bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrastructure and development of phenolic-storing cells in cotton roots
Authors: Mueller W. C. , Beckman C. H.
Published: September 2008

The development of phenolics in the radicle of cotton was determined with the nitroso reaction and light microscopy. In all cotton cultivars tested, phenolics could be detected in the endodermis at a distance of 1.0 to 2.0 mm from the root tip and in the root cap 0.5 mm from the root tip. By 3.0 mm the phenolic-storing cells in the endodermis were mature. The rate of development of the phenolic-storing endodermal cells was similar in all cultivars but varied with temperature, with maximum rates at 35 °C. At this temperature, development and maturation of the phenolic-storing cells occurred in 30 min. Phenolics could first be detected with the electron microscope in the vacuoles of endodermal cells 1.0 mm from the root tip; these cells were essentially mature 3.0 mm from the root tip. Except for the phenolics in the vacuoles, developing phenolic-storing cells were identical with surrounding parenchyma and contained abundant endoplasmic reticulum and ribosomes, mitochondria, dictyosomes, and large, variable plastids. Although several fixation methods were used and the appearance of the cells varied according to the fixation procedure, no positive origin for the phenolic material could be detected in the electron micrographs.
A note on the structural changes in the walls of pericycle cells initiating lateral root meristems in Zea mays
Authors: Sutherland J. , McCully M. E.
Published: September 2008

Pericycle cells in which lateral root meristems are initiated in corn undergo extension and change in polarity, even though these cells initially have thick secondary walls. Structural changes in these walls have been followed by electron microscopy correlated with bright-field, polarizing, and fluorescence microscopy.
Influence of algae on amitrole and atrazine residues in water
Authors: Valentine J. P. , Bingham S. W.
Published: September 2008

Removal of [14C]amitrole (3-amino-s-triazole) from water by three algae was more complete at pH 7.5 or above than at lower pH levels. [14C]atrazine (2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine) removal was affected little by pH. Absorption of [14C]amitrole steadily increased over 24 h, whereas [14C]atrazine removal reached equilibrium by 6 h. [14C]amitrole removal by Scenedesmus quadricauda was directly related to herbicide concentration while [14C]atrazine removal was inhibited by increasing concentrations. Optimum light and temperature for algal growth favored [14C]amitrole uptake. [14C]atrazine removal was unaffected by either darkness or low temperature. [14C]atrazine was not metabolized by Scenedesmus and apparent photosynthesis was inhibited in the four algae. Growth of algae was prevented by 1 ppm by weight atrazine. [14C|amitrole was readily metabolized by Scenedesmus. Three 14C metabolites were extracted from cells while four chromatographically different 14C metabolites occurred in the suspension fluid. Growth of Chlamydomonas reinhardti was particularly resistant to amitrole.
Phenology of shoot growth among diverse populations of yellow birch (Betula alleghaniensis) and sweet birch (B. lenta)
Authors: Sharik Terry L. , Barnes Burton V.
Published: September 2008

The objective of the study was to elucidate the patterns of phenology of growth initiation and cessation among diverse sources of yellow birch (Betula alleghaniensis Britton) and sweet birch (B. lenta L.) along latitudinal and elevational gradients in the Appalachian Mountains. Fruit was collected from parent trees of both species, encompassing a range of 9° of latitude and 3000 ft (914 m) of elevation, and was sown in the greenhouse. The resulting seedling populations were grown in a uniform garden located in southeastern Michigan, where they were analyzed for differences in leaf flushing and growth cessation associated with latitude and elevation of the seed source. Under the conditions of the experiment, northern populations flushed earlier than southern populations. The absence of differences in leaf flushing among populations from different elevations suggests that environmental factors in addition to temperature regulate the initiation of growth. Populations of high latitudes and high elevations ceased growth earlier than populations from low latitudes and low elevations, indicating that populations from shorter growing seasons adapted by ceasing growth earlier. Sixty-seven percent of the variation in the phenology of shoot growth among seedling populations of both species was associated with latitude and elevation of the seed source; the rest was attributed to local variations in topography and resulting microclimates.Observations of parent trees in situ and of half-sib seedling progeny in the uniform garden revealed that individuals of yellow birch exhibit an earlier phenology than individuals of sweet birch from the same field sites. This appears to be an important feature of niche differentiation and a function of the adaptation of yellow birch to colder climates.
An approximate analytic equation for sugar concentration waves in Münch phloem translocation systems
Authors: Ferrier Jack M.
Published: September 2008

An approximate analytic equation for sugar concentration waves is obtained from the equations describing the Münch phloem translocation system. The analytical result for wave phase velocity is checked against numerical results. The analytic equation for phase velocity may provide a means of testing the Münch hypothesis.
Chemotaxonomic studies in the Saxifragaceae s.l. 4. The flavonoids of Heuchera micrantha var. diversifolia
Authors: Wilkins C. K. , Bohm B. A.
Published: September 2008

