bluuebunny/crossref_metadata_2025 huggingface dataset:
TISSUE CULTURE DERIVED CROSSING BARRIERS
Authors: Hughes Karen Woodbury
Published: January 2018

Tobacco plants derived from herbicide (paraquat)‐resistant cell lines and from wild type (non‐resistant) cell lines were self‐pollinated and crossed with sexually‐derived wild type plants. Analysis of the seed germination frequencies from these crosses indicated that seed viability and thus the ability of tissue culture‐derived plants to intercross with sexually derived plants was reduced. Partial reduction was observed when tissue culture‐derived plants were the female parent. Significant reduction in ability to intercross was observed when tissue culture‐derived plants were the male parent. Self pollinations of tissue culture‐derived plants and crosses between tissue culture‐derived plants, both wild type and mutant, did not show the presence of a crossing barrier. The crossing barrier (reduction of seed viability) is due to either: 1) failure of a fertilized ovule to undergo embryonic development, or 2) failure of pollen to fertilize ovules. It is apparently not due to in viable pollen. A possible explanation of the crossing barrier is that genetic changes accumulate as a result of the tissue culture process which reduces the ability of tissue culture‐derived plants to cross with sexually‐derived plants. Since tissue culture‐derived plants are able to intercross with each other and produce viable seed, the genetic changes would be similar in all of our tissue culture‐derived lines, regardless of mutant or wild type origin.
STABILITY AND INSTABILITY IN PLANT COMMUNITIES FOLLOWING FIRE
Authors: Anderson Roger C. , Brown Lauren E.
Published: January 2018

Tree species composition and density were monitored in closed oak‐hickory forest and forest‐prairie edge for a period of five years after a prescribed burn. In the closed forest, tree stem density declined markedly following the burn. Tree basal area and density decreased from 17.5 m2/ha and 630 trees/ha in the preburn sample to 12.0 m2/ha and 310 trees/ha five years later. In contrast, on the forest‐prairie edge, tree basal area and density increased slightly during the same time period from 3.0 m2/ha and 117 trees/ha to 5.2 m2/ha and 172 trees/ha. Our data suggest that closed canopy forests in fire susceptible areas accumulate fuels to levels that encourage fires of sufficient intensity to destabilize forest systems and convert them to open forests or savannahs. Conversely, on the forest‐prairie edge, amounts and patterns of fuel accumulation, and species response to burning, are such that fire can be considered to be a factor promoting stability.
PATTERNS OF STAMEN VASCULATURE IN THE ARACEAE
Authors: French James C.
Published: January 2018

A survey of the three‐dimensional organization of stamen vasculature in 100 genera and over 350 species of Araceae was made using clearings. The Araceae exhibit highly varied stamen vasculature, with three main patterns: 1) vascular bundles unbranched, 1–3 per stamen, 2) forked bundles in some or all stamens, 3) anastomosing vascular systems with several to many bundles entering a single stamen. Three major groups of taxa in the family can be recognized on the basis of their predominant pattern of stamen vasculature. Virtually all genera with bisexual flowers (most Pothoideae, Monsteroideae, Calloideae, Lasieae) have unbranched bundles, one per stamen, except two to three in some species of Holochlamys, Spathiphyllum, and Scindapsus. Forked stamen bundles are virtually restricted to and occur nearly throughout the monoecious Lasioideae, Philodendroideae, Colocasioideae and among certain Aroideae (sensu Engler), including tribes Arophyteae, Spathicarpeae (Asterostigmateae) and Protareae. No forked bundles were found in tribe Areae (Aroideae), except Theriophonum indicum or any Araceae with bisexual flowers, except two species of Cyrtosperma. Anastomosing systems are virtually limited to members of tribe Areae with larger stamens, such as Arum, Helicodiceros, Eminium and Dracunculus species. A similar pattern occurs in some Amorphophallus, but other patterns occur as well. The distributions of forked bundles and anastomosing systems in the family are notable because they are both highly congruent with Philodendroideae‐Colocasioideae, and Aroideae, respectively, in Grayum's new system for the family. Virtually all of the genera with forked bundles are grouped together in the Philodendroideae‐Colocasioideae. All of the genera with anastomosing systems are in the Areae, including the complex and variable Amorphophallus, which has an uncertain systematic placement.
EFFECT OF SEED SIZE ON SEEDLING SUCCESS IN THREE SPECIES OF SESBANIA (FABACEAE)
Authors: Marshall Diane L.
Published: January 2018

Variation in seed size may produce variation in seedling fitness, but the relationship is not simple. Differences in seed size within and among species may not have the same effects. We examined effects of differences in seed size within and among three species of Sesbania, S. macrocarpa, S. drummondii, and S. vesicaria, on seedling emergence and growth in the greenhouse and the field. Of the three species, the largest‐seeded species, S. vesicaria, produced the largest, longest‐lived seedlings in both the greenhouse and the field. Even though plant size differed, annual S. macrocarpa produced the same seed mass as annual S. vesicaria in the greenhouse. Within‐species effects were less clear. In the greenhouse, S. vesicaria seedlings grown from large seeds remained largest until maturity, but the other species did not exhibit this effect. Some persistent within‐species effects of seed size differences on height were observed in the field in 1981, but not in 1980, suggesting that field conditions increase the importance of seed size differences. Unscarified S. drummondii seeds germinated before seeds of the two annual species. Within species, larger seeds of the annuals and smaller seeds of the perennial germinated first. Differences among the species in the importance of seed size to seedling fitness may allow the species to have different patterns of regulation of reproduction in response to stress. Sesbania vesicaria showed the largest within‐species effects of seed size and has the lowest plasticity in seed size, suggesting that patterns of plasticity have been selected such that the most important component of yield varies least.
ON THE NATURE OF INTRA‐ AND INTERSPECIFIC INCOMPATIBILITY IN ULMUS
Authors: Bob C. F. , Redmond B. L. , Karnosky D. F.
Published: January 2018

