摘要:

The developmental anatomy ofZamia pumilaL. root apices was studied during light‐induced nodulation. Dark‐grown roots had an apical organization identical to that of other cycads and similar to that of other gymnosperms. A distinct protoderm was not observed in these roots, which had a large open meristem and a root cap with a well‐defined columella. During nodulation, the meristem became reduced in size, and its constituent cells became vacuolate until all but a few resembled ground tissue. The root cap senesced during nodulation, and a recognizable root cap was absent from mature nodules. A file of densely cytoplasmic cells with centrally positioned nuclei developed in the nodule cortex. This layer was continuous across the nodule apex, and was identical to the presumptive algal‐zone described previously by other authors. Light‐induced nodules branched dichotomously and were identical to algal‐free nodules described by other authors. In dichotomously branched nodules, each lobe was covered by a parenchymatous mantle analogous to a root cap. A unicellular layer similar to the presumptive algal zone spanned the gap between opposite nodule lobes, and extended beneath each lobe before terminating in the cortex. Typical meristematic regions were not observed in these nodules. Based on cell sizes and patterns, a meristematic zone was thought to exist between the mantle and the inner cortex.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb12459.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Cibotium oregonensesp. nov. is described from the Upper Eocene of Medford, Oregon. The fossil comprises petiole bases and stem periphery of a large fern preserved via permineralization. A stele devoid of sclerenchymatous sheathing and a petiole vascularized with a large number of leaf traces in a cyatheacean pattern characterize the fossil. A distinctive U‐shaped interior series of leaf traces allows assignment to the genusCibotium.This fossil provides evidence that the genusCibotiumwas represented by an arborescent species with large leaves in the Early Tertiary of western North America.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb12460.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Heterotheca latifoliaBuckley has been replacingErigeron canadensisL. as the first year dominant in Carolina‐Georgia piedmont old field succession. This species ofHeterothecawas introduced to this area in the 1940's. Both theHeterothecaandErigeronspecies are winter annuals. We used a replacement series experiment to detect competition (interference) under a variety of greenhouse environments to seek a possible explanation for the observed changes in old field succession. Interspecific competition betweenHeterothecaandErigeronplants resulted in significant reductions in the dry weight ofErigeronplants.Erigeronwilted beforeHeterothecain 98.2% of observations of first‐wilting in mixed‐species cultures. At flowering,Erigeronplants in mixed‐species cultures were shorter thanHeterothecaplants. Poor seed dispersal in mixed‐species communities in the field could limitErigeron's ability to populate new areas. Greenhouse flats densely sown with equal numbers of seeds of both species resulted in a winter rosette cover ofHeterothecaonly.Heterotheca's assumption of the role of first year dominant in old field succession may be due to interspecific competition withErigeronat all stages in its life cycle. These competitive effects can be observed under a variety of environmental conditions, especially those in which drought occurs.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb12461.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Nuclear DNA content varies over 20% within the diploid (2n= 18) speciesM. douglasiiandM. bigelovii.Two different intraspecific crosses were made betweenM. douglasiibiotypes which differed by about 10% in 2C nuclear DNA content. The F2progeny of one intraspecific cross showed no striking evidence of segregation for DNA content. The mean DNA contents of F2progeny from two sister hybrids from the second intraspecific cross were significantly different at the 1% level.An interspecific cross was made between biotypes ofM. douglasiiandM. bigeloviithat differed by approximately 10% in DNA amount. The 12 F1progeny did not cluster around the parental midpoint, but instead encompassed nearly the entire range between the parental means. The five families of F2progeny studied each had a mean DNA content corresponding to that of the particular F1from which they were derived, indicating that the F1plants were not of identical DNA content.The results of this study suggest that DNA sequences which account for the DNA content differences among the plants are unstable and can undergo deletion or amplification in a hybrid. The altered DNA content may be heritably stable and show little or no segregation in the F2progeny.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb12462.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

TripsacumsectionFasciculatais characterized by staminate spikelet pairs in which one spikelet is sessile and the other is supported by a long and slender pedicel. In sectionTripsacumboth spikelets of a staminate pair are sessile, or one is supported by a short and stout pedicel. SectionFasciculataincludes five closely allied species.Tripsacum lanceolatumRuprecht ex Fournier (2n= 72) extends from Durango in Mexico to the Huachuca mountains of southern Arizona. It resemblesT. jalapensede Wet&Brink spec. nov. (2n= 72) from Guatemala in having terminal inflorescences with 3–10 racemes, but they differ in growth habit and are genetically isolated. Terminal inflorescences of the remaining three species have 15–50 racemes.Tripsacum laxumNash (2n= 36) from the eastern escarpment of the Central Mexican Plateau is the only species of the group with essentially glabrous basal leaf‐sheaths. It resembles the more widely distributedT. maizarHernandez&Randolph (2n= 36, 72) in respect to inflorescence morphology, but is genetically isolated from this species. The widely distributedT. pilosumScribner&Merrill (2n= 72) was divided into var.pilosumand var.guatemalensede Wet&Brink var. nov.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb12463.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Specimens showing staminate and pistillate inflorescences attached to branches bearingFagopsis longifolia(Lesq.) Hollick foliage, from the Oligocene Florissant flora of Colorado, permit a relatively complete characterization of the extinctFagopsisplant. The alternately arranged simple leaves have pinnate craspedodromous venation and prominent simple teeth. Staminate inflorescences are globose on a stout peduncle and contain anthers with tricolporate pollen. Pistillate inflorescences are ovoid heads with compact, helically arranged three‐flower units and are interpreted to have three styles per flower. The infructescence consists of small wedge‐shaped cupules, each containing three tiny fruits, and subtended by a persistent bract. The cupules unravel from the swollen peduncle at maturity and are often dispersed as strings of adhering fruit‐wedges which frequently take on a regular, more or less circular appearance.Fagopsisis unlike any living genus but has characters which support a relationship to the Fagaceae. Unlike extant members of the family, which typically have fruits adapted for animal dispersal,Fagopsisis less obviously specialized and perhaps adapted for wind dispersal. The striking differences in fruiting structures betweenFagopsisand extant Fagaceae parallel the differences between the extant generaPlatycaryaandJuglansin the Juglandaceae, andAlnusandCorylusin the Betulaceae.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb12464.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Electrophoretic analysis of 11 different clonal freshwaterPeridiniumisolates shows that currently used morphological taxonomic criteria are conservative measures of relatedness and that the presence or absence of an apical pore is an important taxonomic feature. Correlation of malate dehydrogenase and glutamate dehydrogenase isoenzyme patterns with chromosome number variations among our isolates lends no support to polyploidy as a speciation mechanism.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb12465.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

