bluuebunny/crossref_metadata_2025 huggingface dataset:
Confirmation of the infectivity of a free-living actinomycete isolated from Comptonia peregrina root nodules by immunological and ultrastructural studies
Authors: Lalonde Maurice
Published: May 2008

The inoculation of the host plant Comptonia peregrina (L.) Coult. (Myrica asplenifolia L.) by a pure culture of a free-living actinomycete, isolated from Comptonia root nodules by Callaham et al. (1978, Science, 199: 899–902), was successful. Short-term and long-term nodulation tests confirmed the infectivity of the Comptonia isolate. Acetylene reduction assays of the nodules induced by this prokaryote isolate demonstrated nitrogen fixation activity. This nitrogen fixation activity was able to sustain a prolific growth of the nodulated host plants growing in a N-free substrate. Indirect immufluorescence reactions, using specific gamma globulin against the actinomycetal isolate of the Comptonia root nodule, demonstrated the identity of this actinomycete in these in vitro produced Comptonia root nodules. Ultrastructure of the Comptonia isolate, developing as a free-living or endophytic actinomycete, was observed by light microscopy, freeze etching, and transmission electron microscopy. The free-living filamentous and sporulating isolate produced typical hyphae and vesicles when growing as an endophyte in the Comptonia nodule. These endophytic hyphae and vesicles were always encapsulated by a polysaccharide material which was surrounded by a host membrane envelope. A polysaccharide capsule was not demonstrated on the free-living Comptonia isolate. The endophytic vesicles were club shaped and highly septate. Such vesicles were never produced by the free-living isolate growing in an artificial medium. The Comptonia isolate is a spore former in pure culture and was able to sporulate in basal tissues of 5-month-old Comptonia nodules.
Light and electron microscope observations of a meiotic mutant of Neurospora crassa
Authors: Lu B.C. , Galeazzi Donna R.
Published: May 2008

Light and electron microscopy have revealed that the meiotic-1 (mei-1) mutant of Neurospora crassa is defective in chromosome pairing (asynaptic) although plenty of axial components of the synaptonemal complex are produced and occasional tripartite synaptonemal complexes can be formed. The mei-1 mutant is most probably defective in bringing the homologous chromosomes together for pairing and for assembly of the synaptonemal complex. The mei-1 mutant is also defective in nuclear separation which leads to a four-poled spindle at the subsequent division. The lack of chromosome pairing, the incomplete assembly of the synaptonemal complex, and the four-poled spindles account for absence of recombination and for the nondisjunction found in genetic analysis.
Two grasses as common hosts for all species of Ustilago parasitic on wheat, barley, and oats
Authors: Nielsen J.
Published: May 2008

The grass Agropyron tsukushiense var. transiens is native to Far East Asia, and Hordeum compressum is native to southern South America. They were found to be susceptible to all the races that they were tested to of the following: loose smut of wheat (Ustilago tritici): loose, covered, and false loose smut of barley (U. nuda, U. hordei, and U. nigra); loose and covered smut of oats (U. avenae and U. kolleri); and head smut of grasses (U. bullata). The two grasses are the first known common hosts for these smuts and will be used to study the relationships between these pathogens.
Weight loss and nutrient changes in decomposing litter and forest floor material in New Brunswick forest stands
Authors: MacLean David A. , Wein Ross W.
Published: May 2008

Weight loss and nutrient (N, P, K, Ca, Mg) changes with decomposition were examined over a 2-year period fora variety of kinds of litter on five forest sites. Litter types included pine needles, leaves of four deciduous species (red maple, pin cherry, trembling aspen, and white birch), branches of pine and four deciduous species, understory vegetation, and partially decomposed forest floor material, while the study sites consisted of jack pine stands aged 16, 29, and 57 years and mixed hardwood stands aged 7 and 29 years. Statistically significant differences in rate of weight loss were found to occur, with understory and leaf litter significantly faster on the hardwood stands than on the pine stands, understory litter faster on the 7-year-old hardwood stand than on the 29-year-old stand, and forest floor material faster on the 29-year-old pine stand than on the 57-year-old pine stand. Among the four deciduous species examined, significant differences in leaf weight loss also occurred, but differences among branch litter were nonsignificant. The mass of N in samples generally decreased with decomposition, with increases occurring in a few cases (i.e., pine understory and needle litter). Phosphorus mass generally increased on the pine sites and decreased on the hardwood sites; this appeared to be largely a function of the low initial P concentrations of litter on the pine sites. In general, the mass of K, Ca, and Mg decreased in the various samples with decomposition; the loss of K from deciduous leaves in this study was particularly fast and was greater than other values from the literature.
The mineral content of Sphagnum fuscum as affected by human settlement
Authors: Gorham Eville , Tilton Donald L.
Published: May 2008

Nine samples of Sphagnum fuscum (Schimp.) Klinggr., one each of S. magellanicum, S. nemoreum, S. wulfianum, and Dicranum polysetum, and seven samples of Larix laricina have been analyzed for mineral ash content, Al, B, Ca, Fe, K, Mg, Mn, and P. The chief influence upon the ash content of Sphagnum fuscum in ombrotrophic bogs which are dependent for their mineral supply solely upon the atmosphere is clearly windblown soil from cultivated farmlands. Bogs unaffected by human settlement and therefore not subjected to greater mineral supply are now restricted to wilderness areas in the northeastern part of Minnesota. Sphagnum serves as an effective trap for dust fall and is much richer in the lithophile elements Al and Fe than the needles of the tamarack, Larix laricina, from comparable habitats. Presumably dust fall is readily washed off the tree needles by rain. Larix concentrates B to a much greater degree than does Sphagnum.
Chemical element dynamics in decomposing leaf litter
Authors: Lousier J. Daniel , Parkinson Dennis
Published: May 2008

