Showing papers in "American Journal of Botany in 1973"

Classification of the architecture of dicotyledonous leaves

Abstract: A B S T R A C T A classification of the architectural features of dicot leaves-i.e., the placement and form of those elements constituting the outward expression of leaf structure, including shape, marginal configuration, venation, and gland position-has been developed as the result of an extensive survey of both living and fossil leaves. This system partially incorporates modifications of two earlier classifications: that of Turrill for leaf shape and that of Von Ettingshausen for venation pattern. After categorization of such features as shape of the whole leaf and of the apex and base, leaves are separated into a number of classes depending on the course of their principal venation. Identification of order of venation, which is fundamental to the application of the classification, is determined by size of a vein at its point of origin and to a lesser extent by its behavior in relation to that of other orders. The classification concludes by describing features of the areoles, i.e., the smallest areas of leaf tissue surrounded by veins which form a contiguous field over most of the leaf. Because most taxa of dicots possess consistent patterns of leaf architecture, this rigorous method of describing the features of leaves is of immediate usefulness in both modern and fossil taxonomic studies. In addition, as a result of this method, it is anticipated that leaves will play an increasingly important part in phylogenetic and ecological studies.

Effects of plant growth substances on in vitro fiber development from unfertilized cotton ovules

Abstract: Fertilization of cotton ovules was prevented by removal of styles and stamens on the morning of anthesis. Forty-eight hr later ovaries were harvested and ovules were aseptically transferred to liquid culture medium supplemented with various plant growth substances. In the absence of phytohormones, ovules browned and failed to increase in size or produce fibers. Indoleacetic acid and gibberellic acid provided for ovule growth and fiber development. Kinetin provided for ovule growth only. The ovule's capacity for indoleacetic acidor gibberellic acid-stimulation of fiber development was reduced by high concentrations of kinetin or abscisic acid. Low concentrations of kinetin partially reversed the inhibitory effect of

Inhibition of nitrification by climax ecosystems. ii. additional evidence and possible role of tannins

Abstract: The same nine plots were used in this study as in our previous study on inhibition of nitrification (Rice and Pancholy, 1972). These consisted of three stands representing two stages of old field succession and the climax in each of three vegetation types in Oklahoma: tall grass prairie, post oak-blackjack oak forest, and oak-pine forest. Soil samples were analyzed three times during the growing season of 1972 for exchangeable ammonium nitrogen, nitrate, and numbers of Nitrosomonas and Nitrobacter. Results were similar to those obtained during the entire year of 1971. The amount of ammonium nitrogen was lowest in the first successional stage, intermediate in the intermediate successional stage, and highest in the climax. The amount of nitrate was highest in the first successional stage, intermediate in the intermediate successional stage, and lowest in the climax. The numbers of nitrifiers were highest in the first successional stage usually and decreased to a very low number in the climax. These data furnish additional evidence that the nitrifiers are inhibited in the climax so that ammonium nitrogen is not oxidized to nitrate as readily in the climax as in the successional stages. This would aid in the conservation of nitrogen and energy in the climax ecosystem. Some inhibition of nitrification occurred in the intermediate stage of succession also. Previous studies of tannins indicated that these are inhibitory to nitrification, so all important plant species in the intermediate successional stage and the climax were analyzed for total tannin content. A method for extracting and quantifying condensed tannins from soils was developed and the amounts of tannins were determined in each 15-cm level down to 60 cm in the same two plots in each vegetation type. Gallic and ellagic acids, which result from the digestion of hydrolyzable tannins in oak species, were also extracted and quantified in the climax oak-pine forest. All the important herbaceous species, including the grasses, were found to have considerable amounts of condensed tannins. The highest amounts of tannins occurred in the oaks and pine, however. Condensed tannins, hydrolyzable tannins, ellagic acid, gallic acid, digallic acid, and commercial tannic acid (hydrolyzable tannin), in very small concentrations, were all found to completely inhibit nitrification by Nitrosomonas in soil suspensions for 3 weeks, the duration of the tests. Slightly larger concentrations were required to inhibit nitrification by Nitrobacter under similar conditions. The concentrations of tannins, gallic acid, and ellagic acid found in the soil of the research plots were several times higher than the minimum concentrations necessary to completely inhibit nitrification. The inhibition of nitrification was always greater in the climax stand than in the intermediate successional stage in each vegetation type, and the concentration of tannins in the top 15 cm of soil was always higher in the climax stand than in the intermediate successional stage. Moreover, the amounts of tannins calculated to be added to each plot each year are much less than the amounts found in the soil, indicating that the tannins accumulate over a period of time. Thus, it appears that the tannins and tannin derivatives may play a continuous and rather prominent role in the inhibition of nitrification by vegetation.

Genetic differentiation, sympatric speciation, and the origin of a diploid species of stephanomeria.

