bluuebunny/crossref_metadata_2025 huggingface dataset:
Sexual reproduction of Sitka spruce (Picea sitchensis)
Authors: Owens John N. , Molder Marje
Published: April 2011

The phenology of sexual reproduction of Picea sitchensis (Bong.) Carr. was similar at the three sites on Vancouver Island, British Columbia, used in the study. As indicated by cell divisions, cone buds ended dormancy in early March, 2 weeks before dormancy ended in vegetative buds. Pollen mother cells underwent meiosis in mid-March and mature, saccate, four- or five-celled pollen was formed by late April. Megaspore mother cells underwent meiosis in late March and mature female gametophytes were developed by late May. Pollination occurred in late April. A pollination drop was produced by the nucellus and exuded between the two micropylar arms and pollen was drawn down into a nucellar depression where pollen germinated in late April. Fertilization occurred in early June and early stages of embryo development occurred by late June, 9 weeks after pollination. Cotyledons were initiated in late July and seed was mature by mid-August and shed during the early fall.Development of male and female gametophytes and embryos was similar to patterns shown for other species of Picea. In this study seed set was very poor and resulted primarily from a lack of pollination. Other contributing factors were female gametophyte abortion before fertilization, embryo abortion during early development, and insect damage.
Survey of vegetative flavonoids of Sedum section Gormania (Crassulaceae)
Authors: Denton Melinda F. , Kerwin James L.
Published: April 2011

The flavonoids in the leaves and stems of the 12 taxa of Sedum section Gormania were determined. Two of the three compounds occur in all 12 taxa. These two are 3,7-disubstituted kaempferol and laricytrin. The third compound, a highly methylated flavone, shows variation in its occurrence, and its presence or absence serves to substantiate two evolutionary groups of taxa in section Gormania.
On the vascular anatomy and stomates of the lodicules of Zea mays
Authors: Pizzolato Thompson Demetrio
Published: April 2011

The four lodicules of the male spikelet of Zea mays L. are supplied by one, two, or three traces. In the lower regions of the traces intermediary cells and a few phloem transfer cells occur with the companion cells and sieve tubes. Xylem transfer cells with a variety of wall thickenings intermingle in the lower regions of the traces with tracheary elements. Tracheary elements and sieve tubes in this region do not touch but are separated by the phloem and xylem parenchyma. As the lodicule trace nears the base of the lodicule, intermediary cells and transfer cells diminish. A bundle sheath surrounds the lodicule trace but does not surround the minor veins of the lodicule proper. Within the lodicule proper the trace branches prolifically, and the minor veins become peripherally placed. Most of the minor veins contain vessels and sieve tubes but a few contain sieve tubes alone. Companion cells occur in some veins but not in others. Vessels and sieve tubes frequently touch each other. Many minor veins end simultaneously in sieve elements and tracheary elements but some end in one or the other cell type. Parenchyma cells with wrinkled walls occur near the minor veins. The abaxial epidermis of the upper regions of the lodicule contains stomates.
Comparative study of the holdfast structure in four Trichomycetes
Authors: Mayfield Si-nan Dang , Lichtwardt Robert W.
Published: April 2011

An electron microscope study reveals considerable variation in the holdfast structure by which the fungal thalli of Trichomycetes attach to the gut lining of their arthropod hosts. Enterobryus attenuatus (Eccrinaceae) has a compound holdfast system where the holdfast substance is secreted through a reticulate ring complex located at the base of each individual thallus. The ring complex is rich in polysaccharides, as is the outermost layer of the cell wall. Enterobryus elegans produces large, single holdfasts with a fibrous matrix containing numerous parallel channels, some of which open to the gut lumen. Genistellospora homothallica (Legeriomycetaceae) has a dense and homogeneous biconcave holdfast, whereas Pennella angustispora, belonging to the same family and found in the same host, secretes an amorphous cementing substance throughout the length of the basal cell wall.
Primary vascular patterns in root meristems of Pontederia cordata and their relevance to studies of root development
Authors: Charlton W. A.
Published: April 2011

There are several files of metaxylem cells in root apices of Pontederia cordata L., each considered to consist of a series of prospective vessels with their ends in contact. Two longitudinally adjacent vessels may be in the same file of cells produced by the root apex or in adjacent files. As the root grows, successive prospective vessels are added to the apical ends of most of the files but not all files are continued. Addition of prospective vessels appears to take place within the "quiescent centre" of the root apical meristem. Where files are not continued there is no immediate readjustment of remaining files. The longitudinal and transverse distribution of components of the vascular system (including protophloem and protoxylem) is discussed in relation to the means by which the pattern of development may be controlled. Rates of production of vessels and the final lengths of the vessels are estimated. The observations and deductions are discussed in relation to other studies of root growth, vascular differentiation, and vascular pattern formation and maintenance.
Taxonomy of Trifolium (Leguminosae). V. The perennial species of section Involucrarium
Authors: Gillett John M.
Published: April 2011