Chemical element change in decomposing aspen and balsam poplar leaves was followed for 60 months in an aspen woodland site in southwestern Alberta, Canada. The changes in concentration and weights of the various elements and in several C:element and element:element ratios are discussed and compared with literature findings and with the concentrations, weights, and ratios encountered in the soil layers.The initial concentrations of all elements, except K and Na, were similar in both aspen and balsam leaf litter; K was higher initially in balsam leaf litter and Na was higher initially in aspen leaf litter. In the decomposing leaf litter, the concentrations of N, Ca, Zn, Mg, Fe, Mn, Cu, and Na generally increased with time while the concentrations of P and K decreased. A decrease in weight was noted for N, P, K, Ca, Mg, and Zn during decomposition while an increase was found for Fe, Mn, Cu, and Na. The order of mobility of elements after 60 months in decomposing aspen and balsam leaf litter was K > Na > P > Zn > Mg > Ca > N > Mn > Cu > Fe. The effects of site aspect on elemental loss, the elemental change in aerial litter bags, the components of elemental change, and models of elemental loss are discussed.
Vesicular–arbuscular mycorrhizae in the Chenopodiaceae and Cruciferae: do they occur?
Authors: Hirrel Marc C. , Mehravaran H. , Gerdemann J. W.
Published: May 2008

Members of the Chenopodiaceae and Cruciferae were reported to be nonmycorrhizal by early investigators; more recently, some species in these families have been reported to have low or in some cases high levels of vesicular–arbuscular (VA) mycorrhizal infection. In our experiments, a sparse vesicular (chlamydospore) infection by Glomus fasciculatus was found in four species of Chenopodiaceae and two species of Cruciferae but only when grown in the presence of a mycorrhizal companion plant, citrus or onion. No arbuscules were observed in infected roots. Chenopodium album had the highest incidence of infection (5%). Infection was restricted to older tissue and penetration of the vascular cylinder was common, which is atypical of VA mycorrhizae. As hyphae from mycorrhizal companion plants grew through the soil, they encountered older roots of the test plants which probably offered little or no resistance to infection. In documenting the occurrence of VA mycorrhizae in any species, it is important to observe whether the plant is growing by itself or if there are mycorrhizal plants closely associated with it. Also, care should be taken not to confuse common root parasites for the fungal structures of VA mycorrhiza.
Didymella proximella and its Stagonospora anamorph
Authors: Corlett Michael , Smith J. Drew
Published: May 2008

Didymella proximella is reclescribed and illustrated from collections on Carex californien from Mary's Peak. Oregon. The Oregon specimens match the type of D. proximella from Finland. Ascostromata of D. proximella and pyenidia of a Stagonospora species were found on overwintered C. califomica in Oregon; ascospores yielded the same Stagonospora on agar. This species of Stagonosporc is morphologically distinct from Stagonospora stricta and the presence of ascostromata of D. proximella with pyenidia of S. stricta on the same lesions in the type of S. stricta is fortuitous.
Studies on lichen-dominated systems. XXI. The control of seasonal rates of net photosynthesis by moisture, light, and temperature in Stereocaulon paschale
Authors: Kershaw K. A. , Smith M. M.
Published: May 2008

Changes in rates of respiration and net photosynthesis in Stereocaulon paschale (L.) Hoffm. in relation to temperature, moisture, and light have been documented for a woodland population collected in the Abitau–Dunvegan Lake area of the Northwest Territories. The temperature optimum for net photosynthesis is about 20–30 °C and not 0 °C as has been previously reported in the literature. Maximal rates of net photosynthesis are only developed at low levels (100–150% water content by weight) of thallus saturation, suggesting a good degree of adaptation to the xeric conditions normally found in spruce–lichen woodland. Similarly the relatively high light requirement of 1000 μE ∙ m−2 ∙ s−1 correlates well with the open nature of lichen woodland and especially with the disappearance of Stereocaulon paschale in old woodland with the closure of the canopy.The sensitivity of Stereocaulon paschale, when dry, to thermal stress is examined in detail and even the moderate thallus temperature of 35 °C is shown to be highly stressful to this species. Surface temperatures in the low arctic are often above 35 °C and over recently burnt surfaces, temperatures above 45 °C occur on a regular basis. Thus the delayed entry of Stereocaulon paschale into the successional sequence reflects its extreme sensitivity to thermal stress. With the gradual accumulation of an organic layer and an enhanced retention of soil moisture over the initial 60 years of succession there is a significant reduction in both the sensible heat flux and the surface temperatures. At the same time, tree growth leads to a sharp decrease in direct radiation, and the combination of these two developments results in a much cooler surface and one which can be colonized by Stereocaulon.It is suggested that thermal stress tolerance of lichens in an air-dry state, to either high or low temperatures may be centrally important to their overall ecology. Furthermore the net photosynthetic response pattern to temperature, moisture, light, and time of year may, in fact, play a subordinate role in the ecology of a lichen.
Gibberellic acid induced multilocular fruits in tomato and the role of locule number and seed number in fruit size
Authors: Sawhney V. K. , Dabbs D. H.
Published: May 2008

