bluuebunny/crossref_metadata_2025 huggingface dataset:
PHOTOTROPISM OF SELAGINELLA: THE ROLE OF THE SMALL DORSAL LEAVES AND AUXIN
Authors: Bilderback D. E.
Published: January 2018

The creeping dorsiventral stem of Selaginella kraussiana (Kunze) A. Braun has two rows of small leaves on the dorsal surface, two rows of large leaves laterally inserted and no leaves on the ventral surface. When the ventral surface of the stem is illuminated from below, the stem bends 147° below the horizon toward the light. Development of this positive phototropic response requires mature dorsal leaves at the stem tip but not the apical bud or the large lateral leaves. When the small dorsal leaves are replaced with lanolin containing the auxins, indoleacetic or naphthalene acetic acid, stem curvature occurs in the light and dark. Gibberellic acid and kinetin are unable to replace the small dorsal leaves. Auxin paste applied to the ventral illuminated surface of the stem will cause a negative phototropic curvature away from light. Illumination of the ventral surface of stem does not alter the amount of radioactive indoleacetic acid entering the stem from treated dorsal leaves but does increase the asymmetry in the distribution of radioactivity in the stem. Treatment of the small dorsal leaves with the auxin transport inhibitor, triiodobenzoic acid, inhibits the positive phototropic stem curvature.
THE RELATIONSHIP BETWEEN THE PLASTOCHRON INDEX AND THE STRUCTURE OF THE APICAL MERISTEM OF DIANTHUS CHINENSIS L.
Authors: McCauley Michele , Croxdale Judith
Published: January 2018

The purpose of this study was to characterize the structural changes of the shoot apex of Dianthus chinensis during the production of a pair of leaf primordia and to determine if the plastochron index (P.I.) previously developed for this plant could be used to predict the morphological stages of the apex during a plastochron. Height and volume determinations were made on greenhouse‐grown D. chinensis shoot tips prepared for light microscopic examination. These measurements were plotted against the plastochronic fraction of each shoot to evaluate the relationship between apical stage and the P.I. In general, lower fractional plastochron values correspond to smaller apical height and volume values while higher fractional plastochron values correspond to larger apical height and volume values. For the greenhouse plants, there is a 3‐fold increase in height and a 5‐fold increase in volume during a plastochron. Height and volume determinations were made on growth‐chamber‐grown D. chinensis shoot tips prepared for scanning electron microscopic examination. Largely plants in Plastochron 6 were sampled; plants in Plastochrons 3, 4, and 9 were also sampled for comparative purposes. The curves of apical height and volume versus Plastochron 6 show a sigmoidal pattern of growth. The corresponding curves of the Plastochron‐4 and ‐9 plants show a similar pattern of increase. The Plastochron‐6 curves also show that the integer value of the P.I. corresponds to the minimal apical height and volume when a pair of leaf primordia are just discernible, while the integer plus high fractional value of the P.I. corresponds to the maximal apical height and volume just prior to the emergence of the next pair of primordia. During Plastochron 6 there is a 2‐fold increase in height and a 3‐fold increase in volume. Apical height and volume increase was examined by regression analysis to determine whether growth is better described as linear or exponential. The results indicate that the sigmoidal pattern of increase might be better described by some more complex function. It is concluded that during certain stages of a shoot's vegetative growth the P.I. will accurately predict apical meristem structure in D. chinensis two‐thirds of the time.
QUANTITATIVE OBSERVATIONS ON THE PATTERN OF SYNERGID DEGENERATION IN BARLEY
Authors: Mogensen H. Lloyd
Published: January 2018

Serial sections of 75 ovules taken from two pollinations were examined in order to determine the pattern of early synergid degeneration in Hordeum vulgare (Bonus). It was found that synergid degeneration occurs in various patterns in ovules from successful pollinations: either both synergids degenerate, or only one degenerates; in those ovules where only one synergid degenerates, the degenerate synergid is nearly always located either proximal or distal to the placental attachment of the ovule. The results suggest that 1) synergid degeneration depends upon successful pollination, 2) degeneration of both synergids is equally as likely to occur as degeneration of only one synergid, and 3) in those cases where only one synergid degenerates, there is a greater tendency for the degenerate synergid to be located toward the placenta.
SHOOT APICAL MERISTEMS AND MUTATION: FIXATION OF SELECTIVELY NEUTRAL CELL GENOTYPES
Authors: Klekowski Edward J. , Kazarinova‐Fukshansky Nina
Published: January 2018

Shoot apical meristems are interpreted as either structured, that is having a permanent set of apical initials, or stochastic, having apical initials which represent “... momentary representatives of the continuous meristematic residue at the apex of the relevant layer or zone” (Newman, 1965). The two main parameters of stochastic growth are the average number of apical initials (α) and the number of mitotic cycles (r) of the initials and their daughter cells prior to the random selection of subsequent initials. Mathematical analysis and computer simulation studies of stochastic growth have shown that if one starts with 1 mutant initial and α‐1 nonmutant initials, eventually a mosaic plant results. The frequency of shoot apices composed of mutant cells is 1/α and the frequency of shoot apices composed of only nonmutant cells is (1 – α)/α. These asymptotics are only attained after considerable growth, thus mericlinal chimeras can persist for many nodes and give the appearance that a permanent set of initials is present.
SOME CASES OF DELAYED OR INDUCED DEVELOPMENT OF AXILLARY BUDS FROM PERSISTING DETACHED MERISTEMS IN CONIFERS
Authors: Fink Siegfried
Published: January 2018

