bluuebunny/crossref_metadata_2025 huggingface dataset:
BALDCYPRESS SEEDLING GROWTH IN THERMALLY ALTERED HABITATS
Authors: McLeod Kenneth W. , Sherrod Casey
Published: January 2018

Thermal discharges from nuclear production reactors killed large areas of baldcypress‐water tupelo (Taxodium distichum‐Nyssa aquatica) forests along streams on the Savannah River Plant in South Carolina. Recolonization by baldcypress has been slow in areas where present stream temperatures do not exceed ambient by more than 10 C and has not occurred at all at higher temperatures. Since it has been previously shown that cypress germination and establishment are not inhibited at stream temperature below 42 C, the growth of 1‐yr‐old baldcypress seedlings introduced into ambient (Tmax = 32 C) and ambient + 10 C (Tmax = 42 C) stream temperatures was examined during a 16‐month period to determine the response of this growth stage. Growth in height, diameter and biomass of these seedlings was enhanced in a stream habitat with maximum water temperatures of 42 C. Allocation of dry weight into root and shoot tissues was modified by stream temperature, with a lower root/shoot ratio in plants at the 42 C location. In thermally altered (‐42 C) areas, neither establishment nor growth of established cypress seedlings is limited by stream temperature. Thus, slow reinvasion of these sites by baldcypress is thought to be due to a lack of a seed source and/or competitive exclusion.
CALLUS FORMATION AND ORGANOGENESIS FROM CULTURED LEAF SEGMENTS OF CRASSULA ARGENTEA: CYTOKININ‐INDUCED DEVELOPMENTAL PATTERN CHANGES
Authors: Paterson Karol E. , Rost Thomas L.
Published: January 2018

Culturing leaf segments on agar medium with a final concentration of 10–4m isopentenyl adenine inhibits regeneration of plantlets, but stimulates some segments to produce regions of dense callus. The callus is initiated from the basipetal end of a cut vascular bundle, and is therefore the positional equivalent of root initiation during normal regeneration. Once callus has emerged, it forms a sphere of tissue attached to the leaf segment. The cells on the surface of the sphere are smaller than the cells toward the center. Some of these larger cells contain tannins or large starch grains. Shoots are sometimes initiated from organized meristematic regions of surface cells. Roots form endogenously from callus after shoot formation. This regeneration sequence, initially induced by cytokinin treatment, is strikingly dissimilar to the normal pattern, and provides an excellent example of a hormone‐induced alteration to a developmental pattern.
SURVIVAL OF SEVERE DROUGHT BY A NON‐SPROUTING CHAPARRAL SHRUB
Authors: Parsons David J. , Rundel Philip W. , Hedlund Richard P. , Baker Gail A.
Published: January 2018

A 2‐yr drought (1975‐1977) in much of California provided unusually severe water stress on many native plant species. In this paper we evaluate the effects of this drought on Arctostaphylos viscida Parry, a common non‐sprouting chaparral shrub in the foothills of the southern Sierra Nevada. At the peak of the drought, water potentials as low as –74 bars were measured. While only three of 90 shrubs sampled were killed by the drought, all but one showed signs of drought‐induced dieback. First and second year post‐drought twig growth was significantly greater on shrubs with 90% or greater branch mortality than on those suffering lesser dieback. In all cases, new growth occurred only on surviving branches. Midday water stress measurements showed little difference for shrubs exhibiting high and low levels of dieback. These results suggest that drought survival in Arctostaphylos viscida may depend on a mechanism where certain branches are sacrificed with the surviving ones preferentially receiving available resources. The possibility that this may involve the dieback of below ground roots and/or lack of production of new roots to compensate for lack of root turnover is supported by water stress measurements of adjacent fire damaged shrubs. Implications of possible specialized drought survival mechanisms in non‐sprouting shrubs are explored.
SOME SURFACE CHARACTERISTICS OF THE CHLOROPLAST ENVELOPE
Authors: Stocking C. Ralph , Franceschi Vincent R.
Published: January 2018

Pronase, cationic ferritin, and ferritin‐conjugated plant lectins were used to study the chloroplast envelope. Negative charges (binding cationic ferritin) are fairly uniformly distributed over the envelope surfaces in contact with the hyaloplasm and are not appreciably altered by mild pronase treatment of isolated plastids. All surfaces of stroma‐free thylakoids previously exposed to the stroma uniformly bind cationic ferritin. RicinII‐ferritin binding to the membranes of the chloroplast envelope indicates that galactolipids are distributed in the outer membrane in such a way that their galactose moieties are exposed on the envelope surface. In addition, the outer surface of the inner membrane (the intermembrane face) contains uniformly distributed galactose which binds ricinII when this membrane is exposed to the reaction medium. Isolated vesicles of the chloroplast envelope bind ricinII, while isolated envelope vesicles as well as the envelopes of intact chloroplasts failed to bind concanavalin A. Thylakoid surfaces showed minor binding of ricinII as well as concanavalin A.
THE POLLINATION ECOLOGY OF ZENOBIA (ERICACEAE)
Authors: Dorr Laurence J.
Published: January 2018