Efforts to introduce Dutch Elm Disease resistance into the American elm (Ulmus americana L.) through breeding with Asian elms has been hampered by sexual incompatibility. Controlled pollinations of Ulmus americana and the Siberian elm (Ulmus pumila L.) were studied in detail to gain insight into the nature of this incompatibility. Microscopic observations revealed that germination and early pollen tube growth were inhibited on the stigmatic surface following both intra‐ and interspecific incompatible pollinations. Both qualitative and quantitative differences in pollen inhibition on the stigmatic surface indicated that the inhibition may involve the action of an inhibitory substance. Detailed observations on callose deposition indicated that this β‐1,3 glucose polymer may implement the inhibition.
EVOLUTION OF POLYSPORANGIATE ANTHERS IN ONAGRACEAE
Authors: Tobe Hiroshi , Raven Peter H.
Published: January 2018

The microsporogenous tissue of at least some species of all 17 genera of Onagraceae is divided by transverse septa composed only of tapetum or of both tapetum and parenchyma. The presence of these septa apparently constitutes a distinctive characteristic of the family. In Calylophus sect. Salpingia, Gaura, Clarkia, Heterogaura, and two unrelated species of Ludwigia, the septa are transverse and mostly parenchymatous. In Hauya and Calylophus sect. Calylophus, similar transverse septa together with vertical ones divide the sporogenous tissue into many small spheroidal or ellipsoidal packets. The condition in which occasional tapetal septa divide the sporogenous tissue is clearly the ancestral one in Onagraceae. Polysporangiate anthers divided by parenchymatous septa have evolved independently at least twice each in the branches leading to Ludwigia and to all other members of the family, for a total of no less than four times. Based on this feature and the unique pattern of histogenesis of their integuments, Hauya (despite its retention of many plesiomorphic features), Calylophus, and Gaura may well be directly related to one another.
SEEDLING ESTABLISHMENT IN FORESTS AFFECTED BY TEPHRA FROM MOUNT ST. HELENS
Authors: Antos Joseph A. , Zobel Donald B.
Published: January 2018

Seedling density on permanent plots at five sites was monitored for the first four summers following the deposition of 4.5 to 15 cm of tephra from the 1980 eruption of Mount St. Helens. Because the old‐growth forests at the sites were not destroyed by the volcanic eruption, the plots were under a normal tree canopy. Almost no seedlings established in 1980. By 1983 tree seedling density exceeded 35 m−‐2 at all sites. Tsuga heterophylla seedlings were most common, with Abies amabilis seedlings next in abundance. A dense layer of small trees may develop on the tephra and long‐term forest dynamics could be affected. There was no successful invasion by species not already present in the stands. Seedlings of some forest herbs, especially Tiarella trifoliata, were common, but many other common forest species produced none. It is still problematical if or when these species will return to areas of the forest from which they were extirpated.
FERTILIZATION DYNAMICS AND PARENTAL EFFECTS UPON FRUIT DEVELOPMENT IN RAPHANUS RAPHANISTRUM: CONSEQUENCES FOR SEED SIZE VARIATION
Authors: Mazer Susan J. , Snow Allison A. , Stanton Maureen L.
Published: January 2018

Seed weight varies significantly within and among fruits of wild radish (Raphanus raphanistrum). To determine sources of this variation, we studied fertilization and seed development following controlled pollinations. Within fruits, central ovules were fertilized prior to distal ovules and attained greater seed size. Ninety‐seven percent of the variation in mean seed wt per fruit was explained by an analysis of variance incorporating parental effects, pollination date, and the number of seeds per fruit. We document strong maternal effects on the number of ovules per ovary, the number of fertilized ovules per ovary, the number of seeds per fruit, and mean individual seed wt per fruit. Across females, pollen donor had a slight but significant effect on seed wt; no paternal effects on fertilization rate, zygote number, or seed number per fruit were detected. Within females, with one exception, pollen donor had no significant effect on these components of seed development. Stronger maternal main effects may be due to donor x recipient interactions, cytoplasmic factors, the genetic inequity within triploid endosperm, and/or strict maternal control over resource allocation. The large maternal effects relative to paternal effects may limit the rate at which natural selection acts on paternal traits expressed prior to seed maturation.
PHOTOSYNTHETIC RESPONSES TO LIGHT IN AN UNDERSTORY HERB, ASTER ACUMINATUS
Authors: Pitelka Louis F. , Curtis William F.
Published: January 2018

Previous studies of the understory herb, Aster acuminatus, have shown that variation among natural patches in ramet growth, reproduction and population dynamics reflects environmentally induced responses to differences in patch light regimes. This set of experiments was undertaken to determine if photosynthetic responses to variation in light could provide a physiological explanation for the observed differences among patches. Ramets were raised in pots under different light regimes in either the field or growth chambers and then were taken to the lab for analyses of photosynthetic light responses. Ramets acclimated to the light conditions they experienced. Low‐light plants had lower maximum photosynthetic rates, light saturation points and light compensation points compared to high‐light plants. These differences were more pronounced for growth chamber‐grown plants than for those from the field. Differences between ramets grown in deep shade and partial sun in the field were greatest early in the season and then became less as photosynthetic rates for all plants declined. Photosynthetic rates were strongly correlated with leaf nitrogen level, and there was no evidence that nitrogen was any more limiting for one treatment compared to others. These results demonstrate a physiological basis for patch differences in growth, reproduction and dynamics.
RELATION BETWEEN MONTHLY GROWTH OF FEROCACTUS ACANTHODES AND AN ENVIRONMENTAL PRODUCTIVITY INDEX
Authors: Nobel Park S.
Published: January 2018