Sixty flavonoids were isolated from aerial parts of Heuchera micrantha var. diversifolia and identified. The flavonoid aglycones represented were kaempferol, quercetin, isorhamnetin, myricetin, laricytrin (myricetin-3′-O-methyl ether), syringetin (myricetin-3′,5′-di-O-methyl ether), and luteolin. Flavonol glycosylation patterns included 3-O-monoglycosides, 3-O-diglycosides, 3-O-triglycosides, 3,7-di-O-monoglycosides, and 3-O-diglycoside-7-O-monoglycosides. Quercetin- and myricetin-3-O-glucoside-6″-gallates were also found. The sole luteolin derivative was the 7-O-glucoside. Also identified were the 3,5-di-O-glucosides of malvidin and either petunidin or delphinidin and (−)-epigallocatechin gallate. A brief discussion of the flavonoids of the Saxifragaceae is presented. Methods combining column and thin-layer chromatography are described which are generally useful for analysis of complex mixtures of polyphenolic compounds.
Ovule and seed development in Pinus radiata: postmeiotic development, fertilization, and embryogeny
Authors: Lill Barbara S.
Published: September 2008

Development of ovule tissues in Pinus radiata after meiosis, fertilization, and embryogeny is comparable with that of other pines, but P. radiata takes longer to develop. Fertilization occurs 15 months after pollination and morphological embryo maturity is reached 5 months later. In ovules harvested in spring after meiosis, a curved band of small cells with dense cytoplasm extends from the chalazal end of the ovule to the vascular tissue of the ovuliferous scale. It is interpreted as a procambial strand, which in the next year, differentiates basipetally into elongated, thick-walled cells with degenerated nuclei.
Cytokinin production in relation to the development of pea root nodules
Authors: Syōno Kunihiko , Newcomb William , Torrey John G.
Published: September 2008

Quantitative changes in cytokinins were examined in developing root nodules on the lateral roots of seedlings of the garden pea Pisum sativum cv. Little Marvel infected with Rhizobium leguminosarum strain 128 C53.Cytokinin activity was highest in 2- and 3-week-old nodules, when the growth rate was high, and decreased in older nodules. The cytokinin activities of 3-week-old nodules of various sizes were positively correlated with mitotic indices. In 3- and 4-week-old nodules most of the cytokinins were present in the white meristematic tip and not in the infected nitrogen-fixing or senescent cells. Since high cytokinin levels were associated with nodules having high mitotic rates or with the meristematic cells, it is proposed that cytokinins influence nodule morphogenesis by regulating the mitotic activity of the nodule meristem.
A correlated light and electron microscopic study of symbiotic growth and differentiation in Pisum sativum root nodules
Authors: Newcomb William
Published: September 2008

Plants of the garden pea Pisum sativum cv. Little Marvel were grown in aeroponic culture to facilitate observations and microscopy and were inoculated with Rhizobium leguminosarum, and nodules were sampled at five weekly intervals for light and electron microscopy. The invasion of the cortical cells by the infection thread, the structure of the infection thread, and the release of bacteria from it into the host cytoplasm and the subsequent symbiotic growth and differentiation of the two organisms are described in detail. The fine structure of the nodule is correlated with light microscopic observations and morphogenesis. A restriction in the use of the term 'vesicle' is proposed because of the current multiple and confusing usage of the term. The loss of the nodule meristem and its morphogenetic significance are discussed.
The electrical potential difference and resistance of Chara vulgaris
Authors: Murdoch Susan , Sinclair John
Published: September 2008

A study has been made of the electrical properties of the large central internodal cell of Chara vulgaris. The mean electrical potential difference (± standard deviation) measured in the light between the vacuole and the external, artificial pond water was −165 (±10) mV. This was much larger than the Nernst potentials for potassium, sodium, magnesium, and calcium and it was concluded that (a) if these ions were in flux equilibrium, then all of them were actively pumped out of the cell; and (b) no diffusion potential based on these ions alone could account for the large, electrical potential difference. The combined electrical resistance of the tonoplast and plasmalemma in the light was about 20 kΩ cm2. In the dark the electrical potential fell to a value which could have resulted from the diffusion of the above-mentioned cations while the resistance tripled in size. These observations are discussed in terms of Spanswick's model (Spanswick, R. M. 1974. Can. J. Bot. 52: 1029–1034).
Stabilizing selection in Puccinia graminis tritici in Canada
Authors: Osoro Mishael Oichoe , Green G. J.
Published: September 2008

Experiments were designed to show whether or not virulence genes reduce fitness and bring about stabilizing selection. The competitive abilities of seven related races of Puccinia graminis f. sp. tritici were studied on seedlings of three to five susceptible wheat varieties by growing mixtures of the races in greenhouses, growth cabinets, and field plots. In experiments in which simple races with few virulence genes were mixed with complex races with one, two, or three extra virulence genes, the complex races predominated after 4 to 10 generations in five of the six mixtures, and the simple race predominated in one mixture. A complex race predominated over simple races in the field experiment. It was concluded that virulence genes did not impair the fitness of the wheat stem rust races studied.In one race mixture studied in growth cabinets the complex race predominated at 25 °C, and the simple race, at 15 °C. Temperature did not differentially influence the competitive abilities of the races in three other mixtures.Incubation periods for all races were shorter at higher temperatures, but races C18(15B-1L) and C33(15B-1L) developed faster than races C9(15B-1L), C37(15), C38(15B-1L), C42(15), and C49(15) at all temperatures. In addition, races C18(15B-1L) and C33(15B-1L) produced more urediospores per pustule than races C9(15B-1L), C37(15), and C49(15). The differences in incubation period and spore production are considered to be the most important factors studied and they could cause the differences in aggressiveness of the seven races.
Physical and biological effects of experimental crude oil spills on Low Arctic tundra in the vicinity of Tuktoyaktuk, N.W.T., Canada
Authors: Freedman W. , Hutchinson T. C.
Published: September 2008

