (POLEMONIACEAE)
Authors: Minter T. C. , Lord E. M.
Published: January 2018

The effects of water stress, abscisic acid (ABA), and gibberellic acid (GA3) on flower production and differentiation by Collomia grandiflora were investigated. An untreated plant typically produced both small, closed cleistogamous (CL) and large, open chasmogamous (CH) flowers. The larger corolla of CH flowers was due to a greater cell number and size. When plants were water‐stressed or sprayed with ABA, both the percentage of CH flowers and the total number of flowers were reduced significantly. The corolla dimensions and epidermal cell numbers and sizes of CL flowers produced by water‐stressed and ABA‐sprayed plants did not differ from those of CL flowers produced by control plants. Application of GA3 to both well‐watered and water‐stressed plants significantly increased the percentage of CH flowers formed compared to well‐watered controls. In the absence of GA3, water‐stressed plants produced almost entirely CL flowers. GA3‐sprayed plants produced CH flowers whose corolla dimensions were intermediate between those of CL and CH flowers formed by control plants. Epidermal cells of these intermediate corollas were reduced only in number and not in size when compared to control CH flowers. Endogenous levels of ABA and gibberellins may control the type of flower produced by C. grandiflora and may mediate some of the observable effects of water stress on flowering.
RAISED STOMATAL CLUSTERS ON COLEUS (LAMIACEAE) STEMS
Authors: Turner Glenn W. , Lersten Nels R.
Published: January 2018

Stomata on stem internodes of Coleus blumei occur only in clusters on hollow epidermal bulges. We illustrate them here with light and scanning electron microsocpy. Some stomatal clusters are sites for lenticel formation on older internodes. Three Plectranthus species were also examined; two had discrete stomatal clusters while the third showed a more scattered arrangement of stomata, indicating that the stomatal pattern on stems may have some potential as a taxonomic character in Lamiaceae.
LEAF PARENCHYMA WITH TRANSFER CELL‐LIKE CHARACTERISTICS IN THE MOSS, POLYTRICHUM COMMUNE HEDW
Authors: Scheirer Daniel C.
Published: January 2018

Mature leaves of Polytrichum commune Hedw. were examined in regard to structural features and possible solute transport mechanisms. The leaf bundle is organized into several parenchyma layers which are termed passage cells, deuters, and socci. The deuters (leptoids of some authors) are large‐diametered parenchymatic elements which exhibit papillate wall ingrowths characteristic of transfer cells. The deuter cytoplasm is typical of transfer cells, including a large number of mitochondria, numerous polysomes, and a peripheral network of ER associated with the wall ingrowths. Deuters show little ultrastructural similarity to leptoids (sieve elements of bryophytes) of the stem. Socci parenchyma and passage cells have a distinct inner wall layer which is convoluted in places, and therefore, these cells as well as the deuters might be involved in intensive short‐distance fluxes of solutes. A possible translocation mechanism involving an active, carrier‐mediated loading of leaf parenchyma is discussed in relation to these structural features.
SYSTEMATIC STUDIES ON THE MEXICAN ZAMIACEAE. I. CHROMOSOME NUMBERS AND KARYOTYPES
Authors: Vovides Andrew P.
Published: January 2018

Chromosome numbers and karyotypes are reported for seven species in three genera, of Mexican cycads. Karyotypic analysis of Cycads is made difficult by differential contraction, of their large chromosomes but idiograms are presented. Satellite variation is reported for three species of Ceratozamia. No satellites are reported for the three species of Zamia.
NONSYMBIOTIC AND SYMBIOTIC NITROGEN FIXATION IN A WEAKLY MINEROTROPHIC PEATLAND
Authors: Schwintzer Christa R.
Published: January 2018