Abstract: A B S T R A C T Evidence is presented that a geographically peripheral population of the annual Stephanomeria exigua ssp. coronaria (Compositae), a widespread and ecologically diverse species, has recently given rise by a process of sympatric speciation to a diploid species presently designated "Malheurensis." The new species comprises less than 250 individuals and is found only at a single locality in eastern Oregon where it grows interspersed with its parental population. Stephanomeria exigua ssp. coronaria is an obligate outcrosser and "Malheurensis" is highly self-pollinating. Reproductive isolation is maintained by differences in breeding system, a crossability barrier that reduces seed set following cross-pollination between them, and reduction in hybrid fertility caused by chromosomal structural differences. They are very similar morphologically. Electrophoretic analyses of seven enzyme systems demonstrate that all the alleles but one at the controlling 13 gene loci in "Malheurensis" are identical to alleles in ssp. coronaria. The new species displays certain maladapted features including loss of the specific requirements for seed germination characteristic of the progenitor population of ssp. coronaria. The origin of "Malheurensis" appears to be an exception to the theory of geographical speciation because spatial isolation is not necessary at any time for the origin or establishment of its reproductive isolating barriers. The nature of these barriers plus the genetic homogeneity of the species are compatible with the hypothesis that it derives from a single progenitor individual. Very little genetic change is involved initially in this mode of speciation.

The kranz syndrome in the gramineae as indicated by carbon isotopic ratios

Abstract: Ttie Kranz syndrome, as indicated by relatively high "3C/12C ratios is characteristic of 161/2 tribes and about '/2 of the species of the Gramineae. Data are given for 198 species from 129 genera and 47 tribes, and from at least 6 subfamilies of grasses. This information is correlated with data from the literature on anatomical and physiological characters of both Kranz and non-Kranz grasses. All subfamilies, tribes, and genera seem to be uniformly all Kranz or non-Kranz except the subfamily Panicoideae and the genus Palicurn which have both Kranz and non-Kranz species represented.

Seasonal pattern of net photosynthesis of artemisia tridentata

Abstract: Gas exchange studies were carried out on Artemisia tridenztata during the course of a growing season using microclimatically controlled cuvettes and infrared gas analysis. A definite seasonal pattern of net photosynthesis emerged. This pattern was influenced by the interaction of four major factors: plant water potential, leaf temperature, irradiation, and stage of phenological development. In spring and early summer, when plant water stress was minimal, photosynthesis rate was mainly correlated with leaf temperature and irradiation. During mid and late summer, increased plant water stress and phenological changes assumed at least equal importance with temperature and irradiation in limiting net photosynthesis. Indeed, plant water potential, mainly through its influence on stomatal aperture, r,', was probably the single most important factor influencing assimilation rate of this species on a seasonal basis. However, variations in mesophyll resistance to CO2 flux, rm', in response to temperature, water stress, or phenological changes also were involved. Sagebrush photosynthesis under field conditions was highest in late May and early June, and declined thereafter, minimum rates occurring in August during the driest period. Optimal temperatures for net photosynthesis were higher later in the season, indicating a change in gas exchange capacity more suitable to the warmer temperatures later in the

Sexual and subsexual systems in homosporous pteridophytes: a new hypothesis

Abstract: Meiosis in homosporous ferns allows chromosomes to pair within homoeologous sets rather than restricting pairing to homologs; this allows homozygous spore mother cells to give rise to genetically heterogeneous meiospores. It is envisioned that such a meiotic system has evolved in homosporous ferns in response to a life cycle which allows the attainment of total homozygosity in one generation of selfing.

Hormone-induced endoreduplication prior to mitosis in cultured pea root cortex cells'

Abstract: A B S T R A C T One-mm-thick cortical explants excised aseptically from 10-11 mm behind the tip of 3-dayold roots of the garden pea, Pisum sativumn, cv. 'Little Marvel' were cultured on a synthetic nutrient medium supplemented with auxin or auxin and cytokinin. Nuclear DNA contents were measured in cells of the explants at the outset and at specified times during culture up to seven days. Fixed and sectioned preparations were stained with the Feulgen method using the DNA-specific dye auramin-O. Fluorescent microspectro-photometric measurements of individual nuclei were made from each cortical population. At day zero all cortical nuclei measured were either 2c or 4c with respect to their DNA content. In the presence of the auxins, indoleacetic acid and 2,4-dichlorophenoxyacetic acid, and the cytokinin, kinetin, DNA values increased to multiples of the 2c level with populations at the 8c and 16c level predominating after three days of culture as well as at seven days. In the presence of auxins alone no change in DNA values was observed during three days. Kinetin concentrations as low as 0.01 ppm were already effective. The data are interpreted to show that cytokinin, in the presence of auxin, induces two rounds of DNA synthesis prior to the first mitoses, the first round being connected with chromosome doubling by endoreduplication and the second one with normal mitosis. From this we inferred that tetraploid cells in leguminous root nodules might have arisen in the same way, i.e., by endoreduplication prior to the first mitoses induced by the rhizobial division stimulus, unless the chromosome number of root cortical cells had already been doubled by endoreduplication in the normally differentiating root systems.