Data are presented on the effects of simulated crude oil spills on two Low Arctic terrestrial tundra plant communities near Tuktoyaktuk, Northwest Territories. Spills of fresh, unweathered crude oil had a general herbicidal effect, resulting in rapid damage to, and subsequent death of, all aboveground actively growing foliage coming in contact with the oil. Most species were defoliated. Mosses and lichens were especially susceptible and killed. However, within several weeks of the summer oil spillages, a limited number of relatively tolerant vascular plant species began to develop regrowth shoots.Summer spills were markedly more damaging than were equivalent spills made in winter. No increases were seen in active layer depth from spills made in summer. However, winter spills on one of the two sites did show consistent and statistically significant (P > 0.01) increases in depth of thaw. Examination of several key energy budget parameters at these field sites indicated consistently lower albedos and evapotranspiration and consistently higher soil surface temperatures and soil heat flux at all oil spill sites, relative to their controls. However, except for a winter spill on one site, the recorded differences were not sufficiently large in magnitude to produce significant increases in active layer thaw depths.
Etudes du cours des hyphes de Fomes fomentarius dans le bois d'Aesculus hippocastanum au microscope électronique à balayage
Authors: Plank Stefan , Wolkinger Franz
Published: September 2008

In a scanning electron microscope (SEM) study, the passage of penetrating hyphae of Fomes fomentarius (L.ex Fr.)Kickx was observed in a representative specimen of Aesculus hippocastanum L. The fungus hyphae appear in all cells of the wood and break through in numerous areas of the cell walls. It was noted that many pits serving as passageways were found; however, the cell wall was observed to be penetrated in many areas devoid of such pits. Apically secreted enzymes probably played a primary role in the process. The primary bore passages are widened by means of lateral enzyme secretion. The depth and sharpness of the SEM photographs are remarkable in that they allow one to follow the passage of the hyphae quite well.
A mathematical model of conidial germination and appressorial formation for Colletotrichum graminicola
Authors: Lapp Martin S. , Skoropad W. P.
Published: September 2008

A mathematical model, which is a modification of the Gompertz equation, can determine the number of germinations and the number of appressorial formations in a population of conidia of Colletotrichum graminicola. It will determine both the maximum proportion of conidia which will germinate or which will form appressoria and the time for these events to occur. The equation parameters, which are functions of biotic and abiotic conditions, are determined using a nonlinear regression programme. The data used to test the model show that continuous light on the parent fungal colony reduces subsequent conidial germination but does not change the time taken to reach this maximum.
Ultrastructural and cytochemical changes in the basidiomycete dolipore septum associated with fruiting
Authors: Flegler S. L. , Hooper G. R. , Fields W. G.
Published: September 2008

An ultrastructural study of dolipore septa in Psilocybe mexicana. Volvariella bombycina, Amanita muscaria, Favolus alveolaris, Lycoperdon perlatum, Hericium coralloides, and Dacrymyces stillatus indicated the presence of solid pore occlusions in vegetative mycelium while the occlusions were perforate or absent in the hymenium. Dolipore septa in basidiocarp initials, stipes, and lamellae of P. mexicana lacked occlusions or had perforate pore occlusions. Septa in vegetative mycelium of D. stillatus had parenthesomes with no pores while the septa in the hymenium had parenthesomes with a single pore. Pore occlusions in septa of vegetative hyphae of P. mexicana were digested with trypsin and chymotrypsin. Periodic acid, thiosemicarbazide, and silver proteinate stain for polysaccharides produced no staining of the pore occlusion. Nucleic acid extraction with perchloric acid also had no effect on the pore occlusion. Microfilaments in the pore canal appeared to be attached at regions of electron-dense material within the canal and at the pore occlusion. Serial sections demonstrated that electron-dense regions within the pore canal were rings which did not completely block the canal.
NaCl and twig dieback along highways and cold hardiness of highway versus garden twigs
Authors: Sucoff Edward , Hong Sung Gak , Wood Alan
Published: September 2008

The timing and amount of stem damage and bud kill, along with the Cl content of twigs, were observed over one or two winters in Fraxinus pennsylvanica Marsh, Cornus stolonifera Michx, Malus sp. cv. Hopa, Salix pentandra L., and Syringa vulgaris L. growing along Minnesota highways. Depending on species and the year, damage occurred between January and May.Cold hardiness was compared for highway- and garden-grown Syringa vulgaris L. and Fraxinus pennsylvanica Marsh. Hardiness was assessed as percentage of xylem and cambial browning and percentage of bud kill after exposure to test temperatures between −45 and +4 °C. In November, hardiness was the same, but from mid-December into March, highway twigs showed more damage than garden twigs at the same test temperatures. The differences between highway and garden twigs coincided in time with differences in twig Cl.
Paleorosa similkameenensis, gen. et sp. nov., permineralized flowers (Rosaceae) from the Eocene of British Columbia
Authors: Basinger James F.
Published: September 2008