Most productivity studies use destructive harvesting methods, prohibiting continuous plant monitoring under various environmental conditions. Here a nondestructive procedure involving the displacement of areoles from the apex was utilized to study the growth of Ferocactus acanthodes, a common barrel cactus of the Sonoran Desert. Net CO2 uptake measured under controlled conditions of temperature, water, and photosynthetically active radiation in the laboratory was used to indicate how F. acanthodes would respond to field values of these parameters. For example, net CO2 uptake over 24 hr was maximal at day/night air temperatures of 23 C/14 C, the mean annual values in the field, and was approximately halved at 11 C/5 C and 32 C/23 C, the monthly extreme values in the field. An environmental productivity index (EPI), constructed as the product of indices for the three environmental variables, indicated the fraction of maximal CO2 uptake expected. The monthly production of areoles on 33 plants was highly correlated with EPI (r2 = 0.81). Areole production for individual plants, however, tended to be in pulses represented by Fibonacci numbers. EPI predicted an annual stem growth of 8% compared with 9 ± 3% measured previously in the field. Thus, morphological and physiological studies can be usefully combined and applied to indicate field productivity of F. acanthodes and, by extension, of other plants.
PRIMITIVE MIMOSOID FLOWERS FROM THE PALEOCENE‐EOCENE AND THEIR SYSTEMATIC AND EVOLUTIONARY IMPLICATIONS
Authors: Crepet William L. , Taylor David W.
Published: January 2018

Compressed mimosoid inflorescences from a Paleocene‐Eocene boundary locality in western Tennessee are the earliest fossil evidence of the subfamily. The discovery confirms the antiquity of a suite of characters that has been considered primitive based on the comparative morphology of modern mimosoids. The fossil characters are also consistent with the suggested close relationship (ancestral or sister group) between the subfamily Mimosoideae and the Dimorphandra group of the tribe Caesalpinieae (subfamily Caesalpinioideae). These flowers show little change in morphology or size in the basal to Upper Eocene interval.
GEOGRAPHIC DIFFERENCES IN THE SEED GERMINATION OF PAPER BIRCH (BETULA PAPYRIFERA)
Authors: Bevington John
Published: January 2018

The effects of light and temperature on germination of paper birch (Betula papyriferaMarsh.) were examined in seeds from different geographic locations. Under continuous light at 14–18 C northern seed sources germinated more rapidly and achieved higher germination percentages than southern ones. Seed source influenced the range of temperatures over which germination occurred. Northern seeds had a wider temperature range than southern ones due to depression of the low temperature limit in northern seeds. At 15 C, seeds exhibited a photoperiodic‐like response with progressive increases in germination as daily photoperiod was increased. This was not a true photoperiodic effect because seeds responded to the total amount of light rather than to the relative length of light and dark periods. It is suggested that at temperatures near 15 C, this response may be important in preventing fall germination. Prechilling at 3 C promoted subsequent dark germination in most seed sources tested, and northern seeds were much more sensitive to the treatments than southern seeds. In some seeds the prechilling stimulus was lost with protracted storage at 3 C; this was observed in both northern and southern seeds. Prechilling enhanced the seeds’ sensitivity to subsequent light. Although acquisition of the prechilling stimulus does not serve to measure the length of winter in these seeds, the high light sensitivity induced by prechilling probably accelerates spring germination. Northern seeds typically had thinner, more translucent pericarps than their southern counterparts.
SPOROCYTIC CONTROL OF SPORE WALL PATTERN IN LIVERWORTS
Authors: Brown Roy C. , Lemmon Betty E. , Renzaglia Karen S.
Published: January 2018

Extracellular material preferentially deposited in the sporocyte wall during meiotic prophase serves as an exine precursor in development of the distinctively patterned spore exines of the liverworts Haplomitrium hookerii and Pallavicinia lyellii. This unusual occurrence of prepat‐terning of the exine in prophasic sporocytes provides clear structural evidence that control of wall patterning is an integral part of a genetic program triggered in the sporocyte and, at least in some cases, does not depend upon genetic transcription in the haploid nucleus following meiosis.
QUANTITATIVE PHENOLOGY AND LEAF SURVIVORSHIP OF RHODODENDRON MAXIMUM IN CONTRASTING IRRADIANCE ENVIRONMENTS OF THE SOUTHERN APPALACHIAN MOUNTAINS
Authors: Nilsen Erik Tallak
Published: January 2018