Zenobia is a shrub endemic to the coastal plain of the Carolinas and southeastern Virginia. The sole species, Zenobia pulverulenta, appears to be weakly self‐compatible and partially self‐pollinating. Fruit set was reduced, but not eliminated by excluding insect floral visitors. Insect visitors were collected and their pollen loads examined for Zenobia and foreign pollen. Analysis of these pollen loads and observations of insect‐foraging behavior indicate that workers of three species of bumblebee (Bombus bimaculatus, B. griseocollis and B. impatiens) are. the principal pollinators of Zenobia. However, pollinator density and composition appear to be strongly influenced by the habitats in which Zenobia grows. Pollen and nectar serve as the primary rewards for pollinators.
CHROMOSOME NUMBERS OF NORTH AMERICAN SPECIES OF ANTENNARIA GAERTNER (ASTERACEAE: INULEAE)
Authors: Bayer Randall J. , Stebbins G. Ledyard
Published: January 2018

Chromosome numbers are presented for 99 populations of 13 species of Antennaria, including A. plantaginifolia, A. neglecta, A. virginica, A. solitaria, A. racemosa, A. corymbosa. A. rosea, A. media, A. Parlinii, A. fallax, A. neodioica, A. canadensis, and A. petaloidea. Four species from the eastern United States (A. plantaginifolia, A. neglecta, A. solitaria, and A. virginica) were determined as diploid (n = 14), and these are all sexual. Diploid counts were also obtained for two sexual species (A. racemosa and A. corymbosa) from the western United States. Chromosome counts are presented for two heteroploid agamic complexes occurring in the eastern United States; these include what have traditionally been referred to as A. Parlinii, A. fallax, A. neodioica, A. canadensis, and A. petaloidea. Determinations of 2n = 56, 70, 84, and 112 were obtained for the A. Parlinii and A. fallax groups, where 2n = 84 had been the only number previously reported. Numbers of 2n = 84 were confirmed for A. petaloidea and A. canadensis and 2n = 56 for A. neodioica. The western United States polyploid species (A. rosea and A. media) are reported as 2n = 56. The presence of apomixis is correlated with polyploidy. The distribution of chromosome numbers in eastern United States Antennaria demonstrates that two diploids and many polyploids occur above the glacial margin, and thus there is an increase in the frequency of polyploidy with latitude. Colonization of the glaciated region by Antennaria following the recession of the Wisconsin ice sheet is also discussed. Many of the polyploids occur only in the glaciated region, thus suggesting a recent origin for these cytotypes. There is evidence indicating that the original base number in Antennaria may be x = 7.
OLMECA, A NEW GENUS OF MEXICAN BAMBOOS WITH FLESHY FRUITS
Authors: Soderstrom Thomas R.
Published: January 2018

Olmeca, a new bamboo genus of two species is described from southern Mexico. It is unique among New World bamboos in its production of fruits that are large and fleshy, in contrast to the smaller, dry type—caryopsis or achene—that characterizes the other genera. The fleshy fruit is found in few other bamboos, among them Dinochloa, Melocanna, and Ochlandra. These Asiatic genera are not all closely related to each other nor to the new American genus, but do share a similar type of habitat: the tropical lowland rain forest, where ample water is available throughout the year. Besides the rare type of fruit found in Olmeca, the rhizomes of this genus develop necks up to 8 m or more long, an uncommon feature among any world bamboo of the sympodial type. The solitary culms of Olmeca grow widely spaced from one another because of these elongated, intervening necks. One species. O. recta, is known only from the mountain range of Los Tuxtlas, in Veracruz, where it grows on acidic soils derived from basalt; the other, O. reflexa, occurs on calcareous soils and has a wider range that encompasses parts of Veracruz, Oaxaca, and Chiapas.
ADDITIONAL INFORMATION ON THE POLLEN ORGAN HALLETHECA (MEDULLOSALES)
Authors: Taylor T. N. , Millay M. A.
Published: January 2018

Several additional specimens of the medullosan pollen organ Halletheca reticulatus have been discovered in sediments of Middle Pennsylvanian age. The morphology of this small synangiate seed fern pollen organ is clarified and an emended generic diagnosis provided. The newly discovered material indicates that the central column becomes hollow distally and that sporangial dehiscence is internal through the longitudinal splitting of the fibrous hollow central column. It is suggested that Halletheca represents the basic ancestral pollen organ type of the Medullosales.
OBSERVATIONS ON THE ROOT ANATOMY OF RICE (ORYZA SATIVA L.)
Authors: Clark Lisa H. , Harris William H.
Published: January 2018

Rice plants were grown hydroponically and roots were prepared for light and electron microscopy using standard techniques. The roots are bounded by an epidermis, exodermis, and fibrous layer. The exodermis has a suberin lamella along its inner tangential wall. The fibrous layer is composed of thick‐walled lignified cells with little pitting. The cortical parenchyma is compact when young, but expands and separates to form a zone of cell walls and air spaces in a spoked arrangement. Supporting columns of living parenchyma cells are occasionally present, particularly near lateral roots. The endodermis is typical for grasses with Casparian strips, suberin lamellae, and tertiary state walls with numerous pits. The pericycle and pith become sclerified. Protoxylem elements alternate with protophloem in the young root; later, early metaxylem, late metaxylem, and metaphloem proliferate. The exodermis, fibrous layer, lacunate cortex, and endodermis appear to present a formidable barrier to radial ion movement in the mature portions of the root.
TRANSLOCATION OF URANIN WITHIN THE LIVING OVULES OF SELECTED SPECIES
Authors: Mogensen H. Lloyd
Published: January 2018

