摘要:

Platanthera striataLindley is entomophilous and can produce seed via facultative self‐pollination and intraracemic and interracemic pollination. Capsule production is pollinator‐limited and seed set may be pollen‐limited. In experimental plants capsules produced via self‐ and intraracemic pollination contained fewer seeds with normally developed embryos than did capsules produced via interracemic pollination. The inflorescence ofPlatanthera strictais fragrant and is attractive to a wide array of anthophilous insects. It is pollinated by a diverse assemblage of short‐tongued insects. The primary pollinators areEustroma fasciataB. and McD. (Lepidoptera: Geometridae),Bombus flavifronsCresson andB. melanopygusNylander (Hymenoptera: Apidae), an undescribed species ofGreya(Lepidoptera: Prodixidae), and several species ofEmpis, Rhamphomyia, andAnthepiscopus longipalpisMelander (Diptera: Empididae). Small amounts of glucose are present on the raceme. The extrafloral glucose may retain small pollinators on the inflorescence until they locate the floral spur aperture.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb15093.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

We employed high and low pollination treatments to examine the effect of varying offspring number on the allocation of resources to individual seeds in 5 female clones of the dioecious perennial, Canada thistle (Cirsium arvense(L.) Scop.). In comparison to high pollination plants, low pollination plants displayed a significantly reduced seed set, an unchanged rate of seed abortion, a significant increase in mean achene weight, and an altered pattern of achene weight allocation across primary, secondary, and tertiary flowerheads. These data do not support theoretical predictions for a uniform level of provisioning to individual seeds and are most consistent with the hypothesis that limitation of available resources constrains the level of provisioning to individual seeds. We discuss some of the assumptions underlying offspring provisioning theory in light of our results and discuss the usefulness of this theory as a descriptor of plant systems.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb15094.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Population genetic structure was examined in five populations of the xerically adapted homosporous fernCheilanthes gracillima. Fstatistics using allozymic data indicated substantial genetic structure in all populations. To determine the factors responsible for genetic structure, we calculated levels of intragametophytic selfing and the fixation index for each subpopulation of each population and estimated levels of intrapopulational gene flow in each population. These analyses indicated that each subpopulation was a panmictic unit; thus, population genetic structure is not due to family structure, arising via matings between relatives. Intrapopulational gene flow was surprisingly low, given the typically high dispersibility of fern spores. However, it seems unlikely that spore dispersal inC. gracillimais significantly reduced relative to other homosporous ferns. Instead, we propose that the low rates of intrapopulational gene flow reflect limited availability of safesites for spore germination and gametophyte establishment. This ecological factor may play a primary role in generating and/or maintaining population genetic structure inC. gracillima.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb15095.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Tragopogon mirusandT. miscellusare classic examples of recent allopolyploid speciation. Previous studies documented that the diploid parents ofT. mirusareT. dubiusandT. porrifoliusand those ofT. miscellusareT. dubiusandT. pratensis.Restriction fragment analysis of chloroplast DNA (cpDNA) provided additional evolutionary information regarding the origin of the allotetraploids. We analyzed 39 populations of the three diploid and two allotetraploid species with 18 restriction endonucleases. Six restriction site mutations and three length mutations were identified; these unambiguously differentiated the parental diploids. Previous morphological, cytological, and electrophoretic analyses indicated thatT. mirusarose independently at least three times. Chloroplast DNA data suggest thatT. porrifoliushas consistently been the maternal parent ofT. mirus.Chloroplast DNA data also document a minimum of two independent origins ofT. miscellus: 1) populations from Pullman, Washington, haveT. dubiusas the maternal parent; 2) all other populations haveT. pratensisas the maternal parent. Two restriction site mutations implicate certain populations ofT. dubiusin the formation of the Pullman populations ofT. miscellus.The two rare diploid species,T. porrifoliusandT. pratensis, typically appear as maternal parents of the allotetraploids; the widespread and commonT. dubiusis the maternal parent only for two populations ofT. miscellus.These data suggest that pollen load may be an important factor in determining the male and female parents of allopolyploid angiosperms.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb15096.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Populations ofAtriplex triangulariswere grown under laboratory conditions in a growth chamber and manipulated in an inland Ohio saline pond in order to examine the relative effects of salinity, nitrogen fertilization, and population density on growth, reproduction, and survival. For laboratory plants, nitrogen fertilization was the most important variable, with biomass and reproductive effort being greatest at the high nitrogen level. As salinity increased, biomass decreased only in plants not limited by nitrogen. Increasing density caused biomass per plant to decrease at both high and low nitrogen levels. For field plants, density was the most important variable, with biomass per plant and survival both decreasing as density increased. As density increased, size inequality among individuals increased but biomass per unit area and individual reproductive effort remained relatively constant. Nitrogen fertilization slightly enhanced survival, but did not affect biomass. It is suggested that density‐dependent processes may be significant even in relatively harsh physical environments.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb15097.