The perennial species of Trifolium Linnaeus section Involucrarium Hooker are revised. A key to the species, descriptions of species, synonyms, typification, distribution maps, and notes are presented. The following chromosome numbers are reported as new: T. mucronatum Willd. ssp. mucronatum, 2n = 16; T. mucronatum ssp. vaughanae J. M. Gillett, 2n = 16; and T. wormskioldii Lehmann, 2n = 16. The following combinations are made: T. mucronatum Willdenow ssp. lacerum (Greene) J. M. Gillett, T. monanthum A. Gray ssp. parvum (Kellogg) J. M. Gillett, T. monanthum ssp. tenerum (Eastwood) J. M. Gillett, and T. monanthum ssp. grantianum (Heller) J. M. Gillett. A new species, Trifolium siskiyouense J. M. Gillett and a new subspecies, T. mucronatum ssp. vaughanae are described. Taxonomic problems are discussed.
Adaptation and acclimation of higher plants at the enzyme level: thermal properties of NAD malate dehydrogenase of two species of Aster (Asteraceae) and their hybrid adapted to contrasting habitats
Authors: Brouillet Luc , Simon Jean-Pierre
Published: April 2011

Thermal and kinetic properties of NAD malate dehydrogenase (MDH) were investigated in clonal populations of two species of Aster and their hybrid: A. acuminatus, a forest understory species; A. nemoralis, a sphagnum-bog species; and A. blakei, their hybrid occurring at the bog–forest ecotone. The populations were collected within a 300 m radius in southwestern Quebec. Compared with A. acuminatus, the MDH of crude extracts from A. nemoralis had lower thermostability in both 5- and 10-min assays at 55 °C, and reduced apparent energy of activation (Ea) in the temperature range of 15–25 °C. However, these differences were not maintained in purified extracts of the species and may be attributed to higher phenolase and peptidase activity in crude extracts of A. nemoralis. The ratio of MDH activity over total protein concentration, or fresh weight leaf tissue, was higher in A. acuminatus than in A. nemoralis. Most values for these MDH properties of A. blakei were intermediate between those of the two parents. No differences, however, were observed for the substrate binding ability (Km) of MDH in the three taxa. Electrophoretic analyses show no qualitative differentiation in the enzyme profiles of MDH of the three taxa, which consist of two mitochondrial and six cytosolic isozymes. Mitochondrial isozymes were more thermostable but no differences in thermostability were observed among the forms of the species. The thermal and kinetic properties of malate dehydrogenase, as measured in situ, have not been substantially modified by the contrasting microclimatic regimes associated with the habitats of A. acuminatus and A. nemoralis.
Seed input as a factor in the regeneration of strip-mine wastes in Saskatchewan
Authors: Archibold O. W.
Published: April 2011

Seed traps were set out on the spoil banks created by strip-mine coal operations in southeastern Saskatchewan. A total of 2721 seeds (2387 seeds/m2) was collected in the 1st season of which 97% was comprised of forb seeds and 3% of grass caryopses; 4216 seeds (3798 seeds/m2) were trapped in the 2nd year. Kochia scoparia was the most abundant species. Adequate seed input is occurring in the area to provide a good vegetation cover. The general absence of vegetation on the wastes must therefore reflect subsequent removal and deterioration of the seeds.
Organogenesis of the female reproductive structure of Myrica pensylvanica
Authors: Macdonald Alastair D.
Published: April 2011

The female reproductive structure of Myrica pensylvanica comprises a gynoecium and four second-order inflorescence bracts. The gynoecium terminates the second-order inflorescence axis. The receptacle, comprising second- and third-order inflorescence axis tissue, forms most of the gynoecial wall and gives rise to the wax-secreting papillae. Papillae, which are vascularized, are not initiated in the same manner as trichomes. An hypothesis is formulated whereby papillae may be homologized to inflorescence bracts.
The natural vegetation of Saskatchewan prior to agricultural settlement
Authors: Archibold O. W. , Wilson M. R.
Published: April 2011

The natural vegetation of southern Saskatchewan prior to settlement has been reconstructed from 2500 township plats compiled during the Dominion Lands Survey of the 1880's. The north–south section lines within each township were used as transects from which percent cover of grassland, woodland, scrub, brulé, marsh, and open water was calculated and compiled in map form. Although directly comparable modern data are not available, it is concluded that woodland areas have increased over the last 80 or 90 years.
Deposition of atmospheric pollutants as measured by lichen element content in the Athabasca oil sands area
Authors: Addison P. A. , Puckett K. J.
Published: April 2011

The aluminium, potassium, sulphur, titanium, and vanadium contents of the lichens Cladina arbuscula (Wallr.) Hale and W. Culb., Evernia mesomorpha Nyl., and Hypogymnia physodes (L.) Nyl. were determined for up to 69 sites in the Athabasca oil sands area in northern Alberta. The element accumulation by these lichens was related to both gaseous and particulate emissions from industrial sources and to a localized windblown dust component. The deposition of atmospheric emissions around an oil-extraction plant as measured by lichen thallus concentration closely followed the distribution patterns measured by physical and chemical methods. Visible changes in the thallus condition appeared to be related to the element concentrations.
Effect of ethylene on root growth, ectomycorrhiza formation, and Fusarium infection of Douglas-fir
Authors: Graham J. H. , Linderman R. G.
Published: April 2011