Three dictolydonous species having distinctive ovular characteristics were chosen for observation of uranin uptake into their living ovules. Nicotiana tabacum, which has anatropous ovules, showed uranin uptake in a nondifferential manner. Translocation occurred progressively from the funiculus toward the micropylar and chalazal portions at approximately equal rates, then chalazally until the entire ovule had adsorbed the uranin completely. Polygonum capitatum, which has atropous ovules, consistently showed differential uptake of uranin within a given ovule. After the uranin had entered the funiculus and moved about half way toward the micropyle, uranin could already be detected in a small group of cells at the micropylar tip of the ovule. Torenia fournieri, which has hemianatropous ovules with protruding, observable embryo sacs, showed uranin uptake by its ovules, including the egg and synergids, but it was not possible to determine a consistent sequential pattern of translocation. It is suggested that the synergids in the anatropous ovule of N. tabacum are strategically located for early receipt of nutrients as they enter the ovule, while the synergids of P. capitatum are positioned such that they are among the last cells to receive materials entering the ovule. Using the techniques of this study, it is possible that a species having observable embryo sacs, other than T. fournieri, may prove satisfactory for making precise observations on translocation routes within living embryo sacs.
CHROMOSOMAL STUDIES OF SUBGENUS TRIDENTATAE OF ARTEMISIA: EVIDENCE FOR AUTOPOLYPLOIDY
Authors: McArthur E. Durant , Pope C. Lorenzo , Freeman D. Carl
Published: January 2018

The sagebrushes (subgenus Tridentatae of Artemisia—new combination presented in the text) are western North America's most widespread and populous shrub group. Chromosome counts from 120 populations confirm the base chromosome number at x = 9 with numerous 2n = 2x = 18 diploids and 2n = 4x = 36 tetraploids. Few higher polyploids are known, and aneuploidy and supernumerary chromosomes are rare. All 11 Tridentatae species are now known cytologically. All but the narrowly endemic A. argillosa are known from at least three locations: A. arbuscula (2n = 18, 36), A. bigelovii (2n = 18, 36), A. cana (2n = 18, 36), A. longiloba (2n = 18, 36), A. nova (2n = 18, 36), A. pygmaea (2n = 18, 36), A. rigida (2n = 18, 36), A. rothrockii (2n = 18, 36, 54, ca. 72), A. tridentata (2n = 18, 36, 54), and A. tripartita (2n = 18, 36). The chromosome number of A. argillosa, reported here for the first time, is 2n = 36. Chromosome numbers of eight subspecies also have been determined. The subgenus is characterized by autopolyploidy as indicated by morphologically indistinguishable 2x and 4x plants, a few mixed ploidy populations, consistent formation of IVs in 4x PMCs, a relatively uniform 2x karyotype, and a 4x karyotype, which is approximately twice the 2x one. Karyotypic differences, if they exist at all, are on a populational level rather than a systematic taxonomic level. The Tridentatae have apparently rapidly differentiated in situ in North America under the stimulus of recurring aridic cycles since late Tertiary or early Quaternary. They likely derive from more primitive circumboreal stock originating from the Eurasian homeland of Artemisia. The differentiation of myriad forms of Tridentatae was seemingly achieved through genic rather than genomic means. Karyotypic analysis supports a position within Tridentatae of A. rigida, A. bigelovii, and A. pygmaea.
ULTRASTRUCTURAL EVIDENCE FOR SECRETORY PHASES IN THE LIFE HISTORY OF STIGMATIC HAIRS OF COTTON: A DRY TYPE STIGMA
Authors: Sethi Ravinder S. , Jensen William A.
Published: January 2018

Stigmatic hairs of the cotton flower were studied through their developmental stages up to anthesis. Stigmatic hairs invariably develop from a densely straining band of epidermal cells opposite the transmitting tissue cells. At anthesis, these are single cell structures measuring up to 300 μm long. At the 5‐mm stage of stylar length (7–10 days before anthesis), some stigmatic hair cells begin to accumulate an osmiophilic substance between the plasmalemma and the cell wall, possibly synthesized in the endoplasmic reticulum. This material is apparently never secreted outside the cell wall. Immediately following this secretory phase in some stigmatic hair cells a second secretory phase starts. A dense osmiophilic substance, different in appearance from the previous phase, accumulates in the vacuoles of each hair cell. Concomitantly, dimorphism develops in the cytoplasmic densities of stigmatic hair. Some stigmatic hair cytoplasm appears very dense and shows signs of degeneration while other cytoplasm appears normal. A third secretory phase, which begins at anthesis, occurs in the normal hair cells. This phase is characterized by enhanced activity in the cytoplasm of the endoplasmic reticulum and Golgi apparatus. Large vesicles containing granular material are seen fusing with the plasmalemma. Coincident with this activity there is dissolution of the middle layers of the cell wall and the cuticle is ruptured at various points. The dense osmiophilic substance that had accumulated in the vacuole breaks down into fine granular material. Significance of these changes is discussed in relation to the pollen germination mechanism on the dry type stigma of cotton.
AN ULTRASTRUCTURAL STUDY OF THE RELATIONSHIP BETWEEN MICROTUBULES AND MICROFIBRILS IN COTTON (GOSSYPIUM HIRSUTUM L.) CELL WALL REVERSALS
Authors: Yatsu L. Y. , Jacks T. J.
Published: January 2018

The arrangement of cellulosic fibrils in the cell walls of cotton fibers is very unusual; rather than exhibiting a continuous spiraling in one direction, they intermittantly reverse their gyre. Microtubules that line the periphery of the protoplasm, subjacent to the plasmalemma, tend to parallel the deployment of the cell wall microfibrils. It was not known whether this parallelism persisted through the reversal. By studying tangential sections of the cell wall/protoplasmic interfaces at the reversals, we show that congruity continues even through the reversals.