The acetylene reduction assay was used to measure nonsymbiotic and symbiotic nitrogen fixation in a weakly minerotrophic peatland throughout the ice‐free season. Nonsymbiotic nitrogen fixation was found in surface materials and subsurface peat. In surface materials, nitrogenase activity measured in the field contributed about 0.6 kg N ha‐1 yr‐1, was closely associated with Sphagnum, but was not correlated with temperature between 12 and 27 C. No cyanobacteria were found in association with Sphagnum. In subsurface peat, nitrogenase activity measured in situ contributed no more than 0.4 kg N ha‐1 yr‐1 and was closely correlated with temperature between 7 and 21 C. There were uncertainites in these measurements due to presence of ethylene oxidizing activity and a long time lag. Symbiotic nitrogen fixation was found only in actinomycete‐induced root nodules of Myrica gale L. Legumes were absent and the few lichens present lacked nitrogenase activity. Based on acetylene reduction assays, Myrica gale fixed about 35 kg N ha‐1 yr‐1. Nitrogenase activity in Myrica gale showed a strong seasonal pattern which varied little during three consecutive years even though water levels varied substantially. Nitrogen input to the peatland from nonsymbiotic nitrogen fixation was only 15% the amount contributed by bulk precipitation. Symbiotic fixation, in contrast, contributed approximately six times the amount in bulk precipitation.
A THEORY ON THE EVOLUTION OF THE EXINE IN ORCHIDACEAE
Authors: Burns‐Balogh Pamela
Published: January 2018

The development of secondarily derived features in orchid pollen precludes the possibility of applying evolutionary trends hypothesized for dicot pollen to orchid pollen and perhaps even monocot pollen. There are three lines of pollen wall development, all secondarily derived from a possible tectate‐perforate ancestral type, i.e., tectate‐imperforate with incipient columellae (Cypripedioideae), intectate lacking a foot layer (Orchidoideae), and tectate‐imperforate with globular masses of sporopollenin (Vandoid Epidendroideae).
CRUCIFORM NUCLEAR DIVISION IN WORONINA PYTHII (PLASMODIOPHOROMYCETES)
Authors: Dylewski Daniel P. , Miller Charles E.
Published: January 2018

Somatic nuclear divisions in sporangiogenous plasmodia of Woronina pythii Goldie‐Smith were studied with transmission electron microscopy. During metaphase, each nucleus formed a cruciform configuration as chromatin became aligned at the equatorial plate perpendicular to the persistent nucleolus. Except for polar fenestrations, the original nuclear envelope remained intact throughout the mitotic division. Intranuclear membranous vesicles appeared to bleb off the inner membrane of the original nuclear envelope, adhered to the surfaces of the separating chromatin, and eventually formed new daughter nuclear envelope within the original nuclear envelope. During the first 24 hr of vegetative plasmodial growth, each telophase nucleus exhibited an obvious constriction of the original nuclear envelope in the interzonal region. Similar constrictions were not evident in telophase nuclei found in 24–36‐hr‐old plasmodia. This variation in the ultrastructural morphology of cruciform division appears to be related to the age and size of each sporangiogenous plasmodium, and is the first to be documented within this group of fungal pathogens.
PICEA WOLFEI, A NEW SPECIES OF PETRIFIED CONE FROM THE MIOCENE OF NORTHWESTERN NEVADA
Authors: Crabtree David R.
Published: January 2018

Several silicified ovulate cones from the late middle Miocene (Barstovian) represent a new species, Picea wolfei Crabtree. This is the second species of Picea for which structurally preserved seed cones are known to be reported from the Tertiary. The cones are 5.0–8.0 cm long and 1.5–2.0 cm at their greatest diameter. Ovuliferous scales are inserted helically around the cone axis and are recurved at their point of divergence. Each scale is broadly obovate to spatulate with a rounded apex and bore two seeds adaxially. The bract subtending the scale is 4.5–7.3 mm long and is fused to the scale for 1.4–2.0 mm. Each bract has an inflated keel‐like base which projects abaxially between the seeds of adjacent scales. The fossil cones superficially resemble those of the extant Picea breweriana, yet differ from them anatomically. The new species also resembles Picea lahontense, a fossil compression from the Miocene Trout Creek Flora of south‐central Oregon, but the different modes of preservation preclude meaningful comparison. Picea diettertiana, the only structurally preserved fossil cone of this genus previously described, is quite dissimilar in that it lacks a sclerotic pith.
PHILLIPOPTERIS GEN. NOV.—ANATOMICALLY PRESERVED SPORANGIAL FRUCTIFICATIONS FROM THE UPPER PENNSYLVANIAN OF THE APPALACHIAN BASIN
Authors: Hamer Jon J. , Rothwell Gar W.
Published: January 2018