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Erythronium propullansis a narrow endemic restricted to two counties in southeastern Minnesota. It coexists at all sites with the widespread common white trout lily,E. albidum. Erythronium albidumhas both sexual and asexual reproduction; it has been suggested thatE. propullansreproduces strictly by vegetative means. Electrophoretic analysis of 15 enzyme systems encoded by a minimum of 37 genetic loci revealed considerable genetic variation within and amongE. propullanspopulations. However, all measures of variability calculated from allozyme data demonstrate thatE. propullansmaintains lower levels of genetic variation thanE. albidum.There is also evidence for limited gene flow amongE. propullanspopulations, whereas allE. albidumpopulations are genetically similar. Clonal diversity is also lower inE. propullans.Only 21 clones were found in 100 individuals sampled whereas virtually every one of the 70 individuals ofE. albidumsampled had a unique multilocus genotype. The clones ofE. propullanscluster into 3 genetically dissimilar groups; variation within each cluster indicates that some sexual recombination does occur. We discuss the effects of clonality and endemism on genetic variation, reasons why the clonal habit might preserve genetic variation, and suggest that the lower variability inE. propullansis due primarily to the genetic bottleneck it experienced at the time of its origin. Isozyme data suggest thatE. propullansis a derivative ofE. albidum.Based on the degree of genetic similarity and information on the glacial history of the region, we suggest thatE. propullansis a local derivative ofE. albidum, having arisen no more than 9,000 years ago.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb15098.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Phyllotaxis theory typically assumes that an acropetal influence from recently formed leaves acts on the apical dome to initiate new leaves. Biophysical theory postulates that established plant organs elongate because their primary walls, particularly those in the organ surface layer, are transversely reinforced by cellulose to give the organ overall hoop reinforcement. These two postulates are combined here in a biophysical theory for phyllotaxis. The essential acropetal influence from young leaves is proposed to be the stretching of the adjacent dome tissue by the growth of leaf bases. Cytoskeletal responses on the dome produce reinforcement patterns which initiate new hoop reinforced leaves. Growth of these leaves remodels the dome for the next round of organs. Data pertinent to this theory are presented here forVinca major.The surface (tunica) layer of the apical dome was isolated by paradermal cuts. Using polarized light, the cellulose alignment in this surface layer was determined, cell by cell, for various stages of the plastochron. The growing dome is typically elliptical, with the major axis shifting by 90° during each plastochron. The periphery of the dome always has cellulose oriented parallel to its margin; the central region, when the major axis is pronounced, has reinforcement normal to this axis. During the plastochron this reinforcement pattern is modified, by plausible biophysical mechanisms, to account for the three major activities of the dome: 1) production of a hoop‐reinforced leaf at each end of the ellipse, 2) formation of a hoop‐reinforced stem segment, 3) revision of dome structure to produce the same initial reinforcement pattern as at the start of the plastochron, but at 90°.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb15099.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Rhododendron nuttalliiT. W. Booth (Ericaceae) was used to derive concurrent timetables for megagametophyte, pollen tube and early postfertilization development from anthesis through 3 wk after pollination, based on timed collections of self‐pollinated pistils. Stages of development were determined for over 33,500 cleared ovules, including, for selected collection dates, stages on different portions of the placenta. Pollen tube information was obtained by fluorescence microscopy of pistil squashes stained with aniline blue. Because of the very large number of ovules observed, it was possible to recognize a much more closely graded series of stages in megagametophyte development than is usually the case. While a range of stages occurred on all days, development progressed steadily from a majority of functional spores and 2‐nucleate gametophytes on the day of anthesis to mostly a late zygote‐primary endosperm stage at 18 days, and some 2‐celled endosperm stages at 21 days, after pollination. At all times the most advanced stages, including first pollen tube entries, occurred on the outer surface of the lower half of the placenta, and the youngest on the inner surface of the uppermost portion. Fertilizable ovules were not found in any frequency until 8 days after pollination (then in only about 34% of the ovules); a few fertilized ones were seen after 10 days but constituted less than 5% until 12 days after pollination, thereafter increasing to about 60%. Fertilization occurred in any one of three morphologically recognizable stages distinguished by position and state of fusion of polar nuclei. Pollen germinated on the stigma 1–2 hr after pollination, and pollen tubes grew at a rate of about 1–1.25 cm/day, reaching the top of the ovary in 8–9 days with the first ovule entries seen after 10 days. There was a close correlation between megagametophyte development and pollen tube growth, with large numbers of functionally mature ovules not being found until pollen tubes had reached the ovary. While nuclei within ovules could not be distinguished in the squashes, three gametophyte stages that could be recognized—unelongated, elongated either without or with a pollen tube—were tallied for almost 29,000 ovules. The progression in these general stages corresponded well with that documented in more detail from cleared ovules. Unpollinated pistils showed a similar progression of gametophyte stages until the time fertilization would start to occur, after which there was continued accumulation of functionally mature ovules. A variety of abnormally developed and/or collapsing(ed) ovules or gametophytes were seen; collectively, they averaged over 8.6% of all ovules.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb15100.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