Young tomato plants were treated with gibberellic acid (GA3) at a stage before floral initiation. In the first truss produced after the treatment, the fresh weight and size of the fruit was lower than the controls but was significantly higher in trusses 2 to 4. Also, whereas in controls the fresh weight and size of tomato fruits steadily declined from truss 1 to truss 4, in GA3-treated plants there was a progressive increase in the fresh weight and size of the fruit. The number of locules per fruit of GA3-treated plants was also greater than the controls but not the number of seeds per fruit. Regression analyses show that both the locule number and seed number have a significant correlation with the fresh weight of the fruit and that these relationships are independent of each other.
The chloroplasts of Euglena may have evolved from symbiotic green algae
Authors: Gibbs Sarah P.
Published: May 2008

It is proposed that the chloroplasts of Euglena have arisen from the progressive reduction of endosymbiotic green algae. The theory is supported by the presence of a third membrane around the chloroplasts of Euglena which is not endoplasmic reticulum (ER) in origin and may be derived from the plasmalemma of the original symbiont. In addition, Euglena is the only organism in which chloroplast loss can be induced experimentally. Dinoflagellate chloroplasts are also surrounded by three membranes, and it is proposed that they too evolved from symbiotic eucaryotic algae.
Anthocyanin pigments in pea seedlings: genetically controlled and environmentally influenced
Authors: Nozzolillo Constance
Published: May 2008

Anthocyanin pigmentation of the seedling stems of several genetic lines of Pisum was observed. Quantitative determination of the pigments showed that they tend to occur mainly in the lower internodes in a pattern dependent on both genetic constitution and environment. Qualitative determination indicated that the same pigments were present in all but one of the nine lines examined. Delphinidin was dominant in most lines, with cyanidin present in much smaller quantities, and a tentatively identified pelargonidin in trace amounts. Two classes of 3-glycosides were found, namely, monosides and as yet unidentified oligosides which were missing in one of the lines. Glucose was the only saccharide detected in hydrolyzed samples.
Management of forest residues for rapid decay
Authors: Blanchette Robert A. , Shaw C. Gardner
Published: May 2008

Forest residues of two age classes (less than 1 year old and between 1 and 2 years old) were chipped and piled (1.0- to 1.5-m piles) on the cutting site. Chip piles were inoculated with decay fungi [Coriolus versicolor (L. ex Fr.) Quél., Hirschioporus abietinus (Dicks ex Fr.) Donk, or Poria placenta (Fr.) Cke.] alone and in combination with a liquid suspension of yeasts [Saccharomyces bailii Linder var. bailii and Pichia pinus (Holst) Phaff] and nitrogen-fixing bacteria (Enterobaeter spp.). Temperatures were recorded at the surface, middle, and bottom of each chip pile. Samples taken 16 months after inoculation revealed successful colonization and proliferation of the fungal inocula. Postinoculation compression tests showed that significantly more decomposition occurred in wood chips inoculated with wood-destroying fungi than those receiving no inoculation. Even greater losses of wood integrity occurred when the fungi were inoculated in combination with yeasts and bacteria. Morphological examination of wood chips using scanning electron microscopy confirmed successful colonization and glucosamine assays confirmed proliferation of the fungal inoculum in the chip pile.
The fine structure of septal pore apparatus in the lamellae of Pholiota terrestris
Authors: Wells Kenneth
Published: May 2008

The lamellae of Pholiota terrestris, when viewed in thin sections cut perpendicular to the hymenial surface, consist of a hymenial layer of basidia and scattered cystidia, an interwoven subhymenium, and a trama. The inner trama is composed of a zone of relatively large, vacuolated hyphal elements, whereas the outer trama consists of smaller hyphal elements with relatively dense cytoplasmic contents. The septal pore apparatus throughout the lamellae are similar to those described in most other Homobasidiomycetes and saprobic Heterobasidiomycetes. In the center of the septal pore there is a narrow electron-dense zone that intersects the pore canal. In some septal pores similar electron-dense zones occur near one or both orifices. The septal cap consists of three membranes, of which the two defining membranes appear clearly tripartite in cross section. The pores in the septal cap are arranged hexagonally and are 70–105 nm in diameter. The proximal septal caps of the subbasidial septa and those in the subhymenium develop an electron-dense, granular outer cap that is usually delimited externally by endoplasmic reticulum or, less often, by the tonoplast of an adjacent vacuole. The septal pores of the subbasidial septa become plugged by the expanded septal swelling following basidiospore discharge. The septal pore apparatus in the trama are not associated with outer caps; however, many septal pores in the trama become occluded with electron-dense plugs near both orifices. The observations of the septal pore apparatus in the lamellae of P. terrestris are compared with studies of other Homobasidiomycetes and saprobic Heterobasidiomycetes.
New ant-dispersed species in the genera Carex, Luzula, and Claytonia
Authors: Handel Steven N.
Published: May 2008