Paleorosa similkameenensis, gen. et sp. nov., a new species of fossil flower, is described from the Eocene, Allenby Formation of British Columbia. The flowers are permineralized with silicate and are found scattered through a matrix of black chert. Connection with vegetative parts has not been found. The flowers are small (about 2 mm in diameter) and pentamerous, with petals and sepals inserted alternately. Floral parts are fused to form a floral cup. Between 13 and 19 stamens with bilocular, dorsifixed anthers are inserted on the floral cup. The gynoecium consists of five free carpels, each containing two collateral, erect ovules. These features suggest affinities with the Rosaceae, specifically with the more primitive members of the tribes Maleae, Quillajeae, and Sorbarieae.
Quantitative and qualitative aspects of inshore phytoplankton off Barbados
Authors: Sander Finn
Published: September 2008

The report is a 2-year time-series study of qualitative and quantitative aspects of inshore phytoplankton off Barbados with special emphasis on diatoms. Cell counts during a 2-year period averaged 22 536 per litre, of which 94% were diatoms. Amazon River water appeared not to have any consistent measurable effect on the abundance of the phytoplankton over the 24-month period. Chaetoceros and Nitzschia species were the major numerical contributors to the diatoms. A high ratio (17:3) of neritic to oceanic species of the most common diatoms was considered indicative of the existence of a system of retention for the inshore phytoplankters. Species composition of the total phytoplankton community was also considered. A total of 147 taxa included the following: diatoms, 103; blue-greens, 3; dinoflagellates, 35; silicoflagellates, 1; coccolithophores, 2; greens, 3. The latter three were present in consistently low concentrations.
Anatomy and ultrastructure of the young haustorial gland in Comandra (Santalaceae)
Authors: Toth Ronald , Kuijt Job
Published: September 2008

The haustorial gland of Comandra (Santalaceae) originates from an internal meristem-like area in the young haustorium and involves the differentiation of a double layer of palisade-like parenchyma cells in the median region. These cells secrete substances (positive with periodic acid – Schiff s reagent (PAS)) which seem to be deposited by vesicles that migrate to the median plane to deposit their products between the cell membrane and cell wall. Cell walls in the median area become extremely thin and finally disappear, leaving a cavity filled with secretory products. The lower portion of the gland shows a distinct duct region lined with a single layer of cells secreting a fibrous, layered substance apparently by means of endoplasmic reticulum (ER) vesicles; this substance appears to be neither cellulose nor starch and cannot be called wall-like. The duct in Comandra has not been observed to reach the haustorial surface, but events at the time of penetration of host tissues remain undescribed. Despite past speculations as to the digestive function of the gland, convincing evidence supporting this or any other function is still lacking.
Evolution des RNA ribosomaux au cours du verdissement de cotylédons de concombre en présence de 6-benzylaminopurine
Authors: Roussaux J. , Hoffelt M. , Farineau N.
Published: September 2008

Etiolated cotyledons were excised from cucumber seedlings, maintained in darkness for 24 h in vitro, and then illuminated in the presence or in the absence of 10−5 g/ml of 6-benzylaminopurine (6-BAP) for 48 h. During incubation in the dark, 6-BAP markedly increases the incorporation of 32P into cytoplasmic rRNA and, to a lesser extent, into etioplast rRNA. 6-BAP does not significantly affect the light-induced RNA synthesis during the first 24 h of illumination. The chloroplast rRNA synthesis stops after 24 h of light in the control, but it is maintained in 6-BAP-treated cotyledons. These results are discussed in relation to previously reported cytological observations. The conclusion is reached that cytokinin mainly acts at a cytoplasmic level during the differentiation of etioplast into chloroplast.
Preparation and flattening of thick epoxy sections for light microscopy
Authors: Pizzolato Thompson Demetrio
Published: September 2008

A technique is described which allows 4- to 10-μm-thick plastic sections to be routinely flattened for light microscope observation. Samples are fixed in Karnovsky's fluid, embedded in Spurr's resins, and cut with a steel knife on a rotary microtome. Sections are flattened by passage through xylene, ethanol, and a detergent solution, then dried on slides, and mounted in immersion oil and hexane. Sections may either be stained before mounting or examined unstained.
The allelopathic potential of phenolic acids associated with the rhizosphere of Pteridium aquilinum
Authors: Glass Anthony D. M.
Published: September 2008