In the apparently “empty” axils of the needles of Taxus baccata, Sequoia sempervirens, Sequoiadendron giganteum, Cryptomeria japonica, Thuja occidentalis, and Thujopsis dolabrata persisting detached meristems were found, which are derived from superficial layers of the apical eumeristem. In T. baccata delayed development of minute axillary buds occurs from these meristems after 1–4 yr on the intact plant. In the other conifers, development of additional axillary buds from these meristems was induced by natural frost damage or by artificial pruning and disbudding. The discovery of these detached meristems is discussed with regard to the regenerative capacity of the conifers in comparison to other plants.
PRODUCTIVITY OF PODOSTEMUM CERATOPHYLLUM IN THE NEW RIVER, VIRGINIA
Authors: Hill B. H. , Webster J. R.
Published: January 2018

Productivity ofPodostemum ceratophyllum,the dominant aquatic macrophyte in the New River, was measured at four sites representing soft‐ and hardwater reaches of the river. Available dissolved inorganic carbon (DIC) was 4–5 times greater in the hardwater reach. The difference in available DIC was reflected in standing crop and productivity ofP. ceratophyllum.Maximum standing crops ofP. ceratophyllumat the two hardwater sites (Sites 1 and 2) were 244.8 ± 30.7 g ash‐free dry wt (AFDW) m−‐2and 193.8 ± 18.7 g AFDW m−‐2compared to 128.5 ± 14.9 g AFDW m−‐2and 101.3 ± 6.9 g AFDW m−‐2for the softwater sites (Sites 3 and 4). Productivity, based on differences in standing crops, was: Site 1, 1.08 ± 0.12 g C m−‐2d−‐1; Site 2, 0.86 ± 0.08 g Cm−‐2d−‐1; Site 3,0.58 ± 0.06 g C m−‐2d−‐1; Site 4,0.45 ± 0.03 g C m−‐2d−‐1. Corresponding values for productivity as14C uptake were: 2.77 ± 0.44 g C m−‐2d−‐1; 2.10 ± 0.45 g C m−‐2d−‐1; 0.34 ± 0.04 g C m−‐2d−‐1; 0.28 ± 0.03 g C m−‐2d−‐1. Productivity/biomass (P/B) based on14C uptake and standing crop revealed thatP. ceratophyllumproductivity was inhibited at the softwater sites perhaps due to carbon limitation. Because of its abundance and its high productivity,P. ceratophyllumis hypothesized to contribute significantly to the New River organic matter budget.
EMBRYOGENESIS AND DEVELOPMENTAL MORPHOLOGY OF THE SEEDLING IN BRUGUIERA EXARISTATA DING HOU (RHIZOPHORACEAE)
Authors: Juncosa Adrian M.
Published: January 2018

Embryogenetic cell division patterns found in Bruguiera exaristata Ding Hou are variable: the first division of the zygote is usually longitudinal or steeply oblique, though it may also be transverse. Succeeding divisions produce a very wide, short suspensor; differentiation between this and the embryo proper is delayed. The 2 or 3 cotyledons are initiated as separate primordia and usually have three‐trace, trilacunar vasculature. Germination occurs by growth of the hypocotyl after the embryo has filled the ovule, as is usual for non‐viviparous plants. Thus, early organogenesis in B. exaristata resembles that of inland relatives rather than that of other members of its tribe. As in all Rhizophoraceae known, provascular development follows cotyledonary initiation, and the radicle apex differentiates subterminally in the embryo. In Bruguiera, this apex later becomes morphologically terminal and develops a complex meristematic architecture; during dispersal, it is protected by a coleorhiza formed by lobes of the outer cortex. Vascular differentiation occurs first in the median traces of the cotyledons, where xylem matures before “germination.” The vascular tissues of the hypocotyl are initially disjunct from those of the cotyledons and are arranged in alternate xylem and phloem poles; collateral bundles are formed both by tangential xylem differentiation and by de novo differentiation of complementary vascular tissues. Because Bruguiera has only a few specialized developmental characteristics, it is interpreted as being distinctly more primitive than the other genera of the mangrove tribe.
CUTICULAR ANATOMY OF ANGIOSPERM LEAVES FROM THE LOWER CRETACEOUS POTOMAC GROUP. I. ZONE I LEAVES
Authors: Upchurch Garland R.
Published: January 2018

Angiosperm leaf cuticles from the oldest part of the Potomac Group reinforce previous paleobotanical evidence for a Cretaceous flowering plant diversification. Dated palynologically as Zone I of Brenner (Aptian?), these remains show a low structural diversity compared to later Potomac Group and modern angiosperms. All cuticle types conform to a single plan of stomatal construction that is unusual in its extraordinary plasticity: both the number of subsidiary cells and their arrangement vary greatly on a single epidermis, such that the stomata might be classified as paracytic, anomocytic, laterocytic, and intermediate. Such stomatal diversity is uncommon in extant angiosperms but is known from a few Magnoliidae. Many species possess secretory cells comparable to the oil cells of modern Magnoliidae, and a few show the bases of probable uniseriate hairs. None of the cuticle types can be assigned to a single modern family, but several show similarities with Chloranthaceae and Illiciales. These results support the concept that subclass Magnoliidae includes some of the most primitive living angiosperms.
POLLEN MORPHOLOGY AND THE RELATIONSHIPS OF SIMMONDSIA CHINENSIS TO THE ORDER EUPHORBIALES
Authors: Nowicke Joan W. , Skvarla John J.
Published: January 2018