Laboratory tests of foraging behavior of ants show that perigynia of Carex umbellata and C. communis and seeds of Luzula campestris, L. acuminata, and Claytonia virginica have elaiosomes that attract ants to carry the diaspores to their nests. Other morphological features of these species may be interpreted as adaptive for ant dispersal, including the extremely shortened fertile culms of C. umbellata, the bending of C. communis culms when seeds are mature, and the reflexing of pedicles of C. virginica.
Enhancement of senescence in excised rice leaves by hydrogen peroxide
Authors: Parida R. K. , Kar M. , Mishra D.
Published: May 2008

Changes in the catalase activity and the effect of hydrogen peroxide (H2O2) were studied during the senescence of excised rice (Oryza sativa L. cv. Ratna) leaves. Catalase activity declined upon detachment of leaves. Regression analysis showed a strong positive correlation between the decline in the catalase activity with the decline in the soluble protein content (r = 0.9827; n = 13). Infiltration of H2O2 into the leaves accelerated chlorophyll loss and α-amino nitrogen accumulation. Infiltration of glycolate or xanthine (serving as substrates for the formation of H2O2) into the leaves had a similar effect. Application of aminotriazole, a strong inhibitor of catalase, also accelerated the senescence of excised rice leaves. These results indicate that leaf senescence can be accelerated by increasing the endogenous H2O2 level in the leaf tissues.
Generic relationships in Triticeae based on computations of Jardine and Sibson Bk clusters
Authors: Baum Bernard R.
Published: May 2008

The Jardine–Sibson Bk clustering method was applied to a dissimilarity matrix of genera of the Triticeae to obtain sequences of relationships in terms of overlapping clusters. In this way, the clinal relationships in the tribe were portrayed. Selected aspects of the findings are documented in detail and the results are discussed in the light of previous findings. In addition to those that are corroborated by the present study, new relationships are revealed also. For instance, the Aegilops–Triticum group is reconfirmed here, but the relationship of Henrardia to that group is a new finding which, along with others, should be tested by other means so that eventually it might be used in gene transfer.
Morphological observations on leaf haustoria and related organs of the South African genus Hyobanche (Scrophulariaceae)
Authors: Kuijt Job , Visser J. H. , Weber H. Chr.
Published: May 2008

Most haustoria in Hyobanche (Scrophulariaceae) are formed directly from the scale leaves of the extensive rhizome system and may be found on adaxial surfaces, margins, or tips of such leafy organs. The only exceptions are occasional haustoria, emerging from rhizome areas between adjacent scale leaves, and the primary haustorium. Host roots appear to be attracted to the rhizome, growing along its surface and apparently eliciting haustorial formation in adjoining parasitic tissues. The established parasite is completely rootless.
Species relationships of Hieracium (Asteraceae) in British Columbia
Authors: Guppy Geraldine A.
Published: May 2008

The morphology, cytology, reproductive behaviour, and interrelationships of seven Hieracium species in two subgenera were studied. In British Columbia the subgenus Hieracium is represented by the morphologically variable species H. umbellatum, which is triploid and apomictic. The subgenus Stenotheca is represented by H. triste, H. gracile, H. albiflorum, H. albertinum, H. cynoglossoides, and H. scouleri, all of which are diploid and amphimictic. The latter six species fall into three groups; within each of these, considerable intergradation occurs. The groups are morphologically distinct and differ in reproductive strategy but are cytogenetically similar and interfertile. Artificial hybrids between the groups have lowered pollen viability but are meiotically regular.
Effects of a long-term field sulfur dioxide fumigation on Arctic caribou forage lichens
Authors: Moser Thomas J. , Nash III Thomas H. , Clark W. Dennis
Published: May 2008

The gross photosynthetic response of Cladonia stellaris (Opiz.) Pouz. & Vezda., Cladonia rangiferina (L.) Wigg., and Cetraria cucullata (Bell.) Ach. to a continuous, long-term, in situ SO2 fumigation was monitored during the growing season at Anaktuvuk Pass, Alaska. The photo-synthetic capabilities of the test species were either destroyed or significantly reduced depending upon the SO2 stress gradient over the fumigation plot. Additional sampling of the plot 1 year after termination of the fumigation revealed no significant recovery in photosynthesis, and chlorophyll contents of the test species were significantly less than the controls.
Occurrence of mycorrhizae on ericaceous and pyrolaceous plants in northern California
Authors: Largent David L. , Sugihara Neil , Wishner Carl
Published: May 2008

Four hundred and eighty plants in northern California from 27 taxa in the Ericaceae and 5 in the Pyrolaceae were surveyed for presence of ectomycorrhizae, arbutoid, or ericoid mycorrhizae between September 1977 and April 1978. Of these, 337 in the Ericaceae and 8 in the Pyrolaceae had one or more types of mycorrhizae.At least 88% of the plants of larger shrubs or trees (Arbutus menziesii or Arctostaphylos spp.) were mycorrhizal in various locations in northern California. Of the plants in the remaining twenty-two taxa that were mycorrhizal, 67–100% had ectomycorrhizae or arbutoid mycorrhizae. Twenty-three taxa of ericaceous or pyrolaceous plants in the genera Cassiope, Gaultheria, Kalmia, Ledum, Leucothoe, Phyllodoce, Rhododendron, Vaccinium, Pyrola, and Chimaphila were also mycorrhizal. The type and abundance of mycorrhizae appear to depend on as yet undefined ecological factors.Ectomycorrhizae (including the Cenococcum type) or ericoid mycorrhizae are reported for the first time in Arbutus, most Arctostaphylos spp., Gaultheria shallon, Kalmia polifolia, Ledum glandulosum var. columbianum, Leucothoe davisiae, Rhododendron macrophyllum, Vaccinium arbuscula, V. ovatum, V. scoparium, Chimaphila menziesii, and Pyrola picta f. picta.
Nicotiana glauca × Nicotiana langsdorffii tumor hybrid: growth, morphology, polyamines and nucleic acids in vitro
Authors: Fracassini D. Serafini , Bagni N. , Torrigiani P.
Published: May 2008