Colchicine treatment did not appear to inhibit cellulose synthesis but it did abolish microtubules in the cotton fiber cells and deranged normal cell wall microfibrillar orientation. Previously, cotton fibers have been shown to possess most of the familiar organelles, but we found two new features not reported heretofore. They are microfilaments and peculiar “polygonal structures” that appear to be associated with the plasma membrane.
TRACHEID BAR AND VESTURED PITS IN LEGUME SEEDS (LEGUMINOSAE: PAPILIONOIDEAE)
Authors: Lersten Nels R.
Published: January 2018

The tracheid bar, a strip composed of vertically oriented large tracheid‐like cells (tracheoids), occurs only in the hilum of seeds of papilionoid legumes. An anatomical survey of the bar was made from seeds representing 232 species of 97 genera from 29 of the 31 tribes recognized by Polhill. Seeds were sectioned freehand, coated, then viewed by SEM. The tracheid bar is quite uniform in its general features throughout the subfamily, although differences in size and shape of both the bar and the tracheoids were found. Eight species from tribes considered to be among the primitive elements of the subfamily exhibited three variant forms: horizontal tracheary elements instead of the usual bar (2 species), tracheid bar with subtending but separate vascular bundle (1 species), and the tracheid bar with fused horizontal tracheary elements (5 species). Bordered pits of individual cells in the tracheid bar virtually always lacked a membrane and had smooth, warty, or variously elaborate vestures on the border. This appears to be the first report of vestured pits other than in secondary xylem. With some exceptions, bordered pits tended to be vestured in primitive tribes, warty in intermediate tribes, and smooth or only slightly warty in the most advanced tribes.
HETEROCHROMATIN BANDING IN BOYKINIA, HEUCHERA, MITELLA, SULLIVANTIA, TIARELLA, AND TOLMIEA (SAXIFRAGACEAE)
Authors: Soltis Douglas E.
Published: January 2018

Karyotypic differences were sought among species of Boykinia, Heuchera, Mitella, Sullivantia, Tiarella, and Tolmiea utilizing a modification of the Hy‐banding technique. Prominent centromeric and some telomeric heterochromatin banding was observed. Boykinia aconitifolia and species of Sullivantia possess an identical banded karyotype, while four species of Heuchera, Mitella diphylla, Tiarella cordifolia, and Tolmiea menziesii (the latter at the tetraploid level) are characterized by a second, slightly different banded karyotype. In Sullivantia, Giemsa C‐banding stains the same chromosomal regions revealed by Hy‐banding. Larger amounts of heterochromatin are present in chromosomes of species of Heuchera, Mitella, Tiarella, and Tolmiea than in chromosomes of Sullivantia species and Boykinia aconitifolia. These karyological observations confirm generic relationships and demonstrate the systematic applicability of chromosome banding techniques to plants with very small chromosomes.
DISTRIBUTION OF DIURNAL ACID METABOLISM IN THE GENUS ISOETES
Authors: Keeley Jon E.
Published: January 2018

Previous studies have revealed a crassulacean acid metabolism‐like pathway in the submerged aquatic Isoetes howellii (Isoetaceae). A survey of 11 other species in this largely aquatic genus showed all had diurnal fluctuations in titratable acidity and malic acid concentration. The magnitude of the diurnal fluctuation in titratable acidity varied from 119 (μeq g–1 fresh weight) for I. bolanderi to 44 for I. engelmanni. Although these species were grown under similar conditions in a greenhouse, it is questionable whether or not any significance can be attached to observed species specific differences in magnitude of diurnal acid fluctuation. This is suggested by a single species comparison of plants in the field with greenhouse grown plants which indicated nearly as much variation in magnitude of acid fluctuations as observed across all species in the greenhouse. Much of this variation may be due to seasonal differences. Substrate appears to have very little effect on magnitude of acid fluctuations. Since this survey covered most of the range of the latitudinal, elevational, habitat, and morphological variation in the genus, it is likely that diurnal acid metabolism will prove to be common in the genus Isoetes.
DEVELOPMENT AND STRUCTURE OF THE VASCULAR CONNECTION BETWEEN THE PRIMARY AND LATERAL ROOT OF LYCOPERSICON ESCULENTUM
Authors: Byrne John M. , Byrne John M. , Emmitt David P.
Published: January 2018

The primary xylem connection between the diarch parent root and the diarch lateral root was derived from the pericycle and stelar parenchyma. Early in lateral root development stelar parenchyma that was positioned between the parent xylem and the primordium divided transversely. These transverse divisions produced a plate of cells, most of which subsequently differentiated into vessel element connectors. After emergence of the lateral root, xylem maturation began in the stelar vessel element connectors and maturation proceeded acropetally into the lateral root. Protoxylem of the lateral root was connected to the metaxylem of the parent root via stelar vessel element connectors. The circular phloem connection was pericyclic in origin. Axial phloem connections which vascularized the lateral root were established with sieve tube elements of both parent phloem poles. Maturation of the phloem connection occurred prior to lateral root emergence. Transaxial phloem, positioned in arches above and below the lateral root vascular cylinder, was derived from the pericycle; and each arch consisted of three to four sieve tube elements. No transfer cells were found in the transaxial phloem.
SEPTAL PLUGS IN A GREEN ALGA
Authors: Brawley Susan H. , Sears James R.
Published: January 2018