Pollen from Simmondsia chinensis (Simmondsiaceae) was examined in LM, SEM, and TEM. The pollen is shed as monads, triangular in shape in polar view, with a 3‐porate aperture type in which the pores are large and poorly defined. The tectum is irregularly scabrate, sometimes forming minute “islands” topped with spinules. In thin section, the endexine is thickened and lamellate in the aperture regions, and narrow in the mesoporus; the foot layer is well‐defined but noticeably thicker in the mesoporus; and thin columellae support an essentially complete tectum. The pollen of four genera, Buxus, Pachysandra, Sarcococca, and Styloceras, from the Buxaceae to which Simmondsia has been assigned by some authors, was also examined and illustrated. The pollen morphology of two families frequently aligned with Simmondsiaceae, Euphorbiaceae and Pandaceae, is briefly discussed. For the most part pollen morphology supports the treatment of Simmondsia as a monotypic family, Simmondsiaceae.
POST‐BURN DIFFERENCES IN SOLAR RADIATION, LEAF TEMPERATURE AND WATER STRESS INFLUENCING PRODUCTION IN A LOWLAND TALLGRASS PRAIRIE
Authors: Knapp Alan K.
Published: January 2018

The influence of standing dead biomass on available solar radiation, leaf temperature (Tleaf) and leaf water potential (ѱleaf) of Andropogon gerardii in unburned tallgrass prairie was compared to burned prairie in eastern Kansas. The standing dead reduced photosynthetically active radiation incident on emerging shoots by 58.8% in unburned compared to burned prairie during the initial 30 days of the growing season. Aboveground production in unburned prairie was similarly reduced during this period (55.4%) compared to burned prairie. Leaf temperatures in A. gerardii were greater in unburned prairie than in burned early in the season, but were nearly equal by the end of the growing season. The maximum elevation of Tleaf in unburned prairie above burned was 9.5 C. The maximum unburned Tleaf measured was 41.5 C compared to 39.4 C in burned prairie. Lower windspeed adjacent to leaves in unburned prairie resulting in reduced convective cooling may have caused higher Tleaf in unburned prairie. Leaf water potential was significantly lower in unburned prairie than in burned prairie early in the season but was higher in unburned prairie by late season. The seasonal minimum ѱleaf in burned prairie was — 1.60 MPa compared to —1.45 MPa in unburned prairie. The combined effect of these post‐burn differences in solar radiation, Tleaf and ѱleaf may be significant in contributing to the lower production in unburned compared to burned tallgrass prairie.
OBSERVATIONS ON PREMEIOCYTES OF WHEAT
Authors: McQuade H. A. , Young‐Rottler Ann M.
Published: January 2018

Electron microscopic observations of wheat premeiocytes in premeiotic mitosis (PMM) and premeiotic interphase (PMI) are reported. In archesporial cells of columns at last PMM there is a significant increase in activity of endoplasmic reticulum. Characteristic states of chromatin of premeiocyte nuclei in the stages of PMI are illustrated. Changes in the primary walls of PMCs at Stage 1, PMI, precede the formation of callose in Stage 2. In general, callose deposition throughout the PMC column follows the pattern described elsewhere in Sorghum and other Gramineae. The behavior of the plasmalemma during callose synthesis resembles that described elsewhere in Cucurbita. A role for the cell endomembrane system in callose synthesis is suggested. Blebs arising from the inner membrane of the nuclear envelope, described elsewhere in endosperm cells of wheat and by us in wheat PMCs in this report, give rise to vesicles which carry nuclear material into the cell cytoplasm. Differences in this transport mechanism as it appears in the two tissue systems are described.
COUNTERFEIT HYBRIDS BETWEEN TRIPSACUM AND ZEA (GRAMINEAE)
Authors: de Wet J. M. J. , Newell C. A. , Brink D. E.
Published: January 2018

Diploid (2n = 36) Tripsacum australe Cutler and Anderson var. hirsutum de Wet and Timothy, T. cundinamarce de Wet and Timothy, T. dactyloides (L.) L. var. dactyloides and var. meridonale de Wet and Timothy, and T. laxum Nash were crossed with Zea mays L. (2n = 20) as the pollen parent. True hybrids combine the cytologically nonreduced genome of Tripsacum (36 chromosomes) with the haploid (10 chromosomes) or more rarely diploid (20 chromosome) genome of Zea. Maternal offspring with 2n = 36 Tripsacum chromosomes commonly result from parthenogenetic development of cytologically nonreduced eggs. Some individuals with 2n = 36 Tripsacum chromosomes, however, resemble true hybrids in phenotype. These counterfeit hybrids incorporated Zea genetic material into their Tripsacum genomes without true fertilization having taken place. Offspring of counterfeit hybrids that were grown to maturity resembled their mothers in phenotype, and must have originated parthenogenetically. It is proposed that counterfeit hybrids are also produced in nature, and that this process contributes to origins of variation in gametophytic apomicts, and perhaps also in sexually reproducing species.
STABILITY OF NUCLEAR DNA CONTENT DURING ADVENTITIOUS SHOOT FORMATION IN PINUS TAEDA L. TISSUE CULTURE
Authors: Renfroe Michael H. , Berlyn Graeme P.
Published: January 2018