Seasonal plant growth patterns were compared forRhododendron maximumL. in two contrasting subcanopy environments. The two subcanopy, above ground environments differed only in their quantity of irradiance by virtue of the relative dominance of evergreen or deciduous trees in the canopy. A third site had no canopy influence. Overall growth (shoot elongation, woody increment, leaf production) was maximized under the open (BMO) and deciduous dominated canopy (PCD). The leaf pool was significantly smaller under the evergreen dominated canopy (PCE) but average leaf area per leaf was slightly larger at PCE. Individual age‐specific leaf cohorts, identified from shoot morphology, indicated increased leaf survivorship with a decreased irradiance environment. Leaf production was synchronous and rapid (1 week), followed by three weeks of leaf expansion, which created the even‐aged leaf cohorts. Wood growth (diameter increment), in contrast, continued through the beginning of the winter. Reproductive effort increased with increasing irradiance environment. Significant variation in growth was observed between canopy shoot types at all three research sites. The significance of these phenological patterns is discussed in view of the variable subcanopy environment of southwestern Virginia.
EFFECT OF AGING ON FLOWERING OF THE AXILLARY BUDS OF PHARBITIS NIL
Authors: Owens Vivian , Paolillo Dominick J.
Published: January 2018

In Pharbitis seedlings, aging is associated with definite trends in the pattern of flowering of the axillaries: 1) the locus of maximum flowering is displaced continuously upward, 2) there is a continuous loss of responsiveness to induction from the base of the plant, upward, 3) flowering of the axillaries is suppressed in general when the terminal bud fails to flower, and 4) flowering at the distal nodes regresses when the terminal bud fails to flower. Phenomena 1 and 2 start at the base of the plant and move progressively upward, whereas 3 and 4 are tied to the possibly rhythmic responses of the terminal buds to floral induction, with aging.

Buds at axils that form after induction are capable of flowering. Buds at nodes that flower maximally range in development from those not visible with a stereomicroscope to those with enlarging apices ready to form the first leaf primordia at the time of induction. Axillaries that have formed leaf primordia fail to flower in response to one inductive night.
MORPHOLOGY AND ULTRASTRUCTURE OF EMBRYOGENIC CELL SUSPENSION CULTURES OF PANICUM MAXIMUM (GUINEA GRASS) AND PENNISETUM PURPUREUM (NAPIER GRASS)
Authors: Karlsson Sylvia B. , Vasil Indra K.
Published: January 2018

Morphological and ultrastructural changes during the growth of embryogenic cell suspension cultures of Panicum maximum and Pennisetum purpureum have been studied. The suspensions consist almost entirely of cell aggregates of 50–75 embryogenic cells. The cell aggregates vary in size from 90–400 μm in P. maximum and from 70–340 μm in P. purpureum. Following the period of exponential growth starch grains gradually disappear and vacuolation increases. Ten to 16 days after subculture, P. maximum cells enlarge and separate from each other, and organized embryo‐like structures appear. Ultrastructural studies show that the cell aggregates are made up of discrete, individual groups of 2–6 cells each. Each cell group appears to arise from a single cell and breaks away from the ‘mother group’ as cell divisions continue. The embryogenic cells are small (20 μm), isodiametric with many starch grains and contain a large nucleus with a prominent nucleolus. Extensive profiles of endoplasmic reticulum, many small peripheral vacuoles, and several amyloplasts are present. Plasmodesmatal connections exist only between cells within a cell group but not between cells of different cell groups in the large cell aggregates.
PHOSPHOGLUCOMUTASE AND ISOCITRATE DEHYDROGENASE GENE DUPLICATIONS IN LAYIA (COMPOSITAE)
Authors: Gottlieb L. D.
Published: January 2018

Genetic analysis of isozyme segregation patterns in Layia (Compositae) showed that cytosolic phosphoglucomutase isozymes are encoded by duplicated genes, and that the cytosolic NADP‐dependent isocitrate dehydrogenase isozymes are encoded by duplicated genes in species with haploid chromosome numbers of n = 7 and triplicated genes in those with n = 8. The duplicated genes specifying both isozymes assorted independently in all species tested. An electrophoretic survey of phosphoglucomutase in diploid species representing six additional genera of Madiinae, the subtribe to which Layia is assigned, revealed that Achyrachaena, Calycadenia, Hemizonia, Holocarpha, and Madia all possessed duplicated genes. In Lagophylla, one species also had duplicated genes for the isozyme but a second species did not, a loss probably resulting from mutation or chromosomal deletion. The phosphoglucomutase duplication characterizes nearly the entire subtribe and may prove useful to identify phylogenetic relationships between the Madiinae and other subtribes.
COMPARATIVE ULTRASTRUCTURAL STUDIES OF SPERMATOGENESIS IN THE METZGERIALES (HEPATOPHYTA) II. THE BLEPHAROPLAST OF BLASIA PUSILLA
Authors: Renzaglia Karen S. , Duckett Jeffrey G.
Published: January 2018

As in other hepatics, the young spermatid of Blasia pusilla contains a well‐developed blepharoplast comprising a four‐layered multilayered structure (MLS) and two overlying dimorphic basal bodies. The asymmetrical spline (S1 or upper stratum of the MLS) numbers 20 or 21 microtubules (MTs) at its anterior tip and reduces to eight at the posterior limit of the lamellar strip (LS). Behind this the shank of the spline is five or six tubules in width over most of its length, approximately one revolution of the circumference of the gamete. The three‐microtubule spline aperture underlies the anterior basal body and like those of most hepatics, it is closed at its anterior end. The asymmetrical LS (approx. 2.0 μm in length) is characterized by a right‐hand posterior notch which lies below the spline aperture at the region of the cartwheel configuration of the anterior basal body (ABB). The staggered dimorphic basal bodies overlap for approximately one third of their lengths. Both lie parallel to the long axis of the spline. As in other hepatics, the ABB (1.2 μm in length) is subapical and comprises an anterior hub extension with progressive rearward additions of lateral, dorsal and ventral triplets. Over most of its length (2.1 μm) the longer posterior basal body (PBB) consists of a distinct central hub and three ventral triplets. Transition zones of both basal bodies contain stellate configurations into which the two central axonemal MTs frequently extend. The blepharoplast of Blasia shows several features in common with leafy, simple thalloid and complex thalloid liverworts. Compared with the few Metzgeriales observed thus far, the LS is less elongate and the basal bodies less staggered. Dimensions of basal body components and spline dimensions, however, are comparable to those of most leafy and thalloid hepatics. Striking similarities with the complex thalloid liverworts include a posterior notch in the LS and a spline aperture three MTs wide.
POLLEN CAPTURE AND WIND‐INDUCED MOVEMENT OF COMPACT AND DIFFUSE GRASS PANICLES: IMPLICATIONS FOR POLLINATION EFFICIENCY
Authors: Niklas Karl J.
Published: January 2018

