摘要:

Fifteen Eurasian and Australian species ofViscumL. were examined by light, scanning, and transmission electron microscopy. Pollen characters divide the species into two groups, each correlated with differences in habit and inflorescence structure: Group I (12 spp.) characterized by psilate or slightly sculptured exines and a non‐uniform ektexine pattern and Group II (3 spp.) possessing highly sculptured (echinate, rodlet) surfaces and uniform ektexine patterns. Within each of the groups, pollen characters divide the species into several subgroups. Among Group I, speciesV. nepalense, V. heyneanumandV. ovalifoliumare particularly close. The Group I species,V. trilobatum, is placed in its own subgroup primarily because of its uniform ektexine pattern—a unique feature among Asian and AustralianViscum.Of the three Group II species,V. albumandV. alniformosanaeare palynologically almost indistinguishable. Pollen of the Group IIV. cruciatum, though exomorphologically similar toV. album, is closest ultrastructurally to the IndianV. trilobatum.Overall, the most common and probably basic pollen characters among the Eurasian and Australian species include: subprolate, rounded convex almost spherical shapes; tricolporate apertures, and non‐uniform sculpturing and ektexine patterns. Oblate‐spheroidal or prolate‐spheroidal shapes, prominent sculpturing, and a uniform ektexine pattern are derived characters largely restricted to the Eurasian and Asian Group II species (V. album, V. alniformosanae, V. cruciatum).

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1982.tb13230.x

出版商:Wiley    

年代:1982

数据来源: WILEY

摘要:

Seed banks are important in wetland vegetation, but their role on lakeshores has received little attention. The influence of seed banks on lakeshore vegetation was investigated near eastern Georgian Bay in Ontario, where there is a rich shoreline and aquatic flora. Some lakeshore species found there can be considered “coastal plain disjuncts” similar to those of southwestern Michigan and adjacent Indiana, and central Wisconsin. Matchedash Lake in Simcoe Co., Ontario, has a particularly rich assemblage of these shoreline species. Based on short‐term records, and aging of drowned stumps, we demonstrated that yearly mean water levels can and have changed by more than a meter. Such water‐level fluctuations partly result from beaver dams on the single outlet stream. Vegetation data collected in a low‐water phase (1976) document a rich shoreline flora, largely absent in the present (1979) high‐water phase. During this latter high‐water phase, we collected 15 sediment sample units from each of six water depths (0–1.5 m). The sample, representing 0.32 m2of lake bottom, was planted out in a greenhouse; 3,149 seedlings representing 41 species of vascular plants emerged. Six (Rhexia virginica, Rhynchospora capitellata, Panicum spretum, Xyris difformis, Polygonum cureyi, Linum striatum) are rare in Ontario. Estimated seed banks for individual species were as high as 6,500 seeds m“2. If another low‐water phase occurs, a rich shoreline flora should again develop. We hypothesize that water‐level fluctuations are essential to the long‐term survival of these species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1982.tb13231.x

出版商:Wiley    

年代:1982

数据来源: WILEY

摘要:

Petiole development and formation of xylem vessels have been investigated inXanthiumleaves from early ontogeny to maturity. Kinetics of growth was presented in terms of absolute and relative elemental rates of elongation. The process of vascularization was assessed by the number of differentiated xylem vessels. The leaf plastochron index (LPI) developed by Erickson and Michelini (1957) was used for designating the various stages of development. An exponential increase in petiole length was observed between the LPIs –3 and +4 indicating a constant relative rate of 0.20 or 20% increase per day. After cessation of lamina elongation at LPI 8, petiole elongation continued for an additional 5 day period, to LPI 9.5. Relative elemental rate analysis revealed that the basipetal pattern of elongation was maintained throughout the leaf development. At a specific plastochron age, the only growth was due to the petiole elongation. Leaves which ceased elongating had not completed their internal development, since the process of xylem formation continued for several plastochrons, or about 8 days. The highest rate of xylem formation was ten vessels per day at LPI 5. On the average, about five xylem vessels differentiated per day in the middle portion of aXanthiumpetiole. Mature petioles contained an average of 218 xylem vessels. About 12 canals of schizogenous origin preceeded the development of the vascular tissue.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1982.tb13232.x