Septal plugs, resembling those found in red algae, occur in the transverse wall between all cells in a newly discovered marine green alga, Pilinia earleae Gallagher & Humm.3 No plasmodesmata traverse the cross‐wall, and the septal plug blocks cytoplasmic continuity between cells. The septal plug consists of an electron‐translucent core bordered at each end by two electron‐opaque caps. Cytochemical procedures demonstrate that the plug consists of protein and polysaccharide, but lacks peroxidase. The outer cap is highly proteinaceous while the inner cap is composed primarily of polysaccharide. The plug core is not routinely stained by Coomassie Blue but it is pronase sensitive and probably proteinaceous. Historically, septal plugs have been considered unique to the red algae and the fungi, but ultrastructural and biochemical data provide no support for derivation of the septal plug in this green alga from a symbiotic relationship. The discovery of septal plugs in a green alga makes the hypothesis of an independent origin of this structure in a number of plant groups more likely.
ULTRASTRUCTURAL STUDY OF CAMELLIA JAPONICA POLLEN TREATED WITH MYRMICACIN, AN ANT‐ORIGIN INHIBITOR
Authors: Nakamura Sumio , Miki‐Hirosige Hisako , Iwanami Yozu
Published: January 2018

The germination and tube growth of Camellia japonica pollen were stopped on a myrmicacincontaining (50–200 ppm) culture medium, but were restored again when the pollen grains were transferred to a myrmicacin‐free medium. Myrmicacin inhibits the movement of Golgi vesicles utilized for the formation of the callose layer in the pollen grain before the germination, and the growing tube tip wall.
A MORPHOMETRIC STUDY OF THE ULTRASTRUCTURE OF ECHINOCEREUS ENGELMANNII (CACTACEAE). V. COMPARISON WITH THE SHOOT APICAL MERISTEMS OF TRICHOCEREUS PACHANOI (CACTACEAE)
Authors: Mauseth James D.
Published: January 2018

Relative and absolute volumes of organelles in shoot apical meristems of Trichocereus pachanoi are reported and compared with similar values published for three other species in two other families. Cellular ultrastructure varies from one meristem zone to another and from one species to another. It is concluded that there is no single, critical meristem ultrastructure, but rather meristem ultrastructure reflects meristem metabolism and is consequently unvarying within a species at a particular stage of development, but varies among species and as morphogenetic activity changes. Differences appear to correlate well with shoot growth rate and with phylogenetic relatedness.
STUDIES OF SEED FERN POLLEN: DEVELOPMENT OF THE EXINE IN MONOLETES (MEDULLOSALES)
Authors: Taylor Thomas N. , Rothwell Gar W.
Published: January 2018

Monoletes pollen extracted from the seed fern synangium Dolerotheca sclerotica Baxter illustrate four stages in the development of the sporoderm. In the first stage the grains are up to 100 μm long and possess an apparent homogeneous exine in which there is little differentiation between the nexine and sexine. Numerous nexine lamellae and the initiation of sexine expansion mark stage 2 in exine ontogeny. Further expansion of the sexine continues in the third stage until the ratio between the nexine and sexine is approximately 1:5. The final stage in maturation of the sporoderm shows an expanded alveolate sexine with some of the sporopollenin units broken and disorganized. It is at this stage of development that nexine lamellae are most prominent. The formation of sporoderm layers in the fossil grains is compared with pollen grain development in living cycads (Cycadophyta) and a model proposed to account for the apparent early formation of nexine lamellae in Monoletes. The evolution of exine components in early pollen types is discussed.
INFLORESCENCE ARCHITECTURE: HOW FLOWER NUMBER, ARRANGEMENT, AND PHENOLOGY AFFECT POLLINATION AND FRUIT‐SET
Authors: Wyatt Robert
Published: January 2018

The adaptive significance of different types of inflorescences in flowering plants has been largely ignored. The few published studies investigating adaptive aspects of floral displays suggest that numbers of flowers and their arrangement in space and time determine levels of pollination and fruit‐set in natural populations. The frequently conflicting demands placed on inflorescence architecture have led to an evolutionary compromise that maximizes the genetic contribution of an individual plant to the next generation. These conflicting demands include pollinator attraction vs. ovary competition, fruit dispersal vs. fruit predation, and reproductive vs. vegetative resource allocation. In most cases, the inflorescence size most successful in fruit production is also the most frequent in natural populations. In addition to quantity of offspring, inflorescence architecture affects, and in turn is affected by, the quality of offspring that result from selfing vs. outcrossing.
INITIATION AND DEVELOPMENT OF ROOTS IN JUVENILE AND MATURE LEAF BUD CUTTINGS OF FICUS PUMILA L.
Authors: Davies F. T. , Lazarte J. E. , Joiner J. N.
Published: January 2018

Adventitious root formation (ARF) was studied in woody leaf bud cuttings of Ficus pumila L., creeping fig. Juvenile cuttings rooted easily, whereas only mature cuttings treated with indole‐3‐butyric acid (IBA) attained any rooting success. In the rooting process, both juvenile and mature material exhibited dedifferentiation of phloem ray parenchyma, root initial formation, primordia differentiation, and root elongation. The early stages of adventitious rooting were most critical since few primordia were observed in mature controls. The stages leading up to root primordia differentiation and elongation occurred more rapidly in IBA‐treated juvenile vs. mature cuttings; however, time differences in both types between first observable roots and maximum rooting were comparable. Root primordia differentiated from basal callus of some cuttings, but neither these nor the few primordia in mature controls elongated into well‐developed roots. Anatomical differences between the juvenile and mature material did not account for rooting disparity, nor did presence of perivascular fibers, sclereids, and laticifers retard rooting.
DEVELOPMENT OF NORMAL AND SEEDLESS ACHENES IN CICHORIUM INTYBUS (COMPOSITAE)
Authors: Ochan Michael A. , Palser Barbara F.
Published: January 2018

