摘要:

Boltonia decurrens(Torrey&Gray) Wood, a perennial species endemic to the Illinois River Valley, is threatened with extinction. Construction of a system of dikes along the Illinois River has altered flood patterns during the last 100 years, converting wet prairies and natural marshes to cropland. Remaining shore habitats have been modified by heavy siltation and altered flooding regimes.Boltonia decurrensis now confined to areas that are disturbed by occasional cropping, disappearing from sites after 3 to 5 years of natural succession. This study was conducted to determine the role of light and water availability upon growth and reproduction. Our data indicate that under greenhouse conditionsB. decurrensrequires high levels of light for optimal photosynthesis and growth, and is more sensitive to reductions in growth light level than to moderate drought‐stress. This sensitivity to light regime may help explain its disappearance from disturbed areas after several years of natural succession. IfB. decurrensis overtopped by fast‐growing species, it could be shaded to the extent that growth and seed production would be severely affected, increasing the likelihood of its extinction.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15305.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Fossil angiospermous stamens with in situ pollen from the Turonian (ca. 90 million years before present, Late Cretaceous) of New Jersey are described and assigned to the Chloranthaceae. The fossil stamens, which are three‐parted and bear two bisporangiate thecae on the central lobe and one bisporangiate theca on each lateral lobe, are indistinguishable from stamens of several extant species ofChloranthus.The pollen is spheroidal, 13–18μm in diameter, with a reticulate exine and apparently elongate/elliptical apertures. The pollen is similar to that in extantChloranthusin grain size, shape, exine sculpture, and aperture structure. Like pollen of some extant species ofChloranthus,aperture number in the fossil pollen appears to be variable. Because fossil pistillate chloranthoid reproductive structures have not been found at this locality it is unknown whether the fossil stamens described here were borne on the side of the ovary, as in extantChloranthus,or in another arrangement. The three‐parted stamen ofChloranthusis unique in angiosperms and there has been considerable debate concerning the origin and evolutionary significance of the structure. Uncertainty as to whether the three‐parted stamen represents a synapomorphy for the genus or a retained plesiomorphy in angiosperms is the primary reason why these fossil stamens are not assigned to the extant genusChloranthus.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15306.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Tissue mineral concentrations of calcium, copper, iron, magnesium, manganese, nitrogen, phosphorus, potassium, sodium, and zinc, and long‐term water‐use efficiency (as estimated by δ13C±) were measured in the mistletoePhoradendron leucarpumand its hosts to investigate the relationship between nutrient concentrations and water economies of the parasite and hosts. The mistletoe had mineral concentrations 0.97 to 2.88 times greater than the hosts. Mean long‐term mistletoe water‐use efficiency (‐27.89±) was comparable to mean long‐term host water‐use efficiency (‐27.69±) and generally greater than the water‐use efficiency reported for most mistletoe species. Differences between mistletoe and host water‐use efficiency ranged from +0.65 to ‐0.75± and were more similar to mistletoes found growing on nitrogen‐fixing host species as reported in other studies. Mistletoe nutrient concentrations, in particular nitrogen, were not related to changes in mistletoe water‐use efficiencies. Nutrient: calcium ratios indicated that mistletoes acquire nutrients in excess of that which can be delivered by the host xylem. These data are discussed relative to the passive vs. active theories of nutrient uptake.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15307.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Small dispersed anther contents ofClavalipollenitesgrains are reported from the Early Cretaceous (early Aptian) of Patagonia. This report represents the first documentation of in situ grains of this type from the Southern Hemisphere. The anthers are small (0.6 mm long × 0.25 mm wide); no tissues of the androecium are preserved nor is there any indication of how the sacs were attached. Some grains are still in tetrads and closely associated with numerous orbicules and tapetal membranes. Grains are 18–22μm long and up to 15μm wide. The exine consists of an inner homogeneous nexine that supports narrow columellae below a perforate tectum. The mature pollen wall includes uniform microgranules that ornament the muri. The chloranthaceous affinities of these Gondwana pollen sacs are established and the grains are compared with specimens recovered from slightly older or coeval sediments from the Northern Hemisphere. The discovery of these pollen sacs from Patagonia expands our understanding of early angiosperm biogeography.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15308.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Leaf movements, water status, and gas exchange were measured in soybean inoculated withBradyrhizobiumand grown under high and low soil water and nitrate availabilities. We hypothesized that paraheliotropism in low NO3‐grown plants (which have greater N2fixation rates) would differ from that of high NO3‐grown plants (which have lower N2fixation rates), such that carbon return on nitrogen investment into photosynthesis would be enhanced. Low NO3‐low water plants had more vertical leaf angles and received lower solar irradiances at midday than high NO3‐low water plants. Under constant, vertical illumination, low NO3‐low water plants had steeper leaf angles, increased rates of leaf movement, lower photosaturated photosynthetic rates, and lower stomatal conductances for a given leaf water potential than high NO3‐low water plants. Leaves of high NO3plants had lower photosynthetic nitrogen use efficiencies than did low NO3plants. Low water plants had lower leaf osmotic potentials and ratios of intercellular/ambient CO2concentration than high water plants, but NO3treatment did not affect these parameters. Results provided support for our initial hypothesis, and demonstrated a high degree of correspondence between gas exchange and heliotropic response to soil nitrogen and water availabilities in soybean.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15309.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

