摘要:

CalochortussubsectionNudi(sectionCalochortus) comprises four extant species distributed from central California to southern Oregon. To elucidate relationships within this group, morphological, cytological, and electrophoretic investigations were undertaken. Allozyme data revealed two distinct groups in subsectionNudi:a coastal group, comprisingC. uniflorusandC. umbellatus;and a Sierran group, comprisingC. minimusandC. nudus. Calochortus uniflorusconsists of diploids (n= 10) and tetraploids (n= 20). Several lines of evidence suggest that tetraploidC. uniflorusmay be an autotetraploid: 1) quadrivalents were observed during meiosis in tetraploidC. uniflorus;2) the mean genetic identity between the diploid and tetraploid cytotypes was much higher (Ī= 0.963) than between either cytotype andC. umbellatus(Ī= 0.903 and 0.904 for 2xand 4x,respectively); 3) diploid and tetraploid individuals ofC.unifloruswere indistinguishable morphologically; and 4) both cytotypes ofC. uniflorusoccupy vernal meadows, whereasC. umbellatusoccupies exposed serpentine ridges. Data from morphology and enzyme electrophoresis suggest that introgression, or at least extensive hybridization, has occurred betweenC. minimusandC. nudus.Principal coordinate analysis showed that pureC. minimusandC. nudusare morphologically distinct and that putatively introgressive populations are morphologically intermediate. Most putatively introgressive populations displayed reduced pollen viability relative to pureC. minimusandC. nudus.Allozyme data are consistent with the concept that hybridization and possibly introgression may have occurred betweenC. minimusandC. nudus.When allozyme data were analyzed by the unweighted pair‐group method of cluster analysis using arithmetic means, most putatively introgressive populations were placed between theC. minimusandC. nuduspopulations.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb11393.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

A natural habitat of the cycadDioon eduleLindl. in central Veracruz, Mexico is described. Prolonged drought periods and fire are factors contributing to seedling death resulting in a population structure with a reverse ‘J’ or Deevey type III survivorship curve. The cycads exhibited a ‘clumped’ or contagious distribution on shallow soils of the habitat and on rocky outcrops. This distribution was attributed to exclusion by competition from other species for water, soil nutrients, and/or seed dispersal by rodents. Estimated coning frequency varied from 2.8 to 8.8 years in male plants and from 10.0 to 52.0 years in female plants, though shorter intervals are known to occur, especially following exceptionally wet years. Chamberlain's age estimate forD. edulehas been confirmed and a life table is presented.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb11394.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Ulcerate pollen tetrads from the late Barremian‐early Aptian of Gabon, namedWalkeripollis gabonensisgen. et sp. nov., resemble pollen of extant Winteraceae but have finer sculpture and a weakly calymmate tectum, like tetrads reported from the late Aptian‐Albian of Israel. Scanning and transmission electron microscopy reveal additional winteraceous features (tall muri, short columellae, ring of endexine around the ulcus), plus segmented muri recalling the reticulate, zonasulculate to inaperturate genusAfropollis,which is abundant in the Aptian‐Albian of Northern Gondwana.Afropollisalso resembles Winteraceae in having tall muri and short columellae, but it has a thicker endexine. The new zonasulculate genusSchrankipollis,includingS. mawhoubensis(Schrank) comb. nov. from the Aptian of Egypt andS. microreticulatus(Brenner) comb. nov. from the Potomac Group of Maryland, resemblesAfropollisin structure of its muri but differs in its elliptical shape, finer reticulum, and restricted endexine.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb11395.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Comparisons with other fossil pollen types and the distribution of pollen characters in modern angiosperms support affinities of Early Cretaceous ulcerate tetrads (Walkeripollis) and zonasulculate pollen (Afropollis, Schrankipollis) with modern Winteraceae. Cladistic analysis of these fossils plus modern Winteraceae and Illiciales, which have been associated with each other, implies thatAfropollisandSchrankipollisrepresent an extinct sister group ofWalkeripollis,Winteraceae, and Illiciales, derived from a common ancestor before origin of the tetrad condition. The single tricolpate grains of Illiciales are derived from ulcerate tetrads, which helps explain their thin proximal exine and Garside's Rule aperture arrangement. These results imply that extinct relatives of Winteraceae and Illiciales were an important component of Early Cretaceous tropical floras and extended into Laurasia, and that the present austral temperate distribution of Winteraceae was attained later. They are consistent with recent suggestions that absence of vessels in Winteraceae is due to secondary loss.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb11396.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Polytrichum communeis a perennial moss that grows by rhizomatous production of interconnected shoots. It possesses a well‐developed internal system of food‐conducting tissue. Liquid scintillation determinations following pulse‐14CO2treatment of a single shoot in rhizomatously connected groups indicate that tagged photoassimilates are transported into:1) newly developing stems during the early growing season; 2) shared rhizomes (with an increase observed in rhizome allocation toward the end of the year, as well as a year‐end percentage increase in starch reserves); and 3) mature neighboring shoots. Over the course of the growing season, photoassimilate export from pulse‐labeled shoots ranges between 12.9% and 21.4% of total tagged. The amount of export is significantly influenced by defoliation, shading, stem tip removal, and 50 ppm indole‐3‐acetic acid treatments performed on rhizomatously connected neighbor shoots. Physiological integration withinP. communecan be inferred from these results. Control is exerted by endogenous hormones or by changes in the activity of sources and sinks.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb11397.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Polytrichum commune, the common hair‐cap moss, possesses a system of long‐distance food‐conducting cells that can be traced from leaves into stems and down through underground rhizomes. Cytochemical analysis indicates that high adenosine triphosphatase activity is associated with the membranes of sugar‐conducting deuter cells inPolytrichumleaves. Incipient plasmolysis determinations reveal high solute concentrations of leaf deuters. These two lines of evidence suggest that long‐distance transport of photosynthate is initiated in this species by a process analogous to phloem loading of minor veins in leaves of flowering plants. Two sets of experimental observations suggest that sugar loading inPolytrichumis coupled with the transport of protons: the moderating effects of N‐ethylmaleimide, p‐chloromercuribenzenesulfonic acid, sodium orthovanadate, and fusicoccin on labeled sucrose uptake (as determined by liquid scintillation techniques), and correlated effects on acid flux from isolated leaves (as determined by computer‐aided titrimetry).