Cross‐ and partially cross‐pollinated capitula of Cichorium intybus (Compositae, Lactuceae) were examined for a study of normal and seedless fruit development respectively. Embryos develop according to the Asterad pattern, and the free‐nuclear endosperm becomes cellular 15–17 hrs after pollination. A zone of disorganized cellular material surrounds the embryo sac at anthesis, and, in normal achenes, this zone expands as the seed develops. Initially the developing seed elongates and comes into contact with the top of the ovary by 48 hrs. In contrast to this pattern, the ovule in developing seedless achenes degenerates within 72 hrs. Irregularities, such as an abnormally proliferating endothelium, embryo formation without endosperm, and endosperm formation without an embryo often accompany this degeneration. Differentiation of the pericarp in seeded achenes begins between 48 and 72 hrs, starting at the apex and proceeding basipetally; in seedless fruits the process is similar though initiated somewhat later. The normal pericarp at maturity exhibits a pigmented exocarp, a broad mesocarp of thick‐walled lignified cells, and a tenuous endocarp. In seedless achenes the fruit coat is similar except that the exocarp is colorless and the cells of the mesocarp are relatively small.
THE ULTRASTRUCTURE OF THE SALT GLANDS OF CYNODON AND DISTICHLIS (POACEAE)
Authors: Oross J. W. , Thomson W. W.
Published: January 2018

The epidermal salt glands of the grasses Cynodon and Distichlis consist of a small outer cap cell and a large, flask‐shaped basal cell. The wall of the basal cell is contiguous with those of the adjacent epidermal cells and underlying mesophyll cells. The basal cell is connected symplastically with all adjoining cells via plasmodesmata. The outer, protruding portion of the glands is covered by a cuticle continuous with that of the adjoining epidermal cells. However, the lateral cell walls of the glands are not incrusted by this cuticle. The cap cell wall has a loose, mottled appearance quite different from the compact striated appearance of the basal cell wall. The cap cell is characterized by dense cytoplasm containing many organelles and a varying number of small vacuoles. The basal cell cytoplasm is distinguished by the presence of an intricate system of paired membranes that are closely associated with mitochondria and microtubules. These membranes are infoldings of the plasmalemma that originate adjacent to the wall separating the cap and basal cells. The space enclosed by the paired membranes, therefore, is an extracellular channel that is open only in the direction of secretory flow. The consistent orientation of this system of paired membranes suggests that it represents a structural specialization which is directly and functionally involved in the secretory process. The close association of mitochondria and microtubules with the paired membranes implies that these structures are also functionally related to the secretory process. Finally, the results of this study indicate that these glands are ultrastructurally similar to those of Spartina and that the glands of these three grasses are structurally distinct from those of dicotyledonous plants.
VESSEL STRUCTURE OF GNETUM AND THE ORIGIN OF ANGIOSPERMS
Authors: Muhammad A. F. , Sattler R.
Published: January 2018

Vessel structure of Gnetum gnemon L. and G. montanum Mgf. was investigated by means of light microscopy (brightfield, phase contrast and Nomarski interference optics), and scanning and transmission electron microscopy. The gyres of the first order framework are compound, consisting of three elementary strands (subunits). Pits ranging from slit‐shaped to circular are formed either between the elementary strands of one gyre or between adjacent gyres. (Compound gyres are also figured for Alnus and lens‐shaped pits in annular‐helical elements are demonstrated for Juglans and Salix). In the two species of Gnetum studied, scalariform pits occur in addition to the well known circular pits. Scalariform perforation plates are present besides scalaroid, foraminate, and simple perforation plates as well as intermediates between the above types. These findings invalidate a common argument against the gnetalean origin of angiosperms, namely that pits and perforations of Gnetum are totally unlike those of primitive angiosperms and that therefore Gnetum must be ruled out as a potential ancestor of angiosperms. Variation in vessel structure of Gnetum is so great that it encompasses the typically circular pits of the coniferopsids as well as patterns of pits and perforation plates found in angiosperms. Some photographs of angiospermous taxa are interspersed with those of Gnetum to indicate the striking similarities. The determination of the patterns and shapes of pits and perforations is discussed in terms of four parameters: 1) the ratio of the width of the cell face to the distance between the gyres; 2) the types and distribution of the second order framework; 3) the stretching and distortion of gyres and/or second order framework; and in the case of perforations, 4) the pattern of wall and bar breakdown. Since the first parameter may change continuously, a continuum between circular pits or perforations and scalariform ones may occur. Such a continuum actually exists in Gnetum as well as in angiosperms. Patterns due to the other three of the above parameters are also formed in similar ways in both Gnetum and angiosperms. These similarities may, of course, be interpreted as the result of parallel evolution. However, when one considers the large number of angiospermous features of Gnetum, one is led to ask whether Gnetum may not have been close to the ancestral stock of all or at least some taxa of angiosperms.
VARIATION IN AVERAGE SEED SIZE AND FRUIT SEEDINESS IN A FRUIT CROP OF A GUANACASTE TREE (LEGUMINOSAE: ENTEROLOBIUM CYCLOCARPUM)
Authors: Janzen D. H.
Published: January 2018