Attempts to preserve selected genotypes through clonal propagation may be hampered by genetic instability produced during the tissue culture phase of the propagation procedure. To investigate the genetic condition of loblolly pine (Pinus taeda L.) tissue cultures, nuclear DNA content in embryos grown in vitro and in regenerated buds were examined using two‐wavelength microspectrophotometry. Embryos were grown on chemically defined media containing cytokinin as the sole growth regulator. Nuclear DNA content remained at or between 2 C and 4 C with no evidence of polyploidy during nearly 3 months of continuous culture. Benzylaminopurine, even at concentrations which were supraoptimal for shoot regeneration, had no effect on nuclear DNA content. Regenerated shoots also had stable nuclear DNA contents which correspond to a diploid condition. These results are of significance for the development of mass propagation techniques for this commercially valuable species.
FLORAL BIOLOGY AND BREEDING SYSTEM OF BAUHINIA BENTHAMIANA TAUB. (LEGUMINOSAE), A BAT‐POLLINATED TREE IN VENEZUELAN “LLANOS”
Authors: Ramirez Nelson , Sobrevila Claudia , de Enrech Nereida X. , Ruiz‐Zapata Thirza
Published: January 2018

The breeding system and floral characteristics of Bauhinia ungulata L. were investigated during two consecutive flowering cycles (Dec‐Feb). This tree grows in savannas in small sized patches scattered in the grassland and in larger tree clusters called “mata.” Anthesis occurs between 17:00 and 19:30. Anther dehiscence and nectar secretion begin one hour after anthesis. Nectar is produced for 10 to 12 hr with an average sugar concentration of 13.5%. Flowers in small trees secrete nectar at a higher rate than do flowers in bigger trees. Two phyllostomatid bat species, Glossophaga soricina and Phyllostomus discolor, visit the flowers of B. ungulata between 20:00 and 4:00. Visits of variable duration occur every 1 to 2 hr. In general, the times of greatest nectar production, of highest solute concentration of the nectar and of most frequent visits by the main pollinators coincide. The flowers are significantly dimorphic in pistil length, and ovules are abortive in the short‐pistil flowers. Artificial self‐ and cross‐pollinations in long‐and short‐pistil flowers show that B. ungulata is genetically self‐incompatible and functionally andromonoecious.
CAUSAL MECHANISMS OF LEAF DIMORPHISM IN THE AQUATIC ANGIOSPERM CALLITRICHE HETEROPHYLLA
Authors: Deschamp Paula A. , Cooke Todd J.
Published: January 2018

This report investigates the physiological basis for the production of dimorphic leaves on the aquatic angiosperm Callitriche heterophylla. In nature, the leaf morphology of this plant depends on whether the shoot apex is submerged in or emergent from water. The water‐form leaves that develop on submerged apices assume a long, linear shape in contrast to the short, obovate appearance of land forms on emergent apices. The parameters of length/width ratio and stomatal density were used as developmental indices to characterize how natural conditions, fluctuating water levels and other experimental treatments affect leaf shape. Transferring submerged and emergent shoots to the alternative culture conditions caused immature leaves to assume the characteristics appropriate to their new environment. Moreover, the treatments of 0.24 mol mannitol, high temperature (30 C) and 10−‐5 m abscisic acid induced submerged shoots to produce land‐form leaves whereas 10−‐5 m gibberellic acid mediated the development of water‐form leaves on emergent shoots. Water, osmotic and pressure potentials of immature leaves in the control and experimental treatments were determined by thermocouple psychrometry. Under natural conditions, growing water forms exhibited high turgors (3–5 bars) while developing land forms showed much lower turgors (0–1 bar). Similar correlations between turgor pressure and leaf morphology were observed in the case of the gibberellic acid and mannitol treatments. However, abscisic acid and high temperature caused the developing land‐form leaves to exhibit high turgors without a concomitant change to the water‐form morphology. Microscopic measurements of epidermal cells established that irrespective of the experimental conditions, water‐form leaves had longer and narrower epidermal cells with less convoluted anticlinal walls than land forms. Cell counts indicated that the numbers of epidermal cells did not account for the observed differences in leaf morphology. The results are interpreted in terms of how cell expansion might regulate leaf morphology in aquatic angiosperms.
STRUCTURE OF THE LEAF OF PYROSSIA LONGIFOLIA—A FERN EXHIBITING CRASSULACEAN ACID METABOLISM
Authors: Warmbrodt Robert D.
Published: January 2018

The leaf of Pyrossia longifolia (Burm.) Morton, an epiphytic fern known to exhibit CAM, was examined by light and electron microscopy. The relatively thick leaf contains a single‐layered epidermis, “water‐storage” tissue, and a reticulate vascular system embedded in mesophyll tissue not differentiated into palisade and spongy layers. Mesophyll is composed of large, slightly elongate cells each with a thin, parietal layer of cytoplasm and a large central vacuole. The chloroplast‐microbody ratio in mesophyll cells indicates that Pyrossia may be a high photorespirer and thus similar in that sense to C3 plants. Mesophyll is separated from the vascular tissue by a tightly‐arranged layer of endodermal cells with Casparian strips. The inner layer of mesophyll cells and the endodermal cells lack suberin lamellae. The collateral veins contain sieve elements, tracheary elements, pericycle and vascular parenchyma cells, the latter conspicuously larger than the sieve elements. The vascular parenchyma is the only cell type in the leaf which contains plastids with a peripheral reticulum. The parenchymatic elements of the leaf are connected by plasmodesmata, all of which lack neck constrictions and sphincters, or sphincter‐like structures. The connections between sieve elements and adjacent parenchymatic elements are pore‐plasmodesmata characterized by prominent wall thickenings on the parenchymatic‐element side of the wall. The distribution and relative frequencies of plasmodesmata between the various cell types of the leaf indicate photoassimilates may move either symplastically or by a combination of symplast and apoplast from the mesophyll to the site of phloem loading in the veins.
A STUDY OF THE SEED BANK OF A SALT MARSH IN NORTHERN SAN FRANCISCO BAY
Authors: Hopkins Dale R. , Parker V. Thomas
Published: January 2018