Barley plants were grown hydroponically in solutions which exactly reproduced the major phenolic acid composition of the soil associated with Pteridium aquilinum (L.) Kuhn. In CaSO4 solution these compounds severely inhibited root growth as measured by fresh weight, dry weight, and root volume analyses. The form of root growth was also modified by the presence of the phenolic acids in that by 3 weeks extensive lateral root development had occurred, whereas only limited elongation of seminal roots occurred. Inhibition, as measured by fresh weight determinations, was most pronounced when roots were grown at 5 and 30 °C and least pronounced between 15 and 20 °C. Other species examined, with the sole exception of Agropyron repens (L.)Beauv., showed similar responses to the presence of the phenolic acids. Microscopic examination of the tips of barley roots treated with phenolic acid revealed that meristematic cells were prematurely vacuolated.In constrast with the striking effects of these phenolics on root growth in CaSO4 solution, there were no obvious effects on barley root growth when the phenolic acids were dissolved in a complete inorganic nutrient medium.
The partitioning of net energy resources in two populations of Solidago canadensis during a single developmental cycle in southern Ontario
Authors: Bradbury Ian K. , Hofstra G.
Published: September 2008

The partitioning of net energy resources among component organs was measured in two populations of vegetatively produced Solidago canadensis L. individuals on two abandoned pasture sites in southern Ontario. One population was invading a grass-dominated site of comparatively recent abandonment while the other population was well established on a site which was dominated by perennial forbs and which typified a late stage of secondary herbaceous succession. Early in the season there were differences in the proportional contribution of leaf and stem tissue to total new growth, but allometric analysis showed these differences to be a function of developmental stage. New roots emerged earlier in the invading population, which subsequently maintained a higher new root – shoot ratio. The relative growth of new roots was the same in both populations between July and mid-August. Reproductive effort (RE), consisting of both sexual and asexual components, was similar in both populations. Asexual RE was very small (1.5%), but rhizome length was longer in the invading population. It is suggested that rhizome length is determined principally by the size of the photosynthetic apparatus in late season when rhizome extension and leaf senescence are occurring simultaneously. An explanation for differential senescence rates is offered based on the size and density of Solidago clumps and the influence of these characteristics on light attenuation in the canopy.
Taxonomy and distribution of Gaultheria in the Caribbean
Authors: Hersey R. E. , Kloet S. P. Vander
Published: September 2008

Two species of Gaultheria have been reported from the Caribbean: G. domingensis is said to occur on the Greater Antillean island of Hispaniola and G. sphagnicola, for which the specific names of G. buxifolia and G. anastomosans (both species occurring in South America) have been listed in synonymy, is said to occur on the Lesser Antillean islands of Martinique and Guadeloupe. A close examination of living material from Martinique and of herbarium specimens from Martinique, South America. Hispaniola, and Mexico reveals the following: (1) the Martinique and Guadeloupe group is specifically distinct from the South American G. buxifolia and G. anastomosans groups; (2) the Lesser Antilles group and the Greater Antilles group should be placed in a single species with the name of G. domingensis; and (3) there is evidence for a possible Mexican origin for this one Caribbean species.
Occurrence of virions in developing ovules and embryo sacs of barley in relation to the seed transmissibility of barley stripe mosaic virus
Authors: Carroll Thomas W. , Mayhew Dennis E.
Published: September 2008

Electron microscopic examination revealed the occurrence of virions in thin sections of developing ovules and embryo sacs of Atlas barley infected with a seed-transmitted strain of barley stripe mosaic virus, MI-1. It appeared that the virus invaded the primaiy meristem early, then infected the megaspore mother cell. In later stages of ovule development, the virus was seen in megaspores and in the cells of the embryo sac, including the egg. Virions were commonly associated with wall, cytoplasmic, or spindle microtubules. By contrast, virions of the non-seed-transmitted strain of the virus (NSP) did not occur in developing ovules or embryo sacs. Ovule transmission was only demonstrated for MI-1.
An assessment of the modifying effect of kinetin on in vitro tuberization of induced and non-induced tissues of Solatium tuberosum
Authors: Forsline P. L. , Langille Alan R.
Published: September 2008

‘Katahdin’ potato plants (Solatium tuberosum L.) were grown under inducing (26 °C day −12 °C night with an 8-h photoperiod) and non-inducing (28 °C day −25 °C night with a 16-h photoperiod) conditions. Apical, medial, and basal nodal stem segments from each plant harvested were surface sterilized and aseptically transferred to culture flasks containing Murashige and Skoog's medium with and without kinetin. After culturing in dark for 4 weeks at 24 °C, percentage tuberization of segments from induced plants was significantly greater than for non-induced segments. Addition of kinetin to the culture medium eliminated this effect of induction. Apical segments from induced plants tuberized more frequently than those from non-induced plants and those from lower on stem. Addition of kinetin eliminated this stem position effect. Percentage elongation was significantly greater in segments from non-induced than induced plants. Addition of kinetin reduced percentage elongation in non-induced segments to that for induced segments. Percentage elongation was greatest in apical segments from non-induced plants and this position effect could be eliminated by addition of kinetin.
Pollen flow in distylous populations of Amsinckia (Boraginaceae)
Authors: Ganders Fred R.
Published: September 2008

