摘要:

Using the young capitulum ofHelianthus annuusL., a cylindrical plug of undifferentiated receptacle tissue, 1 mm in diameter, was isolated from lateral communication with the rest of the receptacle surface by a vertical circular wound cut, while retaining continuity with the subapical meristem. Within 24 hr, active cell division was induced at the inner and outer surfaces of the wound and in the receptacle epidermis bordering the wound edges, creating a rounded rim at the top of the wound. Within 3–6 days, floral initials, spaced 133–166μm apart appeared on the flanks of both rims and later on the top of the plug and surrounding receptacle surface. The first formed initials developed into involucral bracts or ray florets and the later ones into disc florets which were organized into contact parastichies, the number of which did not conform with the Fibonacci series. The base of the plug developed into a stem‐like structure completing the regeneration of a fully formed functional capitulum. This operation was demonstrated for two sunflower cultivars and occurred in both long and short daylengths.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb14185.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

The pollination of red, pink, and white color morphs ofIpomopsis aggregatawas evaluated to assess whether ethological isolation based on pollinator color discrimination may occur. We observed animal visitors, assessed pollen delivery, seed set per fruit, percentage of flowers setting fruit, nectar production, and timing of flower opening for different color morphs in the Front Range of Colorado. Based on traditional zoophilous flower classifications, we expected hummingbirds to pollinate red‐floweredI.aggregatasubsp.collinaand hawkmoths to pollinate white‐floweredI.aggregatasubsp.Candida.However, ethological isolation does not appear to occur among color morphs ofI.aggregatain the Front Range. Hummingbirds visited red‐flowered plants in excess overall, and, to a lesser extent, so did hawkmoths. Both hummingbirds and hawkmoths visited all color morphs and probably transferred pollen among them. Pollen delivery data and a day‐night bagging experiment also suggest that pollinators do not necessarily behave as predicted by flower classifications. In addition, there is little evidence for major differences between red, white, and pink flowers in any aspects of reproductive biology. Indeed, most variation occurs within a given color morph.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb14186.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

MostAmelanchier arboreaflowers have 10 ovules, but the number of filled (embryo‐containing) seeds per fruit is usually less than 10 and is highly variable within each individual plant. Because fruit developmental time correlates with seed number, this variation in seed number results in asynchronous fruit ripening. Field experiments tested whether seed number was pollen‐ or resource‐limited. Manipulation of resources in the shoot at the time of fruit initiation by defoliation, girdling, fruit thinning, or foliar feeding had no significant effect on seed number per fruit, although fruit set and seed weight were affected. Supplemental cross‐pollination also had no demonstrable effect on seed number. Most ovules that do not become filled seeds are visible as small “undeveloped seeds”; these are not necessarily aborted seeds as this was also the fate of ovules in unpollinated carpels. Alternative hypotheses for the determination of seed number are proposed and discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb14187.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Uniaxial tensile tests of solid and hollow cylindrical plugs of pith parenchyma from potato tubers indicate the tensile modulus of elasticity, E, can vary significantly as a function of tissue transverse area and water potential. E increases from 1.2 to 19 MPa as ψwchanges from ‐1.4 to ‐0.4 MPa. E increases from 5 to 19 MPa as transverse area of solid tissue sample increases from 0.2 to 2.5 cm2. Variations in E accompanying changes in transverse area appear to be related to cell number along the radii of plugs. Hollow cylindrical plugs for which wall thickness is maintained but total tissue area is changed show constant values of E. It is suggested that shear stresses within tissue samples influence E and are dependent upon cell number and tissue water content. Material with these properties would be a “poor choice” for constructing plant organs experiencing repeated stress and periodic dehydration. However, ground tissue may act as a buffer against localized ovaling of stem and leaf cross sections under loading.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb14188.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Salt stress may impose osmotic and respiratory costs on nonhalophytes that limit the availability of carbohydrates for growth. This was examined in kenaf (Hibiscus cannabinusL.) by the analysis of soluble carbohydrates, starch, and respiration rates in mature and expanding leaves from plants exposed to moderate salt stress. Plants were grown for 35 days in solution culture at 1, 37, and 75 mM NaCl under greenhouse conditions. Total carbohydrates increased in mature and expanding leaves with increasing salinity. The majority of this increase was as starch. Mature leaf respiration also increased under salt stress. The net accumulation of non‐osmotically active carbohydrates in expanding leaves suggests that growth was not limited by the generation or availability of carbohydrates but rather by the ability of the plant to effectively utilize this substrate in osmotic adjustment and growth.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb14189.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