The discovery of a new type of sporangial fructification in coal balls from the Upper Pennsylvanian of Ohio provides the basis for describing Phillipopteris globiformis gen. et sp. nov. Sporangia are borne terminally on up to two orders of branching axes. Penultimate axes branch pinnately to produce irregularly branched ultimate axes. Sporangial wall cells are of a single type and show no specialization for dehiscence. Spores are radial and trilete, and reminiscent of the sporae dispersae genus Dictyotriletes. Phillipopteris increases our knowledge of diversity among fernlike plants from the late Paleozoic, and shares several features with Sclerocelyphus Mamay.
NECTAR PRODUCTION PATTERNS IN IPOMOPSIS AGGREGATA (POLEMONIACEAE)
Authors: Pleasants John M.
Published: January 2018

This study describes nectar production patterns for Ipomopsis aggregata and discusses their potential adaptive and ecological significance. It also examines the influence of environmental and other factors on nectar production rate (NPR) and nectar sugar concentration. For I. aggregata there were no NPR differences with flower age. An hypothesis for the presence or absence of such differences is discussed. Ipomopsis aggregata has a relatively constant rate of nectar production during the day and production continues overnight but at a reduced rate. Newly opened flowers already have a sizeable accumulation of nectar. 24‐hr nectar sugar production on overcast days was 62% of sunny day production. NPR values at the beginning of the flowering season were almost twice as great as those near the end but the sugar concentration did not change. Whether nectar was removed periodically (to simulate pollinator visits) or simply allowed to accumulate over 24 hr had no effect on total production. Nectar sugar concentration has a characteristic diurnal pattern: highest in the afternoon and lowest in the early morning, probably in response to diurnal changes in relative humidity. Sugar concentration was also lower on overcast days. These changes are not due to evaporative losses from the open end of the flower. However, evaporation did occur in flowers which had been punctured at the base of the corolla by nectar robbing bees. In general, the results of this study suggest caution in characterizing the NPR or sugar concentration of a species by making measurements at one point in time under one set of environmental conditions.
BRYOPHYTE LEAF EPIFLORA: AN SEM AND TEM STUDY OF POLYTRICHUM COMMUNE HEDW.
Authors: Scheirer Daniel C. , Dolan Heidi A.
Published: January 2018

Epiphytes on leaves of Polytrichum commune Hedw. were observed and studied with SEM and TEM. A unicellular green alga, a fungus, and a rod‐shaped bacterium were present on both leaf surfaces. Culturing experiments led to the identification of the alga as Chlorococcum sp. and the fungus as Trichoderma viride Lk. ex Fr. (Deuteromycetes). No attempt was made to culture and identify the bacterium. Terminal cells of the leaf lamellae form a ventral pseudo‐epidermis which provides a microhabitat for the epiphytes. Fungal hyphae were seen intracellularly as well as penetrating cell walls between lamellar cells. The alga and bacterium were not observed intracellularly. Chlorococcum sp. displayed a distinctive wall morphology which consisted of short (0.3–0.5 μm), blunt papillae. The rod‐shaped bacterium may be similar to the Agrobacterium‐like isolates reported recently from Polytrichum commune. Host‐epiphyte associations relative to potential beneficial and/or pathological aspects of growth require further investigation.
VASCULAR DEVELOPMENT IN THE TRANSITION REGION OF POPULUS DELTOIDES BARTR. EX MARSH. SEEDLINGS
Authors: Sundberg Marshall D.
Published: January 2018