Callus of the tumor hybrid of Nicotiana glauca × N. langsdorffii grew better on agar in flasks than on liquid medium in flasks or on agar medium in Petri dishes. Asymmetric callus without roots produced small leaves and parenchyma cells were the most common type of cell. Few meristematic clusters were present, but these were very active during exponential and deceleration growth phases. The volume of their nucleoli, which were large and stained intensely, was used as a marker of the cell cycle. Shortly after transplantation the tissue divided synchronously, but thereafter it became asynchronous. An investigation of nucleic acids and polyamines showed that subcultures initiated a rapid synthesis and accumulation of DNA; thereafter the levels of tRNA and rRNA increased, especially in the deceleration phase, the amount of tRNA always being higher than rRNA. The polyamines putrescine and spermidine are always in larger amounts than in the normal tissue, and spermine could be detected in trace amounts. Their metabolism is correlated with arginine levels, the most important precursor of putrescine. Polyamine levels increased several fold during the deceleration phase, their increase being positively correlated with increased levels of nucleic acids, mainly during the very beginning of the subculture and, then during the deceleration phase.
Attached and planktonic algal communities in some inshore areas of Great Bear Lake
Authors: Moore James W.
Published: May 2008

The species composition and standing crop of epilithic, epipelic, and planktonic algae were determined in three widely separated inshore areas of Great Bear Lake during the summers of 1976, 1977, and 1978. The most frequently encountered diatoms in the epilithon were Tabellaria ftocculosa and Achnanthes minutissima regardless of location, whereas the predominant chlorophyte was Ulothrix zonata. These species were generally rare in the epipelon and were replaced in importance by Gyrosigma spenceri, Nitzschia obtusa, Cocconeis placentula, Amphora ovalis, and Achnanthes lanceolata, depending on sampling site. The densities of the epilithon and epipelon were low in June but increased gradually during the summer, reaching maxima of 78 × 107 and 120 × 107 μm3 cm−2, respectively (19.5 × 105 and 40 × 105 cells cm−2), in either August or September. These values are among the lowest recorded for fresh waters and are probably due to continually low water temperatures and wave action rather than nutrient limitation. The most important species in the plankton in all three sampling areas were Dinobryon bavaricum, Dinobryon sociale, Rhodomonas minuta, Cyclotella species, Synedra acus var. radians, and Ankistrodesmus falcatus. Plankton standing crops of up to 62 mg fresh weight m−3 were recorded in June at a temperature of 0 °C, and they increased to 70–91 mg m−3 (23.3 × 107−30.1 × 107 cells m−3) by September. These values are again among the lowest on record, a reflection of low water temperatures. The similarity in the species composition and standing crop of the plankton, epilithon, and epipelon in all collection areas was due to the similarity in water chemistry and temperature throughout Great Bear Lake.
Effects of clipping or burning on some morphological characteristics of Agropyron spicatum
Authors: Willms W. , Bailey A. W. , McLean A.
Published: May 2008

The effects of fall clipping or burning on the subsequent morphology of bluebunch wheatgrass were studied in both the big sagebrush – bluebunch wheatgrass and Douglas fir – bluebunch wheatgrass communities. Observations were made to the 2nd year after treatment. Burning, in the big sagebrush community, resulted in a larger ratio of plant weight to volume. Burning also increased tiller density by the 2nd year in the big sagebrush community. Plants that were burned had lighter tillers in the 1st year after treatment. They also had a greater proportion of weight distributed near their base. The morphological characteristics of clipped plants were generally intermediate between those of burned and control plants. In general, the treatment effect was less in the Douglas fir community than in the big sagebrush community.
The determinate and indeterminate dwarf shoots of Pinus longaeva (bristlecone pine)
Authors: Ewers Frank W.
Published: May 2008

The dwarf shoot of the genus Pinus is normally regarded as a determinate short shoot, but the fate of the dwarf shoot apex after needle maturity and the origin of proliferated dwarf shoots remain controversial. To resolve these issues, 1- to 28-year-old dwarf shoots of P. longaeva were microscopically examined and experimentally manipulated. Eighty-eight percent of the lateral long shoots and all trunks had "proliferated dwarf shoots," or dwarf shoots that had become long shoots. On trunks 44.3% of the dwarf shoots had terminal buds, versus 6.6% on lateral long shoots. Most of these buds were microscopic, "interfoliar buds," derived from the original dwarf shoot apex. With advancing age of dwarf shoots there was no statistically significant change in the percentage of dwarf shoots with buds. The fate of the dwarf shoot apex depends upon the position of the dwarf shoot within its age-class and the type of long shoot. On lateral long shoots, only distal dwarf shoots have interfoliar buds and only these may spontaneously proliferate or be experimentally induced to proliferate into long shoots. Proximal dwarf shoots have a suberized apex. On trunks, both distal and proximal dwarf shoots often have buds and can thus proliferate. Dwarf shoot proliferations therefore arise predictably from interfoliar buds and not adventitiously.
Bud development in Picea engelmannii. I. Vegetative bud development, differentiation, and early development of reproductive buds
Authors: Harrison Derek L. S. , Owens John N.
Published: May 2008