Ibyka amphikoma, gen. et sp. n., a new protoarticulate precursor from the late middle devonian of new york state

Abstract: A B STRACT Ibyka gen. n. is described from late Middle Devonian compressions and petrifactions collected in eastern New York State. It is a robust plant of which three orders of branching and ultimate appendages (leaves) are known. The latter dichotomize up to five times, are arranged spirally on all orders of branching, are three-dimensional, and all orders are terete in cross section. Fertile appendages, homologous with the sterile, are terminated by sporangia. The protostele has five or six arms, the maturation is mesarch, and the protoxylem disintegrates leaving lacunae at the tips of the arms. Traces to appendages are terete and arise spirally from the tips of the arms. The primary xylem consists of tracheids only, the phloem of thin-walled cells and probable tanniniferous cells. The cortex consists of parenchyma and groups of sclereids. Secondary xylem is lacking. Ibyka is placed in a new order, Ibykales, close to the Hyeniales (protoarticulates) and to the Pseudosporochnales all three of which probably evolved from Trimerophytina.

Macrocysts in the life cycle of the Dictyosteliaceae. II. Germination of the macrocysts

Abstract: Macrocyst germination was demonstrated in the five species of the Dictyosteliaceae known to produce these structures. The morphological changes that occurred during germination appeared to be identical in all of the strains examined, showing the following stages: (1) swelling of the dark, contracted content of the dormant cysts, (2) gradual loss of color and reappearance of cells within what previously appeared as a homogeneous protoplasmic mass, and (3) rupture of the heavy cellulosic cyst wall to liberate the myxamoebae. The age of the macrocyst appeared to be the most critical factor in determining whether or not germination would occur, since the cysts in many of the strains needed to age for several weeks or months before germination could be demonstrated. In Dictyostelium mucoroides strain DM-7, upon which the current study was centered, light was necessary to stimulate germination of young macrocysts-a requirement that gradually diminished as the cysts aged. The rate of germination and the temperature permitting germination were also age dependent: older macrocysts germinated more rapidly and at considerably higher temperatures than did young cysts. Although light was not essential for germination in every strain, the results obtained with strain DM-7 seem to be generally applicable to the germination process. MACROCYSTS are multicellular post-aggregative encystment structures produced by certain strains of the cellular slime molds (Dictyosteliaceae) under appropriate environmental conditions (Blaskovics and Raper, 1957; Nickerson and Raper, in press). Their formation is signalled by the deposition of a loose primary wall which delimits the incipient macrocyst(s) soon after the myxamoebae have moved into aggregation centers. As this initial wall is deposited, a large cell appears in the center of the developing macrocyst as reported by Dengler, Filosa, and Shao (1970) and since confirmed in an independent EM study by Erdos, Nickerson, and Raper (1972). This cell enlarges, ingests the peripheral myxamoebae, and encloses each in a vacuole. The process of phagocytosis continues, progressing outward from the center, until all of the myxamoebae have been ingested by the giant cell. A heavy secondary wall rich in cellulose is then laid down just outside the plasma membrane of the giant cell. (Under the phase contrast microscope, the macrocysts during this stage of development appear to consist of closely packed seemingly firm-walled cells, termed "endocytes" by Blaskovics and Raper in 1 Received for publication 14 June 1972. This paper represents a part of a thesis offered by the senior author in partial fulfillment of the requirements for the Ph.D. degree, University of Wisconsin, Madison. The work was supported by research grants GB-8624 from the National Science Foundation and AI-049 15 from the National Institutes of Health, U.S. Public Health Service. 1957). Some days later the cyst slowly develops a brownish coloration. As it darkens, the ingested amoebae are digested losing their cellular identity so that the content of the cyst appears homogeneous within the heavy macrocyst wall. In its fully mature and dormant state, the cyst content shrinks somewhat and loses contact with the heavy wall. It is now tightly bounded by an elastic tertiary wall, which instead of being thin, as reported by Blaskovics and Raper (1957), is now seen to be comparatively thick. Blaskovics and Raper (1957) reported a 7.2% germination of 10-day-old endocyte-filled macrocysts following incubation for 22 days at 15 C. Treating the cysts with cellulase, alternately freezing and thawing, and mechanically breaking them were all ineffective in increasing the rate or percentage of germination. However, better germination did occur in sixto eight-week-old macrocysts. Unfortunately, the sequence of changes between the time when the cyst content appeared homogeneous and the rupture of the walls to liberate the myxamoebae could not be determined. The purpose of this study was threefold: (1) to establish the sequence of morphological events that occur during the transition from the homogeneous condition of the mature dormant macrocyst to the liberation of myxamoebae at germination; (2) to identify a strain in which the process of germination could be studied advantageously; and (3) to use this strain to examine carefully the