Stigmatic pollen loads were analyzed from naturally pollinated pin and thrum form flowers of Amsinckia douglasiana and A. vernicosa var. furcata. Pin stigmas captured more total pollen than thrum stigmas. Pins experienced either net self-pollination or random pollination. Thrum stigmas experienced significant disassortative pollination. Comparing pollen loads from intact and emasculated thrum flowers of A. douglasiana indicated that self-pollination and geitonogamy were relatively unimportant in the pollination of the thrum form. The level of disassortative pollination of A. vernicosa var. furcata does not appear to be high enough to account for the level of disassortative mating observed by progeny testing, suggesting that this species may possess an incomplete stylar self-incompatibility system such as has been reported in A. grandiflora.
The effect of a Rhizoctonia solani phytotoxin on potatoes
Authors: Frank J. A. , Francis S. K.
Published: September 2008

Rhizoctonia solani produces a nonenzymatic, low-molecular-weight phytotoxin in liquid culture. Many of the disease symptoms on potato attributed to this pathogen can be induced with this toxin. These include root necrosis and stolon pruning, leaf curling, stunting, and leaf margin chlorosis. In cases of extreme susceptibility, the plants could be killed within 1 week. The toxin has similar effects on radish, beet, and corn seedlings and acts as a growth hormone in low concentrations. A technique was designed to evaluate potato clones for their resistance to the root necrosis phase of the disease syndrome. With additional purification, the toxic fraction was identified as phenylacetic acid and its metahydroxylated derivative.
Effects of acidity on the phytoplankton and primary productivity of selected northern Ontario lakes
Authors: Kwiatkowski R. E. , Roff J. C.
Published: September 2008

The effects of acidity on primary production, species composition, and abundance of phytoplankton were investigated in six lakes in the Sudbury area of Ontario, where pH values lay between 4.05 and 7.15. Significant relationships showing an increase in water transparency and decrease in chlorophyll a concentration with declining pH were found. Percentage similarity of community (PSc) and community coefficient (CC) values were highest between lakes closest in pH, reflecting progressive changes in species composition. As the pH declined, Chlorophyta diminished in importance and the Cyanophyta became dominant. The phytoplankton diversity index (DI) remained relatively unchanged between pH values of 7.0 to 5.0 but decreased at lower values. Primary production in milligrams C metre−3 hour−1 was reduced in lakes below pH 5.5; however, as a result of the increase in depth of euphotic zone accompanying more acidic conditions, primary production in milligrams C metre−2 hour−1 remained high down to pH 4.4, below which it was drastically reduced.
Zygosporogenesis in Phycomyces blakesleeanus
Authors: O'Donnell K. L. , Hooper G. R. , Fields W. G.
Published: September 2008

Zygosporogenesis in Phycomyces blakesleeanus Burgeff was observed via scanning and transmission electron microscopy. The surface architecture of the initial stages of conjugation up to mature whole and longitudinally cryofractured zygospores was described and illustrated. The development and structure of the fusion wall, gametangial septum, appendages, and the lateral wall layers of the developing zygospore were investigated with the transmission electron microscope.
Growth of Polyporus tomentosus cultures derived from basidiospores, sporophore tissue, and decayed wood
Authors: Whitney R. D. , Bohaychuk W. P.
Published: September 2008

Polyporus tomentosus Fr. cultures originating from basidiospores grew faster on artificial media than those originating from either sporophore tissue or decayed wood. Brown pigmentation in the mycelial mat was most intense in cultures originating from decayed wood. Growth rate was fastest on prune agar and the lowest production of chlamydospores was recorded on malt extract agar. Some sporophore isolate groups (a sporophore isolate group, or SIG, consists of the three isolates obtained from the tissue of a single sporophore, basidiospores from this sporophore, and mycelium in the wood on which the sporophore was growing) grew significantly faster than others, and one such group produced significantly higher numbers of chlamydospores than all others.
Pectolytic enzymes of Sclerotinia sclerotiorum and their localization in infected bean
Authors: Lumsden R. D.
Published: September 2008

Sclerotinia sclerotiorum produced at least three pectolytic enzymes, each of which was similar in both diseased tissue and in culture. An endopolygalacturonase (endo-PG) (PG, EC 3.2.1.15) was most abundant 24 h after inoculation of bean plants and after 2–3 days incubation in culture but decreased thereafter. Production in culture was suppressed by glucose. The activity of this enzyme was localized in the advancing margins of young lesions in infected plants but was usually not present later than 48 h after inoculation. An exo-PG was detected at lesion margins after 48 h and also in cultures of S. sclerotiorum in Na polypectate (NaP) medium and on autoclaved bean hypocotyls. Increases in exo-PG activity with time of incubation was correlated with rapid growth of the fungus. Pectin methylesterase (PME, EC 3.1.1.11) was detected early in pathogenesis and at the margins of advancing lesions. PME activity increased with age of diseased tissue and age of cultures on NaP medium and bean hypocotyl medium. Fungal PME was distinguished from healthy bean PME on the basis of differing pH optima for activity and lack of NaCl or CaCl2 activation of the fungal PME. The action of PG and PME on apple tissue infected with S. sclerotiorum was detected histochemically. Alteration of pectic substances in the middle lamella of infected apple fruit tissue was detected one to two cells in advance of the invading hyphae. The importance of these pectolytic enzymes in relation to pathogenesis and colonization of host tissues is discussed.
Mediation of rapid electrical, metabolic, transpirational, and photosynthetic changes by factors released from wounds. II. Mediation of the variation potential by Ricca's factor
Authors: Sambeek Jerome W. Van , Pickard Barbara G. , Ulbright Corinne E.
Published: September 2008