The motion induced by wind of Setaria geniculate (Lam.) Beauv. and Agrostis hiemalis (Walt.) B.S.P. panicles is shown to have harmonic characteristics that can influence pollination. During each cycle of its motion, the panicle of S. geniculata repeats a sequence of reorientations to the direction of ambient airflow. This repetition is correlated with a reiteration of airflow patterns through which airborne pollen grains must pass to reach floral surfaces. The panicle decelerates as it moves toward either of the two extreme positions of its oscillatory motion. The decelerations introduce a bias in the time the panicle spends in each of its orientations. This bias generates “preferred orientations” to the direction of ambient airflow which in turn results in biasing the aerodynamics of pollen capture. Similar phenomena are reported for the panicle of A. hiemalis, although a more complex pattern of oscillatory motion is observed. The reciprocity between the mechanics of oscillatory motion and the aerodynamics of pollen capture is shown to have deterministic properties which may surface above the “noise” produced by other, stochastic features influencing wind pollination.
BIOMASS ALLOCATION IN AN AGROPYRON SMITHII‐GLOMUS SYMBIOSIS
Authors: Miller R. Michael , Jarstfer Amiel G. , Pillai Jan K.
Published: January 2018

The type of response the steppe grass Agropyron smithii Rydb. exhibits to mycorrhizal fungi is dependent upon where along the resource gradient the experiment is conducted. At the lower end of a soil‐phosphorus (P) gradient (2 μg P g‐1 soil) mycorrhizal A. smithii biomass was 35% greater than its nonmycorrhizal counterpart; while at the high end of the gradient (20 μg P g‐1 soil) no difference in host biomass production was evident. Mycorrhizal plants were shorter in stature (P < 0.002) and produced more tillers (P < 0.0001) than nonmycorrhizal plants. The stature and tiller response was more pronounced at the high end of the soil‐P gradient. The partitioning of the mycorrhizal fungus was influenced by the soil‐P gradient. At the lower end of the gradient the majority of the fungus was produced extramatrically, where over 5,000 cm of hyphae per plant were encountered after 10 wk growth. While at the high end of the gradient, the majority of fungus was produced internally. The highest mycorrhizal dependency values were measured at the lower end of the soil‐P gradient where cost to the host (as measured by fungus biomass expressed as a percentage of the root system) was also highest. Increasing shoot and root‐P concentrations were correlated with decreasing external fungus biomass. A positive association between tiller production and internal fungus biomass also existed. The significance of these findings, as well as the need to consider characteristics which measure fitness of a host in evaluating the mycorrhizal association of grasses, are discussed.
A COMPUTER GRAPHICS PROGRAM FOR THE THREE‐DIMENSIONAL RECONSTRUCTION OF PLANT ORGANS FROM SERIAL SECTIONS
Authors: Delozier Gregory , Eckard Kathleen , Greene Marie , Lord Elizabeth M.
Published: January 2018

Morphological and anatomical studies have long utilized qualitative means to reconstruct 3‐dimensional transparent images from serial sections. With the advent of computer graphics systems, more accurate images can be constructed to visualize growing plant parts in transparent 3‐D. We have developed a computer program which allows such reconstruction from stained serial sections. Advantages include 3‐dimensional imaging without the use of stereo pairs and the ability to rotate an image to see all angles.
ANATOMY AND AFFINITIES OF PENTHORUM
Authors: Haskins Melanie L. , Hayden W. John
Published: January 2018

The genus Penthorum L. consists of two species of perennial herbs, P. sedoides of eastern North America and P. chinense of eastern Asia. Penthorum has long been considered intermediate between Crassulaceae and Saxifragaceae. An anatomical study of both species was undertaken to contribute to a better understanding of the relationships of these plants. Prominent anatomical features of Penthorum include: an aerenchymatous cortex and closely‐spaced collateral vascular bundles of stems; one‐trace unilacunar nodes; brochidodromous venation, rosoid teeth bearing hydathodes, and anomocytic stomata of leaves; angular vessel elements with many‐barred scalariform perforation plates and alternate to scattered intervascular pits; thin‐walled non‐septate fiber‐tracheids; abundant homocellular erect uniseriate and biseriate rays; and absence of axial xylem parenchyma. In general, Penthorum possesses neither the morphological nor the anatomical synapomorphies which define Crassulaceae, and features shared with Saxifragaceae are largely symplesiomorphous. Thus Penthorum is probably best classified in the monogeneric Penthoraceae.
EMBRYOLOGY AND SYSTEMATIC POSITION OF HETEROPYXIS (MYRTALES)
Authors: Tobe Hiroshi , Raven Peter H.
Published: January 2018

