摘要:

Populations of a fern gametophyte presumed to be of the genusVittariaoccur commonly in the uplands of the southeastern United States. The gametophytes occur on non‐calcareous rock outcrops of various composition in areas which provide continuous moisture and protection from temperature extremes. Gametophytes in these habitats are robust and long lived, frequently forming the dominant vegetation in areas covering several square feet. Reproduction is exclusively vegetative by production of gemmae. Although sex organs are present in most populations, viable sporophytes are never produced. The gametophytes have previously been considered most likely to beV. lineata, which occurs in Florida, but morphological and physiological comparisons do not support that conclusion. Significant differences between Appalachian and Florida gametophytes occur in growth form, growth rate, cold hardiness, sporophyte production, and patterns of gemma production. The distribution of the Appalachian gametophytes correlates with old, unglaciated land masses suggesting antiquity rather than recent introduction. Present evidence favors the interpretation that the AppalachianVittariagametophytes either belong to a tropical American species from which they have long been separated, or that they represent a distinct species of which the sporophyte no longer exists.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb10828.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

The radial symmetry of shoots and roots arises from a center of symmetry within the apical meristem. When a lateral axis forms at a distance from the tip, a new center of radial symmetry must arise. We have studied the biophysics of this kind of transformation in the epidermal layer of the succulentGraptopetalumwhere a stem “regenerates” from organized leaf tissue. Study of the epidermal cell pattern (with scanning electron microscopy) shows that reorganization involves neither a cellular pre‐pattern blocked out by oriented cell divisions nor a callus‐like stage where cell files, expansion direction, and primary cell wall cellulose orientation are randomized throughout. Rather, developmental events are a function of initial position. In regions of geometrical compatibility between parent axis and prospective lateral, there is little or no modification of files, expansion, or cellulose. In regions requiring 90° changes in orientation, cellulose orientation (studied with polarized light) conforms to the new symmetry first. This is followed later by changes in the surface growth pattern and in the cell division pattern. The early establishment of a circumferential cellulose pattern in the epidermal layer could account for both the cylindrical shape of the new axis and the subsequent rearrangement of directional growth and cell file pattern.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb10829.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

Electron microscope observations onPhycopeltis epiphyton, a subaerial green alga found growing on the leaves of vascular plants and bryophytes, revealed the presence of a densely staining material within the inner and outer zones of the cell walls. This material resists acetolysis, is degraded by chromic acid, is unaffected by ethanolamine and exhibits secondary fluorescence when stained with the fluorochrome Primuline. These characteristics, together with infrared absorption spectra indicate that, on the basis of currently accepted criteria, the densely staining material is a sporopollenin and that it is a major component of the cell wall. Tests for cellulose, chitin, and lignin were negative, and little if any silica is present. It is suggested that negative results in tests for cellulose may be due to a masking effect by the sporopollenin. Comparison of the fine structure of the cell walls ofP. epiphyton, pollen grains, and algal cells (known to contain sporopollenin) supports the suggestion that sporopollenin deposition on “unit membranes” is universal. Morphological similarity among sporopollenin lamellae inP. epiphyton, pollen grains, spores of land plants, and the trilaminar sporopollenin sheath inChlorella, Scenedesmus, andPediastrumindicates that the structures may be analogous. As in pollen grains, sporopollenin may provide protection against desiccation and parasitism. It may also be involved in the adhesion ofPhycopeltisto host plants and in the adhesion between adjacent filaments of the thallus.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb10830.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

Scanning electron microscopy (SEM) was used to study the surface features of the anthoecia (fertile lemma and palea) ofPanicum elegansElias from the Late Cenozoic deposits in Ellis County, Kansas. Examination of the lemma revealed a well developed germination lid, irregularly arranged, simple, rounded papillae and a crescent‐shaped scar of attachment. The presence of a germination lid indicates that this structure has been present in some members of the Gramineae since at least the Late Miocene‐Early Pliocene. Evidence is presented which contradicts current ideas regarding the distribution of the germination lid in extant Gramineae. The surface of the palea is characterized by simple, rounded papillae spaced in regular rows. The arrangement and form of these papillae are like that present in some modernDichanthelium.Both the epidermises of the lemma and palea are composed entirely of long cells with strongly sinuous, interlocking cell walls. The pattern of cells on the lemma indicates that the systematic placement ofPanicum elegansis correct.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb10831.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

Application of 1.5 μg indoleacetic acid (IAA) in a lanolin droplet to the exposed apical meristem ofLupinus albusseedlings caused: (1) axillary buds to form closer to the apex than normal, (2) displacement of primordia formed during the first two plastochrons following treatment, and (3) significant increases in concentration of RNA, protein, and unsaturated lipids in the meristems. Primordial displacement tended to be random relative to the site of the treatment, which may be a feature common to dicotyledonous plants exhibiting spiral phyllotaxis. That IAA conferred initiation site capabilities to all of the peripheral zone for a short time was indicated by (2) and (3) above, and by decreases in concentrations of the observed compounds toward control levels after the second plastochron following treatment. Effects of IAA on RNA suggest that nucleic acid metabolism, and possibly gene action, was involved in the response. Kinetin or gibberellic acid had no apparent morphogenetic effect onLupinusmeristems.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb10832.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

