摘要:

Lathyrus latifolius(everlasting pea) is a perennial vine native to Europe. Naturalized populations ofL. latifoliusoccur in fields and on roadsides over large areas of the United States. Widely cultivated as a garden flower,L. latifoliusproduces abundant racemes of showy flowers that are bumblebee‐pollinated. The seeds are heavy, large, and round, and exhibit no specialized means of dispersal. Allozyme diversity and population structure were determined for 32 populations ofL. latifolius—30 from the southeastern United States and two from Oregon. Results from 21 allozyme loci indicate that genetic diversity is higher and population divergence is lower than expected based on the life history characteristics of the species. No association was found between genetic identity statistics and geographic distance between populations. Although the range in genetic diversity statistics among populations was unusually large, genetic drift did not appear to play a major role in structuring genetic variation. We conclude that the level of genetic diversity maintained withinL. latifoliuspopulations, and the level of population divergence found, is strongly influenced by its status as a cultivated garden flower and its human‐associated mode of gene flow via seed dispersal.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb11409.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

During Late Cretaceous to Oligocene times, fossil pollen of the Triprojectacites group (also known as Aquilapolles or triprojectates), comprised a temporally and environmentally distinctive element of palynofloras in eastern Asia and western North America. Several species of this group serve as biostratigraphic index fossils for this interval. Using electron microscope and numerical analyses, primarily of North American triprojectate pollen, it is possible to recognize the presence of three distinct subgroups. One group, corresponding to the fossil genusMancicorpus, has no morphologically close modern representative. Characters resembling those in Santalaceae (Santalales, Rosidae) occur in the second group, which is represented by a previously underscribed fossil triprojectate genus. The third group contains retipilate, isopolar pollen and strioreticulate, isopolar pollen. Forms exhibiting the latter morphology are commonly assigned to the genusIntegricorpus, while the retipilate morphology characterizes another underscribed genus. This third group may have some phylogenetic connection to Apiaceae (Apiales, Asteridae). Pollen of some other extant families exhibits triprojectate features, although no close fossil representative can be presently identified. The triprojectate morphology is thus interpreted in modern and fossil forms as resulting from convergence rather than close phylogenetic relationships at the group level.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb11410.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Spore wall morphogenesis of the microspore ofIsoetes japonicawas studied by transmission electron microscopy. The microspore wall consists of four layers: the perispore, outer exospore, inner exospore, and endospore. The perispore consists of electron‐dense materials. The exospore is divided into outer and inner sections, with a large gap between the two. The outer exospore appears as an undulating plate consisting of tripartite lamellae with homogeneous sporopollenin. The inner exospore consists of an accumulation of tripartite lamellae on the microspore cell membrane. Immediately after meiosis, the tripartite lamellae of the outer exospore forms around the microspore. The lamellated inner exospore forms next, which adheres to the cell membrane of the microspore. The deposition of homogeneous sporopollenin material on the tripartite lamellae causes the plates of the outer exospore to thicken. Some homogeneous material may also be deposited on the inner exospore. Lastly, the electron‐dense perispore is deposited on the outer exospore, and the electron‐lucent endospore forms beneath the inner exospore. We conclude that the lamellae of the outer exospore, inner exospore, and endospore are formed and derived, in that order, from the gametophytic microspore cytoplasm. The homogeneous sporopollenin material of the outer exospore and perispore may be derived from the sporophytic tapetal cytoplasm.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb11411.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Scarcity of red spruce(Picea rubensSarg.) seedlings in declining spruce‐fir forests of Camels Hump mountain, Vermont, prompted a study on some contributing factors involved in failure of spruce regeneration. Cones were shorter than those from low elevation red spruce trees from unaffected sites. Seed number in cones collected in declining areas of Camels Hump was low as were seed sizes and weights. Seed germination was at control levels only in good seed years. Capacity of seeds to form seedlings was reduced relative to that of controls, although seedling growth was normal. Coniferous litter contains presumed allelopathic substances leachable by contemporary precipitations that affect seed germination and seedling root development in red spruce, but not in balsam fir. Shield fern contains leachable substances that reduce seed germination and seedling root development in red spruce, but not balsam fir. Roots of red spruce germlings have lower capacity to penetrate through the increased forest duff depths of declining forests than do balsam fir roots. It is anticipated that substantial reproduction of red spruce will not occur in declining montane conifer forests under present conditions.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb11412.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Foliar injury to red spruce(Picea rubensSarg.) occurred during the winter of 1989–1990. A range of damage was observed among individual trees, first‐year needles on a shoot, and often within an individual needle. Anatomical comparisons of first‐year foliage were made to establish patterns of necrosis due to winter injury. Mesophyll tissue was most affected by winter damage. Guard cells adjacent to injured mesophyll cells were also consistently damaged. Early evidence of injury was apparent as an off‐color staining of the cytoplasm and slight plasmolysis of the protoplast. Organelle integrity was lost, and there was an extensive reduction of cytoplasmic volume. Spherical bodies of unidentified composition often appeared within the cytoplasm as subcellular integrity was lost. Severe damage resulted in complete loss of cellular structural integrity and adhesion of residual cellular contents to the cell walls. Narrow transition zones between healthy and necrotic tissues were observed, and upper surfaces tended to be more severely affected. There appeared to be a cellular specificity to winter injury within the mesophyll. Completely necrotic cells were often adjacent to apparently healthy cells, and a wide range of injury could be observed within a relatively small area of the needle in partially damaged foliage.