摘要:

Patterns of activity in the vascular cambium of Carboniferous arborescent lycopods (ParalycopoditesandStigmaria) were studied by analysis of serial tangential sections of the secondary xylem. The analysis assumes that cell patterns in the wood accurately reflect those of the corresponding cambium. An evaluation using indirect evidence indicates that the assumption is valid as far as can be determined from comparison with living plants. The tracheids of the secondary xylem enlarge in a centrifugal pattern, suggesting a progressive enlargement of the fusiform initials. There is no evidence of periodic anticlinal division of these initials, and it is proposed that the increase in cambial circumference was accommodated primarily by an increase in fusiform initial size. In some axes with abundant secondary xylem there is evidence that isolated initials or groups of initials sporadically subdivided to form numerous, spindle‐shaped meristematic cells. Some of these cells subsequently developed into typical cambial initials. Tissues presumably formed during the cessation of cambial growth inLepidodendronandStigmariaare described; the structure of the tissues is suggestive of a postmeristematic parenchymatous sheath. It is concluded that cambial activity in these arborescent cryptogams was clearly different from that of modern seed plants, further attesting to the distinctive nature of this ancient group.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08369.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Enzyme electrophoresis was employed to examine genetic variation at 20 loci in 16 populations ofLasthenia minorand 18 populations of its presumed derivative speciesL. maritima.The purposes of the study were to ascertain levels of genetic variation in each species, to assess how the variation at enzyme‐coding genes is apportioned within and among populations of each species, and to determine the level of divergence between the two species. The two species are both diploid annuals, similar morphologically, and produce fertile F1hybrids when crossed.Lasthenia minoris self‐incompatible and restricted to mainland California, whereasL. maritimais self‐compatible and probably largely autogamous; it occurs on seabird rocks from central California to British Columbia. Mean genetic identities for pair‐wise comparisons of populations of the two species are similar to values for populations of the same species, indicating they have not diverged at the 20 genes coding for soluble enzymes. Despite its more extensive geographical range,L. maritimaexhibits only 50% of the genetic diversity ofL. minor.The latter species apportions a greater amount of its diversity within populations, whereas the former harbors more diversity among populations than within them. This is probably a reflection of the different breeding systems of the two species. Six unique alleles were detected inL. minor,whereas only one novel allele was found in a single individual ofL. maritima.The electrophoretic data are concordant with the suggestion thatL. maritimais relatively recently derived fromL. minor.The switch from outcrossing to selfing and selection of genotypes adapted to the chemically and physically unusual substrate on the seabird rocks are considered the critical steps in the evolution ofL. maritima.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08370.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Characteristics of the flowering trees ofAcacia terminalismay be interpreted as adaptations for bird pollination. Each leaf bears a single red nectary up to 12 mm long on its petiole. Nectaries show greatest secretory activity at flowering (max. 15μl/nectary/day), and nectar was found only in the early morning. The nectar contains a mean of 16% sugars (max.>50%) and is hexose rich with 18 amino acids, especially glutamine and phenylalanine. Analyses of foraging dynamics and pollen loads from feathers of passerine birds further support this interpretation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08371.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

The uptake, distribution, and recovery of nitrogen by field populations ofT. latifoliaL. (cattails) were determined using (15NH4)2SO4. The results show that 75.3% (53.6% in the plant and 21.7% in the soil) of the isotopically labeled nitrogen added to sampling cylinders containing a single cattail plant could be recovered at the end of one growing season, whereas only 34.6% could be recovered from control cylinders. The increased recovery of15NH4+‐nitrogen in cylinders containing actively growingT. latifoliacompared to cylinders not containing plants suggests thatT. latifoliarapidly assimilates labeled nitrogen before it is lost via denitrification or uptake by free‐living soil microorganisms.Measurements of redox potentials in a 60‐cm‐deep field core planted or not planted withT. latifoliashowed that only the top 2 and 5 cm of the water column was oxidized (greater than 200 mv at pH 7), respectively. The remaining 58 and 55 cm of the column, including the soil‐water interface, was reduced (less than 200 mv at pH 7). The presence or absence of actively growingT. latifoliaplants in the soil cores did not appear to alter significantly the redox profile. The presence of an oxidized zone overlying a reduced zone in cores collected from the field indicates that a portion of the15NH4+‐nitrogen added to cylinders during the field experiment may have been lost through nitrification‐denitrification reactions.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08372.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Pinwheel flowering African violets are bicolor forms that have a patterned arrangement of colors on the corolla segments. A median band of one color extends radially from the central portion of the corolla on each corolla segment and contrasts with the marginal color. In vitro culture of various tissues was accomplished, and observation of the flowering patterns of the regenerated plants supports the hypothesis that the cultivars ‘Valencia’, ‘Dardevil’, and ‘Desert Dawn’ are periclinal chimeras. Adventitious plants display a high proportion of monochromatic flowers of the same color as the lateral margin of the corolla segments. Petiole cultures from which the epidermal layers were removed yielded plants with flowers of the color of the central stripe of the corolla segments. Pinwheel flowering plants were regenerated through short‐term culture of whole inflorescences, suggesting that the African violet inflorescence may possess axillary vegetative meristems. These results support the contention that adventitious shoots may arise from the epidermal layer only (L.I), or with the participation of the epidermal and subjacent layers (L.I and L.II). These results contradict the recent conclusion that all three histogen layers of African violet participate in adventitious shoot organization.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08373.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Nuclear 2C DNA content was microspectrophotometrically determined for 19 diploid (2n=34) species ofHelianthusL. DNA amount varied over a fourfold range.Helianthus neglectushad the lowest (53.40 ± 0.51 Feulgen absorbancy units [FAU]) andH. agrestisthe highest (216.30 ± 2.30 FAU) DNA content. Chromosome size ranged from 1.1–1.7μm long inH. neglectusto 3.2‐5.0μm long inH. agrestis.When the highly divergentH. agrestiswas excluded from analyses, the mean of the annual species (70.05 FAU) was significantly different from the mean of the perennials (97.70 FAU). No correlations of DNA content with habitat, soil type, annual precipitation, or geographical location were apparent among species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08374.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