Ozone-induced membrane permeability changes

Abstract: The effect of 0.5 ppm ozone for 0.5-1 hr on plant cell membrane permeability was ascertained. Permeabilities to both water and solutes were estimated by measuring leaf disc weight changes and following tritiated water and 86Rb fluxes. Measurements were made immediately after ozone exposure and 24 hr after exposure. The reflection coefficient, o, an index of solute permeability, decreased in ozone-treated primary leaves of pinto bean (Phaseolus vulgaris). The latter indicates an increase in membrane solute permeability or internal solute leakage. Water and THO flux estimates both indicated a decrease in membrane permeability to water; both the hydraulic conductivity (Lp) and the water diffusional coefficient (LD) apparently decreased, an anomaly which is discussed. These data indicate that ozone has a direct effect on membrane function by altering permeability characteristics. We assume from these data that cell membranes are primary target sites for ozone injury.

Ultrastructural changes of plants exposed to low temperatures

Abstract: A B S T R A C T Effects of low temperatures on cell ultrastructures of three grass species were studied. Secale cereale L., Cynodon dactylon (L.) Pers., and Paspalum notatum Flugge seedlings were given treatments of -5, 0, 10, or 25 C for 3 days and then evaluated for cellular response. Electron micrographs showed chloroplasts to be the most sensitive organelle in all three species, with the temperate Secale plastids responding differently than plastids from the subtropical and tropical species. Rough endoplasmic reticulum increased, but dictyosome numbers decreased in all species as treatment temperatures were lowered to 0 C. Mitochondria expanded slightly at reduced temperatures, but with little difference detected between species. The study indicated that the various cellular components of these species responded differently to reduced temperatures, with the species differing mainly in degree of response.

Ultrastructural aspects of shoot initiation in tobacco callus cultures

Abstract: An ultrastructural investigation of shoot initiation in tobacco (Nicotiana tabacum L. var. W. 38) callus cultures was made. Zones of preferential division were observed in the basal portion of the tissue by eight days in culture and these led, sequentially, to meristemoids, primordia, and shoots. During the initial stages of meristemoid formation, protein inclusions and large accumulations of plastid starch were present in the cells, while vacuoles were filled with membranous and cytoplasmic protrusions. At later stages of meristemoid development, these features were not observed in the cells, which were also smaller in size and possessed numerous small, peripheral vacuoles. It appears that the membranous and cytoplasmic protrusions are involved in vacuolar reduction during meristemoid formation. It would also appear that the storage materials supply the energy and other reserves needed for the organogenetic process. By contrast, tissue cultured under nonshoot-forming conditions and nonmeristemoid regions of shoot-forming tissue remained parenchymatous over the same time period. ZONES OF preferential cell division occur in the parenchymatous tissue of callus cultures of tobacco by day 8 (Thorpe and Murashige, 1970). Meristemoids arise from these areas, although not all areas of preferential cell division give rise to these structures. Meristemoids (Torrey, 1966) are the meristem-like aggregations of small, nonpolar cells which appear to be nonvacuolate at the light microscope level and from which primordia and ultimately leafy vegetative shoots are formed (Murashige, 1964; Thorpe and Murashige, 1970). The mechanism of meristemoid formation in tissue cultured under organ-forming conditions is not yet known, although it has been suggested that these could arise from single cells (Torrey, 1966). Associated with meristemoid development is a rapid increase and decrease in the amount of stored starch in tobacco callus (Thorpe and Murashige, 1968, 1970). This starch may serve as a source of energy for shoot formation which, judging by the respiratory activity of the tissue (Thorpe and Meier, 1972; Ross and Thorpe, 1973), has a high energy requirement. In this study, ultrastructural changes during meristemoid formation and shoot initiation were investigated. MATERIALS AND METHODS-Tobacco (Nicotiana tabacum L. var. 'Wisconsin 38') callus was isolated from stem pith segments and maintained on three-quarter strength Murashige-Skoog (MS) 1 Received for publication 27 November 1972. Supported by NRC of Canada grant no. A-6467 to T.A.T. medium (Murashige and Skoog, 1962). For shoot production, the tissue was grown on the modified MS medium reported earlier (Thorpe and Murashige, 1970) except that the concentrations of Ltyrosine, adenine sulphate, and NaH2PO4 H20 were reduced by half. The medium contained indole-3-acetic acid and kinetin in final concentrations of 10-5M. Cultures were maintained in darkness in 125-ml Erlenmeyer culture vessels containing 50 ml of medium. Sections of tobacco callus, each measuring ca. 3 x 3 x 2 mm, were used as inoculum. Thin sections, cut by hand, parallel to the surface in contact with the medium were irrigated with fixative (2/2 % glutaraldehyde) and scanned under a binocular microscope. Areas of preferential division, with prominent nuclei, and areas of shoot initiation were excised and prepared for electron microscopy. Each piece of tissue was ca. 1 mm3. Tissue was sampled from 8-, 10-, 12-, and 14-day-old shoot-forming tissue and from 8-, and 14-day-old nonshoot-forming tissue. Freehand monitor sections were also stained with iodinepotassium iodide (Jensen, 1962). Heavy blueblack staining for starch occurred in the regions visually determined as areas of preferential cell division or meristemoids (Thorpe and Murashige, 1968). The tissue samples were prefixed in 21?% glutaraldehyde in 0.1 M phosphate buffer, pH 6.8 -+ 0.5 for 4 hr. Following buffer washes, the material was fixed in 1 % unbuffered Os04 for 50 min. The tissue was then dehydrated in an ethanolic series after a further buffer wash and embedded in ERL-4206 (Spurr, 1969). Staining was