Seed and developing seedlings of Populus deltoides Bartr. ex Marsh., through 2 wk old, were embedded in Paraplast or Spurr's resin and serially sectioned at 7 or 2 μm, respectively, to examine vascular development in the root‐hypocotyl transition region. The procambial template is well established in the dormant embryo. Protophloem forms a continuous system connecting the root with the cotyledons but protoxylem is restricted primarily to the cotyledons. With the onset of germination there is rapid elongation of both the root and hypocotyl. The basipetal progression of protoxylem from an initiating center at the cotyledonary node is correlated with the establishment of a second initiating center in the collet at the base of the hypocotyl. The relation between procambium, initiating layer, and metacambium, and their derivatives is similar to that described for the cottonwood shoot. The primary vascular system of cottonwood should be considered a single unit, both conceptually and functionally. The vascular pattern of the root may be, in part, determined by a basipetal stimulus from the cotyledonary node.
DEVELOPMENTAL ANATOMY OF LIGHT‐INDUCED ROOT NODULATION BY ZAMIA PUMILA L. SEEDLINGS IN STERILE CULTURE
Authors: Webb David T.
Published: January 2018

The developmental anatomy of Zamia pumila L. root apices was studied during light‐induced nodulation. Dark‐grown roots had an apical organization identical to that of other cycads and similar to that of other gymnosperms. A distinct protoderm was not observed in these roots, which had a large open meristem and a root cap with a well‐defined columella. During nodulation, the meristem became reduced in size, and its constituent cells became vacuolate until all but a few resembled ground tissue. The root cap senesced during nodulation, and a recognizable root cap was absent from mature nodules. A file of densely cytoplasmic cells with centrally positioned nuclei developed in the nodule cortex. This layer was continuous across the nodule apex, and was identical to the presumptive algal‐zone described previously by other authors. Light‐induced nodules branched dichotomously and were identical to algal‐free nodules described by other authors. In dichotomously branched nodules, each lobe was covered by a parenchymatous mantle analogous to a root cap. A unicellular layer similar to the presumptive algal zone spanned the gap between opposite nodule lobes, and extended beneath each lobe before terminating in the cortex. Typical meristematic regions were not observed in these nodules. Based on cell sizes and patterns, a meristematic zone was thought to exist between the mantle and the inner cortex.
USE OF THE DCB TECHNIQUE FOR EXTRACTION OF HYDROUS IRON OXIDES FROM ROOTS OF WETLAND PLANTS
Authors: Taylor Gregory J. , Crowder A. A.
Published: January 2018

Replicate samples of Phragmites communis roots coated with hydrous iron oxide were analyzed for internal and external Fe using the dithionite‐citrate‐bicarbonate technique (hot DCB), a modified DCB technique (cold DCB), Ethylenediamine tetraacetic acid (EDTA), Diethylenetriamine pentaacetic acid (DTPA), and a total Fe analysis. EDTA and DTPA were found to be inefficient in extracting FeOOH while both DCB techniques were efficient. Concentrations of Fe extracted (8.93% and 9.37% by weight) and percent of total Fe extracted (98.3% and 98.6%) by the hot and cold DCB techniques (respectively) were not significantly different. Results of the total Fe analysis (8.58% Fe by weight) were the same as extracted Fe and total Fe determined by the DCB techniques. This may reflect the large external Fe : internal Fe ratio of the sample roots. Despite equivalent results, the cold DCB technique is preferred over the hot DCB technique due to a reduced likelihood of structural damage to roots.
FUNGAL REMAINS IN THE DEVONIAN TRIMEROPHYTE PSILOPHYTON DAWSONII
Authors: Stubblefield Sara P. , Banks Harlan P.
Published: January 2018