A three‐dimensional reconstruction of a fertile floret stele ofPanicum dichotomiflorumapproaching anthesis was made by a new technique using superimposition of tracings of 80, 1‐μm thick serial sections, cleared tracing film, and mounting adhesive. From a collateral bundle, which also served as the median trace to the fertile lemma, most of the vascular tissue branched adaxially and horizontally to become the sole vascular supply to the two lodicules, three stamens, and pistil. The xylem branched at a low level to form a broad and long vessel plexus. The phloem branched at a higher level to overlay the vessel plexus on the right and left with an arc of horizontal sieve tubes in a phloem plexus. Those sieve tubes and vessels which rose after branching from the horizontal plexi assumed a more vertical course in the floret stele. Traces to the right and left lodicules arose from the lower abaxial portions of the flanks of the floret stele. Vessels ascended vertically from the xylem plexus and passed through the phloem plexi and joined with the sieve tubes there to exit at the same level and become the right and left lodicule traces. The vascular tissues to the three filament traces arose from different higher levels of the stele. The sieve tubes for the median filament trace arose vertically from the abaxial side between but above the lodicule traces. At higher levels the sieve tubes for the lateral filaments rose from the horizontal arcs of the flanks of the stele and departed it tangentially. The vessels destined to the filament traces arose in the center of the floret stele from adaxial portions of the horizontal plexus, ascended between the arcs of phloem, exited the stele simultaneously above the phloem of the traces, and followed the courses of their respective sieve tubes. The adaxially displaced apex of the floret stele then contained the vascular tissue related to the pistil. All the sieve tubes and vessels of the floret stele were embedded in a matrix of intermediary cells. The peripheral intermediary cells associated with the vessel plexus were xylem transfer cells with pronounced wall ingrowths. At higher levels in the floret stele, intermediary cells in scattered locations near sieve tubes or vessels had less conspicuous wall ingrowths. No preferred orientation of transfer cells with any particular trace was noted.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb12466.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Field data from a saxicolous lichen community in Shenandoah National Park, Virginia, suggested that the slugPallifera variagrazed more frequently on certain lichen species than would be expected if it fed randomly. Two hypotheses might explain this grazing pattern. The preference hypothesis, that slugs select lichens of highest quality, was tested by measuring the concentration of essential elements in lichens eliciting high and low preference by slugs. Lichens with the highest element contents were assumed to be of the highest quality to herbivores. The avoidance hypothesis, that preference by slugs actually results from the rejection of unpalatable species, was tested by offering slugs choices of baited filter‐paper disks impregnated with secondary products of the lichen species in question. Results suggested that preferred lichens had significantly lower concentrations of N, P, and Ca, and that avoided lichens produced secondary products that effectively inhibitedPalliferagrazing activity. These results suggested that the avoidance hypothesis was the better explanation for nonrandomPalliferagrazing patterns. Furthermore, they suggested that lichens with the highest concentrations of essential elements are most likely to produce defense compounds, an observation that supports predictions to explain patterns of chemical defense in vascular plants.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb12467.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Anatomical observations were made on 1‐, 2‐, and 3‐yr‐old plants ofYucca whippleiTorr, ssp.percursaHaines grown from seed collected from a single parent in Refugio Canyon, Santa Barbara, California. The primary body of the vegetative stem consists of cortex and central cylinder with a central pith. Parenchyma cells in the ground tissue are arranged in anticlinal cell files continuous from beneath the leaf bases, through the cortex and central cylinder to the pith. Individual vascular bundles in the primary body have a collateral arrangement of xylem and phloem. The parenchyma cells of the ground tissue of the secondary body are also arranged in files continuous with those of the primary parenchyma. Secondary vascular bundles have an amphivasal arrangement and an undulating path with frequent anastomoses. Primary and secondary vascular bundles are longitudinally continuous. The primary thickening meristem (PTM) is longitudinally continuous with the secondary thickening meristem (STM). Axillary buds initiated during primary growth were observed in the leaf axils. The STM becomes more active prior to and during root initiation. Layers of secondary vascular bundles are associated with root formation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb12468.x

出版商:Wiley    

年代:1983

数据来源: WILEY