A detailed examination of the ordinary 1980 fruit crop of an ordinary large adult guanacaste tree (Enterolobium cyclocarpum) in Guanacaste Province, Costa Rica (1980) shows that for fruits with about 6‐16 seeds (range, 1‐18 seeds per fruit) there is about ***1 g dry weight fruit tissue per seed (seeds averaging about 820 m each). Fruits that have about 1‐5 seeds on average have 1.5‐3 times as much dry fruit tissue per seed as do the seed‐rich fruits, and also contain seeds that weigh about 8% more on average than the seeds in the seed‐rich fruits. The average seed weight per fruit was found to decrease slightly if all sizes of fruits are considered, but to remain essentially constant over the range of 7‐16‐seeded fruits. This category contained 78% of the fruits. These findings suggest that different parts of the seed crop may end up in different dispersers and dispersers with different preferences for fruit seediness and tolerances for seed size may remove different portions of the seed crop.
POLLEN MORPHOLOGY IN NORTH AMERICAN SPECIES OF TRILLIUM
Authors: Takahashi Masamichi
Published: January 2018

The pollen morphology and tapetal membranes of 17 species of Trillium from North America have been examined by scanning and transmission electron microscopy. The pollen grains of the genus are consistently spherical and inaperturate. The exine is unstratified and ultra‐thin. Five types of exine structure are recognized, namely, echinate‐, corrugate‐, granulate‐, verrucate‐ and spinulate‐type, based on the variations in the components of the exine. The granulate‐type is the most common and is divided into six subtypes. The features of tapetal membranes also vary in relation with the variation of the exine structures. This study demonstrates the potential of palynological evidence in assessment of taxonomic relationships within the genus.
SHORT‐WAVE ULTRAVIOLET LIGHT CLOSES LEAF STOMATA
Authors: Wright Lawrence A. , Murphy Terence M.
Published: January 2018

The irradiation of detached tobacco leaves with short‐wave ultraviolet light (254 nm, 600 Jm‐2) causes guard cells to lose potassium, and stomata to close, within 30 minutes. Stomatal closing has been correlated with an increased rate of senescence of detached oat leaves (Thimann and Satler, Proc. Natl. Acad. Sci. USA 76: 2295, 1979). Thus, closing of stomata may account for the acceleration of senescence that is induced by ultraviolet light.
WIND STRESS AND ELFIN STATURE IN A MONTANE RAIN FOREST TREE: AN ADAPTIVE EXPLANATION
Authors: Lawton Robert O.
Published: January 2018

Physiognomic trends in a population of Didymopanux pittieri Marchal (Araliaceae), a dominant shade‐intolerant tree of the elfin forests of Costa Rica, are related to a gradient of wind stress. Wind stress in this forest increases with proximity to ridgecrests. For a given tree height, trunk girth increases with proximity to the ridgecrest. At the same time twig slenderness decreases. These responses are produced in part by slower elongation of twigs which are exposed to stronger winds. These trends suggest that elfin stature is an adaptive response to greater wind stress along exposed ridges.
NATURAL HISTORY OF GUACIMO FRUITS (STERCULIACEAE: GUAZUMA ULMIFOLIA) WITH RESPECT TO CONSUMPTION BY LARGE MAMMALS
Authors: Janzen Daniel H.
Published: January 2018

Guazuma ulmifolia (Sterculiaceae) is a shrubby tree common in the Central American lowlands in deciduous forest, and in the pastures cut out of it. The tree flowers in April‐May (end of dry season) and bears dormant, incompletely expanded fruit until the end of the rainy season (November‐December), at which time the fruits rapidly expand and ripen to fall during the first half of the dry season. The fruits are avidly eaten by livestock. A horse may consume 300‐2, 100 fruits in a meal, does not distinguish between fresh fruits that have been attacked by bruchid beetles and intact fruits, and defecates large numbers of viable seeds 2‐5 days later. Moistened seeds germinate readily in horse dung or in soil. There are hard letter‐shaped structures in the mesocarp of the fruit wall and a very hard core, both of which are large enough to function in preventing complete occlusion of the molar mill, an act which would crush the soft small seeds. Guazuma ulmifolia (guacimo) is probably one of the trees whose fruits would have been eaten and the seeds dispersed by the Pleistocene herbivorous megafauna that once roamed Central America.
SYSTEMATICS OF TRIPSACUM DACTYLOIDES (GRAMINEAE)
Authors: deWet J. M. J. , Harlan J. R. , Brink D. E.
Published: January 2018

Tripsacum dactyloides (L.) L. extends across the range of this genus from about 42°N to 24°S latitude in the New World. It is recognized to include T. dactyloides var. dactyloides (North America), var. meridonale deWet et Timothy (South America), var. hispidum (Hitchc.) deWet et Harlan comb. nov. (Mesoamerica) and var. mexicanum deWet et Harlan var. nov. (Mesoamericana). The genus is divided into sections Tripsacum and Fasciculatum. Mesoamerican members of section Tripsacum are classified into T. bravum Gray, T. dactyloides (L.) L., T. intermedium deWet et Harlan spec, nov., T. latifolium Hitchc., T. manisuroides deWet et Harlan spec. nov. and T. zopilotense Hern,*** et Randolph. A key to the species of section Tripsacum is presented.
THE FLORAL AND EXTRA‐FLORAL NECTARIES OF PASSIFLORA. II. THE EXTRA‐FLORAL NECTARY
Authors: Durkee Lenore T.
Published: January 2018