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb11398.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Since the initial discovery of double fertilization in angiosperms in 1898, a number of reports of double fertilization‐like events in the genusEphedrahave appeared. Until recently, convincing documentation of double fertilization inEphedrahad not been presented. InEphedra nevadensis,following entry of a single binucleate sperm cell into the egg cell, one sperm nucleus migrates in a chalazal direction to fuse with the egg nucleus. Contemporaneous with this first fertilization event, the ventral canal nucleus regularly migrates from its initially apical position within the egg cell to a more central position within the egg cytoplasm, where it fuses with a second sperm nucleus. Based on quantitative microspectrofluorometric analysis, occasional supernumerary nuclei within the egg cell (derived by migration through pores in the cell walls between jacket cells and the central cell or egg cell) can be ruled out as participating in the second fertilization event. The evolutionary establishment of double fertilization inEphedra(or its ancestors) was dependent on a number of specific developmental preconditions: 1) persistence of the ventral canal nucleus (which is degenerate in many groups of nonflowering seed plants) through the time of normal fertilization; 2) regular displacement of the ventral canal nucleus from its initially apical position within the egg cell to a position within the egg cytoplasm where fusion of the egg nucleus with the first sperm nucleus earlier occurred; 3) acquisition of egg‐like features by the ventral canal nucleus that allow it to attract and fuse with a sperm nucleus; and 4) consistent entry of a second sperm nucleus into the archegonial cavity to participate in a second fertilization event. Although it cannot be determined definitively whether double fertilization inEphedrais evolutionarily homologous with double fertilization in flowering plants, comparative evidence is consistent with the hypothesis that double fertilization arose in a common ancestor of the Gnetales and angiosperms.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb11399.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