The absence of phloem in some Viscaceae may be a direct result of morphological reduction.Viscum minimumis a highly reduced, South African mistletoe that parasitizesEuphorbia.The aerial portions of this species are 2–3 mm long and consist of only 1–2 intemodes with a terminal triad of flowers. The collateral vascular bundles are composed of tracheary elements, parenchyma, and sieve tubes with associated companion cells. The sieve‐tube members are similar to those described from other angiosperms, exhibiting simple sieve plates, P‐protein, stacks of ER, plastids, and mitochondria. The morphological reduction ofV. minimumthus is not associated with a loss of phloic elements in contrast to other reduced viscaceous mistletoes.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08375.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

In order to test the hypothesis that mistletoes (Phoradendron tomentosum) are differentially adapted for the host species that they occur on, mistletoe seeds from the three most common hosts in central Texas (hackberry,Celtis occidentalis,elm,Ulmus crassifolia,and mesquite,Prosopsis glandulosa) were planted onto different individuals of each of the three hosts. Germination of seeds and formation of haustorial disks by seedlings were followed in the subsequent 17 months. Germination of seeds was very high for all nine combinations of maternal (source) and seed (experimental) hosts (range 82%–98%). There were no significant differences in seed germination between the two groups when source and experimental hosts were the same species and when they were different species. In contrast, development of haustorial disks when source and experimental hosts were the same species was significantly greater than when experimental host and source host species were different. The data suggest that populations of mistletoes are genetically differentiated such that early seedling development is greatest when there is correspondence between maternal and seedling host species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08376.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

The minor veins and contiguous tissues of mature leaves ofPopulus deltoidesBartr. ex Marsh. were examined with the electron microscope to determine the ultrastructural characteristics of the component cells and to determine the structure, distribution, and frequency of plasmodesmata between the various cell types. In addition, plasmolytic studies were carried out to determine the solute concentrations of the various cell types of the minor veins and contiguous tissues. The cells comprising the mesophyll and bundle sheath contain all the components typical of photosynthetic cells. Paraveinal mesophyll cells and bundle‐sheath cells have fewer microbodies and smaller chloroplasts than do palisade parenchyma cells. Vascular parenchyma and companion cells tend to intergrade with one another structurally but can be distinguished from one another by their characteristic plastids. The mature, enucleate sieve‐tube member is lined by a parietal layer of cytoplasm consisting of plasmalemma, endoplasmic reticulum, mitochondria, plastids, and P‐protein. Plasmodesmata occur along all possible routes from the palisade parenchyma cells to the sieve tubes of the minor veins, and their frequency increases with increasing proximity to the sieve‐tube members. Plasmolytic studies revealed that the paraveinal mesophyll cells had a higher C50(estimated mannitol concentration plasmolyzing, on the average, 50% of a given cell type) than any other cell type of the leaf. Concentration gradients existed along the palisade cell/bundle‐sheath cell/companion cell (or vascular parenchyma cell) route as well as along the paraveinal mesophyll cell/bundle‐sheath cell/companion cell (or vascular parenchyma cell) route. Considering the frequency of plasmodesmata along these routes, it is conceivable that photosynthate diffuses from palisade cells to the companion cells along concentration gradients. Within the minor veins, the C50was higher for sieve‐tube members than for either companion cells or vascular parenchyma cells, indicating that loading of the sieve tubes is an active, energy‐dependent process.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08377.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Pollen of the scrophulariaceous generaMelospermaandMontteawas studied with light and scanning electron microscopy. Both have single, radiosymmetric, isopolar, trizoniaperturate pollen grains with usually ruptured colpus membranes, tectate‐perforate to semitectate exines with a columellate interstitium and pitted or perforate nexines. Intergeneric differences in pollen morphology are established based on the differential correlation of sculpturing characters. Comparisons of the pollen ofMelospermaandMontteawith that of the tribe Minuleae sensu stricto reveals no difference in the case ofMelospermaand the existence of intermediate morphologies and “reticulate” similarities in the case ofMonttea; the taxonomic significance of this morphological intergradation is considered. The transfer ofOxycladus aphyllustoMontteais consistent with the pollen evidence, but proposed affinities betweenMontteaand tribe Antonieae of the Loganiaceae are not supported.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08378.x

出版商:Wiley    

年代:1985

数据来源: WILEY