Extra‐floral nectaries of nine species of Passiflora were studied with light and electron microscopy prior to and during secretion. There is no evidence of ER or Golgi participation in the secretion of nectar. The vascular tissue supplying the nectary is characterized by companion and phloem parenchyma cells which are usually larger than the sieve elements, a configuration similar to that found in leaf minor veins. In the petiolar nectaries, large masses of membrane‐bound protein are commonly found in these cells. This protein is absent in laminar nectaries.
MORPHOLOGICAL DIFFERENTIATION OF PROBOSCIDEA PARVIFLORA SSP. PARVIFLORA (MARTYNIACEAE) UNDER DOMESTICATION
Authors: Bretting P. K.
Published: January 2018

Aboriginal groups in the southwestern United States have grown Proboscidea parviflora ssp. parviflora for basketry fiber. It has been hypothesized that cultivated plants of this subspecies with white seeds and long‐clawed fruit (which provide the fiber) have been domesticated. Cluster, multiple discriminant, and unvariate statistical analyses presented here show that the putative domesticate is indeed morphologically distinct from “wild” plants. It has clearly been domesticated, and has diverged from wild populations to the extent that a new variety, var. Hohokamiana, is proposed for the domesticate. Wild and domesticated varieties differ especially in seed color, rostrum, crest, style, and anther lengths. Most characteristics of the wild variety seem to be genetically dominant to those of the domesticate, which may account for absence of a weedy form intermediate between the wild and domesticated varieties. The wild variety is morphologically more variable than the domesticate, probably because of its broader geographical range and its intergradation with another subspecies. Ethnological data and the variational patterns reported here suggest that the domesticate originated in southern Arizonanorthern Sonora, but probably not north of that region.
DYNAMICS OF GENE FLOW IN AN EXPERIMENTAL POPULATION OF CUCUMIS MELO (CUCURBITACEAE)
Authors: Handel Steven N.
Published: January 2018

Gene flow in an experimental garden of Cucumis melo (Cucurbitaceae), the cultivated muskmelon, was measured by placing plants carrying a dominant gene (green cotyledons) in the center of an 18 × 18‐m field of recessive plants (yellow cotyledons). At the end of the growing season, all fruits were collected, and seeds planted for analysis of the progeny. The 123 fruits yielded 41,875 seedlings whose genotypes were recorded. Gene flow decreased with increasing distance from the central plot, while the variance increased. The decrease in frequency of the green gene did not follow a leptokurtic pattern over the distance measured, and there was a marked asymmetric and patchy pattern of gene flow in the field. The directionality contributed to a bimodal pattern of gene frequencies among fruits at the edges of the field, some fruits with no green seedlings, some with many. Bumblebee movements were recorded during 4,296 flower visits in an identically arrayed melon field. Bees usually moved to very nearby plants and visited only a few flowers on any one plant. This suggests that pollen carryover from the central patch out was quite high in the test garden. These findings show that local gene flow patterns in plant populations may be complex, and do not always follow regular and symmetrical models. The complex arrangement of progeny genotypes, when acted upon by local selective forces, may contribute to small‐scale differences often seen in plant populations.
STUDIES OF PALEOZOIC MARATTIALEANS: THE MORPHOLOGY AND PROBABLE AFFINITIES OF TELANGIUM PYGMAEUM GRAHAM
Authors: Millay M. A.
Published: January 2018

Telangium pygmaeum Graham is known from Upper Pennsylvanian coal balls from the Calhoun coal mine (Illinois). The species was described as possessing radial synangia consisting of 3‐5 sporangia fused laterally for about f13 their length. Synangia were believed to be sessile and borne terminally or laterally on a branching rachis without lamina. Examination of new coal ball material of the same age indicates that the synangia are borne abaxially on the pinnules of a compound frond with the anatomy of a Psaronius leaf (Marattiales). Synangia are sessile and borne in two rows, one on either side of the pinnule midrib, under the unbranched lateral veins. Synangia are radial, 0.6 mm in diam, and consist of a ring of thin‐walled sporangia fused to near their apices prior to dehiscence, but separating on dehiscence to release spores along their inner midline. Spores are spherical, trilete, 30‐48 μm in diam, with a granulate ornamentation. The new genus Araiangium is proposed for this material based on the organization of the sessile thin‐walled synangia. Araiangium is compared with other marattialean genera with sessile synangia (Acaulangium, Acitheca), and with the pedicellate synangia of various species of Scolecopteris. Criteria used in the delimitation of genera in Paleozoic anatomically preserved marattialean fertile foliage are discussed.
LEAF ANATOMY OF TISSUE‐CULTURED LIQUIDAMBAR STYRACIFLUA (HAMAMELIDACEAE) DURING ACCLIMATIZATION
Authors: Wetzstein Hazel Y. , Sommer Harry E.
Published: January 2018

Structural changes accompanying the acclimation process were observed in leaves of sweetgum, Liquidambar styraciflua, using light and transmission electron microscopy (TEM). Comparisons were made of leaves obtained from tissue culture, plantlets acclimated after transfer from the in vitro environment to soil, and field grown trees. Leaves of cultured plantlets lacked a differentiated palisade parenchyma and had spongy parenchyma interspersed with large air spaces. Field grown leaves showed distinct palisade and spongy tissues and a high cell density. New leaves from acclimated plantlets showed an elongation of the upper mesophyll with fewer intercellular spaces than cultured plants. Cells from leaves from in vitro plantlets had large vacuoles, limited cytoplasmic content and flattened chloroplast with an irregularly arranged internal membrane system. Acclimated and field leaf cells had a greater cytoplasmic content than cultured leaves, with the former having more dominate vacuoles. Chloroplasts had evident grana. Acclimated and field leaves had a well developed cuticle unlike leaves from culture.