An extract of Lycopersicon leaf tissue applied to the base of an excised Lycopersicon leaf causes a variation potential to spread through the leaf. This spread of an electrical wave is closely dependent on the spread of the extract via the transpiration stream, and the amplitude of the variation potential depends on the concentration of extract applied. Extract from 5–10 mg fresh leaves diluted to 1 ml elicits threshold response, and saturation is accomplished with a concentration about 40 times greater. Evidently, the active factor or factors are effective at very low concentrations. A variety of substances cause electrical disturbances when applied to the excised leaf, but plant extract is the only tested material which under the given conditions desensitizes the leaf to an application of saturating extract 5 min after the initial application.The active factor or set of factors has been extracted from plants in several families and appears to be closely related to the substance implicated by Ricca in 1916 in trauma-induced closure of Mimosa leaves. In recognition of this early discovery, the material is at present called Ricca's factor.
The shoot apex of trees of Picea mariana of differing rooting potential
Authors: Riding Richard T.
Published: September 2008

Scion material was collected from the upper and lower portions of the crown of black spruce trees of high and low rooting potential. Scions from the lower crown positions rooted better than those from upper crown positions. There appeared to be a positive correlation between rooting potential and RNA concentration in cells of the shoot apex. In apices from trees which did not root, RNA staining was very slight and total protein and carbohydrates were concentrated near the cell walls.
Cytoplasmic streaming in Elodea
Authors: Forde Janice , Steer Martin W.
Published: September 2008

Cytoplasmic streaming in the higher plant Elodea canadensis has been studied by light and electron microscopy. Calcium ions inhibited streaming in detached leaves, whereas magnesium ions stimulated the streaming rate. Ethylenediaminetetraacetic acid (EDTA) at low concentrations relieved calcium ion inhibition, while at higher concentrations it inhibited the magnesium ion stimulation. Chloride ions had a slight dual effect, accentuating the differences produced by calcium and magnesium ions. Cytoplasmic streaming was reversibly inhibited by cytochalasin B, although there was a considerable delay in these effects. Possible binding sites for cytochalasin B were localized using light microscope autoradiography of leaf sections. Vacuoles, cell walls, and nuclei were unlabelled; chloroplasts were labelled to a limited extent, while the rest of the label was distributed throughout the cytoplasm. Ultrastructural studies failed to reveal large aggregates of microfilaments; instead much smaller bundles were found together with a fibrillar-granular material associated with the endoplasmic reticulum. The possibility that this material generates cytoplasmic streaming by imparting movement to the endoplasmic reticulum is considered.
The effect of heavy metals on some aspects of lichen physiology
Authors: Puckett K. J.
Published: September 2008

The effect of the heavy metals cadmium, cobalt, copper, lead, mercury, nickel, and silver on the lichen Umbiliearia muhlenbergii (Ach.) Tuck, is described in terms of membrane integrity, chlorophyll damage, and changes in photosynthetic 14C fixation. Increasing concentrations of copper, mercury, and silver produced a gradual potassium loss from the thallus while the other metals tested initiated an abrupt efflux at a specific concentration. Copper, mercury, and silver caused both a displacement and a decrease in the absorption spectrum of chlorophyll, whereas no detectable changes were induced by the other metals. The relative toxicities of these metals on photosynthesis is reflected in the series Ag. Hg > Co > Cu, Cd > Pb, Ni for short-term exposures, and Ag. [Formula: see text] for extended exposures. The tendency for the metals studied to fall into two distinct groups on the basis of their effects on lichen metabolism is discussed in terms of their physicochemical properties.
New species of Humicola: an approach to genetic and biochemical classification
Authors: Bertoldi Marco de
Published: September 2008

Thirteen new species of Humicola are described: H. aurea, H. glauca, H. lutea, H. piriformis, H. repens, H. sardiniae, H. variabilis, H. atra, H. austera, H. globosa, H. nivea, H. rugosa, and H. veronae. The classification is based not only on morphological characters but also on genetic and biochemical ones. In Hyphomycetes similarities in morphology do not necessarily indicate genetic relationships. DNA base composition (guanine–cytosine percentage, GC%) and electrophoretic characteristics of enzymes used together with morphological features have proved to be useful and of taxonomical value in the classification of the new species of Humicola.
A synopsis of American Salix
Authors: Dorn Robert D.
Published: September 2008

The classification of American Salix (willows) is updated to account for nomenclatural changes, new species and sections, and new data. Evolutionary relationships, biology, and nomenclatural difficulties in the genus are briefly discussed. A preliminary, simplified key to sections is presented along with a synopsis of subgenera, sections, and subsections. One new section and two new subsections are described. Six new combinations are also made. The important literature is cited.
Leghemoglobins and nitrogenase activity during soybean root nodule development
Authors: Nash Dudley T. , Schulman Herbert M.
Published: September 2008