The ninety‐year period for dr. beal's seed viability experiment

Abstract: In 1879 Dr. W. J. Beal selected seeds of 23 different species of locally common plants, mixed 50 seeds of each species with moist sand in unstoppered one-pint bottles, and buried the bottles in a sandy knoll to be unearthed and the viability of the seeds tested periodically. The year 1970 marked the ninetieth year the seed had been buried, and the thirteenth bottle was recovered to test for seed viability. Of the three species which had germinated in the 1960 test (curly dock, Rumex crispus; evening primrose, Oenothera biennis; and moth mullein, Verbascum blattaria), only V. blattaria had viable seed with 20% germination. No other species germinated. All ten seedlings of V. blattaria were grown to maturity, and seeds were then harvested to study the possible deviations from normality and the requirements for seed germination. All seedlings emerging from the first progeny seed appeared normal. The most prominent requirement for germination was light, and this is a possible explanation of why the seeds had remained viable but dormant for so long a period. One-third of the freshly harvested seed germinated in darkness and, furthermore, redrying of dark-moistened seed in the absence of light induced additional germination. Germination of dark-moistened seed was not completely restored when the still moist seeds were subsequently exposed to light. However, when dark-moistened seeds were dried and then remoistened in the light, germination was about 95 %. About 5 % of the seed did not germinate under the conditions used. We find that 5 % of the population of V. blattaria seeds are dormant for unknown reasons, that 30 % will germinate if supplied only with moisture, and that 65 % are inhibited and require light and moisture simultaneously for germination. Supplying this 65 % of the population with moisture in darkness results in the development of a second type of inhibition which is no longer light reversible. It appears that the simultaneous requirement for light and moisture is an important factor in permitting V. blattaria seeds to remain dormant during prolonged burial. THE SPRING OF 1970 marked the 90-year period for the seed viability experiment initiated by Dr. W. J. Beal, then professor of botany and forestry at the Michigan Agricultural College in East Lansing. The experiment is best described by Dr. Beal (1905): "In the autumn of 1879 I began the following experiments, with the view of learning something more in regard to the length of time the seeds of some of our most common plants would remain dormant in the soil and yet germinate when exposed to favorable conditions. I selected fifty freshly grown seeds from each of twenty-three different kinds of plants. Twenty such lots were prepared with the view of testing them at different times in the future. Each lot or set of seeds was well mixed in moderately moist sand, just as it 1 Received for publication 12 May 1972. This work was supported, in part, by The National Science Foundation (GB-18353X). Journal Article No. 5920 from the Michigan Agricultural Experiment Station. We wish to thank Professor J. A. D. Zeevaart and Mr. Donald E. Davis for their help and consultation and for the use of greenhouse facilities supported by the Atomic Energy Commission, Contract AT-(11-1)-1338. was taken from three feet below the surface, where the land had never been plowed. The seeds of each set were well mixed with the sand and placed in a pint bottle, the bottle being filled and left uncorked, and placed with the mouth slanting downward so that water could not accumulate about the seeds. These bottles were buried on a sandy knoll in a row running east and west." During the first 35 years of the experiment, germination tests were performed every fifth year, and every tenth year thereafter (Beal, 1884, 1885, 1889, 1894, 1904, 1905, 1911; Darlington, 1922, 1931, 1941, 1951; Darlington and Steinbauer, 1961). The thirteenth bottle was recovered for testing on April 18, 1970, leaving seven more bottles for future tests. GERMINATION TESTS WITH THE BEAL SEEDSGermination tests were performed in a greenhouse during the summer months of 1970. A soil mixture, consisting of approximately equal parts of well-sifted loam, sand, and muck soil, was steamsterilized for 12 hr under 10-12 lb pressure. Three clean plastic trays, with perforated bottoms