Abundance, species composition, and distribution of buried seeds in a San Francisco Bay salt marsh were studied by collecting soil samples in October and February and observing seedling emergence in the greenhouse. Results were compared with existing vegetation patterns and field germination. Average numbers of buried viable seed down to a 5‐cm depth were 380/ m2 in October and 700/m2 in February, with field germination averaging 118/m2. Salicornia virginica dominated the seed bank in the greenhouse and in field germination. Most other marsh species were present in the seed bank but numbers of seeds were low. A significant correlation was found between highest species diversity and proximity to channels. The nature of this low‐diversity, low‐density seed bank reflects dominance of long‐lived perennial species, seed dispersal patterns and selective environmental pressures.
REPRODUCTIVE BIOLOGY OF APIACEAE. I. FLORAL VISITORS TO THASPIUM AND ZIZIA AND THEIR IMPORTANCE IN POLLINATION
Authors: Lindsey Anne H.
Published: January 2018

Based on the ready availability of nectar and pollen, and on the large numbers and great diversity of insect visitors, species in the Apiaceae have been labeled promiscuous. The distinction between floral visitors and effective pollinators, however, is extremely important and is rarely discerned. Floral visitation was documented for plants of nine populations in a comparative study of three species of the closely related apioid genera, Thaspium Nutt. and Zizia Koch. A pollinator importance index was calculated for each floral visitor using visitor abundance, pollen load composition and foraging behavior as its basic components. Results showed that, despite a high diversity of insect visitors, generally 1–4 species accounted for a minimum of about 74% of the pollinations in all populations. This specialization in pollination appears in part to be the result of an oligolectic relationship between Andrena ziziae (Hymenoptera; Andrenidae) and plants of the taxa studied, but solitary bees of Andrenidae, Colletidae and Halictidae in general were efficient and important pollinators. This study emphasizes that visitation records, when considered alone, effectively disguise specialization in the pollination system.
THE PLATYCARYA PERPLEX AND THE EVOLUTION OF THE JUGLANDACEAE
Authors: Wing Scott L. , Hickey Leo J.
Published: January 2018

We report on the leaves, fruits, inflorescences, and pollen of two fossil species in the genusPlatycarya.The association of these dispersed organs has been established by their repeated co‐occurrence at a large number of localities, and for two of the organs (fruit and pistillate inflorescence, and pollen and staminate inflorescence) by apparent organic attachment of compression fossils. Each of the two species can be distinguished by characteristics of all the known megafossil organs. We also review the fossil record of dispersed platycaryoid fruits and inflorescences, recognizing three additional species ofPlatycaryaand two ofHooleya.Two of the fossilPlatycaryaspecies are morphologically very different from the livingPlatycarya strobilaceaSieb. et Zucc., but they show the diagnostic features of the genus.Hooleyais a generalized member of the Platycaryeae that is probably close to the ancestry ofPlatycarya.

The twoPlatycaryaspecies known from multiple organs provide a remarkable example of mosaic evolution in which fertile and foliar structures have attained different levels of morphological specialization. The leaves, often considered the most plastic of plant organs, retain several features that are otherwise seen only in the Engelhardieae. These similarities in leaf architecture between the fossilPlatycaryaspecies and Engelhardieae are advanced features for the Juglandaceae, and thus indicate a sister‐group relationship between the two lines. In contrast to the leaves, the fruits, inflorescences, and pollen of the fossilPlatycaryaspecies are almost as specialized as those of the extantP. strobilaceaand bear little resemblance to the same structures in other genera of the family.

The morphology, taphonomy, sedimentary setting, and geographic and stratigraphic distribution of three of the fossil platycaryoid species suggest that they were wind‐dispersed, early successional plants that grew in thickets. This habit is retained byPlatycarya strobilaceaand is typical of many of the amentiferae (e.g. Myricaceae, Betulaceae). Ther‐selected life‐history pattern of thePlatycaryaline may well have contributed to its low diversity through geologic time.
ANT INHIBITION OF POLLEN FUNCTION: A POSSIBLE REASON WHY ANT POLLINATION IS RARE
Authors: Beattie Andrew J. , Turnbull Christine , Knox R. B. , Williams E. G.
Published: January 2018

Ant pollination systems are remarkably rare. We show that pollen exposed to ants for brief periods exhibits reduced viability, reduced percent germination, and shorter pollen tubes relative to control pollen. Pollination with ant‐borne pollen also results in lower seed‐set than pollination with untreated pollen. This disruption of pollination processes must have exerted a powerful selection pressure against the evolution ofant‐pollination systems. It is suggested that the nestbuilding and brood‐rearing habits of ants require that they secrete large amounts of antibiotics to combat pathogenic microorganisms. It is these secretions that disrupt pollen function. Bees and wasps exhibit very different nesting behavior, consequently there are no chemical barriers to their coevolving with flowers as pollinators.
DEVELOPMENT OF THE OVULE AND FEMALE GAMETOPHYTE IN EUSTACHYS PETRAEA AND E. GLAUCA (POACEAE)
Authors: Aulbach‐Smith Cynthia A. , Herr J. M.
Published: January 2018