Fungal reproductive structures were found within aerial axes of the Late Devonian trimerophyte, Psilophyton dawsonii Banks, Leclercq and Hueber from Quebec, Canada. Specimens are spherical to oval, up to 175 μm in maximum diam, and exhibit two distinct wall layers. They are restricted to the inner cortical region of infected axes. The fungal bodies resemble species of Palaeomyces from the well‐known Rhynie Chert flora, and are also similar to the chlamydospores commonly found in Pennsylvanian coal ball plants. Among extant organisms they are most similar to oomycetous oogonia and endogonaceous chlamydospores.
TWO NEW SPECIES OF LIAGORA (NEMALIALES, RHODOPHYTA) AND NOTES ON LIAGORA FARINOSA LAMOUROUX
Authors: Abbott Isabella A.
Published: January 2018

Two new species of Liagora (Rhodophyta) are described: one from Hawaii that is a short‐seasonal annual, strongly gelatinous and soft and with little calcification; the other from Belize that is also gelatinous and soft but with moderate calcification. They are distinguished from each other on a number of internal features, chiefly differences in the development of sterile filaments below the gonimoblast. Liagora farinosa, the basionym of Ganonema farinosa of Fan & Wang is restored to Liagora because an examination of features upon which Ganonema was based demonstrates them to be variable and unsuitable for generic distinction.
UNIDIRECTIONAL ORGAN INITIATION IN LEGUMINOUS FLOWERS
Authors: Tucker Shirley C.
Published: January 2018

The order of initiation of floral organs is compared in several legumes. In Bauhinia fassoglensis, a caesalpinioid, the sepals are initiated helically, with the first one forming abaxially. In Genista tinctoria and Lupinus affinis (both papilionoids) the sepals are initiated unidirectionally, with the first forming on the abaxial side of the floral apex and subsequent sepals initiating laterally and then adaxially. All three taxa show unidirectional order of initiation for petals, first‐whorl stamens, and second‐whorl stamens. In each whorl, the first member or members form on the abaxial side, next to the subtending bract, then the lateral ones, and lastly the member(s) on the adaxial side, next to the axis. In Lupinus and Genista there are overlaps in time of initiation between organs in different whorls; for instance, the first stamens begin initiating before the last petals appear. Size differences among members of a whorl are evident in early stages, but may disappear after organogeny ceases, when the members become equal in size in each whorl. This precocious onset of dorsiventrality in floral development is viewed as a specialized feature.
AUTOPOLYPLOIDY IN TOLMIEA MENZIESII (SAXIFRAGACEAE)
Authors: Soltis Douglas E.
Published: January 2018

Tolmiea menziesii comprises diploid (2n = 14) and tetraploid (2n = 28) cytotypes that differ in geographic distribution. Chromosome counts now available indicate that the diploid and tetraploid cytotypes occupy the southern and northern portions, respectively, of the range of Tolmiea. Available data strongly suggest that Tolmiea represents an example of autopolyploidy. The genus is monotypic and very distinct in both floral and vegetative morphology among genera of tribe Saxifrageae. Infraspecific taxa have not been recognized in T. menziesii, and the two cytotypes appear to be indistinguishable morphologically. Karyotypic, flavonoid chemical, and preliminary allozymic data are all in agreement with the contention that the tetraploid cytotype is of autopolyploidal origin.
THE DEVELOPMENTAL BASIS OF TRISTYLY IN EICHHORNIA PANICULATA (PONTEDERIACEAE)
Authors: Richards Jennifer H. , Barrett Spencer C. H.
Published: January 2018