Roots of 2-month-old Douglas-fir seedlings were exposed to six ethylene concentrations, ranging from 0.006 (soil ambient control) to 0.5 ppm, by adding ethephon, an ethylene-releasing compound, as a soil drench to the root zone. After 2 months exposure, 0.01–0.05 ppm had stimulated, 0.05–0.15 ppm had no effect, and concentrations > 0.15 ppm had inhibited lateral root formation. Root dry weight increased and shoot dry weight decreased as the ethylene concentration was increased.Ectomycorrhiza formation on 4-month-old seedlings inoculated with Hebeloma crustuliniforme was not increased by exposure of the root zone to 0.1 ppm ethylene for 3 months, whether or not the seedling roots had been previously exposed to ethylene for 2 months before inoculation. By contrast, when 2-month-old seedlings preinoculated with Fusarium oxysporum f. sp. pini were exposed to 0.1 ppm ethylene for 2 months, disease incidence was significantly increased. These data suggest that the presence of ethylene in the root zone may have a different effect on root infections by pathogenic fungi than by mycorrhizal fungi.
The effects of shade on shoot growth of Vaccinium angustifolium Ait. after fire pruning in southeastern Manitoba
Authors: Hoefs M. E. G. , Shay Jennifer M.
Published: April 2011

Five plots (15 m × 0.3 m) containing similar numbers of Vaccinium angustifolium shoots were laid out within a clearing in a natural Pinus banksiana stand. The area was burned in late April. Wooden screens were then erected to provide 0,25, 50,75, and 100% shade over the plots. Growth of blueberries and competing vegetation was monitored throughout the growing season using 10 quadrats (930 cm2) per plot. Soil characteristics, temperature, moisture, and light were measured.Quadrats with low preburn densities showed a greater increase in shoot numbers than those with high densities, regardless of shade. The times of shoot emergence and apical abortion were also independent of shade. Other blueberry characteristics were influenced by shade. Shoot density, shoot branching, and number of branches per shoot were highest in the open; frost damage was also greatest.However, blueberries under intermediate shade grew faster, had larger leaves, longer and stouter shoots, and experienced a more favorable water economy. In general, shade, considered detrimental to blueberries in the Atlantic Provinces, may be essential for optimal growth in Manitoba's continental climate.
The perispore in Polypodium and related genera (Polypodiaceae)
Authors: Lloyd Robert M.
Published: April 2011

Light and scanning electron microscopy (SEM) have been used in a study of spore surface features in Polypodium and in the related genera Crypsinus, Solanopteris, and Synammia. Under SEM, spores of nearly all taxa exhibit deposits interpretable as perispore. Spores of Polypodium species are characterized by an exospore which varies from smooth to verrucose or with knoblike verrucae, and by perispore deposits which vary from thin, tightly affixed layers to thick, platelike, highly ornamented layers. Folded or "winged" perispores are present in several species and some species exhibit two perisporial layers which are dissimilar in structure. Sporoderm features of Synammia are similar to those exhibited within Polypodium; however, the perispores of Crypsinus and Solanopteris are spinulose. Although the majority of species investigated do not have elaborate or well-developed perispores, sufficient diversity is present to suggest that this feature could be useful in delineating some of the natural groups in this complex family.
Etude ultrastructurale des relations hôte–parasite au cours de l'infection des pommes par le Phytophthora cactorum
Authors: Mourichon X. , Sallé G.
Published: April 2011

An electron microscopic study was performed on haustoria of Phytophthora cactorum (L. et C.) Schroeter developed in tissues of two cultivars of apple fruits: a susceptible variety ('Golden delicious') and a resistant one ('Belle de Boskoop'). Ultrastructure of intercellular hyphae and some aspects of their penetration between contiguous host cells were described. A light dissolution of the host cell walls was observed. Ontogenic investigations indicated that in the susceptible host, the wall of the fungal haustoria was covered with a dense-stained extrahaustorial matrix. Its origin and its polysaccharide nature were demonstrated. On the other hand, the resistant host developed, immediately after the inoculation, a papilla which gave rise, later on, to a sheath enclosing adult haustoria. The role of these callosic structures in the phenomenon of resistance was discussed.
Ectomycorrhizal specificity in the genus Alnus
Authors: Molina Randy
Published: April 2011

Only three of nine test fungi formed ectomycorrhizae on Alnus glutinosa, A. incana, A. rhombifolia, and A. sinuata in pure culture syntheses: Alpova diplophloeus, Astraeus pteridis, and Paxillus involutus. Pisolithus tinctorius formed ectomycorrhizae to a very limited extent on Alnus glutinosa. It is suggested that the entire genus Alnus may be very specialized regarding its ectomycorrhizal fungus associates, yet, display little infrageneric mycorrhizal specificity.The role of phenolics and possible mechanisms determining ectomycorrhizal specificity are discussed, and the need for research on host–fungus recognition factors is emphasized.
The influence of a severe drought on net photosynthesis of white oak (Quercus alba)
Authors: Dougherty Phillip M. , Hinckley Thomas M.
Published: April 2011

