摘要:

Chromosome counts are reported for 372 individuals from 202 populations in 26 taxa ofAcmella(Asteraceae: Heliantheae). Chromosome numbers for 15 taxa are first reports. A review of previous counts and the new reports supports a basic chromosome number of 13 for the genus. The results show that polyploidy, sometimes accompanied by hybridization and asexual reproduction, is widespread inAcmellaand has contributed to the taxonomic difficulties in the genus. These factors have produced a variable polyploid pillar complex in sect.Acmella.In one taxon in this complex,A. oppositifoliavar.oppositifolia,intrataxon and even intrapopulational chromosomal variation has been detected. Morphological studies in conjunction with observations of meiotic pairing suggest that most polyploids are alloploid in origin. The occurrence of polyploidy in 16 of the 27 taxa known chromosomally emphasizes the important role this process has had in speciation withinAcmella.Although intrataxon chromosomal variation has limited the taxonomic utility of chromosome numbers, a few examples are presented in which these data have been valuable for separating some pairs of closely related taxa (A. decumbensvar.affinisfrom var.decumbensandA. poliolepidicafromA. oppositifolia).

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08457.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

The vegetative (Ruflorinia sierra) and fertile (Ktalenia circularis) organs of an Early Cretaceous pteridosperm collected from Santa Cruz Province in Argentina are described. The sterile leaf is at least tripinnate and bears decurrent secondary pinnae with obliquely attached, sharply pointed pinnules. The fertile member arises from the base of the vegetative rachis and bears two types of appendages, cupules and bracts. Bracts are attached to the main axis near cupules and are present in clusters of up to six. Cupules are sessile, spherical, and arranged in opposite or subopposite pairs along the axis. A small lip is present on one surface of the cupule. The number of seeds per cupule may be one or two, with each characterized by a distal nucellar beak and circular, chalazal scar. Cuticular anatomy, including the fine structure of the stomatal complex, is described for both vegetative and reproductive organs. The cupules ofKtaleniaand other Mesozoic seed plants are compared, and a discussion presented regarding the possible function of the cupule.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08458.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Cleared leaves of taro (Colocasia esculenta) were examined microscopically to determine changes in the distribution of both druse and raphide idioblasts during a late developmental process—leaf unfurling and expansion. Druse crystal idioblasts are small spherical cells found throughout the lamina, mostly in subepidermal areas. Two types of raphide idioblasts were observed in taro leaves: the nondefensive raphide idioblasts, which are elongated cells usually found embedded in tissues of the leaf margins; and the defensive raphide idioblasts, also elongated cells, but usually found suspended between mesophyll cells in leaf airspaces. The densities of both druse and raphide cells were highest at the fully furled stage and least in the mature, unfurled stage, after substantial leaf expansion. During leaf unfurling, the raphide cells showed a bilaterally symmetrical distribution during all stages from fully furled to mature, unfurled leaves. The distribution of druse cells was bilaterally symmetrical during the fully furled and unfurled stages, but, during unfurling, when one half of the lamina is unfurled and the other half is still tightly furled, up to 80% of the druse cells were found on the unfurled half of the lamina.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08459.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Resting spores ofThalassiosira scotiaFryx. et Hoban were abundant in phytoplankton net hauls collected from the Scotia Sea south of South Georgia in December 1981. Primary valves are distinguished from secondary valves by the presence of marginal striae with rounded, shoelike protrusions, villi surrounding marginal areolae and marginal striae, greater numbers of central strutted processes, and differences in structure of occluded processes. Densities of marginal strutted processes also tend to differ, though ranges overlap.Thalassiosira scotiais most closely related toT. antarctica,differing from that taxon by having coarser areolation, heavier silicification, and more prominent occluded processes. Rudimentary valves ofT. scotiadiffer from those ofT. antarctica.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08460.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Pollen of 16 species ofParkia(ca. 30 spp.) was examined in the light, scanning and transmission electron microscopes (LM, SEM and TEM). Pollen is shed as large (61‐236 μm), globose, 16–32‐grained polyads that remain united following acetolysis. Thin sections reveal that polyad cohesion is maintained through fusion and/or adhesion and/or appression of adjacent ektexines in lateral and/or proximal and/or distal regions. In lateral and proximal regions the ektexine is often embedded in a dense granular endexinous matrix. Individual grains of the polyad are clearly outlined in most species but are completely obscured in several New World species. Sculpturing varies both in pattern and type of element. Nonuniformly sculptured polyads, in which the sculpturing of individual grains differs between the peripheral and central portions of the distal face, occur only among Old World species. Uniformly sculptured polyads occur among both New and Old World taxa. Two main sculpturing types are present amongParkiaspecies: verrucate and tectate‐perforate, the latter particularly well developed in the reticulate polyads of the neotropicalP. uleiandP. multijuga p.p.Ultrastructurally, allParkiapolyads exhibit ektexine and endexine continuous around the individual grain. Distal ektexine is prominent and clearly stratified, usually exhibiting a thick, perforate tectum, columellate interstitium, and a thin, locally discontinuous foot layer. Lateral and proximal ektexine is significantly thinner and less structured. Individual grains within the polyad possess three to four peripheral‐distal apertures usually at the points of contact between adjacent grains. Proximal and central grain apertures occur in most, but not all, species. Polyad characters suggest a particularly close relationship among the New World speciesP. decussata, P. discolor, P. gigantocarpa, P. igneiflora, and P. nitida. Parkia ulei,though sculpturally closest toP. multijuga p.p.,is ultrastructurally most similar to the AfricanP. biglobosa.The large tectate‐perforate‐fossulate polyads ofP. pendulaandP. platyparkiaare unique in the New World.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08461.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