Eichhornia paniculata is a tristylous, self‐compatible, emergent aquatic. A given plant produces flowers with either long, mid or short styles and two levels of stamens equal in length to the styles not found in that flower. Flowers of each morph have two whorls of three tepals, six stamens and three fused carpels. The six stamens differentiate into two sets of three stamens each. A relatively short set, having either short‐ or mid‐level stamens, occurs on the upper side of the flower, while a relatively long set, having either mid‐ or long‐level stamens, occurs on the lower side. Stamen level depends on differences among stamens in filament length and position of insertion on the floral tube. Floral parts arise in whorls of three, but the two stamen whorls do not form the two sets of stamens found in each mature flower. Instead, stamens from both whorls make up a given set. Floral differences among morphs are not present at flower origin or floral organ initiation. Morphological differences arise first among stamen sets. The two sets within a flower differ prior to meiosis in the size, number, and timing of comparable developmental events in the sporogenous cells. After these initial differences arise, anther size diverges. In later developmental stages differences in filament and floral tube length, cell size, and cell number, as well as differences in the length, cell size, and cell number of styles, develop among morphs. This sequence of developmental events suggests that the genes controlling development in different morphs do not control flower and floral organ initiation but are first morphologically visible in sporogenous cell differentiation.
ANAEROBIC SUBSTRATE TOLERANCE IN SPOROBOLUS VIRGINICUS (L.) KUNTH.
Authors: Donovan Lisa A. , Gallagher John L.
Published: January 2018

The purpose of this study was to determine if and how the two genetically distinct forms, marsh and dune, of Sporobolus virginicus (L.) Kunth. tolerate anaerobic substrates. The treatments in the hydroponic study, conducted in the greenhouse for approximately 6 months, involved growing the marsh and dune forms in aerobic, anaerobic, and alternating aeration treatments. Plants were examined for morphological and physiological responses to the aeration treatments. In response to the continuous anaerobic treatment, the dune form of S. virginicus exhibited increased stolon biomass, but no difference of total biomass or rhizome aerenchyma when compared with the aerobic treatment. In response to alternating aeration, rhizome aerenchyma increased, total biomass decreased, and stolon biomass remained constant. Belowground transport of oxygen enabled the root tissue in all of the aeration treatments to maintain aerobic respiration. The marsh form grown in the alternating aeration treatment had the same total biomass but more rhizome aerenchyma when compared to the aerobic treatment. Growth in the continuous anaerobic treatment resulted in a reduction of total biomass and increased rhizome arenchyma. Marsh form roots did not appear to be respiring anaerobically or producing ethanol or additional malate at the time of harvest; however, root respiration was higher in the anaerobic and alternating treatments. The marsh and dune forms of S. virginicus were able to adjust morphologically or physiologically or to use existing morphological features to tolerate anaerobic substrates. Thus, it appears that the distribution of the two forms of S. virginicus found in coastal sand dunes and in salt marshes is not limited by differences in ability to tolerate waterlogged soils.
RESPONSE TO PHOTOPERIOD AND TEMPERATURE BY SPARTINA ALTERNIFLORA (POACEAE) FROM NORTH CAROLINA AND SPARTINA FOLIOSA FROM CALIFORNIA
Authors: Seneca Ernest D. , Blum Udo
Published: January 2018

Seedlings of Spartina alterniflora Loisel. from Oregon Inlet, North Carolina were generally taller and produced significantly more culms and total dry weight than those of S. foliosa Trin. from two California populations (Alameda Beach and Marin County) in eight photoperiod‐temperature treatments over a 17‐wk period. Seedlings of S. alterniflora produced maximal biomass in 30–26 C whereas those of S. foliosa produced maximal biomass in 22–18 C, both under long‐day conditions. The average photosynthesis rate for S. alterniflora (3.0 mg C g dry wt−‐ hr−‐1) was 1.6 times higher than that for S. foliosa (1.9 mg C g dry wt−‐1 hr−‐1), but the dark respiration rates (0.3 and 0.4 mg C g dry wt−‐1 hr−‐1, respectively) were not significantly different. The proportion of rhizomes was greater under short than long‐day conditions for both species in most temperature regimes. The average shoot soluble carbohydrate and starch concentrations were higher for S. foliosa (8.4 and 0.9%, respectively) than those for S. alterniflora (6.0 and 0.4%, respectively). The average rhizome soluble carbohydrate concentration (18%) for S. alterniflora under long‐day conditions was significantly lower than that under short‐day conditions (28%) and also lower than those for S. foliosa under both long (26%) and short‐day (25%) conditions. Rhizome starch concentrations of S. alterniflora were significantly higher in the short than in most long‐day temperatures and were generally higher for S. alterniflora than for S. foliosa under short‐day conditions. The root starch concentration of S. alterniflora under short‐day conditions (1.3%) was higher than that under long‐day conditions (0.2%) and also higher than those of S. foliosa under both long (0.2%) and short‐day (0.7%) conditions. The two species exhibited similar patterns of carbohydrate storage in belowground organs, similar flower initiation processes not under strict photoperiod control, and similar respiration rates, but significantly different photosynthetic rates and growth responses with S. alterniflora having the potential to be the more productive species.
EVOLUTION OF C3 AND C4 PLANTS ALONG AN ENVIRONMENTAL MOISTURE GRADIENT: PATTERNS OF PHOTOSYNTHETIC DIFFERENTIATION IN HAWAIIAN SCAEVOLA AND EUPHORBIA SPECIES
Authors: Robichaux Robert H. , Pearcy Robert W.
Published: January 2018