A prolonged and intense drought during the summer of 1976 caused soil water potential in the upper 45 cm of the soil profile to decrease below −2.5 MPa. Predawn xylem pressure potential (P) frequently was less than −1.8 MPa. Under conditions of high soil moisture, net photosynthesis averaged more than 8.0 mg CO2∙dm−2∙h−1 between 0500 and 1800 hours, and maximum rates of net photosynthesis were above 14.0 mg CO2∙dm−2∙h−1. Average and daily maximum net photosynthesis decreased to less than 1.0 and 8.0 mg CO2∙dm−2∙h−1, respectively, during the peak of the drought. Maximum rates of net photosynthesis observed under controlled light and temperature conditions remained above or near 14.0 mg CO2∙dm−2∙h−1 even when predawn P equalled −1.83 MPa. Net photosynthesis seldom decreased below zero if quantum flux densities were greater than the compensation point during this period of record low soil moisture. Environmental conditions, such as fog and clouds, which reduced leaf temperatures and atmospheric evaporative demand, increased net photosynthesis although predawn P was less than −1.8 MPa. During cloudy days, rates of net photosynthesis were within 80% of those observed under ideal soil moisture conditions. The photosynthetic characteristics of white oak noted during this drought are coupled with other physiological traits of white oak to explain its relative success in the oak–hickory forest type.
Dry matter accumulation and distribution in winter wheat grown in a humid continental climate
Authors: Hunt L. A. , Edgington L. V.
Published: April 2011

The growth of a crop of 'Arrow' winter wheat (Triticum aestivum L. em Thell.) was studied in detail from 2 weeks before ear emergence to maturity. Aboveground dry weight increased up to 4 weeks after ear emergence, when it reached a maximum value of 1.4 kg∙m−2, and then decreased marginally. The rate of aboveground dry matter accumulation over a 6-week period beginning 2 weeks before ear emergence averaged 24.4 g∙m−2∙day−1.Rapid ear growth commenced some 2 weeks after ear emergence and continued until after the crop had lost all green coloration. Dry matter accumulation in the ears in the period beginning 3 weeks past ear emergence was greater than accumulation in the aboveground parts of the crop as a whole. This indicated that much of the ear dry matter increase in the latter part of the grain filling period occurred as a result of translocation of previously accumulated assimilates. The stem fraction (including leaf sheaths), the major aboveground reservoir of material that is translocated to the ear, decreased from 800 g∙m−2 at 3 weeks after ear emergence to 493 g∙m−2 at maturity.
The life history of Halosaccion ramentaceum
Authors: Meer John P. van der
Published: April 2011

The complete life history of Halosaccion ramentaceum has been determined. It is very similar to that of Palmaria palmata, consisting of haploid male and female gametophytes alternating with a diploid tetrasporophyte. As for P. palmata, there is no carposporophyte. Male and female gametophytes attain sexual maturity almost a generation apart. Whereas male plants require approximately 1 year's growth before producing spermatia, female gametophytes are microscopic and reach sexual maturity only a few days after tetraspore germination. The diploid tetrasporophyte initiates its development on the female, but almost immediately forms an independent holdfast on the substratum beside the female. The first diploid fronds arise from that holdfast after it is well established.The existence of a complete sexual cycle was proven by demonstrating: fertilization of trichogynes by spermatia; meiosis in tetrasporangia, with a chromosome number of n = ~24 in gametophytes and 2n = ~48 in tetrasporophytes; and by documenting the Mendelian transmission of a mutant phenotype from the male parent to the F1 gametophytes.
Leader growth and the architecture of three North American hemlocks
Authors: Hibbs David E.
Published: April 2011

Height growth in hemlock (Tsuga canadensis (L.) Carr., T. heterophylla (Raf.) Sarg., T. mertensiana (Bong.) Carr.) is by rhythmic growth of a monopodial axis with continuous branch production throughout the growing season. Leader growth is plagiotropic and leader erection is a process lasting several years. Two types of events disrupt the basically monopodial nature of the axis. (1) Frequent (43%) apical meristem death shifts dominance to a nearby lateral branch in T. canadensis. (2) Weak apical control allows occasional shifts in dominance from the leader to a branch without meristem death (13 and 24% in T. heterophylla and T. canadensis, respectively, but none in T. mertensiana). These growth patterns contain elements of several tree architectural models but fit none well.
Effect of fatty acid salts on the growth of Botrytis cinerea
Authors: Puritch George S. , Tan W. C. , Hopkins J. C.
Published: April 2011

The toxicity of a range of potassium salts of fatty acids was bioassayed against Botrytis cinerea Pers. in agar culture. Growth inhibition increased with number of carbon atoms of the short chain fatty acid salts, reached a peak around C10 (caprate), and then declined. Salts of dicarboxylic acids were nontoxic at the highest levels tested, while the unsaturated C11:1, undecylenate, was as potent as caprate. Caprate at 0.1% inhibited growth of most B. cinerea isolates tested and prevented the remaining isolates from forming sclerotia. Conidial germination of all isolates was prevented by 0.05% caprate. Discrepancies in the literature regarding control of B. cinerea with soft soaps are suggested to be due to varying fatty acid composition of the soaps used.
Sulfur and molybdenum nutrition effects in tall fescue
Authors: Bush L. P. , Legget J. E. , King M. J. , Vincent J. E.
Published: April 2011