Seasonal variation in the volatile terpenoids of juniperus scopulorum (cupressaceae)

Abstract: The volatile oils of four trees of Juniperus scopulorum were examined at 9 am, 12 noon, 3 pm, 6 pm, 10 pm, 2 am, and 6 am on consecutive days with a temperature range of 64 F and 88.5 F daily. Three-way analysis of variance of 37 compounds revealed 36 with significant differences among trees, 11 with significant differences between days, 13 compounds with significant diurnal variation and 9 compounds which showed some significant interaction term differences. Most of the variation occurred among trees. Oxygenated terpenes and sesquiterpenes tended to increase during the day while sabinene decreased until late evening and increased during the early morning. Correlations with temperature appeared to lag and did not match the pattern in three species of Juniperus reported by other investigators. The effect of diurnal variations on chemosystematic classifications was estimated by using numerical taxonomy and principal coordinate analysis. Diurnal effects were not found to be important sources of error for chemosystematics in J. scopulorum if character weighting were used to maximize the genotype differences. However, this may not be true for work involving population sampling of other species over large regions.

Genetic load in osmunda regalis populations

Abstract: A B S T R A C T Osmunda regalis sporophytes form haploid spores which develop into functionally hermaphroditic gametophytes. The self-fertilization of such gametophytes results in zygotes which are completely homozygous. Spore samples collected from sporophytes in natural populations were used to establish gametophyte cultures. The majority of these gametophytes were unable to form viable embryos when only self-fertilization was possible. Controlled selfing and crossing experiments revealed that the inability of these homozygous embryos to develop normally is attributable to the presence of recessive lethals. To account for this genetic load, an hypothesis is proposed integrating the morphology and ecology of the gametophyte generation with the polyploid genetic system of the sporophyte generation.

Reproductive biology of weedy and cultivated mirabilis (nyctaginaceae)

Abstract: The reproductive biology of Mirabilis nyctaginea (Michx.) MacM. contributes to the plant's success as a weed and invader of disturbed habitats whereas that of M. Jalapa L. reflects its success as a cultivar. Plants of M. nyctaginea flowering in early summer produce chasmogamous flowers whereas plants flowering in late summer produce cleistogamous flowers. Plants of both species are self-compatible and flower behavior contributes to self-pollination. The flowers open late in the afternoon and close late the following morning. In M. nyctaginea flowers are effectively pollinated by bees both in the afternoon and morning, and during the night moths are effective pollinators. Mirabilis Jalapa is self-pollinating. Anther closure during rain showers, a result of water droplets falling into open anthers, minimizes pollen loss and is highly adaptive. The reproductive biology of M. nyctaginea and M. Jalapa is contrasted with that of the obligate outcrossing species M. multiflora (Torr.) Gray and M. froebelii (Behr) Greene. THE EVOLUTION of weedy and cultivated plants from obligate outcrossing ancestors is often paralleled by significant changes in the breeding systems of those plants (Baker, 1965, 1967; Rick, 1950; Hutchinson, 1965; Cruden, unpublished). Such changes include a decrease in flower size, decrease in the pollen-ovule (P/0) ratio, switching from self-incompatible to self-compatible, and changing from cross-pollinating to self-pollinating. Within Mirabilis (Nyctaginaceae) are included a weedy species, M. nyctaginea (Michx.) MacMill.; a cultivar, M. Jalapa L.; and numerous native selfincompatible, obligate outcrossing species, e.g., M. multiflora (Torr.) Gray and M. froebelii (Behr) Greene. Differences in floral behavior and reproductive biology in Mirabilis illustrate some of the changes that occur during the evolution of either a weed or a cultivar. In this paper I describe the reproductive biology of M. nyctaginea, comment on the floral behavior of M. Jalapa, suggest that pollination need not result in fertilization, and compare the reproductive biology of these species with those of M. multiflora and M. froebelii.

Morphology of glandular hairs of cannabis sativa from scanning electron microscopy

Abstract: Three distinct types of glandular hairs of increasing morphological complexity which occur on flowering tops of Cannabis sativa L. (marihuana) are described from scanning electron microscopy. These gland types-termed bulbous, capitate-sessile, and capitate-stalked, described from pistillate plants-occur in greatest abundance on the outer surface of bracts ensheathing the ovary. Bulbous and capitate-sessile glands, which arise at an early stage in bract development, are scattered over the bract surface. Mature bulbous glands have a small swollen head on a short stalk, whereas capitate-sessile glands have a large globular head attached directly to the bract surface. Because of their numbers and large size, capitate-sessile glands are the most conspicuous gland type during the early phase of bract development. Capitate-stalked glands, which have a large globular head on a tall, multicellular stalk, differentiate during subsequent bract development. These stalked glands arise first along the bracteal veins and then over the entire bract surface. A voluminous, fluid secretory product accumulates in the glandular head of all three types. These glands are believed to be a primary site of localization of the marihuana hallucinogen, tetrahydrocannabinol.

