摘要:

Survivorship and fecundity of the polycarpic perennialMentzelia nudawere investigated to help understand its population dynamics. Between 1978 and 1984, all 685 individuals found in a Nebraska sandhills prairie plot were marked and their fate followed. Three plants lived seven years, but the average lifespan was less than two years. Most plants spent their first year as nonflowering rosettes: only 9% flowered the first summer after germination. Overall, first‐year survivorship ranged from 0.20 to 0.50 between 1978 and 1984. Fifty‐two percent of rosettes survived to flower. Survivorship of flowering individuals was about the same as the survivorship of rosettes, although actual survivorships varied significantly between years. Both rainfall and age affected survivorship and fecundity.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08682.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Changes in stem anatomy with radial position and height were studied for the arborescent palmsWelfia georgii, Iriartea gigantea, Socratea durissima, Euterpe macrospadix, Prestoea decurrens, andCryosophila albida.Vascular bundles are concentrated toward the stem periphery and peripheral bundles contain more fibers than central bundles. Expansion and cell wall thickening of fibers within vascular bundles continues throughout the life of a palm, even in the oldest tissue. Within individual vascular bundles, the fibers nearest the phloem expand first and fiber cell walls become heavily thickened. A front of expanding fibers moves outward from the phloem until all fibers within a vascular bundle are fully expanded and have thick cell walls. Peripheral vascular bundles differentiate first and inner bundles later. In the stem beneath the crown, vascular bundles and ground tissue cells show little or no size increase, but marked cell wall thickening during development forWelfia georgii.Beneath the crown, diameters of peripheral vascular bundles increase more than twofold forIriartea gigantea, while diameters of central bundles do not increase. InIriarteastems, ground tissue cells at the periphery elongate to accommodate expanding vascular bundles and cell walls become thickened to a lesser degree than in fibers; central ground tissue cells elongate markedly, but cell walls do not become thickened; and large lacunae form between central parenchyma cells. ForIriartea, Socratea, andEuterpe, sustained cell expansion results in limited, but significant increases in stem diameter. For all species, sustained cell wall thickening results in dramatic increases in stem stiffness and strength.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08683.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Aurealcaulis crossiigen. et sp. nov., is based on permineralized trunks of an osmundaceous tree fern from the Paleocene Fort Union Formation from near Bitter Creek Station of southwestern Wyoming. This new species is characterized by centripetal (exarch) development of its xylem strands which form part of the leaf traces. Most of the leaf traces depart the stele as two segments that fuse into a single C‐shaped petiole vascular strand outside of the outer cortex. Stipular expansions of the petiole bases of this species lack sclerenchyma, and roots arise from the lateral edges of leaf traces in the inner cortex. The family Osmundaceae and subfamily Osmundoideae are slightly emended to accept genera assignable to this family and subfamily with exarch protoxylem in their steles. Foliage similar toOsmunda greenlandica(Heer) Brown, which is possibly the leaf form ofA. crossii, occurred next to an axis of this species which was in growth position. This axis was anchored in a lignite suggesting that this species grew under swampy conditions.Aurealcaulis crossiiis the first arborescent member of the Osmundaceae of Tertiary age and the second arborescent form in this family reported from the Northern Hemisphere.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08684.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