The degree of leaf dissection differs dramatically among populations of theAchillea millefoliumcomplex along an altitudinal gradient in the Sierra Nevada. The purpose of this study was to determine whether there was a genetic basis to differences in leaf shape among populations, and also to determine the importance of genetic variability within populations, plastic responses of leaf shape to the growth environment, and genetic differences among populations in plastic response to the environment. A second major goal of the research was to investigate the effects of differences in leaf dissection on the capacity for leaf temperatures to become uncoupled from air temperatures. Greenhouse experiments using clonal replicates of plants collected at different altitudes revealed that there were genetic differences among populations in the degree of dissection, and that other sources of phenotypic variation, such as plasticity, were also significant. Leaves from the highest altitude population had the most compact shape under all conditions, while those from lower altitude populations were always more open and highly dissected. In both simulations and actual measurements the dissected leaves of low altitude plants remained close to air temperatures, while the compact leaves of high altitude plants had the capacity to warm up substantially above air temperatures.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb14190.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Seeds collected from fiveAmaranthus dubiusplants of the same population were weighed and tested in continuous light or darkness at three temperatures in controlled conditions. Different seed families differed in weight, germination percentages and rate, and responded differently to an increase in temperature from 25 to 38 C. Plants derived from these seed families and grown outdoors, either singly or in mixtures, differed in several growth characteristics and in time to flowering. Significant interactions between growth characteristics and growth conditions, as measured with a two‐way ANOVA, suggest that plants derived from different individuals differ in their competitive ability. The progeny of different individuals may thus be favored in different environmental conditions.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb14191.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Two types of tubular secretory reservoirs occur inAmbrosia trifida, the first such example known in plants. Paraffin and resin sections, and clearings showed that, although each type consists of many separate unbranched tubes, they differ in anatomy, secretory contents, distribution, and length. Reservoirs (PAR) containing a red substance (presumably a polyacetylene) and lined with a biseriate epithelium parallel the largest leaf and stem vascular bundles. One PAR arises near the base of each leaf lobe midrib and extends through the petiole to the node or continues in the stem cortex to the node below. Other PARs start at the cotyledonary node or in cotyledons and extend down into the primary root, where they have only a single layer of unspecialized epithelium. PARs realign themselves, and more form de novo, until the primary root has two to four separate arrays of PARs abutting the endodermis, each with three to six parallel PARs. Branch roots have similar PAR arrays but unconnected to PARs of the parent root. Inflorescence PARs occur only in bracts, and in petals of male flowers. The second type of reservoir (OR) has a uniseriate epithelium and contains an unidentified oil. ORs occur in phloem, and in pith next to xylem, of stem and large leaf bundles. They dwindle in successively smaller veins until the two smallest orders lack them. ORs occur only in phloem in the hypocotyl; none occur in cotyledons, roots, or floral parts.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb14192.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

In many plants, the frequency of geitonogamous (within‐plant) pollination is likely to increase as a function of the number of simultaneously blooming flowers. This increase in self‐pollination often produces inbreeding depression. Thus, a dilemma may exist in that individuals cannot increase seed production without lowering the average fitness of each seed. Conditions necessary for the existence of the dilemma were confirmed in large individuals of the herbaceous perennialGeranium caespitosum.Manually geitonogamously pollinated flowers initiated as many fruits as manually outcrossed flowers, but showed a subsequently greater number of embryo abortions, matured fewer seeds, and had a lower average seed weight. Observations of pollinators and dye transfer showed that geitonogamous bee pollinations increased as the number of flowers per plant increased. A simple model predicted that detrimental effects from geitonogamy become likely when 55 flowers are simultaneously blooming. Plants with 55 or more flowers produced 30% of the flowers in populations. The effect, and possible circumvention, of the dilemma onGeranium, and angiosperm breeding systems in general, is discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb14193.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Budgets of organic matter dynamics for plant communities of the Great Dismal Swamp were developed to summarize an extensive data base, determine patterns of biomass allocation, transfer and accumulation, and make comparisons with other forested wetlands. Aboveground net primary production on the flooded sites (1,050–1,176 g m‐2yr‐1) was significantly greater than on a rarely flooded site (831 g m‐2yr‐1). Estimates of belowground net primary production were comparable to aboveground production on flooded sites (824–1,221 gm‐2yr‐1). However, productivity was nearly three times greater belowground than aboveground on the rarely flooded site (2,256 g m‐2yr‐1). Aboveground productivity in Dismal Swamp forests is relatively high compared to other forested wetlands. This is attributed to the timing and periodic nature of flood events. Fine root turnover is shown to be an important source of soil organic matter. Estimates indicate that roots contribute about 60% of the annual increment to soil organic matter. Leaflitter contributes 6–28% and wood debris contributes 5–15%. Comparisons with other forested wetlands suggest that detritus accounts for greater than half of the total organic matter (living + dead) in many wetland systems.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb14194.x

出版商:Wiley    

年代:1988

数据来源: WILEY