The unilocular pistil in Eustachys contains a single ovule with lateral placentation. In E. petraea and E. glauca, the mature ovule is bitegmic, tenuinucellate, and amphitropous with the endostomic micropyle oriented toward the base of the locule. A single hypodermal archesporial cell enlarges to form the megasporocyte. The chalazal dyad member is larger than the micropylar one, and meiosis II is nonsynchronized. Two‐thirds of the tetrads are linear and one‐third T‐shaped. The chalazal megaspore is functional. Initially ovoid, the two‐nucleate female gametophyte becomes curved as it enlarges. The four‐nucleate stage becomes wider at its extremities and constricted in the center. Synchronous mitotic divisions establish the eight‐nucleate stage with four nuclei at each pole separated by a large central vacuole. In E. petraea, the maturation sequence begins with antipodal differentiation, followed by differentiation of the egg apparatus, migration of the polar nuclei to the center, and division of the antipodals to produce twelve cells. The sequence in E. glauca begins with migration of the polar nuclei followed by differentiation of the antipodals, egg apparatus, and antipodal replication to six cells. The polar nuclei fuse to form a secondary nucleus appressed to the egg cell in E. glauca and separated from it by a vacuole in E. petraea. T‐tests for length measurements for various stages of development indicate that the functional megaspore and two‐nucleate female gametophyte are significantly larger in E. glauca than in E. petraea. There is no significant difference in gametophyte length at the four‐nucleate stage, and at the eight‐nucleate stage, length in E. petraea surpasses that in E. glauca. This gap widens significantly at the mature stage. Nuclear volumes are significantly greater in E. glauca than in E. petraea in the functional megaspore and two‐nucleate stage, but the volumes are similar at the four‐nucleate stage. Consideration of the differences in structural complexity between the sporophyte and gametophyte generations leads to the conclusion that the female gametophytes of these species are more distinctive than are the sporophytes.
THE GROWTH AND MINERAL COMPOSITION OF THREE SPECIES OF SPERGULARIA AS AFFECTED BY SALINITY AND NUTRIENTS AT HIGH SALINITY
Authors: Okusanya Olubukanla T. , Ungar Irwin A.
Published: January 2018

The effects of salinity on the growth of three species of Spergularia and the effects of some levels of different nutrients on the growth and mineral composition of the three species under high salinity were investigated in sand culture. In response to the effects of salinity, S. marina and S. rupicola behaved like true halophytes in terms of survival, mean dry weight and plant part weight ratios. Spergularia rubra also behaved like an ecological halophyte in terms of dry weight but in terms of survival, it behaved like a glycophyte. The poor growth exhibited by the halophytes, S. marina and S. rupicola under high salinity condition was significantly reversed with the addition of most nutrients, while the glycophyte, S. rubra showed no favorable response, rather the combination of some nutrients further reduced its growth. The increased growth in S. marina was as a result of increased root growth while in S. rupicola it was as a result of increased root and stem growth. High salinity conditions resulted in a marked reduction in calcium and potassium content and an increase in sodium and chloride content of leaves of the species. Addition of many of the nutrients to plants under high salinity condition generally resulted in increased sodium, calcium, potassium, and magnesium content of leaves, except that the addition of phosphate resulted in decreased amounts of calcium and magnesium. Results are discussed in relation to the salt tolerance of the species and how the supply of nutrients to these species in their natural habitats might help them overcome high salinity problems.
THE EFFECT OF SALINITY AND TEMPERATURE ON THE GERMINATION OF POLYMORPHIC SEEDS AND GROWTH OF ATRIPLEX TRIANGULARIS WILLD.
Authors: Khan M. A. , Ungar I. A.
Published: January 2018

Polymorphic seeds of Atriplex triangularis were germinated at various temperatures (5–15 C, 5–25 C, 10–20 C, 20–30 C) and salinity regimes (0 to 1.5% NaCl) in order to determine their germinability and early seedling growth under these conditions. Larger seeds generally had a higher germination percentage in saline medium. The rate and percentage of germination decreased with increased salinity stress. A thermoperiod of 25 C day and 5 C night, 12 hr/12 hr, temperature enhanced germination of seeds. Early seedling growth is promoted in larger seeds at lower salinity, and at high‐day and low‐night temperatures. Polymorphic seeds have different physiological requirements which provide alternative situations for seed germination in natural habitats.
NITROGEN FIXATION ASSOCIATED WITH NATURAL AND CULTIVATED STANDS OF TYPHA LATIFOLIA L. (TYPHACEAE)
Authors: Biesboer David D.
Published: January 2018

Acetylene reduction by bacteria associated with Typha latifolia L. roots and rhizomes was studied in the field and in the laboratory. In situ studies indicated that the rate of acetylene reduction in a natural cattail population was ca. 4‐fold higher than in a cultivated cattail stand. Nitrogenase activity was found to occur principally in the rhizosphere of roots and rhizomes with the greatest activity occurring in association with mature roots. Scanning electron and light microscopy, and 2, 3, 5 triphenyltetrazolium chloride reduction showed that bacterial associations were limited to the rhizoplane of this angiosperm. One diazotrophic bacterial genus was found to be associated with roots and rhizomes and was identified as the facultative anaerobe Bacillus. Contribution of free‐living cyanobacteria to total nitrogen fixation in the natural stand was negligible. Calculations show that a natural stand of cattails may fix 18 kg nitrogen ha−‐1 yr−‐1 or ca. 8.2% of the total nitrogen present in the standing crop.
THE ROOT APICAL MERISTEM OF OSMUNDA REGALIS
Authors: Freeberg John A. , Gifford Ernest M.
Published: January 2018