In the Araceae, as in many other monocotyledons, the stem undergoes gradual thickening as successive internodes are produced. Along with this primary thickening of the stem, successive foliage leaves will be larger and often more complex. In many species, in addition to these and other gradual changes, there are abrupt changes, metamorphoses, that occur under certain conditions. Some metamorphoses are the result of endogenous cycling (e.g.,Syngonium,Rhektophyllum,Philodendron linnaei), some are a response to changes in conditions in the environment, usually the gain or loss of contact with a substrate (e.g.,Syngonium, Monstera, Rhodospatha, PhilodendronsectionPteromischum), and some occur when the plant reaches a certain level of maturity (e.g.,Monstera). Some of these latter changes are associated with a transition from monopodial to sympodial growth (e.g.,Philodendron, Anthurium). Metamorphosis enhances the developmental plasticity of the Araceae in two distinct ways: it allows for a more complex relationship between size and shape in the development to maturity, and it allows shoots to engage in dispersal activities and developmental holding patterns when conditions are not suitable for development to the adult form and reproduction.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb11400.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Hydraulic conductivities of stems, stipes, and elongate leaf stipes were determined for greenhouse‐grownBlechnum(B. fraxineum, B. fragile, B. buchtienii, B. sprucei) andSalpichlaena(S. volubilis) plants collected in tropical rain forests of Costa Rica. Organ conductivity was examined in relation to morphology and tracheid characteristics in order to gain an understanding of factors influencing water flow. Hydraulic conductivity of plant organs was determined by measurement of transpiration rates, leaf areas, and water potential gradients. Erect stemmed species develop larger whole plant water potential gradients than elongate stemmed species for a similar transpiration rate. Elongate leaves develop even smaller water potential gradients for a given transpiration rate. Stems have larger hydraulic conductivities but smaller leaf‐specific conductivities (LSCs) than stipes. Small conductivities and small LSCs are associated with short, erect stems. Elongate structures have large conductivities and large LSCs. Of the tracheid characteristics examined, the most important characteristics determining the magnitude of organ hydraulic conductivity are diameter, pit aperture area between tracheids, taper length, and cell length. Large conductivities ofS. volubilisclimbing leaf stipes are associated with very large‐diameter tracheids (some>200 μm), large tracheid number, exceptionally long tracheids (some>4 cm), large pit aperture area between tracheids, short tracheid taper, and smooth tracheid lumen walls. Hagen‐Poiseuille estimates of hydraulic conductivity range from 1.1 to 3.3 times the measured values. Conductivity of stipes is highly correlated with leaf area supplied by stipes. Conductivities of stems and elongate leaf stipes also correlate with leaf area supplied by these structures. Estimated hydraulic conductivities of field‐grownBlechnumandSalpichlaenademonstrate that larger conductivities are associated with larger plants. This study contributes toward our knowledge of fern water relations and extends previous growth form/hydraulic architecture characterizations by providing a more comprehensive comparison of closely related species. In addition, this study provides evidence for the relative importance of tracheid characteristics in determining the magnitude of organ hydraulic conductivity.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb11401.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

The ability of neotropical forest shrubs to reproduce by establishment of severed fragments was demonstrated experimentally in a lower montane forest in Costa Rica. Twigs (N= 307) broken from 78 individual shrubs or large herbs (representing 22 species, 14 genera, and eight families) were individually marked, dropped to the forest floor, and measured periodically over 5 years. Ninety‐two percent of the fragments and all but one species persisted for 4 months (rainy season) or more. Adventitious roots were produced after the first month. For all fragments, both the net number of leaves and total stem length declined initially. Mortality was concentrated in a 10‐month period (that included the first dry season), in which 35% of the fragments (average by species) and 85% of the species survived. Species’ survivorship then was steady or declined slowly. Fourteen species, representing seven genera in three families (Piperaceae, Rubiaceae, and Acanthaceae) persisted for all 5 years of the study. A fragment's original size did not affect the likelihood that it would survive. Although there was continuous production of new leaves, few fragments showed a net gain in leaf number by 5 years. In contrast, most fragments showed a net gain in stem length (up to five‐fold), with vertical growth accounting for the gain. By the third year, most surviving fragments were upright plants and some had flowered and borne fruit. Several, broken again by falling branches, fragmented naturally. Regrowth from fragments is likely to be important in the persistence of individuals and in the structure and dynamics of populations of shrubs in tropical wet forests.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb11402.x

出版商:Wiley    

年代:1990

数据来源: WILEY