This study was conducted in a phryganic (East Mediterranean) ecosystem at Daphni, near Athens, Greece. The Labiatae, represented by ten species belonging to nine genera, dominate in this ecosystem type. They flower from February to July. Both flowering time and nectar quantity are related to the species ability to tolerate intense water stress. Labiatae are visited by 201 insect species. Of these, 43 are exclusively supported by the family and 37 are monotropous. Solitary bees (mainly Anthophoridae, Megachilidae, Halictidae) constitute 47.3% of pollinators. The family is important in hosting specialized bees (15 species) in phrygana, particularly late in the flowering season. Labiatae species form two equally represented groups in this system; namely, the late winter‐early spring (early) flowering, visited by relatively few pollinator species, and the late spring‐summer (late) flowering species, visited by numerous pollinators. This temporal distinction is accompanied by different pollination profiles that include duration of anthesis, reward to pollinators, floral attractiveness, and flower character differentiation. All of these attributes are maximized in the early flowering period. This strategy suggests a mechanism for resource partitioning at a time when the pollinator resource is limited and competition for the services of pollinators is expected to be intense. Contrary to the current theory concerning cornucopian species, the copiously rewarding flowers of Labiatae in phrygana are not those abundantly serviced by pollinators.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15310.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Flower biology and pollination ofMoneses uniflora, Orlhilia secunda, Pyrola minor, P. rotundifolia, P. chlorantha,andChimaphila umbellataare described and discussed in relation to patterns in sexual traits and possible evolution of buzz‐pollination within the group. The large number of pollen grains are packed into units of monads inOrthilia,tetrads inMonesesandPyrola,or polyads inChimaphila.Pollen is the sole reward to visiting insects except in the nectar‐producingO. secundaandC. umbellata.Correlations are present between several sexual traits. Pollen: ovule ratios are very low, indicating efficient pollen transfer. Use of polyads may reduce the number of siring males. This trend may be counteracted by larger stigmas as in C.umbellata.Increasing pollen unit size may enhance relatedness of seeds, reduce abortion, and improve seed set. This may explain the evolution, within the Pyrolaceae and other families, of higher ovule numbers with larger pollen units. The plants are mainly pollinated by bumblebees.Chimaphila umbellatais visited by nectar‐collectors;Moneses uniflora, Pyrola minor, P. rotundifolia,andP. chloranthaare visited exclusively by pollen‐buzzers; andOrthilia secundais visited by both nectar‐collectors and pollen‐buzzers. Nectar secretion is suggested to be an ancient attractant in the group with C.umbellatahaving the least specialized pollination system, and buzz‐pollination inM. unifloraand in the studiedPyrolaspecies regarded as an advanced system.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15311.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

I describe patterns of sex allocation and gamete packaging in the andromonoecious lilyZigadenus paniculatus.In this species, pistil length was continuously, but bimodally, distributed within plants, and smaller pistils contained fewer mature ovules. In hermaphrodite flowers, ovule number per flower increased with blooming rank in small plants but decreased with blooming rank in large plants. Flowers with pistils less than three‐fourths stamen length almost never produced fruits and were classified as males. The pedicel, tepals, stamens, and pistil of hermaphrodite flowers were all heavier than those of males. Hermaphrodite flowers were concentrated on the terminal raceme, males on the lower racemes. In combination with acropetal blooming, this spatial separation of flower types resulted in a seasonal decline in the proportion of open flowers that were hermaphrodite. However, individual flowers were protandrous, so that the population sex ratio, initially strongly male‐biased, declined as the season progressed. Hand pollinations showed that plants were self‐incompatible. Inflorescence size was positively correlated with bulb size, and plants with large inflorescences had a higher proportion of male flowers. Nutrient supplementation had no effect on inflorescence size, but increased the proportion of hermaphrodite flowers. Nutrient‐supplemented plants also began blooming earlier than controls. I discuss these patterns in relation to the adaptive significance of andromonoecious breeding systems.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15312.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Nepenthes gracilis, a dioecious carnivorous plant, has inconspicuous flowers lacking petals. Nectaries distributed on the upper surface of four sepals secrete dilute nectar (3%–12% sugar concentration) at night, but the nectar immediately disappears during the day by evaporation in the sunny environment of Sumatra. Male flowers have a higher nectar production rate but lower sugar concentration of nectar than female flowers. Flowers of both sexes were visited by pyralid moths at night and by calliphorid flies in the evening. Pollen was found attached on these insects visitingNepenthesflowers. The pattern of nectar production of sepals is regarded as attracting nocturnal flying insects and avoiding ants, while the pitchers attract ants by nectar secreted on the pitcher rim.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15313.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Medullary bundles are absent from the pith of the leafy, relictual cacti (genusPereskia) but are present in most members of subfamily Cactoideae. They are absent only from tribes Hylocereeae, Rhipsalideae, and some members of Cacteae and Notocacteae. Presence of medullary bundles tends to be correlated with presence of a broad pith, but exceptions occur. Most medullary bundles are collateral, and in all genera phloem is produced and accumulates throughout the lifetime of the bundle. Xylem definitely accumulates as medullary bundles age in some groups, but it definitely does not accumulate in others, being produced only while the bundle is young. Pith can be broad (up to 75 mm in diameter), can constitute half the shoot volume, and is long‐lived, remaining alive as long as the shoot is alive. Medullary bundles appear to be adaptive in allowing this large pith to be used for storage of water and starch. Medullary bundles have fewer, narrower tracheary elements than does the stele xylem in the same region; medullary bundles probably could not carry out significant longdistance transport if a major part of the stele becomes damaged.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb15314.x

出版商:Wiley    

年代:1993

数据来源: WILEY