We present here the first study of the embryology of Heteropyxis, in order to evaluate its relationships with Myrtaceae, a family in which it has often been placed. On the basis of embryology, Heteropyxis is undoubtedly very closely allied to Myrtaceae, but is distinct in possessing 1) a bisporic Allium type embryo sac, 2) a condition in which the two microsporangia of the theca are remotely separate from each other and dehisce by their respective longitudinal slits instead of by a common slit, and 3) an ovule and seed that has wings on both ends. All of these embryological characteristics are apomorphic features; they contrast with many other characteristics of the genus, such as its completely superior ovary and separate staminal traces, which are clearly primitive ones. Like the unique monotypic Psiloxylon, an endemic of Mauritius, Heteropyxis clearly diverged early from the evolutionary line leading to Myrtaceae before the origin of the common ancestor of that family (excluding Heteropyxis and Psiloxylon). Heteropyxis could logically be regarded either as a subfamily of Myrtaceae distinct from all other members of the family or as a separate but related family. We shall return to this question when our review of the embryological features of Psiloxylon has been completed.
IS DIOECY ASSOCIATED WITH FLESHY FRUIT?
Authors: Muenchow G. E.
Published: January 2018

The floras of the northeastern U.S. and California were analyzed with respect to the question whether dioecy is associated with fleshy fruit. These analyses control for mode of pollination, woodiness, and flower color. Weak associations between dioecy and fleshy fruit were observed, unconvincing because of the difficulty of controlling for phylogenetic constraint. Other such studies are reviewed, however, and, because the better studies all do show a weak association, it is concluded that the weak association may be real. An ecological explanation is postulated and defended. The much stronger association between dioecy and floral biology is noted.
AN UNUSUAL KIND OF DISTYLY IN QUINCHAMALIUM CHILENSE (SANTALACEAE) ON VOLCÁN CASABLANCA, SOUTHERN CHILE
Authors: Riveros Magaly , Arroyo Mary T. Kalin , Humaña Ana María
Published: January 2018

In mature flowers of the southern Andean parasitic herb, Quinchamalium chilense (Santalaceae), the stigmas and anthers are closer together in the pin morph than in the thrum morph. While the stigmas and anthers of the two morphs are in reciprocal positions as the flowers open, such reciprocity is lost as the result of post‐anthesis allometric growth of the styles and stamens. Experimental pollinations reveal that both morphs of Q. chilense are self‐compatible. Natural fruit set is higher on the pin morph. The latter is also statistically under‐represented in natural populations with respect to a 1:1 ratio for pins and thrums. Pin flowers produce larger numbers of pollen grains than thrum flowers and pollen of pin flowers is smaller in size than that of thrum flowers. Higher fruit set on the pin morph is consistent with some tendency towards subdioecious breeding behavior, although an expected excess of geitonogamous pollinations on the pin morph might also be contributing to the difference in fruit set on the two morphs. The unusual floral morphology of Q. chilense could have evolved as a result of selection for larger flowers by certain pollinator groups less likely to effect geitonogamous pollination. Alternatively, extended development of post‐anthesis flowers might be a reflection of selection for an array of flower sizes on individual inflorescences, producing a target effect for pollinator attraction. The evolution of such inflorescence morphology would have been facilitated by the fact that a trend in the direction of subdioecious breeding behavior accrues the same outcrossing advantages as strict distyly. Precise information on periods of stigma receptivity is required to further our understanding of the floral morphology of Q. chilense.
APOMIXIS AND SEXUALITY IN THREE SPECIES OF AMELANCHIER, SHADBUSH (ROSACEAE, MALOIDEAE)
Authors: Campbell Christopher S. , Greene Craig W. , Bergquist Scott E.
Published: January 2018

We used Nomarski differential interference contrast microscopy of cleared, whole ovules to examine megasporogenesis and megagametogenesis in tetraploid (N = 34) individuals of three species of Amelanchier in Maine. Amelanchier canadensis and A. stolonifera conform to the general pattern of apomixis in the Maloideae by being aposporous and by frequently forming more than one megagametophyte per megasporangium. These species are also pseudogamous; both self and foreign pollen elicit fruit set. Amelanchier bartramiana follows a sexual pattern by producing a triad of megaspores and almost always only one megagametophyte per megasporangium. This boreal shrub, strikingly distinct morphologically and in its habitat preference from other North American species of the genus, is primitive in its sexuality and self‐incompatibility relative to other species we have studied.
SYNUROPHYCEAE CLASSIS NOV., A NEW CLASS OF ALGAE
Authors: Andersen Robert A.
Published: January 2018

The silica‐scaled algae (Synuraceae, Chrysophyceae sensu lato) are compared to other Chrysophyceae, Phaeophyceae and Bacillariophyceae with occasional comparisons to other chlorophyll c‐containing algae, scaled protozoa and oomycete fungi. The silica‐scaled algae have several unique characters which separate them from the above groups and based upon these differences a new order, Synurales ord. nov., and a new class, Synurophyceae class. nov., are described. The major distinguishing characters of the Synurophyceae class. nov. are: they have chlorophylls a and c1 but lack chlorophyll c2; their flagellar apparatus includes a microtubular root that loops around two parallel flagella and a flagellar root system which occurs in four absolute orientations; the photoreceptor consists of paired flagellar swellings which are not associated with the cell membrane and chloroplast; no eyespot is present; the nuclear envelope is not or is only weakly associated with the chloroplast endoplasmic reticulum. The Synurophyceae class. nov. are about equally distinct from the Chrysophyceae sensu stricto, Phaeophyceae and Bacillariophyceae when the class level characters are compared. Although the Phaeophyceae have a long history of being placed by themselves in the division Phaeophyta, and the Bacillariophyceae and Chrysophyceae have recently been placed alone in the Bacillariophyta and Chrysophyta, respectively, the similarities found among these classes suggest these algae are not so distinct that they require separate divisions. Tentatively, therefore, the Synurophyceae are placed in the division Phaeophyta along with the Bacillariophyceae and Chrysophyceae sensu stricto.
SEED BANK OF A FRESHWATER TIDAL WETLAND: TURNOVER AND RELATIONSHIP TO VEGETATION CHANGE
Authors: Leck Mary Allessio , Simpson Robert L.
Published: January 2018