Studies of a marine grass, thalassia testudinum. i. ultrastructure of the osmoregulatory leaf cells

Abstract: A B S T R A C T Thalassia testudinum (Turtle Grass), a marine monocot which grows completely submerged, differs from intertidal and other halophytic angiosperms in that it has no specialized saltsecretory glands. Osmoregulation appears to be accomplished by the epidermal leaf cells which have highly invaginated plasmalemmas with numerous mitochondria situated in the interdigitations. The ultrastructure and proposed mode of secretion are similar to that of the salt-marsh monocot Spartina, but differ from that found in dicots. Evidence is presented to show why monocots are the only angiosperms which have adapted to a completely marine environment. OF ALL VASCULAR PLANTS only certain monocotyledons can survive completely submerged in salt water. Both monocots and dicots live in freshwater habitats, and both are found as intertidal species. The most obvious difference between a

Post-pollination phenomena in orchid flowers. iv. effects of ethylene

Abstract: Treatment of Cymbidium (Orchidaceae) flowers with 10,ul/liter ethylene for up to 78 hr induces anthocyanin formation in both gynostemia (columns) and labella (lips). After that, pigment levels decrease. During 24-hr exposures, ethylene concentrations of 0.1, 1, and 10,ul/ liter cause increased anthocyanin levels in both lips and columns. Ethylene also brings about color changes in the calli and wilting of the perianth, but it does not cause straightening of gynostemia and stigmatic closure. Emasculation effects are similar to those of ethylene, whereas pollination and NAA induce anthocyanin formation and closing of stigmas, as well as swelling and loss of curvature in gynostemia. The effects of ethylene are correlated with its action in other systems. ETHYLENE CAUSES certain post-pollination phenomena in orchid blossoms including anthocyanin formation, fading, shortened flower life, and wilting of sepal tips known as "dry-sepal" injury (Crocker, Zimmerman, and Hitchcock, 1932; Lindner, 1946; Davidson, 1949; Fischer, 1950; Akamine and Sakamoto, 1951; Jester, 1952; Saylor, 1954; Kendrick et al., 1956; Middleton et al., 1956; Anonymous, 1960; Akamine, 1963; Burg and Dijkman, 1967; Clayton and Platt, 1967; Dijkman and Burg, 1970; Hindawi, 1970). Pollination, emasculation, and auxin treatments can all cause ethylene evolution which, at least in Vanda, is autocatalytic (Akamine, 1963; Burg and Dijkman, 1967; Dijkman and Burg, 1970). This is particularly noticeable during shipment of flowers in closed containers, where damage such as simple dislodgement of pollinia, can induce ethylene evolution from a single flower (Akamine and Sakamoto, 1951). When this happens, a blossom may evolve enough ethylene to cause either direct damage or bring about production by 1 Received for publication 11 January 1973. Supported in part by grants from the American Orchid Society Fund for Research and Education, the National Science Foundation (GB-13417), and the Orchid Digest Corporation Research Fund; as well as Office of Naval Research Contract, NR 1008-796 (to J. A.) and an NSF undergraduate summer research award (to N. M. H.) We thank Mrs. Samuel Mosher and Mr. Robert I. Norton, Dos Pueblos Orchid Co., Goleta, California for donating the flowers; Mr. C. L. Knowles, Acme Glass and Vial Co., for a gift of orchid tubes and caps; Drs. Fred B. Abeles and Stanley P. Burg for reading and commenting on the manuscript, and Ms B. Flick for technical assistance. 2 See Arditti and Knauft, 1969, for part I; Arditti, Flick, and Jeffrey, 1971, for part II; and Arditti, Jeffrey, and Flick, 1971,-for part 111. other flowers. Eventually enough ethylene may accumulate in a box to damage all blossoms. Since auxins induce ethylene formation in a number of systems, including orchids (Burg and Dijkman, 1967), some of their effects have been attributed to the gas. The same is true regarding several post-pollination phenomena in orchid flowers (Burg and Dijkman, 1967; Arditti, 1969, 1971a, b; Arditti and Knauft, 1969; Dijkman and Burg, 1970; Knauft, Arditti, and Flick, 1970; Arditti, Flick, and Jeffrey, 1971; Arditti, Jeffrey, and Flick, 1971). In addition, both abscisic acid (ABA) and gibberellin (GA) have been suggested to initiate ethylene evolution (Addicott and Lyon, 1969; Pratt and Goeschl, 1969). Therefore, their effects on orchid flowers could be due, at least in part, to ethylene evolution they may induce. Thus, to understand the causes of postpollination phenomena in Cymbidium flowers better, it was necessary to determine the exact effects of ethylene itself. MATERIALS AND METHODS-Flowers of Cymbidium 'Samarkand' (Dos Pueblos Orchid Co., Goleta, California) were selected for uniformity and freshness. Ovaries and pedicels were surface sterilized by a 5-minute immersion in saturated calcium hypochlorite (Wilson, 1915)-a treatment previously shown to have no deleterious effects. The flowers were then inserted into rubbercapped tubes (Acme Glass and Vial Co., Los Angeles, CA.) containing a modified Knudson C medium (Knudson, 1946; Ito, 1961; Arditti and Knauft, 1969). Culture vessels and media were sterilized by autoclaving several days before they were used to allow for dissipation of any ethylene