The development of stipules especially their spatial and temporal pattern of initiation in relation to the leaf was investigated inVitis ripariaMichx., cv. Concord,Parthenocissus tricuspidata(Sieb.&Zucc.) Planch.,Cissus oblonga(Benth.) Planch.,Cissus hypoglauca(F.v.M.) A. Gray, andCissus rhombifoliaVahl. Early initiation is characterized by the occurrence of a single primordium with a wide insertion on the flank of the shoot apex. Distinguishing between stipule primordia and the leaf primordium is impossible at this early stage. Distinct primordia can only be seen in later stages of development. At maturity, the stipules occupy free lateral positions. Developmental processes such as timing of initiation and zonal growth seem to play an important role in early development. In five of the six taxa examined in this study, the early initiation of stipules, their close association with the leaf and also their faster relative rate of growth during early development appear to give them a characteristic protective function. In contrast,C. rhombifoliastipules are initiated later than the leaf and seem to develop at a slower rate than the leaf proper. Consequently, they never enclose their associated leaf but instead cover the next youngest leaf. Many different criteria are used to distinguish the broad category of stipules, and therefore many interpretations have been made depending on the type of approach that is used. This study attempts to look at stipules in terms of developmental processes and demonstrates a more accommodating leaf/stipule concept which provides a clearer comprehension of the nature of the stipule.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb15101.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

The relative dominance of deciduous trees having diffuse, semiring, or ring porous xylem is considered in relation to percent slope, site, vertical stratification within site, and to disturbance. Xylem type relative dominance was calculated on the basis of basal area by a procedure that is generally employed for the determination of species relative dominance. The study area was located within the central hardwoods region of the Eastern Deciduous Forest. On a moisture gradient, the sites were a hydric floodplain, a mesic river terrace and cove, and a xeric hillside spur. There was an increase from lowland to upland sites in absolute number of species having diffuse porous and those having ring porous xylem; however, the data showed no significant difference among the four sites or between the cove's northwest and southwest aspects in the percentages of species having diffuse porous xylem and those having ring porous xylem. In contrast to species number data, relative dominance data showed that diffuse porous species were dominant on the floodplain, on the northwest aspect of the cove, and in lower strata beneath the dominant ring porous upper canopy on the spur and southwest aspect of the cove. Ring porous species were dominant in the upper canopy only on the spur and on the southwest aspect of the cove. Semiring porous species had a high dominance level on the disturbed terrace site, a much lower level of dominance on the less disturbed floodplain, and very low dominance on the relatively undisturbed cove and spur sites. The results demonstrated that sets of closely and distantly related tree species having the same xylem anatomy share some common ecological characteristics, suggesting that xylem structure is a critical character in the adaptation of trees to variations in the environment over small geographical areas.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb15102.x

出版商:Wiley    

年代:1989

数据来源: WILEY