Depletion during spring germination (turnover), longevity, and successional relationships were studied at High Marsh (HM), Cattail (CT), and Shrub Forest (SF) sites in a freshwater tidal wetland over three years. There was significant seasonal reduction in size and composition of seed banks from all sites. Turnover was greatest in HM surface (0–2 cm) samples where 29 x more seeds germinated in March than in June. In CT and SF samples turnover was considerably less. Magnitude (34–97%) was related to species composition and factors affecting field germination. Decrease in density with depth (0–10 cm) was log‐linear in March samples. Except for SF 30–32 cm, few seeds and species were found at 8–10, 15–17, or 30–32 cm. Three seed bank strategies were distinguished: (a) complete turnover (Type II, sensu Thompson and Grime 1979), (b) high turnover with some reserve (Type III), and (c) large long‐term seed reserve (Type IV). Longevity of many species appeared to be restricted; 31–56% at each site were present only in surface samples, and 29–52% germinated only in March samples. Although some species were important at all three sites, the seed bank composition of each was distinct, and was related to vegetation composition at each site. Because the bulk of the seed bank at each site resembles its site vegetation more than that of another site, it is not possible to predict succession.
WATER RELATIONS OF TWO CALIFORNIA CHAPARRAL SHRUBS
Authors: Hart Jonathan J. , Radosevich Steven R.
Published: January 2018

Water use patterns of two California chaparral shrub species, chamise (Adenostoma fasciculatum H. and A.) and Stanford manzanita (Arctostaphylos stanfordiana Parry), were compared during summer drought. Observations of diurnal and seasonal courses of shoot water potential, leaf conductance and transpiration revealed that chamise was more conservative in water use than manzanita. Evidence obtained cast doubt on a hypothesis previously proposed to explain an anomalous pattern of shoot water potential in chamise.
SOLUTE CONCENTRATIONS IN THE PHLOEM AND APEX OF THE ROOT OF ZEA MAYS
Authors: Warmbrodt Robert D.
Published: January 2018

Plasmolytic studies utilizing a graded series of mannitol solutions (0.1–1.4 M in 0.1 M increments) were conducted on adventitious roots of Zea mays to determine solute concentrations of cell types at various locations in the root. Results indicated that mature sieve‐tube members had the highest solute concentration as determined by their C50 (the estimated mannitol concentration plasmolyzing an average of 50% of a given cell type) of any cell type in the root. In tissue 12 cm from the tip, C50 values calculated for proto‐ and metaphloem sieve‐tube members were 1.15 and 1.19 M, respectively, while in tissue 0.5 cm from the root tip, values for the same cell types were 0.68 and 0.46 M, respectively. The C50 values for sieve elements in tissue 5 cm from the tip were intermediate (1.08 and 1.11 M). Although the companion cells generally plasmolyzed at nearly the same concentrations of mannitol as the sieve elements, their C50 values were slightly lower than adjacent mature sieve elements. The lowest C50 (0.35 M) for any cell type examined was associated with meristematic cells in tissue 0.1 cm from the root tip. Taken collectively, the results indicate that positive concentration gradients exist between mature sieve tubes and meristematic cells of the root apex of maize.
FACTORS AFFECTING GERMINATION IN GREENHOUSE‐PRODUCED SEEDS OF OXALIS CORNICULATA, A PERENNIAL WEED
Authors: Holt Jodie S.
Published: January 2018

A study was conducted to investigate the physiological responses of greenhouse‐produced Oxalis corniculata seeds to light, temperature, moist heat treatment, aging, and season of production. Fresh seeds exhibited over 90% germination and required low levels of light (5 μmol m‐2 s‐1, 400–700 nm) to germinate. Seeds germinated over a broad, yet seasonally‐dependent range of incubation temperatures. Seeds produced in winter had the narrowest temperature range of germination (15 to 25 C) and the lowest germination percent (44% at 2 wk) at optimum temperature (17 C); seeds produced in summer had the widest temperature range of germination (10 to 30 C) and the highest germination percent (93% at 2 wk) at optimum temperature (17 C). Incubation at non‐optimum temperatures between 5 and 40 C suppressed or slowed the rate of germination until seeds were placed at optimum temperature, where full germination subsequently occurred. Moist heat treatment at temperatures over 40 C resulted in varying degrees of inhibition of subsequent germination. When seeds were stored dry in laboratory conditions, three of four seed lots examined retained over 80% germination capacity until ca. 8 months; 50% capacity remained after ca. 15 months. These results indicate that the seasonal temperature and daylength effects on maternal plants in the greenhouse environment are major determinants of seed germination characteristics of O. corniculata.
INITIATION OF THE VASCULAR SYSTEM IN THE FERTILE FLORET OF ANTHOXANTHUM ODORATUM (GRAMINEAE)
Authors: Pizzolato Thompson Demetrio , Robinson‐Beers Kay
Published: January 2018