出版商:Wiley    

年代:1982

数据来源: WILEY

摘要:

A recent increase in research into ecological leaf anatomy is based partly on the effects of leaf structure upon photosynthesis. Hence, it is desirable to have efficient methods for measuring various aspects of internal leaf anatomy, such as percent air space and cell wall area per unit volume of tissue. Stereological methods make use of point counts and of counts of the number of intersections of sampling lines with tissue outlines on planar sections. Their practical use for measuring plant tissues is described, with special reference to highly directional tissue like palisade mesophyll and wood. In particular, the method for estimating cell wall area per unit volume requires the choice of a numerical factor which varies with tissue type. The factor has values of 2 for unoriented tissues, pI/2 for cylinders cut in cross section, and (p/2)2for cylinders. in longitudinal section. An interpolating function to derive a value of the factor for tissues of intermediate type is also described. Leaves from two species of composites from contrasting habitats are compared, to demonstrate the usefulness of the methods.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1982.tb13233.x

出版商:Wiley    

年代:1982

数据来源: WILEY

摘要:

A general survey of pollen morphology in Hydrophyllaceae, using scanning electron microscopy, is presented. Hydrophyllaceous pollen grains are relatively homogeneous, tricolpate or tricolporate, and with a tectate‐perforate to semitectate exine structure. Surface ornamentation is basically reticulate, but varies sufficiently from genus to genus, and sometimes from species to species, to permit interesting comparisons, but not to draw profound phylogenetic conclusions.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1982.tb13234.x

出版商:Wiley    

年代:1982

数据来源: WILEY

摘要:

Secondary wood of three species ofCallixylonof Lower Mississippian age, preserved by three different modes (fusinization, silicification, and phosphatization), have been studied and characterized in detail. Problems of interpretation at the SEM level of permineralized woods, both containing (silicified wood ofCallixylon erianum) and essentially lacking (phosphatized wood ofC. arnoldii) original organic cell wall material, are analyzed and discussed. In particular, it is concluded that the flat to curved surfaces showing no evidence of apertures, observed in bordered pit pairs, commonly represent pit membrane surfaces. It is accepted, however, that some concave surfaces might be the mineral accretion surfaces of incomplete pit cavity casts as proposed by Leo and Barghoorn (1976). Regions between groups of pits, previously interpreted as crassulae, may be artifacts of preservation. The fusinized wood has the general appearance of charcoal, but unlike commercially produced charcoal provides evidence of its original microfibrillar structure. The origin of fusain in the fossil record is discussed, and it is concluded that it probably had several origins, including forest fire. Since charcoal can be produced naturally in the absence of O2(Brown and Davis, 1973), the suggestion that fusain (charcoal) in the geologic column provides a basis for “assessing oxygen levels in paleoatmospheres” (Cope and Chaloner, 1980) is not supported. Natural sites of fusain production in the absence of O2are regions of vulcanism and organic sediments inhabited by anaerobic microorganisms. A circular pattern of crystal orientation in the pit borders ofC. arnoldiiis interpreted to represent the original microfibrillar pattern. Pit apertures in C.arnoldiiare shown to be circular to slightly elliptical. Interpretive evidence of heterogeneous pit membranes inC. arnoldiisuggests but does not prove the presence of a torus. The distinctive central region in some pit membranes of the fusinized wood ofCallixylonsp. might represent accumulations of waste metabolites. It is argued that a torus would be highly adaptive in large pits with circular apertures.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1982.tb13235.x

出版商:Wiley    

年代:1982

数据来源: WILEY

摘要:

Callus tissue cultures were initiated from immature embryos, mature embryos and young inflorescences of Guinea grass (Panicum maximumJacq.) on Murashige and Skoog's (MS) medium supplemented with 2.5–10 mg/l 2,4‐dichlorophenoxyacetic acid (2,4‐D). Calluses were transferred onto the same nutrient medium with 0.2 mg/l 2,4‐D, or without 2,4‐D. In callus cultures derived from immature embryos and young inflorescence segments, plantlets were produced via somatic embryogenesis after 3–5 wk. Young plants were successfully transplanted to pots and grown in the greenhouse. Plant development in callus obtained from mature embryos took place through the organization of shoot meristems. Regenerated plants were shown to have the normal tetraploid chromosome number of 2n= 4x= 32.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1982.tb13236.x