Tall fescue (Festuca arundinacea Schreb.) seedlings were grown in an intermittently irrigated gravel culture system in the greenhouse. Nutrient molybdate levels were 0, 0.1, or 0.21 μequiv./L with sulfate levels of 0 to 1.0 mequiv./L. Leaf tissue was harvested 28, 42, and 49 days after seeding. Molybdenum content of leaf tissue increased with increased solution Mo concentration. Increased solution SO42− levels increased tissue S and nitrate reductase activity (NRA), but decreased tissue Mo and NO3− content. When low tissue S was limiting NRA, and when Mo and NO3− were available, NRA was not increased by 2- to 4-h incubations of leaf tissue in SO42− solution. The MoO42− × SO42− interaction for tissue Mo concentration was significant and the effect of SO42− was relatively greater in the presence of Mo than in the absence of Mo.99Mo root uptake studies indicated the first increment of SO42− added to nutrient solution results in the greatest reduction in Mo accumulation. The data indicated that the greatest effect of SO42− on leaf Mo levels occurred during the absorption process with small reduction of Mo translocated from root to leaf tissue.
A numerical analysis of major groupings in Medicago employing traditionally used characters
Authors: Small Ernest
Published: April 2011

Numerical taxonomic analyses (particularly agglomerative clustering and ordination) were conducted on 55 species of Medicago, using 75 mostly vegetative and fruiting characters. The material studied represents all conservatively accepted species of the genus, as well as 14 "problematical" species of which many are often considered to belong to the genus Trigonella, rather than to Medicago. Although the characters employed are substantially the same as those used by recent monographers who evaluated the genus by traditional subjective procedures, the present numerical examination suggests many relationships not previously appreciated.As a result of the analyses, it was judged appropriate to recognize 12 groupings. These are group 1: M. sativa (alfalfa) and 11 allied species; group 2: M. lupulina and M. secundiflora; group 3: eight problematical species which have troubled taxonomists with respect to whether they should be placed in Medicago or Trigonella; groups 4–8: each made up of a single divergent species, respectively: M. carstiensis, M. radiata, M. orbicularis, M. heyniana, and M. arborea; groups 9–12 four subgroupings of a larger group of 28 annual species. In the main, the composition of the seven polytypic groups is similar to those of taxa accepted by recent monographers, although some realignments of particular species are suggested by the present study. Groups 1 and 2 are much more similar to each other than indicated in recent treatments. Medicago arborea was discovered to be much more dissimilar to all other species examined than thought previously. Medicago hybrida of group 1 was found to be a "master link" between species traditionally placed in Medicago, and many placed in Trigonella (group 3).The 12 groupings in turn fall into three assemblages that could be recognized as subgenera, or even as genera. These are A: groups 1, 2, 9, 10, 11, and 12; B: groups 3–7, inclusive; and C: M. arborea. Further research is suggested before formal categorization is undertaken.
The taxonomic value of floral characters in tribe Trigonelleae (Leguminosae), with special reference to Medicago
Authors: Small Ernest , Crompton C. W. , Brookes Brenda S.
Published: April 2011

The legume tribe Trigonelleae comprises Medicago (with M. arborea sometimes segregated as the monotypic genus Rhodusia), Melilotus, Trigonella, and the monotypic Factorovskya. The wisdom of segregating the two monotypic genera may be questioned, and many species have been claimed to represent intergrading variation between Medicago and either Melilotus or Trigonella, or between the latter pair. Previous morphological studies have not provided a satisfactory means of resolving generic delimitation in the Trigonelleae. In the present investigation numerical taxonomic analysis (agglomerative clustering and ordination) of floral characters indicated that Medicago, Melilotus, and Trigonella could be distinguished on the basis of combinations of floral attributes, although no single characteristic was capable of separating them completely. Trigonella section Bucerates proved to be quite distinctive from the remaining species of Trigonella examined. Limited evidence was found for segregating Medicago arborea as a monotypic genus. Factorovskya aschersoniana proved distinctive, but its relationships remain enigmatic. Discriminant analysis was employed to test the affinities of "problematical" species allegedly intermediate between Medicago, Trigonella, and Melilotus. Most of the putatively intermediate species proved to be much closer to one of the genera than to the others. A syndrome of morphological features was discovered to separate the Trigonelleae into two classes of plants, the one group including Medicago, Factorovskya, and Trigonella section Bucerates, and the other comprising Melilotus and the remaining examined species of Trigonella. The former group contrasts with the latter by possessing interlocking wing and keel petals, relatively less apical fusion of the keel petals, and relatively well-developed wing petal horns; and by having a greater frequency of species with dilated filaments, with staminal tubes which are conical at the apex rather than blunt, and with standard petals having more than three clusters of veins. The latter three differences, however, are less frequent between the two groups than the first three. The floral syndrome could reflect adaptation of the former group of plants to outcrossing (perhaps relictual adaptation in the inbreeding species) by means of the "tripping" mechanism which is well-known in Medicago. If so, the taxonomic significance of the syndrome is difficult to ascertain, as it may have developed independently in the different genera in which it occurs.
Organogenesis from cultured floral meristems of a male sterile tobacco hybrid
Authors: Hicks G. S. , Browne Robin , Sand S. A.
Published: April 2011

Very young floral meristems of a male-sterile tobacco hybrid were excised and cultured on Linsmaier and Skoog medium in continuous light. Basal medium was supplemented with kinetin and gibberellic acid, singly and in combinations. On medium with kinetin, all four types of floral organs arose in the normal sequence and pattern and the male sterile phenotype was expressed, GA3 suppressed the formation of these organs. The data show that male sterile organs may form and begin differentiation in vitro without direct influence from the plant.
Embryo and endosperm development in ovules of Papaver nudicaule after in vitro placental pollination
Authors: Olson A. Randall
Published: April 2011