Roots of the Osmundaceae differ from most ferns in having more than one apical cell. The size of the apical initial group, which includes cells that are considered to be apical cells, varies directly with root diameter in Osmunda regalis L. Mitotic indices were 6.63% for apical cells, 7.45% for the entire apical group, 6.25% for distal derivatives, and 7.15% for developing cortical cells. Cytophotometric measurements of Fuelgen‐stained nuclei indicated no endopolyploidy in the populations of cells studied. These findings demonstrate that there is no quiescent center in the roots of O. regalis.
XYLEM ANATOMY, WATER FLOW, AND HYDRAULIC CONDUCTANCE IN THE FERN CYRTOMIUM FALCATUM
Authors: Gibson Arthur C. , Calkin Howard W. , Nobel Park S.
Published: January 2018

Xylem anatomy and water relations were studied in holly fern (Cyrtomium falcatum, Aspidiaceae) to determine the details of the pathway for water flow through an entire plant and the influence of tracheid number and lumen diameter on water flow. Each leaf has two adaxial traces and an abaxial trace, which are supplied by diarch adventitious roots attached to the dictyostele of the rhizome near the leaf base. Anatomical observations and dye experiments showed that each adaxial bundle vascularizes the approximately seven pinnae on its side of a leaf. An abaxial bundle is intermittently connected to an adaxial bundle as well as other abaxial bundles, forming a minor vascular pathway between the bundles of the leaf axis. Changes in both number and diameter of tracheids result in an acropetal decrease in hydraulic conductance per unit length along the rachis, although tracheid number locally increases when the trace for a pinna is produced in an adaxial bundle. Water flow was determined from the transpiration distal to the point in question or by forcing a solution through an axis with applied pressure. The water potential gradient along the plant axis was quite constant, indicating that hydraulic conductance per unit length varied with leaf area to be supplied. About 40% of the overall water potential drop occurred from the rachis into the pinnae, which reflected factors controlling water potential gradients in the lamina and not a very low conductance in the petiolule xylem. Hydraulic conductances calculated using the Hagen‐Poiseuille equation and tracheid diameters were generally double those of measured conductances. Since the values tended to vary by a constant factor, tracheid number and diameter may largely control water flow in the xylem.
LIGHT AND ELECTRON MICROSCOPY OF THE RESIN GLANDS OF PASSIFLORA FOETIDA (PASSIFLORACEAE)
Authors: Durkee Lenore T. , Baird Chris W. , Cohen Paul F.
Published: January 2018

Petiolar, bracteolar, and stipular glands from two varieties of Passiflora foetida were studied by both light and electron microscopy. These glands have previously been called nectaries. They do resemble the sugar‐secreting glands of other Passiflora species with respect to their location and morphology. However, cytological studies together with chemical tests of the exudate support the view that the glands in the varieties studied actually secrete a resin‐like substance which possibly functions as an anti‐herbivore mechanism.
SOMACLONAL AND GAMETOCLONAL VARIATION
Authors: Evans D. A. , Sharp W. R. , Medina‐Filho H. P.
Published: January 2018

For several years it has been recognized that introduction of plant cells into culture results in genetic changes. These genetic alterations have been recovered in the plants regenerated from cell cultures. More recently it has been recognized that this method of introducing genetic changes into crop plants could be used to develop new breeding lines. The technology of introducing genetic variation by using cell culture has been termed somaclonal and gametoclonal variation. This paper reviews the history of this technology and offers genetic documentation of somaclonal variation in tomato. As this variation represents a new tool for the plant breeder, breeding strategies for the use of this variation are presented and discussed. Somaclonal and gametoclonal variation are new tools for the geneticist and plant breeder that permit reduction in the time period for new variety development and that permit access to new classes of genetic variation.
SYSTEMATIC IMPLICATIONS OF SEED COAT MORPHOLOGY IN NAMA (HYDROPHYLLACEAE)
Authors: Chance Gail D. , Bacon John D.
Published: January 2018

Seeds from 37 species of Nama (Hydrophyllaceae) were examined by scanning electron microscopy in order to assess systematic implications of seed coat structure. Generally, seed coat morphology is species specific. Nevertheless, similarities among species in seed coat organization, particularly, outer testa anatomy and wall thickening‐pitting patterns allow the recognition of six groups among examined taxa; furthermore, seed coat features often suggest both intra‐group and inter‐group relationships. Recognized groupings do not correspond well with the more classicial treatments of Nama; rather, they suggest that a restructuring of the infrageneric and even the generic taxonomy of Nama is in order.
THE HISTOCHEMISTRY AND ULTRASTRUCTURE OF JACK PINE MICROSPORANGIA DURING THE WINTER
Authors: Cecich Robert A.
Published: January 2018

