摘要:

Vegetative and fertile frond segments ofBotrychiumhave been recovered from Paleocene deposits of central Alberta, Canada. Specimens are preserved as coalified compressions that yield information about frond structure, sporangia, and spore ultrastructure. These fossils, described asBotrychium wightoniisp. nov., establish a megafossil record for the Ophioglossales, and demonstrate that modern‐appearing species of the order were present in western North America by the earliest Tertiary. The largest vegetative fragments are up to 4.6 cm long and tripinnately compound, with opposite to subopposite branching. Ultimate segments are pinnatifid with dentate pinnules and open dichotomous venation. Fertile specimens are also tripinnately compound with a long rachis and subopposite to alternate pinnae. Sporangia are either submarginal and superficial, or marginal, and are all directed toward one surface of the pinnule. They are ovoid to subspheroidal and 0.8‐2.0 mm in diameter. Some sporangia are apparently stalked, while others appear to be sessile. This variation results both from the ultimate frond segments being compressed in several different planes, and the fossils being exposed at different levels. Spores macerated from the sporangia are radial and trilete, and range 30–67μm in diameter. Most are psilate, but some have a densely striate surface.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11359.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Results were compared between the latex paint and compressed air methods for determining total vessel lengths, and between the sectioning and maceration methods for determining vessel diameters. The minimum, mean, median, and maximum vessel diameters were less with the sectioning method than with the maceration technique. Vessel diameter distributions were always nonnormal and had roughly similar patterns with the two techniques, but were statistically different from one another. In all six species where the paint and air methods for determining vessel length were compared, both methods showed a similar skewed vessel length distribution, with many short vessels and few long ones. Although there was no consistent pattern to the difference in results with these two methods, the vessel length frequency distributions were statistically different from one another. With the paint method, many vessels, especially many of the narrowest ones, were not paint‐filled at the paint infusion port. The air method utilized the paint method, in part, and, in addition, is based upon the incorrect assumption that all vessels in the stem are the same diameter. Both techniques tended to exclude vessel lengths of the narrowest vessels. However, the narrow vessels, although numerous, contributed an insignificant amount to the total theoretical hydraulic conductance in stems.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11360.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Eighty‐three chromosome counts are reported for 72 taxa of the Bromeliaceae. Fifty‐eight of these counts are the first known chromosome number reports for their respective taxa. A model of chromosomal evolution in the Bromeliaceae (n= 25) is presented. The model is parsimonious and consistent with existing data on meiotic chromosome numbers within the family and in the closely related Velloziaceae (n = 9). Two hypothesized paleodiploids (n= 8 andn= 9) hybridized to form a tetraploid that in turn hybridized with then= 8 lineage. The resultantn= 25 is the extant base number for the family. Two alternative hypotheses could explain the unique extant base number (n= 17) forCryptanthus: 1)Cryptanthusrepresents the paleotetraploid level, i.e., prior to the second round of hybridization, or 2) the lower number represents the result of a more recent series of aneuploid reductions fromn= 25. Given the existence of intergeneric hybrids involvingCryptanthus, aneuploid reduction is the more likely interpretation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11361.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

The thallus of the lichenRamalina menziesiiTayl. is comprised of subunits which resemble planar nets. The nets arise upon older nets as buds which develop perforations and expand. Microphotographic study of thallus development in the field shows several features which differ from a recently proposed model of development for this species. New perforations develop continually in new tissue produced at the apical margin of the net. The apical margin is inrolled, and may furcate. This type of branching is developmentally distinct from the formation of new nets from buds borne upon expanded parts of the net. Anatomical study of net apices appears to support assertions that programmed tissue necrosis contributes to perforation formation at sites where gaps are present in the algal layer.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11362.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Antennariais a genus of dioecious, perennial, herbaceous Composites that are especially diverse in the cordillera of western North America. SectionAlpinaeconsists of about nine taxa, among themA. aromatica, A. densifolia, A. media, A. pulchella, andA. umbrinella.Although diploids are morphologically distinct, the polyploid derivatives of the diploids obscure the morphological distinctness of the groups. A survey of 19 putative isozyme loci indicates that the diploids have diverged only moderately from one another with respect to biochemical genetics (I= 0.838 to 0.961). Additionally, only moderate amounts of genetic diversity were detected. Isozyme data are supportive of a hypothesis of a rapid mode of speciation inAntennaria, where morphological differentiation has been accompanied by small amounts of allozyme divergence. Polyploids have significantly higher amounts of heterozygosity than diploids and tetrasomic inheritance is inferred. Evidence from morphology and biochemical genetics suggests that the polyploids represent a continuum between interracial autopolyploids and segmental allopolyploids. In light of the relatively low degree of genetic and morphological divergence among manyAntennariaspecies, taxonomic conservatism is advocated.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11363.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