Embryo development in Papaver nudicaule L. following in vitro placental pollination is of the Solanad type. Nuclear endosperm develops within 2–3 days and a filamentous proembryo is established. Endosperm cellularization is underway at the time the embryo proper begins to differentiate from the terminal and subterminal cells of the proembryo. After 6 days, the highly vacuolate endosperm is completely cellular; there is also a small globular embryo with no apparent endosperm degradation. Endosperm breakdown is initiated at the embryo–endosperm interface between 8 and 9 days postpollination. At day 10 of incubation, endosperm cytoplasm is dense and there is a large globular embryo. Substantial crenulation of the outer tangential wall of the protoderm occurs at this time. This phenomenon is presumably related to aspects of endosperm degradation. The primary tissue systems are discernable between 12 and 15 days when cotyledon initiation occurs. Seed development is complete within 27–28 days after placental pollination and the majority of the seeds germinate. This experimental approach provides a useful system for the study of a number of factors influencing seed ontogeny.
Anatomical effects of 2,4-DB on tomato internodes
Authors: Pizzolato Thompson Demetrio , Regehr David L.
Published: April 2011

Anatomical changes induced in the first internode by an aqueous spray of 4-(2,4-dichlorophenoxy)butyric acid (2,4-DB) (0.56 kg acid equivalent per hectare) confirmed the intolerance of tomato to this herbicide. Hypertrophy, hyperplasia, and plastid destruction occurred rapidly in most tissues. Many of the hyperplastic phloem cells differentiated into unusual supernumerary sieve tube members which were shorter and narrower than normal and which approximated the size of the co-differentiating companion cells. The supernumerary sieve tube members usually possessed several sieve plates and formed sieve tubes which did not follow a vertical course. Although obliteration of the supernumerary sieve tube members was stimulated, it was not associated with the formation of necrotic masses. Secondary wall formation was prevented in the protophloem fibers which became multiseptate following the stimulation of mitoses. The cambial initials were converted into a tissue of squat cells with little organization. Xylem which differentiated after treatment lost its normal heterogeneity and became a tissue of squat tracheary elements and parenchyma with scanty secondary thickening resembling wound xylem. Included phloem differentiated from parenchymatous masses within the xylem, and tylosis formation was stimulated. Pith volume increased by hypertrophy unaccompanied by hyperplasia. Although protophloem fibers did not mature in the internal phloem and limited hyperplasia and hypertrophy did occur, the internal phloem was much less affected than the external. Similarities between the anatomical effects of 2,4-DB and those reported for certain growth regulators and pathogens were noted.
Chronological analysis of cytological responses in powdery-mildewed barley leaves
Authors: KIta Nobuhiro , Toyoda Hideyoshi , Shishiyama Jiko
Published: April 2011

The cytological responses against Erysiphe graminis f.sp. hordei, race I, of barley epidermal cells from either highly resistant, resistant, or susceptible barley leaves were chronologically examined by light and fluorescent microscopy. Small papillae and aggregations of epidermal cytoplasm around the papillae were observed beneath appressorial tips of the fungus in all barley leaves 12–13 h after inoculation. In all barley leaves, if papillae increased in size and fluoresced 18 h after inoculation, the mass of aggregated cytoplasm disappeared and there was no fungal penetration. If successful penetration was accomplished 15 h after inoculation in highly resistant and resistant barley, the aggregated cytoplasm fluoresced and increased in amount and fluorescent intensity until 18 h. Eventually, all the cytoplasm of the affected epidermal cells became granulated and showed strong fluorescence 48 h after inoculation. In resistant barley, about 10% of conidia resulted in successful penetration of the nonfluorescent papillae and in small, fluorescent and distorted haustoria; in these cases, the fluorescence of the aggregate in the invaded epidermal cells was delayed. In resistant and susceptible barley, 30 and 70%, respectively of conidia yielded penetration hyphae which successfully penetrated the nonfluorescent papillae and resulted in normal haustoria 48 h after inoculation. Aggregation of epidermal cytoplasm around the penetration sites in these was also observed 15 h after inoculation but was not noticeably fluorescent and had dispersed 48 h after inoculation. These results suggest that in barley leaves compatibility or incompatibility is established by 15 h after inoculation, incompatibility being expressed by the aggregation and fluorescence of the epidermal cytoplasm.
Sexual reproduction of Pinus contorta. I. Pollen development, the pollination mechanism, and early ovule development
Authors: Owens John N. , Simpson Sheila J. , Molder Marje
Published: April 2011