The development of jack pine (Pinus banksiana Lamb.) microsporangia from October to April was investigated with a microdensitometer and a transmission electron microscope. DNA, RNA, and protein content of sporogenous cells was measured at monthly intervals. DNA was unreplicated (2C) until March when DNA synthesis was first noted, coinciding with a loss of heterochromatin. Protein content doubled in April. RNA staining increased in December and then decreased. Numerous whorls and stacks of rough endoplasmic reticulum and ribonucleoprotein‐like granules appeared in December and may be related to the RNA increase. A fibrillar, light‐staining region was found in the cytoplasm of the sporogenous cells from November to March. It was hydrolyzed in the presence of protease and may be a winter morphology of microfilament bundles or dictyosomes. Lipid bodies and vacuoles were abundant in the tapetum and sporangial wall cells during the winter. Observations substantiate reports that winter is not a time for cessation of development.
OBLIGATE OUTCROSSING IN A HOMOSPOROUS FERN: FIELD CONFIRMATION OF A LABORATORY PREDICTION
Authors: Haufler Christopher H. , Soltis Douglas E.
Published: January 2018

While homosporous ferns are potentially capable of producing totally homozygous sporophytes in one generation via selfing of their bisexual gametophytes, laboratory analyses indicate that a variety of mechanisms promote gametophytic outcrossing. The operation of these mechanisms in natural sporophyte populations, however, has not been previously demonstrated. Laboratory analyses of gametophyte ontogeny show that Bommeria hispida is obligately outcrossing. Electrophoretic data presented here indicate that individuals from natural sporophyte populations of this species are highly heterozygous. Electrophoretic data, therefore, corroborate evidence from the in vitro analysis of gametophyte development and demonstrate that sporophytes of B. hispida in nature typically are products of outcrossing between genetically different gametophytes. Extrapolations from the literature, together with our findings, indicate that outcrossing mechanisms may operate frequently in ferns, thereby maintaining genetic variability between individuals within populations. This evidence questions whether most ferns are highly inbred and therefore predominantly homozygous.
TRANSFER CELLS IN THE PLACENTAL PAD AND CARYOPSIS COAT OF PAPPOPHORUM SUBBULBOSUM ARECH. (POACEAE)
Authors: Rost Thomas L. , de Artucio Primavera Izaguirre , Risley Edward B.
Published: January 2018

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.
KARYOTYPIC VARIATION OF EASTERN NORTH AMERICAN CLAYTONIA CHEMICAL RACES
Authors: Doyle Jeff J.
Published: January 2018

Considerable karyotypic differentiation has occurred within the group of taxa comprising the eastern North American members of the genus Claytonia. Patterns of karyotypic differentiation are congruent with evolutionary groupings based on flavonoid chemistry, particularly at the diploid level. The 2n = 16 diploid chemotype found in both C. caroliniana and C. virginica possesses a karyotype composed entirely of metacentric chromosomes, while acrocentric chromosomes predominate in the karyotypes of the 2n = 12 and 2n = 14 diploid chemotypes of C. virginica. The 2n = 16 diploid also has a karyotype significantly larger than those of the other diploid cytotypes. Polyploid karyotypes of both species show varying degrees of divergence from their presumed diploid progenitors.
STEM AND LEAF CUTICLE OF KARINOPTERIS: SOURCE OF CUTICLES FROM THE INDIANA “PAPER” COAL
Authors: DiMichele William A. , Rischbieter Michael O. , Eggert Donald L. , Gastaldo Robert A.
Published: January 2018

Cuticular or “paper” coal‐shale is a local deposit of an organic‐rich, highly clastic rock, with abundant leaf and stem cuticles, associated with the Upper Block Coal Member in Parke County, Indiana. Fresh blocks of cuticular coal can be split along bedding surfaces to reveal a fossil flora of low diversity, dominated by pteridosperms and lycopods, with minor amounts of ferns and sphenopsids. Karinopteris is a subdominant component of this flora and the great abundance of well‐preserved cuticles of this plant allows for a reconstruction of its frond and growth habit. Karinopteris appears to have been a vine, indicative of structural diversity in the plant assemblage. The plant assemblage of the cuticular coal is dissimilar to most midwestern coal‐ball floras of slightly younger age. This is probably a result of the depositional setting in an upper deltaic‐fluvial dominated environment.
TISSUE PREPARATION AND FINE STRUCTURE OF THE RADICLE APEX FROM COTTON SEEDS
Authors: Vigil Eugene L. , Steere Russell L. , Wergin William P. , Christiansen M. N.
Published: January 2018

A comparative methodological study was made of the fine structure of apical cortical cells in excised radicles from cotton (Gossypium hirsutum L. var M‐8) seeds. Radicles from dry seed had 12% moisture content and were prepared for electron microscopy using several different techniques. These included different methods of chemical fixation or freeze‐fracture and etching of unfixed tissue for transmission electron microscopy (TEM) and cryofracturing of fixed and dehydrated radicles for scanning electron microscopy (SEM). Cortical cells had a similar appearance regardless of the method used in tissue preparation. Cell walls had a pronounced waviness which was particularly evident in SEM images of cells lining the elongated intercellular air spaces. The plasma membrane (PM) delimited the cytoplasm of each cell as an intact unit membrane. Single layers of tightly‐packed lipid bodies (LB) were apposed to the PM and protein bodies (PB). Distension of cells, membranous organelles and LB was observed in radicles fixed by immersion in aqueous solutions, suggesting that a certain amount of hydration occurred during fixation. This interpretation was supported by the compact appearance of cells and organelles in tissue prepared by freeze‐etch or vapor fixation. We conclude that freeze‐fracture and etching of unfixed tissue provided the best information for cell morphology and structure of membranes and organelles in dry tissue. Complementary data on the fine details of nuclei and cytoplasmic organelles were best observed with TEM of fixed tissue. These data when viewed collectively indicate the advantage of using several techniques to obtain analogous and complementary information essential for establishing a baseline level of information on the fine structure of cells in dry tissue.