Vegetative buds of Engelmann spruce (Picea engelmannii Parry) from the Prince George Forest District (British Columbia) were collected and studied. In mid-April, dormancy ended as determined from mitotic divisions within the leaf primordia; 2 weeks later mitotic activity occurred in the bud apices. Bud-scale initiation began in terminal buds by late May followed by that in axillary buds 2 weeks later. Shoot elongation began in late May, bud burst occurred in late June, and both shoot elongation and bud-scale initiation were complete by late July. Terminal buds began to differentiate by the initiation of leaf primordia, into vegetative buds early in August whereas axillary buds began to differentiate 1 week later. Leaf initiation was completed in all vegetative buds by late September and buds were dormant by mid-October. Pollen cones initiated microsporophylls after bud-scale initiation. Microsporangial initiation began in late August. Microsporangial enlargement began in mid-September and continued until dormancy when pollen mother cells were observed in a premeiotic stage. Seed cones initiated bracts directly after bud-scale initiation. In mid-August, ovuliferous scales began to be initiated. Two ovule primordia formed adaxially, one on each side of the median longitudinal axis of each ovuliferous scale. Each ovule formed one large central megaspore mother cell which overwintered in a premeiotic stage.
Fruit size variation and its effects on germination and seedling growth in Xanthium strumarium
Authors: Zimmerman Jesse K. , Weis I. Michael
Published: May 2008

Fruits of Xanthium strumarium L. from a population in southwestern Ontario exhibited an eightfold range in size. The effects of fruit size on seed size, germination, and seedling growth were investigated. Correlations between fruit size and seed size were strongly positive. In general, germination percentage and germination rate were both correlated positively with fruit size, although germination rate appeared to level off for the largest fruits. Cotyledon area and primary root length of newly emerged seedlings also were positively correlated with fruit size, although both variables and especially primary root length showed smaller increases over larger fruit sizes. The weights of newly emerged seedlings were highly positively correlated with fruit size. However, this relationship was not maintained for older seedlings. Weights of 15- and 30-day-old seedlings were constant over the majority of fruit sizes. This trend resulted from a negative correlation between seedling growth rate and fruit size which could, in part, be explained by a decline in the ratio of cotyledon area to the weight of newly emerged seedlings with fruit size.
Influence of abscisic acid on the derepression of the acid phosphatases in Ipomoea sp. cultured in vitro
Authors: Zink M. W.
Published: May 2008

The effect of abscisic acid on the levels and the developmental patterns of the two acid phosphatases in the culture medium, in the soluble fraction, and in the particulate fraction of Ipomoea sp. (morning glory) cultured in vitro depends upon the phosphate status of the cells. Under conditions of mineral stress or phosphate deprivation the enzymes are derepressed and this derepression is suppressed by abscisic acid. No inhibition of the synthesis of the phosphatases by the hormone occurs when the cells are grown under conditions of high phosphate. The significance of the abscisic effect on the derepression of the acid phosphatases is discussed.
Anatomy and frond architecture of Neuropteris ovata and N. scheuchzeri from the Upper Pennsylvanian of the Appalachian Basin
Authors: Beeler Hazel E.
Published: May 2008

Two medullosan fronds have been reconstructed from permineralized fragments collected at one late Pennsylvanian outcrop in the Appalachian Basin. Fragments are assignable to Myeloxylon, Neuropteris ovata, N. scheuchzeri, Mixoneura, and Cyclopteris and attached stems correspond to Medullosa noei. The fronds are pinnately compound. Branching patterns, anatomical features, and size ranges intergrade from the largest to the smallest axes. Thin areas in the hypodermal sclerenchyma zone on the adaxial sides of rachises and primary pinnae are sites of attachment of intercalary vascularized emergences. Vascularized emergences and tertiary pinnae are identical in configuration: they have five–seven vascular bundles and are about 2 mm in diameter. Neuropteris ovata pinna rachises and N. scheuchzeri petiolules are similar in size and vascular configuration to vascularized emergences and tertiary pinnae. Mixoneura pinna rachises are identical to axes sometimes found attached to Neuropteris ovata pinna rachises. The differences in the epidermal features of N. ovata and N. scheuchzeri pinnules support the conclusion that they represent two distinct species. Proximal frond members are identical in anatomy and general architecture.
Chromosome numbers in some mosses from western Canada
Authors: Ramsay Helen P.
Published: May 2008

Chromosome numbers are reported for six moss species from western Canada, four from British Columbia, two from Alberta. These give data on chromosome numbers from new localities in Canada for populations of five species and the first record for Kiaeria starkei from Canada. Chromosome numbers reported are n = 13, Grimmia afftnis; n = 14, Kiaeria starkei; n = 14 (13 + m), Dicranum scoparium; n = 20, Bryum pseudotriquetrum; n = 11, Ptilium crista-castrensis; and n = 6, Hypnum circinale.
The systematic value of stigma morphology in the legume tribe Trifolieae with particular reference to Medicago
Authors: Small Ernest , Brookes Brenda S.
Published: May 2008