Monotropa uniflora: ultrastructural details of its mycorrhizal habit'

Abstract: A microscopic survey of the achlorophylus plant Monotropa uniflora L. reveals an ectendotrophic mycorrhizal fungus with dolipore septa associated with the roots. Special transfer regions are found in the root cell wall ensheathing all but the ruptured tip of the fungal intrusion. MONO)TROPA HAS long fascinated biologists because its waxy white appearance indicates that it is unusual among flowering plants. Its absence of chlorophyll (less than 0.001 mg per gram fresh weight) and therefore its inability to produce metabolic materials by the photosynthetic fixation of CO2 has led many experimenters to investigate the mysteries of its rather novel existence. The historical details as well as the descriptive and physiological literature has been admirably re

Abnormal reductional and nonreductional meiosis in ceratopteris: alternatives to homozygosity and hybrid sterility in homosporous ferns

Abstract: Natural and synthesized hybrids of Ceratopteris were investigated to determine the effect of hybridization on the genetic system. Studies indicated that the hybrids exhibited massive spore abortion and pairing abnormalities at meiotic prophase, characteristic of "sterile diploids and triploids" reported in hybridization studies of other fern genera. However, a small percentage of viable spores also was produced by the hybrids. Cytological investigations indicated the presence of previously unreported meiotic adaptations that allowed the production of unreduced spores and reduced spores exhibiting chromatid heterozygosity. The reduced spores allow haploid gametophytes to form heterozygous zygotes in spite of intragametophytic selfing. The unreduced spores were shown to be responsible for the fertility of the "sterile" hybrid and allowed the subsequent production of up to three generations of sporophytes. The literature suggests that these meiotic adaptations are present in other fern genera and may play a significant role in evolution through hybridization.

Cytokinin-gibberellin regulation of shoot development and leaf form in tobacco plantlets'

Abstract: cytokinin 6-(3-methyl-2-butenylamino)purine (2iP). Increasing levels of both growth substances resulted in the production of greater amounts of both callus and shoot tissue. More buds were induced when the cytokinin level was increased, and this effect was counteracted by raising the GA.3/2iP ratio. Furthermore, the size and form of the shoots depended on the GA3/2iP ratio. High ratios resulted in tall, spindly plants with narrow leaves while low ratios resulted in short shoots with rounded leaves.

Conidiogenesis in ceratocystis ulmi, ceratocystis piceae, and graphium penicillioides

Abstract: Conidiogenous cells of both the synnematous and mononematous conidiophores in Cer-atocystis ulmi and C. piceae develop by sympodial proliferation. Holoblastic conidia are produced on nodules or short denticles from the synnematous conidiogenous cells and on well-defined denticles from the mononematous conidiogenous cells. Graphium penicillioides is characterized by percurrent proliferation of the conidiogenous cells and the conidia are holoblastic and annellidic. A comparison of the type material of G. penicillioides with the lectotype specimen of C. piceae indicates that G. penicillioides is not the conidial state of C. piceae. The method of conidial development in C. ulmi and C. piceae is distinct from that of G. penicillioides, the lectotype species of Graphiumn; these conidial states are, therefore, placed in a new hyphomycete genus, Pesotum, as the Pesotuin state of Ceratocystis ulmi and C. piceae, respectively. THE CONIDIAL STATE of Ceratocystis ulmi (Buism.) C. Moreau was described as Graphium ulmi by Schwarz (1922). She recognized three stages of this form species: the mycelium stage, termed Cephalosporium-like, in which the hyphae were slightly swollen at the tip, with numerous sterigmata that delimit the small spores which she called primary conidia, or form A; the yeast-like stage, or form B, which consists of secondary conidia formed by budding of the primary conidia; and the stilbaceous stage which was the basis for placing this fungus in the genus Graphium Corda. Wollenweber (1927), May (1931), May and