摘要:

Monotropa uniflorais an achlorophyllous angiosperm consisting of a mycorrhizae‐dependent root system that produces floriferous, aerial shoots. Each of the numerous, minute ovules is anatropous, unitegmic, and contains aPolygonumtype female gametophyte. Following double fertilization, a lipid‐rich, cellular endosperm develops in association with both chalazal and micropylar haustoria. The vacuolate zygote elongates prior to a cytoplasmically unequal division resulting in a small terminal cell subtended by a larger, vacuolate basal cell. The basal cell eventually degenerates, isolating the terminal cell which is completely surrounded by endosperm. The terminal cell undergoes a cytoplasmically equal transverse division resulting in a two‐celled embryo embedded in endosperm. In final stages of seed maturation, lipids decrease and reserve proteins increase in the cytoplasm of both the endosperm and embryo. The morphological reduction of the mature embryo may be associated with a specialized mode of nutrition.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb12576.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

The order of floral initiation and subsequent organogeny ofErigeron philadelphicusL. (Asteraceae: Astereae) was found to deviate from the acropetal pattern generally reported for the Asteraceae. Light micrographs show periclinal divisions in the first, second, and deeper subsurface layers of cells on the flanks of the inflorescence apex as the earliest evidence of floral initiation. Scanning electron microscope micrographs indicate that the disk flowers appear first and arise as small protuberances approximately one‐third of the way up the previously and undifferentiated highly convex inflorescence apex. A succession of disk flowers arises acropetally in a complex anthotaxy characterized by about 21 dextrorse and 12–15 sinistrorse parastichies (although this pattern is obscured at the apex). After one to three disk flowers have been initiated in each parastichy, the first ray flower initials can be seen to initiate in sites proximal to the oldest and largest disk flowers. Additional ray flowers then initiate basipetally following the dextrorse parastichies established by the disk flowers. Overall floral initiation on the inflorescence apex proceeds acropetally for the disk flowers and basipetally for the ray flowers until the available space is filled. Floral development adheres to the same plan—proceeding bidirectionally on the inflorescence meristem with the oldest and most complete flowers of both types located on the equator established at initiation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb12577.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Crosses were performed within and between 19 Hawaiian populations of the mostly dioecious woody shrubWikstroemia.These populations are from a variety of habitats on the six major islands and are morphologically diverse. The populations are referrable to eight of the 12 species recognized by Peterson. Almost all hybrid combinations produced seeds, and seed‐set was not significantly different among three categories of hybrids (within population, between populations on the same island, and between populations on different islands). F1s from many of the crosses were vigorous and fertile, leading to the conclusion that these populations are not reproductively isolated from each other and the assumption that they are genetically very similar. Natural hybridization was difficult to detect because the species described by Peterson intergrade morphologically and ecologically. The crossability and interfertility of populations ofWikstroemiamay be explained by one or more of the following hypotheses: 1) recency of colonization, 2) the founder effect, 3) lack of selection for barriers to interbreeding, and 4) gross morphological changes without associated large genetic changes.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb12578.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Seeds of tree species commonly invading old‐fields (Fraxinus americana, Gleditsia triacanthos, Morus rubra, Platanus occidentalis,andPrunus serotina) were germinated at eight temperatures from 5 C to 40 C, with six moisture levels (2% to 18% gravimetric moisture content) at each temperature. For most species, total seedling emergence and emergence rate exhibited approximate bivariate Gaussian response surfaces. Emergence of all species, exceptGleditsia,was much more sensitive to differences in temperature than to differences in moisture. Species differed considerably in their response breadths across the interactive gradients, with moisture response bearing little relationship to temperature response.Seeds ofAcer saccharum, Crataegus mollis, Fraxinus americana, Gleditsia triacanthos, Morus rubra,andPrunus serotinawere sown into old‐field vegetation patches dominated by eight different plant species, across three different soils.AcerandMorusemergence exhibited no significant differences among vegetation patches. Emergence of other tree species differed among patch types, but identity of the vegetation (often early successional) most conducive to emergence typically varied from year to year. Emergence of most species responded more strongly to vegetation than to soil series. HighFraxinusandPrunusemergence was associated with dampened temperature ranges, while highCrataegusemergence was associated with low amounts of plant litter. Despite great variability, vegetation differences can predict tree seedling emergence better than do year‐to‐year or soil differences. Extrapolations from the laboratory experiments predicted approximate levels of overall seedling emergence in the field, but prevailing temperatures and moisture differences among plant neighborhoods alone were not sufficient to explain observed differences in seedling emergence among these patches.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb12579.x

出版商:Wiley    

年代:1991

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb12580.x

出版商:Wiley    

年代:1991

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb12565.x

出版商:Wiley    

年代:1991

数据来源: WILEY