We have examined the changes in soybean leghemoglobins in relation to plant age, nodule size, and nitrogenase (EC 1.7.99.2) activity. The ratio of nitrogenase activity to leghemoglobin content declines throughout plant development and senescence. This results from a slower rate of increase of leghemoglobin compared with that of nitrogenase activity during early nodule development and a more rapid decline in nitrogenase activity after flowering. Larger nodules were generally found to have higher leghemoglobin contents but lower nitrogenase activity per unit fresh weight than nodules of intermediate size. The concentration of leghemoglobin in the nodules increases until the plants have flowered, at which time it represented 40% of the total soluble protein of the nodules. The proportions of the two major leghemoglobin species separable by electrophoresis (LbF and LbS) were measured and it was found that although LbF was the major component of all samples examined, the ratio of LbF:LbS decreased with increasing nodule size and age.
Virus-like particles in the green alga Cylindrocapsa
Authors: Hoffman Larry R. , Stanker Larry H.
Published: September 2008

Icosahedral, virus-like particles (VLPs) have been studied in attached germlings of Cylindrocapsa geminella Wolle after the settling of zoospores produced by a heat-shock treatment. About 26 h after zoospore attachment, 3–10% of the resulting one-celled germlings contained a massive concentration of VLPs filling a region at the basal (i.e., attached) end of each cell. This includes the area normally occupied by the nucleus which is completely lysed by the time the VLPs are first observed. VLPs were found only in single-celled germlings, although the samples included multicellular germlings. Organelle degeneration occurs in the infected germlings and this apparently leads to cell lysis. Mature VLPs generally appear six-sided in section and have a maximum diameter of 200–230 nm. They possess a finely fibrillar core surrounded by a multilayered, membranous coat. The varied appearance of the virogenic stroma is discussed as well as putative stages in viral assembly. Cultures of Cylindrocapsa are being maintained from which VLP-infected germlings can be routinely obtained. The possibility that these cultures may be carrying a latent virus infection which can be induced by heat shock is discussed.
Plasmodesmata: a freeze-fracture view
Authors: Willison J. H.M.
Published: September 2008

The structure of plasmodesmata in the longitudinal walls of cells close to the meristematic region of Phaseolus vulgaris root tips were studied in freeze-fractured material not treated with glycerol. There were accumulations of membrane-associated particles on plasmalemmata at the junctions between plasmodesmata and plasmalemma. There was some indication that these particle clusters might be associated with the control of symplastic flow via sphincters into plasmodesmata. The junction between endoplasmic reticulum and the desmotubule, where visualized, appeared to be blocked. In other respects plasmodesmatal ultrastructure corresponded well with that described using conventional electron microscopical techniques.
The effect of methoxychlor on carbon assimilation by freshwater phytoplankton
Authors: Page Deanna L. , Colman Brian
Published: September 2008

The effect of the insecticide methoxychlor (2,2-bis(p-methoxyphenyl)-1,1,1-trichloroethane) on photosynthetic carbon assimilation by natural phytoplankton populations was determined by incubation of plankton samples in situ at a 1.0-metre depth with [14C]bicarbonate for 4-h periods with or without 100 parts per billion (ppb) (100 μg/l) pure or technical grade methoxychlor. The different algal populations occurring over a 5-week period in May and June in Lake Opinicon, Leeds County, Ontario, were found, in 19 experiments, to be seldom affected by the insecticide. In the few cases where carbon assimilation in methoxychlor-treated samples was found to be significantly lower than that of the controls, the inhibition ranged in extent from 9.7% to 67.4% and these effects could not be correlated unequivocally with cell number or with the presence of any particular algal species.
The genus Dermea and related conidial states on Douglas fir
Authors: Funk A.
Published: September 2008

The following elements of the genus Dermea (Ascomycetes), and related conidial states, are reported from diseased Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) in British Columbia, Canada: Dermea pseudotsugae Funk, Micropera pinicola (Linder) comb, nov., Dermea tetrasperma sp. nov. (conidial state: Micropera lunaspora (Linder) comb, nov.), Micropera fosteri sp. nov., and Micropera uncinata sp. nov.
Evidence of microevolution in an escaped pear population
Authors: Waldron Gerald E. , Hilton R.J. , Ambrose J. D.
Published: September 2008

A population of 87 wild pears (Pyrus communis L.) of fruiting age, growing in a relatively homogeneous old field environment, was found to be highly variable, with coefficients of variation up to 40%. Generally, variability was greater in size than in meristic characters, in meristic characters than in shape characters, and floral traits were less variable than vegetative. Tree trunk core samples showed the population to have been founded circa 1905 to 1908, by three trees. Establishment of progeny began about 19 years later. The population is high in 1975 and still expanding logarithmically. Numerical taxonomic clustering techniques using morphological characters showed the population to contain two very diverse groups. Trees of both groups are of all age classes and are distributed randomly over the site. Trees phenetically like and unlike the oldest trees were analysed as to growth rates. Those trees similar to the oldest trees were significantly slower in growth rate than trees that were morphologically dissimilar. This suggests that natural selection is operating to remove the less fit genotype from the population.