The effects of interference on community structure of subalpine meadows were investigated. Adults greatly reduced seedling survival in the greenhouse, and natural seedling survival was low. In fell fields, nurse plant effects were common, while survival was confined to gaps in productive meadows. A greenhouse experiment demonstrated that community dominants were strong competitors able to suppress subordinates. Simulated grazing ofFestuca,a dominant, reduced its yield relative to most subordinates. Interference intensity appears to be a function of productivity and proximity. The proportion of negative species associations increased as productivity increased. Morphological similarity between species is least in the most productive community, but greatest where productivity is only moderate. Interference may permit only relatively dissimilar species to coexist unless it is ameliorated by factors such as grazing or heterogeneity. Spacing patterns suggest that minimal contact between dominants and other species is a characteristic of communities with intense interference. The evidence points to this hypothesis: interference acts contemporaneously to limit niche width in productive communities, but evolutionary changes are unlikely where complete dominance is possible and specialization is not a viable option. In contrast, species in unproductive communities, where abiotic stress is likely to have been an evolutionary force, appear genetically more niche differentiated. Where contemporary interference is moderate, evolutionary effects are possible because species may use resources not preempted by the dominants.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08462.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Increased activity of α‐amylase in bean stems occurred during cellular autolysis in the pith region. In etiolated pea seedlings, α‐amylase activity increased sequentially in the first, second, and third internodes. In light‐grown seedlings, the increase was initially observed in the first internode, then simultaneously in the second and third internodes. In all internodes, these changes were observed in regions undergoing cellular autolysis in the cortex region. As in bean hypocotyls, α‐amylase activity occurred in tissues virtually devoid of starch. Sequential accumulation and then decline in protein and sugar concentrations in each internode indicate a remobilization of materials from nongrowing regions of the stem. These results are consistent with the hypothesis that regulation of α‐amylase activity is related to this remobilization.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08463.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Immature embryos ofPanicum maximumJacq. (Guinea grass) were cultured on Murashige and Skoog's medium containing 2,4‐dichlorophenoxyacetic acid (5 mg/1) and coconut milk (5%). The epidermal and subepidermal cells of the scutellum at the coleorhizal end either formed somatic embryos directly or gave rise to embryogenic callus at several loci. Somatic embryos were formed later also at the periphery of these embryogenic calli. The embryoids originated from single, densely staining, nonvacuolated and starch‐containing cells with thickened walls and developed through characteristic stages of grass embryogeny.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08464.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

The young guard cell ofSelaginellainherits a single plastid from the division of the stomatal guard mother cell (GMC). During early stomatal development the single plastid undergoes a complex series of migrations and divisions. The regular pattern of plastid behavior appears to be an expression of the genetic program controlling division plane and cytomorphogenesis. The plastid in the GMC becomes precisely aligned with its midconstriction intersected by the plane of a preprophase band of microtubules (PPB) oriented parallel to the long axis of the leaf. This alignment with respect to the future division plane of the cytoplasm ensures equal plastid distribution to the daughter cells. Cytokinesis occurs in the plane previously marked by the PPB and the plastid in each daughter cell lies between the lateral wall and the newly formed nucleus. Following cytokinesis the plastid in each young guard cell develops a median constriction and migrates to the common ventral wall where the isthmus is associated with a system of microtubules in the vicinity of the developing pore region. Plastid division is completed while the plastid is adjacent to the common ventral wall. Following division, the two daughter plastids move back toward the lateral wall. Each plastid may divide again during guard cell maturation but no further migrations occur.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08465.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

The ultrastructure of carposporophyte development is described for the red algaGloiosiphonia verticillarisFarl. The auxiliary cell produces gonimoblast initials, which divide to produce two types of gonimoblast cells—the nondividing vacuolate cells and terminal generative gonimoblast cells. The generative gonimoblast cells form clusters of carpospore initials, which eventually differentiate into carpospores. After gonimoblast filaments are formed, the auxiliary cell undergoes autolysis, causing degeneration of septal plugs between the auxiliary cell and adjacent cells, thus forming a fusion cell. Since this cell lacks starch and appears degenerate throughout carposporophyte development, a nutritive function cannot be ascribed to the fusion cell. Carpospore differentiation is simple and proceeds through three developmental stages. Young carpospores structurally resemble gonimoblast cells, because they contain undeveloped plastids, large quantities of floridean starch, and are surrounded by extensive mucilage instead of a distinct wall. In addition, dictyosomes form and begin to produce vesicles with fibrous contents representing carpospore wall material. During the intermediate stage, dictyosomes continue to produce vesicles that contribute additional carpospore wall material, thereby compressing the mucilage and creating a darker‐staining layer outside the carpospore wall. Plastids form internal thylakoids by invaginations of the inner membrane of the peripheral thylakoid. The endoplasmic reticulum forms large granular vacuoles that appear to be degraded during subsequent stages of development. Mature carpospores form cored vesicles. They also contain mature chloroplasts, large amounts of floridean starch, and occasionally granular vacuoles. During this stage, interconnecting carpospore‐carpospore and carpospore‐gonimoblast cell septal plugs begin to undergo degeneration. This process may be mediated by tubular structures.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08466.x

出版商:Wiley    

年代:1985

数据来源: WILEY