Treating shoot apical meristems ofPinus elliottiiseedlings with 1.5 μg kinetin results in bud scale formation and the onset of dormancy. IAA and GA produce no morphogenetic effects. According to cytochemical analyses, levels of ribonucleic acid (RNA) in kinetin‐treated meristems exceed controls through the sixth day following treatment, during which time unsaturated lipids fall sharply below control values. Rapid declines in RNA by day eight, when cytoplasmic protein may also be at a relatively low concentration, coincide with the first appearance of bud scales, signaling the onset of dormancy in kinetin‐treated meristems. Changes in concentration of RNA and lipid (and possibly protein) suggest that kinetin may effect nucleus‐based events and/or membranes in the cytoplasm in the apical meristem. These effects may be related to the subsequent development of bud scales in the subapical region and to the onset of dormancy throughout the shoot tip. The central mother cell zone is not metabolically quiescent in the vegetative shoot apical meristem ofPinusseedlings.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb10833.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

Radicle growth of the corn inbred Oh51A was reduced by imbibitional chilling at 5 C. The effect was mediated by the initial moisture of the kernel prior to hydration. Five percent initial moisture kernels were injured while 13% initial moisture kernels were not. The formation of a structural lesion in the radicle during the first 24 hr of hydration at 5 C of 5% initial moisture kernels was correlated with subsequent radicle growth reduction at 25 C. The lesion did not form during hydration of 13% initial moisture kernels at 5 C, in kernels hydrated at 25 C, in unimbibed kernels, or in heat‐killed, cold‐imbibed kernels. The lesion also did not appear during the imbibitional chilling of the corn inbred B8 which did not exhibit radicle growth reduction. Two sources of Oh51A with similar lesion frequencies were different in the severity of growth reduction. While the lesion became sealed at 25 C subsequent to cold hydration, growth reduction differences were not fully explained by this phenomenon. In one source more seedlings exhibited reduced growth than expected from the frequency of observable lesions. Therefore, other types of damage contributed to the reduction of radicle growth.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb10834.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

The pollination of a large mixed population ofDicentra canadensisandD. cucullariawas studied in a beech‐maple forest in southwestern Ohio. Analyses of pollinator frequencies and species, pollinator behavior, sugar components and concentrations in nectar, corbicular pollen loads carried by pollinators, spectral reflectance from corollas including ultraviolet reflectance, fragrance, blooming phenology, insect‐related fertility, and hybridization potentials suggested that these sympatricDicentraspecies are reproductively isolated by internal mechanisms but not by external barriers to hybridization. Both species were exclusively and obligately dependent upon queen bumblebees for their pollination unlike other members of the spring ephemeral flora to which they belong. The occurrence of one or both species in one area is considered primarily the result of their adaptive preference for different edaphic and possibly climatic situations and not the consequence of competitive exclusion by pollinator behavior.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb10835.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

Ceanothus greggiivar.perplexansis a common shrub in the southern California chaparral. Clusters of nodules found under the canopy of this species are modified roots which contain a nitrogen‐fixing endophyte,Frankia ceanothi(Actinomycetales), within the cortex. The nodule density per m2obtained from root system excavations is much lower than that reported for differentCeanothusspecies in northern California. Field observations indicate that soil moisture is an important factor in nodule formation. Anatomical studies with the scanning electron microscope and acetylene reduction assays support the hypothesis that the vesicles, spherical swellings of hyphal endings (1.2–3.0 μm in diam), are indeed the sites of N2fixation. No bacteria‐like bodies were found. The acetylene reduction rates ofC. greggiiendophytes were of the same order of magnitude as those reported for other members of the genusFrankia.It is estimated that 100 grams of nitrogen are fixed per year per hectare for a specific area in the southern Californian chaparral whereC. greggiicomprises 1/3 of the ground cover. This amount appears to be large enough to replace the nitrogen that is lost annually by drainage and runoff from winter rain storms.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb10836.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

Experimental results show that predominant cell arrest in G2 and the presence of endoreduplicated cells are coincident with presence of secondary vascular tissues while preponderant cell arrest in G1 and absence of polyploid cells are coincident with an absence of secondary vascular tissues in mature root tissues of intact and cultured roots ofRaphanus sativusL. In mature tissues of intact seedling roots, most cells arrest in G2, and both polyploid cells and secondary vascular tissues are present. If excised roots are grown on simple medium, most mature cells arrest in G1, none undergo endoreduplication, and only primary vascular tissues are present. When bases of these excised roots are later placed in a medium with auxin, cytokinin, and myo‐inositol that produces secondary vascular tissues in vitro, preponderant cell arrest occurred in G2 with some polyploid cells. The general relationship of predominant period of cell arrest, presence of polyploid cells, and presence of secondary vascular tissues in mature roots among plants of various taxa is surveyed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb10837.x

出版商:Wiley    

年代:1978

数据来源: WILEY