The endemic Hawaiian species of Scaevola and Euphorbia grow in a wide variety of native habitats and exhibit a wide range of variation in photosynthetic responses. Light‐saturated photosynthetic capacities range from 12.0 to 24.7 μmol CO2 m−‐2 s−‐1 in the Scaevola species and from 18.2 to 51.4 μmol CO2 m−‐2 s−‐1 in the Euphorbia species. Within each genus, differences in light‐saturated photosynthetic capacity are paralleled by differences in mesophyll and leaf conductances to CO2. Within each habitat, the C4 Euphorbia species exhibits a significantly higher photosynthetic capacity and a significantly higher mesophyll conductance than the corresponding C3 Scaevola species. These differences are greatest in the dry scrub habitat and least in the wet forest habitat. One photosynthetic characteristic that exhibits little variation among the species within each genus, yet that exhibits a consistently large difference between the species within each habitat, is photosynthetic water‐use efficiency. The C4 Euphorbia species possess water‐use efficiencies that are 2–3½ times as high as those of the C3 Scaevola species, regardless of whether these species are native to very dry or very wet habitats. At present, the ecological significance of this large inherent difference in photosynthetic water‐use efficiency is unknown. Indeed, it appears that neither photosynthetic pathway has imposed any major inherent constraints on the ability of the Scaevola and Euphorbia species to diversify into a wide variety of habitats.
INTERNODE ELONGATION IN XANTHIUM PLANTS TREATED WITH GIBBERELLIC ACID PRESENTED IN TERMS OF RELATIVE ELEMENTAL RATES
Authors: Maksymowych Roman , Elsner Charlotte , Maksymowych Andrew B.
Published: January 2018

Xanthium plants were grown vegetatively and their developmental stages were designated by a previously described plastochron index (PI). Internodes of plants, both treated with gibberellic acid (GA3) and untreated, were marked with India ink and photographed during 3 successive days. The relative elemental rates of elongation d(dX/dt)/dX were estimated between 15.7 and 19.0 plastochrons. The rate of growth of the GA3‐treated internodes was at least twice that of the control. The emerging pattern of acropetal internode elongation was similar in both GA3‐treated and control plants. Only rates of growth were significantly higher in the GA3‐treated plants. The acropetal pattern of internode elongation was the opposite of the basipetal pattern observed in Xanthium leaves but followed the acropetal pattern observed in Helianthus and Phaseolus internode growth.
PHENOTYPIC PLASTICITY OF ANNUAL PHLOX: TESTS OF SOME HYPOTHESES
Authors: Schlichting Carl D. , Levin Donald A.
Published: January 2018