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb11413.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Selected branches of red spruce{Picea rubensSarg.) saplings growing at 900 m in elevation on Camels Hump Mountain, Vermont, were treated with an acrylic polymer antitranspirant (Adkar Cloud Cover) in October 1989. Winter injury was subsequently apparent on first‐year foliage on 1 February 1990. Addition of antitranspirant significantly increased chloroform extractable wax (plus antitranspirant) weight and cuticle (plus antitranspirant) thickness. The treatment reduced cuticular transpiration under laboratory conditions, but did not lessen the severity of visually apparent winter injury. Xylem water potential of damaged and undamaged branches did not differ. Fresh to dry weight ratios revealed a tendency for damaged needles to desiccate rapidly following winter injury. Foliar pigment concentrations were negatively correlated with severity of winter damage. These results suggest that winter desiccation plays a minor role in inducing winter injury to red spruce foliage.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb11414.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Phylogenetic relationships among the 21 taxa comprisingHelianthussect.Helianthusand three outgroup species were assessed by restriction site mapping of the 18S‐25S nuclear ribosomal RNA gene family. Wagner parsimony analysis of the 41 restriction site or length mutations observed produced a single 59‐step most parsimonious tree. This tree was then compared to a cytoplasmic‐based plastid phylogeny for this group. Several major discrepancies were observed between the two phylogenies suggesting both recent and ancient introgression. Furthermore, three cases of diploid hybrid speciation are unambiguously documented and a fourth case is suggested. These data are interpreted to suggest that evolution inHeliathusis reticulate rather than exclusively dichotomous and branching.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb11415.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Nuclear 2C DNA content was determined by laser flow cytometry for 13 diploid (2n =34) lines (cultivated varieties and inbred lines) ofHelianthus annuus.Mean DNA amount of second leaf nuclei varied from 6.01 to 7.95 pg (32%) among lines. Mean DNA content varied up to 19% within lines. Variability in mean DNA content exceeding 27% and 48% was detected among leaves from different nodes of plants of the open‐pollinated variety, Californicus, and the inbred line, RHA 299, respectively. The root tip and shoot tip nuclei ofH. annuushave been reported to consist of a mixture of aneuploid (17 to 33 chromosomes) and diploid (34 chromosomes) cells, a condition called aneusomaty. Chromosome counts of root tips and an analysis of the distribution of DNA content of large numbers of nuclei from leaves indicate that aneusomaty either does not occur, or is not common, among the lines investigated. The intraspecific, intraline, and intraplant variation in DNA content inH. annuussupport the concept that a sizable portion of a plant genome is unstable and subject to rapid changes in DNA amount.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb11416.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Pinus pungensLambert (Table Mountain pine) is characterized by serotinous cones that are borne several (two to five) per whorl. Sporophytic and gametophytic tissues from whorls collected in different canopy zones of eight trees were electrophoresed and surveyed for six allozyme loci. Pollen allele frequencies received by individual trees, whorls on trees, and cones in whorls were estimated and used to estimate outcrossing rates and the distribution of genetic diversity within and among each level. Significant differences in pollen allele frequencies were detected at all levels, indicating that the genetic composition of the pollen pool available to different female strobili is heterogeneous. The fine‐scale genetic structure in the seed pool is a record of past reproductive events and is the precursor to genetic structure in the next generation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb11417.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Shoots ofOpuntia ficus‐indica(L.) Miller consist of a sequence of flattened stem segments (cladodes) in contact over only a small portion of their periphery. The maximum angular deflection for an upper terminal cladode under a weight equal to its own fresh mass applied perpendicular to its face increased from 5° to 9° as cladode length increased from 20 cm to 60 cm, consistent with an increase in mass proportional to length2.83. Just over half of the angular deflection of an upper cladode represented flexure of the cladode‐cladode junction; the angular deflections averaged fourfold more for mass loadings perpendicular to the cladode face compared with those parallel to it. Compared with such static loading by mass, dynamic loading by wind for a 31‐cm‐long cladode led to a maximum angular deflection of only 0.13° at a wind speed of 1 m sec−1and 2.3° at 10 m sec−1. Drought caused the angular deflections to increase 9% for 21‐cm‐long cladodes over a 90‐day period and to decrease 45% for 44‐cm‐long cladodes. Increases in stem temperature from 0 C to 20 C increased angular deflections of a 27‐cm‐long cladode about 10%, with little further increase up to 50 C. Even though the cladodes were thin compared with stems of many perennials and the cladode‐cladode junction comprised only about 3.5% of their peripheral area, the shoots ofO. ficus‐indicaproved to be quite rigid, as angular deflections of cladodes were only slightly influenced by temperature and wind, were not markedly enhanced by drought, and were less than 10° under loading by a cladode's mass.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb11418.x

出版商:Wiley    

年代:1991

数据来源: WILEY