The axillary complex of female cones ofCryptomeriais initiated as a tangentially extended triangular structure with a rounded apex. It is bilaterally symmetrical. Structures interpreted as prophylls are differentiated first, but they become insignificant in later development. They are succeeded by two successive pairs of lobes, each lobe being the common primordium for an adaxial ovule and a tooth. The ovule initially much exceeds the tooth. The apex of the complex has a diversity of fates and may differentiate as an ovule‐tooth pair. A one‐to‐one relation between teeth and ovules may be lost by abortion of ovules. The initial relation between teeth and ovules is obscured in later development due to extension of tissues at the base of the complex associated with considerable enlargement of the teeth. Histogenesis of the various parts is described, together with the vascular system. There is a vascular supply to the tooth but not the ovule. The results support a direct comparison with the extinct transition conifersPseudovoltziaandAethophyllumbut do not fully support Florin's generalized model for the arrangement of parts in the axillary complex of conifers.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11364.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Anatomical features ofEriastrum densifoliumpopulations in southern California show variation that correlates well with ecological setting and geographical distribution. Vessel element size and density in shoots suggest strong adaptation among different subspecies to efficient water movement in different habitats. Indices of mesomorphy, devised by Carlquist to indicate relative adaptivity of wood, likewise show considerable variation among populations, suggesting that different subspecies have anatomical components that can define them. Relationships among the five subspecies ofE. densifoliummay be explored through MI value relationships.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11365.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

The floral ontogeny ofPisum sativumshows a vertical order of succession of sepals, petals plus carpel, antesepalous stamens, and antepetalous stamens. Within each whorl, unidirectional order is followed among the organs, beginning on the abaxial side of the flower, as in most papilionoids. Unusual features include the four common primordia which precede initiation of discrete petal and antesepalous stamen primordia, and the marked overlap of organ initiations between whorls which are usually separately initiated. The stamens arise in free condition, then become diadelphous by intercalary growth at the base of nine stamens, and finally become pseudomonadelphous by surface fusion between the vexillary stamen filament and the adjacent edges of the filament tube. The early initiation of the carpel is not unique among papilionoids, but is somewhat unusual.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11366.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

One explanation for low fruit sets in plants with hermaphroditic flowers is that total flower production by a plant is controlled primarily by selection through male function. This male function hypothesis presupposes that success in pollen donation increases more strongly with flower number than does seed set. I tested this prediction by measuring male and female components of reproductive success as functions of flower number in natural populations of the self‐incompatible, perfect flowered plant,Ipomopsis aggregata.Fruit set in this hummingbird‐pollinated plant averaged 4.9 to 40.3% across the 4 years of study. Both the total amount of pollen donated and the total amount received, as estimated by movement of fluorescent powdered dyes, increased linearly with number of flowers on a plant. Total seed production, however, increased disproportionately quickly because plants with larger floral displays were more likely to set at least one fruit. An estimate of the functional femaleness of a plant, based on pollen donation and seed production, increased with flower number. These results do not support the male function hypothesis.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11367.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

The development of the phytomelanin layer in the achenes ofAgeratum conyzoides(Compositae, Eupatorieae) was studied using light and electron microscopy. At the level of the embryo sac, the young ovary wall contains an outer zone, consisting of an epidermis and two hypodermal layers, and an inner zone, consisting of developing fiber cells and 3–5 layers of parenchyma. A schizogenous space forms between the developing fibers and the inner hypodermis at about the time that the embryo sac is fully organized. At this stage, the developing fibers contain papilla which are outgrowths that connect the fibers to the inner hypodermal cells. After fertilization, phytomelanin accumulates on the cell walls lining this space. Subsequently, by the time the fruit matures, the phytomelanin fills the space completely and forms a solid, black layer. The surface of the inner hypodermis that faces the space forms a mold; the characteristic peglike projections of the mature phytomelanin layer develop by filling the invaginations between the hypodermal cells. During phytomelanin accumulation, abundant smooth endoplasmic reticulum is present in the hypodermis, especially in the outer layer. It is hypothesized that the precursors of the phytomelanin are synthesized in this endoplasmic reticulum and that these precursors migrate into the space where the phytomelanin is polymerized.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11368.x

出版商:Wiley    

年代:1989

数据来源: WILEY