Details of development and the phenology of postdormancy cone-bud development, microsporogenesis, pollen development, and pollination were similar for Pinus contorta var. contorta and var. latifolia growing near Victoria, B.C., but comparable stages of development for var. latifolia occurred about 1 month later near Prince George, B.C. Several developmental aspects were found which affect the reproductive potential of the species. Only 25% of the ovuliferous scales, mostly in the distal part of the cone, bear fertile ovules. Secretions formed on the ovules and micropylar arms which caused pollen to adhere to these surfaces. Pollination is by means of pollination drops which began to be exuded from the ovules about 2 weeks after the conelets began to emerge from their bud scales. Pollination drops were present within each conelet for 2 to 4 days. At that time conelets were most widely open. Pollination drops were then withdrawn as ovuliferous scales enlarged and sealed the conelets. Pollination drop exudation and withdrawal were affected by humidity and water stress within the tree. Cells lining the micropylar canal enlarged and sealed the micropyle after the conelet closed. Pollen settled into a pollen chamber in the nucellus tip where it germinated about 2 months after pollination. Ovules lacking germinating pollen aborted after megasporogenesis and before free nuclear division began. If many ovules aborted within a conelet, the conelet aborted before winter dormancy. Ovules began free nuclear female gametophyte development and pollen tubes extended into the nucellus before conelets stopped developing in mid-August.
Seasonal studies of vegetative buds of Helianthus tuberosus: concentration of nuclei in phase G1 during winter dormancy
Authors: Tepfer S. S. , Nougarède Arlette , Rondet Pierre
Published: April 2011

The following vegetative buds were studied at several developmental stages during the course of the year: from November through February dormant terminal buds of subterranean tubers; in March, newly reactivated buds of young shoots; in June, terminal buds of horizontal underground stolons that will form tubers; and in July, the terminal buds of erect aerial shoots. Microdensitometric studies of DNA levels after Feulgen staining showed that during the winter period of dormancy, from November through February, the temporary arrest of growth and morphogenesis is accompanied by a concentration of nuclei in phase G1 (2C level) of a diploid cycle for all nuclei in the terminal meristems of the tubers. In March, reactivation occurs uniformly throughout the meristem without any zonal differences. The G1 phase remains predominant in the cycle and mitotic activity increases uniformly. In the meristems of young underground stolons, beginning in the month of June, signs of concentration at the 2C level again are perceptible. The nuclei of the apical meristems of erect shoots are also diploid at 2C and 4C. In the very large nuclei in the central zone of the tunica where the mitotic index is very low, the distribution of DNA levels shows that nuclei are present at all phases of the cycle. These results are discussed and compared with other species in temporary dormancy and in regard to the concept of nonpolysomatic species.
A microautoradiographic study of 14C-labelled picloram distribution in soybean following root uptake
Authors: O'Donovan J. T. , Born W. H. Vanden
Published: April 2011

A microautoradiographic technique was evaluated with a view to determining the distribution of 14C-labelled picloram (4-amino-3,5,6-trichloropicolinic acid) in soybean (Glycine max (L.) Merr.) tissue following root uptake. The method involved embedding the tissue in a gelatin medium, rapidly freezing at −78 °C, sectioning in a cryostat at −20 °C, mounting the sections on cover slips coated with dry photographic emulsion in the dark, and photographically exposing the section to the emulsion at −25 °C. After processing, the cover slip was mounted with the autoradiograph above the section. Examination of microautoradiographs indicated that comparatively little radioactivity was retained in the roots and the amount that was present appeared to be associated mainly with the protoplasm of the root cortical cells. In the stem, radioactivity was present in both the xylem and phloem with comparatively little movement into the other tissues. Considerably more radioactivity was present in the younger apical leaves than in the older primary leaves. In the primary leaves the radioactivity was present only in the xylem whereas in the apical leaves it was present in both xylem and phloem.
Ultrastructural cell wall modifications in secondary xylem of American elm surviving the acute stage of Dutch elm disease: vessel members
Authors: Ouellette G. B.
Published: April 2011

Modified vessel wall layers and their ultrastructural characteristics in branches of artificially inoculated elm (Ulmus americana L.) trees surviving the acute disease stage and of naturally infected, chronically diseased trees are described. Walls of large early-wood vessels in zones where disease action was prevalent have a strong stain reaction and may be uniformly or locally three to four times thicker than normal.In smaller vessels (some including vessel tracheids), an extra lignified-like, often discontinuous layer may be present. This layer is generally demarcated from the normal by a dense band. Pit membranes and vessel end plates are likewise much thickened through the presence of an opaque material similar to that of the pit membrane. This material differs from that forming the coating layer which like tyloses is generally present inside the thickened or extra vessel wall layer.The possible significance of these observations, particularly in relation to disease development and tree resistance, is discussed.
Nitrate reduction and nitrogenase activity in excised corn roots
Authors: Pereira Pedro Antonio A. , Baldani José Ivo , Döbereiner Johanna , Neyra Carlos A.
Published: April 2011

Root segments obtained from field-grown corn plants were divided into small sections and assayed for acetylene (C2H2) reduction. After overnight preincubation, C2H2 reduction started immediately and linear rates were observed for several hours. Addition of NO3− (1 mM) delayed the start of C2H2 reduction but linear rates followed thereafter. A similar pattern was observed with excised roots inoculated with Azospirillum lipoferum.Addition of malate did not eliminate the NO3− effect. Inoculation with A. lipoferum resulted in relatively large rates of C2H2 reduction and a shorter lag than normal (4 to 8 h). A transient accumulation of NO2− accompanied the disappearance of NO3− and C2H2 reduction started only after all the NO2− had been reduced. A very sizable fraction of the reduced NO3− and NO2− was accounted for as N2O accumulation. Thus, the results provided support for the in situ operation of both N2 fixation and denitrification in A. lipoferum – corn root associations and it is proposed that mature corn roots are able to provide sufficient carbon to support both processes.
Isozyme variation between species and formae speciales of the genus Puccinia
Authors: Burdon J. J. , Marshall D. R.
Published: April 2011