Examination by scanning electron and light microscopy was carried out on all genera of the legume tribe Trifolieae (Medicago, Trigonella, Factorovskya, Melilotus, Trifolium, Ononis including Passaea, and Parochetus) and on some genera of tribe Loteae (Lotus, Tetragonolobus, and Dorycnium) which have been alleged to be closely related to the former assemblage. It was found that the stigmas of Medicago, including those of problematical species often placed in other genera, were fungiliform, with a basal circumferential ring of papillae and an apex apparently free of papillar outgrowths. The monotypic genus Factorovskya, a segregate from Trigonella, possesses a stigma substantially like that of Medicago. Moreover", several of the sections of Trigonella have stigmas like that of Medicago and quite unlike those of the bulk of Trigonella species. Medicago, Factorovskya, and these sections of Trigonella appear to form a distinct phylad, separable on the basis of stigma features from all of the other genera examined.
Factors affecting growth of Ptelea trifoliata seedlings
Authors: McLeod Kenneth W. , Murphy Peter G.
Published: May 2008

With the limited supplies of nutrients and water in the Lake Michigan sand-dune habitat, environmental factors which affect seedling growth also strongly affect survival. In this study, soil temperature, rainfall frequency, nutritional status of the soil, and species-specific water relations were studied as to their effects on the growth of Ptelea trifoliata L. seedlings. Root development was examined carefully since previous studies had indicated that root growth sufficient to reach a permanent water supply was critical for survival. Growth was stimulated by the temperature and soil-moisture conditions which occur in early spring. Fertilization, especially N and P, strongly stimulated growth. In addition, P. trifoliata produced adventitious roots when buried. Survival of seedlings was not enhanced by any adaptation to conserve water because plant resistances to water flow were typical of mesic species. Consequently, high transpiration rates occur in the sand-dune habitat, increasing the importance of good root growth. If adequate water is available, the high transpiration rates may help the seedling tolerate the high temperatures of this environment. Thus, Ptelea trifoliata seedlings possess no single characteristic that explains their ability to survive in the rigorous dune habitat, but possess many characteristics that contribute to their success.
The morphology and growth of Arctostaphylos uva-ursi (bearberry): an architectural analysis
Authors: Remphrey W. R. , Steeves T. A. , Neal B. R.
Published: May 2008

A study was made of the morphology and architecture of the prostrate ericaceous shrub, Arctostaphylos uva-ursi (L.) Spreng. (bearberry) from a sand-dune area and to a lesser extent a boreal forest area. In the open where more compact patches were recognized, a largely subterranean woody frame was found to support an aerial photosynthetic mat. The mat was made up of shoot complexes defined as consisting of not more than the four youngest annual growth increments or shoots. Two kinds of shoot complexes were recognized: (i) colonizing complexes consisting of a succession of long, low dominant shoots common in the periphal or colonizing zone of a patch and (ii) maintaining complexes consisting of short, essentially upright nondominant shoots and (or) intermediate shoots designated as subdominant, chiefly in the maintaining zone of a patch. Downward reorientation of older shoot increments which were not originally horizontal was recorded. The architecture of colonizing complexes was analysed quantitatively, including such parameters as shoot length, patterns of bud release, and divergence angles of daughter shoots. Several interesting patterns were revealed. The woody frame was analysed architecturally according to such principles as orders of branching, previously applied to trees. It was found to consist essentially of an ordered system of horizontal woody frame units, recognizable segments of the structural framework organized in a much branched hierarchical sequence. Two basic types of frame units were recognized: (i) major units constructed by colonizing complexes and (ii) minor units constructed by maintaining complexes. The initiation of the architectural pattern, including the establishment of original colonizing complexes, was investigated in seedlings. The reestablishment of bearberry following disturbance was also examined.
The morphology and growth of Arctostaphylos uva-ursi (bearberry): an architectural model simulating colonizing growth
Authors: Remphrey W. R. , Neal B. R. , Steeves T. A.
Published: May 2008

Plan view simulations of the growth and spread of the prostrate shrub, Arctostaphylos uva-ursi (L.) Spreng. (bearberry) are presented using quantitative data from the colonizing zone in open sand-dune sites. The model was based on statistical analyses of the lengths of dominant horizontal shoots, the frequency and location of daughter shoots on parental shoots, and the divergence angles between daughter and parental shoots. A sequence of 10 rules was devised which described the structural relationship between parent and daughter shoots. To accommodate observed variability in architectural parameters, several stochastic elements were incorporated into the model. Consequently, there was virtually no possibility of two simulations being identical. The simulations showed growth patterns similar to colonizing complexes observed in nature. The advantages and limitations of the model are discussed.
The history and pattern of fire in the boreal forest of southeastern Labrador
Authors: Foster David R.
Published: May 2008