About six bryophyte species (including both mosses and liverworts) are generally thought to be restricted to copper‐enriched substrates and are consequently known as “copper mosses.” One of these,Scopelophila cataractae(Pottiaceae), is known from several sites in southern Arizona and occurs at six localities in the eastern United States. Chemical analyses of substrates from the eastern U.S. localities showed that all but one population grew on copper‐enriched soil. The one substrate sample low in copper was very high in iron. Plants from five of the six eastern U.S. localities forS. cataractaewere grown experimentally on four soil types ranging from highly to not contaminated, and all grew best on the soil contaminated with copper, lead, and zinc. There was no significant variation in growth between populations on the four soil treatments. This lack of population differentiation is in contrast to flowering plants and may be related to the absence of sexual reproduction inS. cataractaein North America.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08685.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Mature sunflower leaves were exposed to partial shading (35 or 14% of normal sun) or darkness (0% of normal sun) for approximately 8 hr. During this period one‐half of each test leaf was shaded; the other half was used as a normal sun control. Palisade cell structure from both halves of each leaf was compared. Shading of leaves had little effect on organelle percent volume values (Vv) with exception of the starch compartment which decreased as shading increased. The surface to volume ratio (Sv) of the chloroplast thylakoids increased while the Svof the mitochondrial membranes decreased as shading increased. Palisade cell volume did not change in shaded portions of the leaf, except in the fully shaded (dark) tissues where cell volume decreased. Changes in the actual volume of organelle compartments were strongly correlated with changes in cell volume. Thus a general osmotic response may account for some of the volume changes associated with differences in light intensity. Shading increased thylakoid surface areas 10–30% over the full sun controls. The ratio of stromal to granal thylakoid surface area remained constant in both the control and partially shaded samples. However, in darkened samples this ratio decreased as stromal membranes increased more than granal membranes. Changes observed in thylakoid surface areas associated with shading did not support thylakoid models which propose the interconversion of granal membranes to stromal membranes and vice versa.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08686.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Pollen morphology for 12 genera of the Lythraceae is described, using light microscopy (LM), scanning (SEM) and transmission electron microscopy (TEM). The genera surveyed areHaitia, Heimia, Hionanthera, Lafoensia, Lagerstroemia, Lawsonia, Lythrum, Nesaea, Orias(=Lagerstroemia),Pehria, Pemphis, andPeplis.Among results of taxonomic significance are 1) the similarity of pollen betweenHaitiaandGinoria, suggesting that future classifications reflect a close relationship between these genera, 2) a comparable similarity in pollen betweenPehriaandAdenaria, 3) the distinction ofHionantherapollen from that ofAmmannia, 4) an exine similar in certain ultrastructural characteristics betweenOriasand some species ofLagerstroemia, although in general aspect they appear quite different, 5) that within theDidiplis‐Lythrum‐Pepliscomplex, there are three palynologically distinct groups, withDidiplisstanding apart from the somewhat more similar, but nevertheless, distinctLythrumandPeplis, and 6) that considerable differences exist between pollen ofPemphis acidulaandPemphis madagascariensis, supporting removal of the latter species to a new genus. This pollen survey is part of a multi‐disciplinary effort to clarify generic limits in the Lythraceae, and evaluate relationships within the family and among families of the Myrtales.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08687.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Using cross‐pollination experiments, pollinia viability of the common milkweedAsclepias syriacaL. (Asclepiadaceae) did not change significantly over the five‐day life of the flowers, but stigma receptivity decreased over threefold over this period. During most of the season pollinators inserted over 90% of their pollinia into flowers during the first two days following anthesis. However, pollinators were scarce during the first few days of flowering, and they inserted over 60% of their pollinia into flowers three or more days old. This behavior potentially decreased outcrossing success and increased the relative male contribution of the flowers. Pollinator visitation patterns may play an important role in determining the functional sexuality of these plants.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08688.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Linum usitatissimumstem growth parameters were quantified by computer‐assisted analyses of scanning electron micrographs of shoot apical meristems throughout ontogeny. There were progressive decreases in the plastochron and relative plastochron rates of radial and vertical stem growth which resulted in the generation of progressively higher orders of contact parastichy phyllotaxis throughout ontogeny. The change in the relative spacing of primordia initiation on the stem coupled with the iterative differentiation of leaf gap and interfascicular ray parenchyma associated with each leaf primordium resulted in the delimitation of progressively higher orders of leaf trace interconnections throughout ontogeny. A set of developmental rules was generated which should permit simulation of many leaf trace patterns.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08689.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

The response of normal soybean (Glycine max[L.] Merrill) cultivars to gibberellins (GAs) and to an inhibitor of GA biosynthesis indicated that, as in other species, endogenous GAs are involved in controlling internode length. The responses to GA of several pairs of isogenic dwarf and normal genotypes (isolines) were compared. Dwarf genotypes T209, T244, T256, and M64–503‐Duddy apparently are not dwarfed by lesions in the biosynthetic pathway similar to the well‐studied mutations in pea and corn. Although these genotypes responded to GA3, their growth as a percentage of initial shoot length was less than that of the normal isolines following GA3treatment. Dwarf genotype T210 responded to GA3treatment with a much smaller increase in stature than the other dwarf genotypes. Roots of T210 seedlings were of normal size, which indicated that the mutation in T210 primarily affects shoot growth. Transport and metabolism of GA3were equivalent in T210 and its non‐dwarf isoline, Lincoln. The slight response in shoot length of T210 to GA3was accounted for by cell elongation, which GA3promoted to at least the same extent as in Lincoln. Gibberellin A3had no effect on cell number in T210, although GA3increased cell number in Lincoln by 53%. Thus, T210 is dwarfed by an inability to carry out GA‐promoted cell division.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08690.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Paramylon, the euglenoid storage carbohydrate, was studied by transmission electron microscopy (thin sectioning, negative staining, and freeze‐etching) and scanning electron microscopy in order to develop a three‐dimensional model of paramylon structure. The paramylon granule is a membrane‐bound crystal composed of two types of segments, rectangular solids and wedges. The segments meet in the central region of the crystal. Both the segments and the granule as a whole are composed of several layers. Fibers traverse the paramylon granule in an overall concentric pattern. These fibers appear to be composed of bundles of microfibrils, which measure 4.0 nm in diameter and are similar to cellulose elementary microfibrils.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08691.x

出版商:Wiley    

年代:1987

数据来源: WILEY