Soluble proteins extracted from germinating urediniospores of 11 different species of Puccinia Pers. and from three formae spéciales of each of 3 of these species were subjected to starch gel electrophoresis and the resultant isozyme banding patterns compared.Isozyme patterns obtained for the 11 different species showed considerable differentiation between species, indicating that all species were distinct taxonomic entities. Patterns obtained for the formae speciales were, in general, much more similar and suggested relationships which agree with existing knowledge from taxonomic and fertility studies.
The taxonomy and distribution in eastern Canada of Polygonum arenastrum (4x = 40) and P. monspeliense (6x = 60), introduced members of the P. aviculare complex
Authors: McNeill J.
Published: April 2011

The introduced nonmaritime knotweeds have generally been regarded in North America as comprising a single species called P. aviculare L. In recent years cytological and morphological studies have suggested that at least two chromosome races are present and that certain morphological features are correlated with chromosome number. There have been, however, discrepancies in the reports of the distribution and relative abundance of the two races. Studies of the morphology and cytology of introduced knotweeds in eastern Canada confirm the existence of two groups that are recognizable at species rank, and establish that the most common knotweeds in open habitats, e. g., along roadsides and sidewalks, are tetraploid plants distinguishable from their hexaploid relatives by the relatively uniform size of their leaves, the short and narrow free portion of the perianth segments, and by one side of the fruit being very much narrower than the other two. These plants are referable to P. arenastrum Boreau. This species is compared with the heterophyllous hexaploid, usually called P. aviculare sensu stricto, or, if that is considered a nomen ambiguum, P. monspeliense Pers. A table of distinguishing features, illustrations of the two species, and maps of their distribution in eastern Canada are provided.
The effect of sulphate concentration on the uptake and incorporation of [35S]sulphate in Chondrus crispus
Authors: Jackson Susan G. , McCandless Esther L.
Published: April 2011

The effect of different sulphate concentrations (2 × 10−5 to 10−2 M) in the labelling medium on [35S]sulphate uptake and incorporation into National Research Council of Canada gametophytic strain T4 Chondrus crispus has been investigated. Sulphate uptake appears to be multiphasic as in higher plants. An apparent Km for sulphate uptake has been determined over the range of concentrations 10−4 to 10−2 M. Sulphate incorporation is also altered at different sulphate concentrations.
The germination of pollinium and the organization of germ furrow in some members of Asclepiadaceae
Authors: Sreedevi P. , Namboodiri A. N.
Published: April 2011

The asclepiad pollinium germinates through a specific region of the pollinial wall designated as the germ furrow. In untreated and ungerminated pollinia of Asclepias and Calotropis, the germ furrow is indistinguishable, by light microscopy, from the rest of the pollinial wall. Under the scanning electron microscope, however, the furrow appears as a discontinuous region marked by apertures of various sizes and shapes. On acetolysis, the wall materials that separate or surround the various openings on the germ furrow region dissolve and a characteristic narrow continuous opening (referred to as the slit) becomes visible.The position of the germ furrow, as revealed by the slit on acetolysis, is genus specific in all the 14 genera screened in this study. This specificity is maintained even in the relatively large pollinia of colchicine-induced tetraploids of Asclepias curassavica.By culturing sealed and cut pollinia and by standard bioassay methods it was shown that the polarity of pollen tubes within the pollinium is governed by the permeability of the germ-furrow region and not by the previously attributed factors such as innate orientation of pollen grains or chemotropic factors.
Membranous film on the developing apothecium of Sclerotinia sclerotiorum and its relationship to ascospore discharge
Authors: Tu J. C.
Published: April 2011

A membranous film (MF) covers the hymenium of the ascocarp of Sclerotinia sclerotiorum (Lib.) de Bary. The MF is reported for the first time using a scanning electron microscope. Development of the MF is described in relation to the morphogenesis of apothecia. At the early stage the MF develops centripetally from the edge of the hymenium adjoining the rim of the ascocarp. At the beginning of the intermediate stage, the surface of the hymenium is fully covered by the MF which has many small holes and a few fenestrations. The MF is thin and smooth at the center but thick and wavy near the margin of the ascocarpic disc. Since the MF ruptures at or just before the massive ascospore discharge which occurs at the intermediate stage, it may protect the developing asci from loss of moisture before the initial spore discharge.
A comparison of two techniques for growing minimally water-stressed plants
Authors: Hubick Kerry T. , Drakeford David R. , Reid David M.
Published: April 2011

Two watering systems used for growing minimally stressed plants are described. An aeroponics system, which relies on a mist of nutrient solution applied to roots without a root support medium, affords control over water availability and easy access to roots. A continuous circulation system, which constantly circulates nutrient medium, also provides control over water availability as well as control over pO2 and stress duration in flooded plants. A comparison is made of the growth characteristics of plants grown in the two systems with those grown by traditional watering methods. The significance of watering prehistory to stress physiology experiments is discussed.