The fire history of the wilderness of southeastern Labrador is marked by a patchy distribution of large fires in time and space. During the 110-year period encompassed by this study, major fires occurred in four decades, 1870–1879, 1890–1899, 1950–1959, 1970–1979. From 1900 to 1951 only 1125 km2 burned; this represents approximately 10% of the total area consumed from 1870 to 1980. Fire records indicate an asynchroneity of the important fire years in southeastern Labrador and adjacent provinces and within Labrador itself. This observation suggests that the meteorological conditions controlling fire occurrence in this portion of the eastern boreal forest are local in nature and extent. The fire rotation for southeastern Labrador is calculated at approximately 500 years, significantly longer than that estimated for other regions of boreal forest. The rare occurrence of large fires is explained by high levels of precipitation and by the preponderance of fire breaks, primarily lakes and peatlands. On the basis of physiographic criteria the region is subdivided into two types of landscape displaying contrasting fire regimes. The large interior plateau, which is covered by extensive peatlands and numerous lakes, has a low fire incidence and extremely long fire rotation. In contrast, large fires are common in the watersheds of the Alexis, Paradise, and St. Augustin rivers where the topographic relief is quite varied and peatlands are scarce. The regional pattern of fire activity has important phytogeographical implications. The lichen woodlands and birch forests are fire-dependent vegetation types; their distribution in the modern landscape is strongly correlated with the historical occurrence of fire during the past 110 years. In addition it is postulated that the historical absence of fire across the large plains in southeastern Labrador has contributed to the development of extensive peatlands in these areas.
Ultrastructure of conidium development in Erysiphe pisi
Authors: Martin M. , Gay J. L.
Published: May 2008

The ultrastructure of all vegetative and reproductive cell types throughout the cycle of conidium development in Erysiphe pisi has been examined using light and electron microscopy. The conidial apparatus comprises a conidiophore with, in succession above, a generative cell, and first- and second-stage conidial initials. At approximately 23 °C in a 16 h light: 8 h dark period, the onset of elongation and division of the generative cells, onset of elongation of first-stage conidia, and maturation and abscission of second-stage conidia were individually synchronized in one diurnal cycle. Synchrony was also maintained between 24 and 30 °C, and 12 h light: 12 h dark photoperiods but the generative cells elongated more slowly, achieving greater lengths than at lower temperatures. At 23 °C in continuous light, development was not synchronized. The ultrastructure of each cell was characteristic of its type and developmental phase. Glycogen became progressively abundant in maturing conidia and occurred in all other cells except hyphal apices and generative cells. In addition to the organelles usually found in Ascomycetes, two special endomembrane components have been found. One is a reticular vacuolar system which is expanded as a major vacuole at one end. The whole system encloses a region (vacuole-associated body) 1-2 μm across, rarely 8 μm, which is continuous with the main ground plasm via pores in the network. The vacuole-associated bodies always lacked ribosomes but sometimes contained glycogen. The other component is a compact endoplasmic reticulum organized as spheres 0.5–5 μm in diameter and composed of branching tubules which terminated in diverticulae and were sometimes interspersed with 8-nm filaments. Evidence for the functions of these organelles is discussed. The development and structure of the septa, of cytoplasmic components associated with conidial abscission, and of the walls of hyphae and conidia are discussed. All subaerial cell walls are covered with an osmiophilic cuticle with characteristic trilamellar structure and sometimes bearing granules and platelets. Evidence is presented that the cuticle is renewed following damage.
Kinetics of iron transport into the leaf symplast during recovery from iron stress
Authors: Young Terry Forrest , Terry Norman
Published: May 2008

The iron concentrations of chloroplasts (isolated by nonaqueous methods) and of chloroplast lamellae (isolated by aqueous procedures) were determined and used to investigate the kinetics of iron transport across the plasmalemma into the leaf symplast during the recovery of sugar beet plants from iron stress due to iron deprivation. Iron concentrations in chloroplasts isolated by the nonaqueous procedure were greatly reduced during iron stress and recovered to over 200% of control levels within 24 h. Iron concentrations in lamellae from aqueous isolations increased significantly within 24 h of resupply and reached values in excess of control levels in 48–72 h. These results indicate that a substantial quantity of the iron that entered the leaf blade during the first 24–48 h of iron resupply crossed the plasmalemma. The effect appeared to be specific to iron because there was no evidence that manganese, zinc, and copper were transported into chloroplasts and lamellae in enhanced amounts.
Étude de l'influence des réserves azotées dans l'estimation par 15N de la fixation symbiotique d'une plante pérenne, Trifolium pratense
Authors: Lescure Chantal , Chalamet Alain
Published: May 2008

A 15N dilution technique is proposed to determine the role of nitrogen reserves in the plant on the estimation of dinitrogen fixation, during regrowth of perennial legumes. It is based on labelling of nitrogen compartments of the plant. Since the kinetics of utilization of nitrogen reserves of ryegrass (Lolium italicum L.) and red clover (Trifolium pratense L.) appear similar, ryegrass would be a good control plant. Despite this observation, the comparison of two methods (based on two or three sources of nitrogen) to estimate dinitrogen fixation shows the difficulty in applying the technique using 15N-labelled substrate over earlier periods of regrowth. In this case, the 15N method described for determining symbiotic dinitrogen fixation could be applied in controlled conditions.
Fruit development in tomato: the role of temperature
Authors: Sawhney V. K. , Polowick P. L.
Published: May 2008

Tomato (Lycopersicon esculentum Mill.) plants grown under low (LTR), intermediate (ITR), and high (HTR) temperature regimes produced fruits which were significantly different in certain characteristics. Under LTR, fruits were larger, both in fresh weight and size, and contained a greater number of locules than the fruits produced under ITR, which were larger than those developed under HTR. Fruits from plants maintained in temperature-controlled growth chambers before and after pollination were generally larger than those transferred to a greenhouse after pollination. Some abnormalities were observed in fruits grown under LTR but not in those produced under ITR and HTR.