Procambium was initially isolated near the insertions of lemma and stamen primordia in the grass Anthoxanthum. The palea was initiated before its procambium. The acropetal, continuous differentiation of procambium involved in the siting of leaves on shoots of many other megaphyllous plants, does not occur in the rachilla of this grass. A portion of the vascular system of the fertile floret of Anthoxanthum became connected with the vascular system of the rest of the spikelet by basipetal differentiation of the procambial trace of the fertile lemma. A core of residual meristem persisted in the fertile floret above the procambial trace to the fertile lemma. Vascular continuity between the procambial trace to the fertile lemma and the procambial traces of the stamens was achieved by the differentiation of procambium from this core of residual meristem.
ORGANOGENESIS FROM HELIANTHUS ANNUUS INBREDS AND HYBRIDS FROM THE COTYLEDONS OF ZYGOTIC EMBRYOS
Authors: Power Christopher J.
Published: January 2018

Dormant mature and immature zygotic embryos of sunflower (Helianthus annuus L.) inbreds and hybrids were dissected and cultured on modified Murashige and Skoog's medium supplemented with 0.1 mg/l benzyl adenine (BA), 0.5 mg/l naphthalene acetic acid (NAA), adenine sulfate, and casamino acids. For certain inbreds and hybrids, adventitious shoot formation occurred from callused cotyledonary tissue, particularly along the cut edges. The developmental stage of the zygotic embryo was critical. Eighty percent of immature H. annuus ‘Mammoth Russian’ embryos produced adventitious shoots from cotyledons, while mature embryos did not. The organogenic potential of mature cotyledons diminished as soon as one day after germination was initiated. Different forms of regeneration were observed in two inbred lines, and when these were crossed, both forms of regeneration were observed at a lower frequency from the immature embryos of the hybrid. Rooted shoots were successfully grown to maturity in a greenhouse.
PHYTOTOXIC EXUDATES FROM VELVETLEAF (ABUTILON THEOPHRASTI) GLANDULAR TRICHOMES
Authors: Sterling Tracy M. , Houtz Robert L. , Putnam Alan R.
Published: January 2018

Nonvolatile exudates from velvetleaf glandular trichomes inhibited root and shoot growth of several weed and crop species in petri plate bioassays, but had no effect on seed germination per se. The exudate was efficiently collected by wiping both the stems and petioles with cotton swabs or by leaching with water, but was absent on the leaves of velvetleaf plants. Cress (Lepidium sativum L.) was the most sensitive indicator species. Four types of trichomes appeared on the stem surface as revealed by scanning electron microscopy. Water soluble globules on the apices of 12‐ to 15‐celled glandular trichomes recurred and demonstrated their original potency within eight days after removal with cotton swabs. Both the quantity and phytotoxicity of the exudates from velvetleaf plants cultured under varying environmental conditions were determined. While total exudate production was not affected at 16, 24, or 36 C, the exudates from plants cultured at 24 and 36 C were about twice as toxic as the exudate collected from plants grown at the lower temperature. Water stress decreased the amount of exudate collected, but the phytotoxic activity was increased by approximately the same factor.
BIOMASS ALLOCATION AND GEOMETRY OF THE CLONAL FOREST HERB LAPORTEA CANADENSIS: ADAPTIVE RESPONSES TO THE ENVIRONMENT OR ALLOMETRIC CONSTRAINTS?
Authors: Menges Eric S.
Published: January 2018

Using a conceptual model, I predicted the direction of biomass allocation and geometric responses to several environmental variables for Laportea canadensis, a clonal forb dominating the herbaceous stratum of many North American floodplain and mesic forests. Laportea stems and plants, especially dominant ones, generally (60%) respond as predicted to canopy opening, conspecific leaf area and density, and poor drainage, but are merely reduced in growth when growing on sandier soils. However, allometric relationships explain most of the variation in geometry and allocation. Still, variation in geometry and allocation (as great as among 21 species of herbs studied by Givnish [1982]), helps explain the success of Laportea in a range of microenvironments.

In upland forests, stems in canopy gaps are tallest but allocate relatively less biomass to leaves than shaded stems, suggesting that interherb competition is the major problem faced under canopy gaps. Leaf morphology also changes with increasing canopy opening—individual leaves are larger, heavier, and thicker and are displayed on more steeply ascending petioles. Floodplain plants respond to light gaps mainly with changes in leaf morphology and display.

With increasing conspecific density and leaf production, Laportea stems in both uplands and floodplains grow taller, allocate relatively more biomass to stems, and display leaves higher on the stem. The allocation and geometry of taller stems are more independent of density, and more closely affected by tree‐canopy opening, than are small stems.

Intermediate soil textures in floodplains promote maximum Laportea production; variations in other factors are less important. Poorly drained soils in floodplains (heavy‐textured soils at low elevations) cause decreased Laportea height and absolute leaf weight, but increase relative allocation to leaves and roots, as predicted. On the other hand, Laportea appears poorly adapted to sandier soils. Rather than responding to sandier soils as predicted, Laportea's overall growth is reduced.

Geometric responses of Laportea to environment are mediated by allometric realities: an increase in height favored in productive environments produces a concomitant decrease in relative leaf allocation. Although predicted (presumably adaptive) shifts are significant when plant size is accounted for, most of the variation in allocation and geometry is due to allometry.