出版商:Wiley    

年代:1982

数据来源: WILEY

摘要:

Pollination mechanisms and pollinators are reported for a total of 137 species (75% of the non‐abiotically pollinated flora) as they occur at three altitudinal levels (subandean scrub: 2,200–2,600 m; cushion‐plant zone: 2,700–3,100 m; subnival feldfield: 3,200–3,600 m) in the Andean (alpine) zone on the Cordon del Cepo (33°17'S) in central Chile as part of community oriented research in reproductive biology in the high temperate Andes of South America. Only around 4% of the species studied failed to be visited by potential pollinators. Hymenopterans (principally bees) are important pollinators of 50% of the biotically pollinated flora, butterflies of 24% and flies of 46%. Other vectors include beetles, moths, and hummingbirds. An estimated 17% of the flora is anemophilous.Bee species‐richness, specialist feeding, and melittophily reach maxima in the subandean scrub; thereafter, bees diminish rapidly in number, with bees pollinating only 13% of the subnival flora as contrasted with 68% of the subandean flora. Although fly and butterfly species‐richness also decline with increasing altitude, the proportions of species pollinated by these vectors actually increases. High‐altitude populations of melittophilous species with broad altitudinal ranges are invariably serviced by fewer bee species as compared with lower populations.The rich bee fauna at the lower end of the Andean zone in central Chile appears to have resulted from upward colonization from that of the subtending lowland Mediterranean sclerophyllous woodland vegetation. Altitudinal variation in pollination spectra is discussed in relation to contrasting life history characteristics and different modes of thermoregulation in the insect groups involved.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1982.tb13237.x

出版商:Wiley    

年代:1982

数据来源: WILEY

摘要:

The tracheid bar, a strip composed of vertically oriented large tracheid‐like cells (tracheoids), occurs only in the hilum of seeds of papilionoid legumes. An anatomical survey of the bar was made from seeds representing 232 species of 97 genera from 29 of the 31 tribes recognized by Polhill. Seeds were sectioned freehand, coated, then viewed by SEM. The tracheid bar is quite uniform in its general features throughout the subfamily, although differences in size and shape of both the bar and the tracheoids were found. Eight species from tribes considered to be among the primitive elements of the subfamily exhibited three variant forms: horizontal tracheary elements instead of the usual bar (2 species), tracheid bar with subtending but separate vascular bundle (1 species), and the tracheid bar with fused horizontal tracheary elements (5 species). Bordered pits of individual cells in the tracheid bar virtually always lacked a membrane and had smooth, warty, or variously elaborate vestures on the border. This appears to be the first report of vestured pits other than in secondary xylem. With some exceptions, bordered pits tended to be vestured in primitive tribes, warty in intermediate tribes, and smooth or only slightly warty in the most advanced tribes.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1982.tb13238.x

出版商:Wiley    

年代:1982

数据来源: WILEY

摘要:

Karyotypic differences were sought among species ofBoykinia, Heuchera, Mitella, Sullivantia, Tiarella, andTolmieautilizing a modification of the Hy‐banding technique. Prominent centromeric and some telomeric heterochromatin banding was observed.Boykinia aconitifoliaand species ofSullivantiapossess an identical banded karyotype, while four species ofHeuchera, Mitella diphylla, Tiarella cordifolia, andTolmiea menziesii(the latter at the tetraploid level) are characterized by a second, slightly different banded karyotype. InSullivantia, Giemsa C‐banding stains the same chromosomal regions revealed by Hy‐banding. Larger amounts of heterochromatin are present in chromosomes of species ofHeuchera, Mitella, Tiarella, andTolmieathan in chromosomes ofSullivantiaspecies andBoykinia aconitifolia.These karyological observations confirm generic relationships and demonstrate the systematic applicability of chromosome banding techniques to plants with very small chromosomes.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1982.tb13239.x

出版商:Wiley    

年代:1982

数据来源: WILEY