Phenotypic plasticity is an important means by which individual plants respond to environmental heterogeneity. Relative plasticities were compared for three species of annual Phlox grown in a set of six environmental treatments. Two measures of plasticity were computed for 18 characters per species: the Coefficient of Variation to measure amounts of plasticity and a new measure, the correlation of responses between species, which compares patterns of plasticity. Three hypotheses concerning the species’ amounts and patterns of plasticity were examined. The heterozygosity hypothesis states that levels of heterozygosity and amounts of plasticity should be inversely related. The relatedness hypothesis states that more distantly related species should have less similar patterns and amounts of plasticity. The ecological hypothesis states that species from similar habitats should have more similar amounts and patterns of plasticity than species which evolved under differing conditions. The results suggest that heterozygosity, relatedness, and ecology may all affect patterns and amounts of plasticity, and that no single hypothesis is sufficient to explain the observed results. Some data from previous studies are examined in relation to the proposed hypotheses.
GRAPEVINE LEAF DEVELOPMENT IN RELATIONSHIP TO POTASSIUM CONCENTRATION AND LEAF DRY WEIGHT AND DENSITY
Authors: Freeman Brian M. , Kliewer W. Mark
Published: January 2018

The plastochron index (PI) was developed forVitisand related to lamina K+concentration. The concentration of lamina K+declined with increase in leaf age and PI, whereas total lamina K+content increased. Part of the decline in lamina K+concentration was attributed to an initial decrease in lamina density. Therefore, expression of K+concentration on a leaf area basis is recommended rather than on a dry weight basis.
EPIFLUORESCENCE MICROSCOPY FOR THE STUDY OF NITROGEN FIXING BLUE‐GREEN ALGAE ASSOCIATED WITH FUNARIA HYGROMETRICA (BRYOPHYTA)
Authors: Scheirer Daniel C. , Brasell Heather M.
Published: January 2018

Funaria hygrometrica Hedw. gametophytes collected in a clearfelled and slash‐burned eucalypt forest in southern Tasmania were removed from core samples yielding high rates of nitrogen‐fixing activity (acetylene reduction) and were examined with epifluorescence optics to determine the microorganism(s) responsible for nitrogen‐fixing activity and their location on the moss gametophytes. This technique revealed heterocystous blue‐green algae (Nostoc sp. and Anabaena sp.) as epiphytes on stem and leaf surfaces and within the rhizosphere. Heterocysts and akinetes were observed and could be distinguished from vegetative cells by morphology and a decrease in relative fluorescence in the case of heterocysts. Epifluorescence microscopy is a rapid and reliable method for detecting the epiphytic blue‐green algae associated with Funaria. Other examples of nitrogen‐fixing organisms associated with bryophytes are discussed in relation to the present study.
AN ULTRASTRUCTURAL AND STEREOLOGICAL ANALYSIS OF POLLEN GRAINS OF HYOSCYAMUS NIGER DURING NORMAL ONTOGENY AND INDUCED EMBRYOGENIC DEVELOPMENT
Authors: Reynolds Thomas L.
Published: January 2018

Selected nuclear and cytoplasmic changes of pollen grains of Hyoscyamus niger during normal gametophytic development and embryogenic development, induced by anther culture, were analyzed and compared ultrastructurally using stereological methods. Potentially embryogenic, uninucleate pollen could be identified within 6 hr of culture by an increased ratio of the volume density of the nucleolar granular zone to the volume density of the fibrillar zone and an increased ratio of dispersed to condensed chromatin in the nucleoplasm. Nonembryogenic pollen in vitro and in vivo possessed prominent nucleolar fibrillar zones and low ratios of dispersed to condensed chromatin. These differences may reflect changes in nuclear activity in potentially embryogenic pollen grains during early stages of culture. Following the first haploid mitosis, in potentially embryogenic pollen the generative cell maintained its large granular nucleolus and high ratio of dispersed to condensed chromatin through its first division to form a proembryoid. The volume fraction of the cytoplasm occupied by mitochondria and plastids and the area fraction occupied by RER and Golgi cisternae differed in the generative cells of potentially embryogenic and nonembryogenic pollen. Those changes only detected in generative cells of potentially embryogenic pollen include: increased area and complexity of cytoplasmic membranes, increased mitochondrial volume, and the presence of plastids at all stages of development. These results support the idea that embryogenic induction of H. niger takes place at the uninucleate stage of development and that subsequent nuclear and cytoplasmic changes are essential for continued sporophytic development.