THE CHEMICAL CONTROL OF WATER WEEDS IN THE GEZIRA AREA OF THE SUDAN

Chlorophenoxyacetate weed-killers have been tested for the control of aquatic weeds in the canals of the Sudan Gezira. Using water in tanks, it was shown that 10 parts per million of sodium 2-methyl-4-chlorophenoxyacetate (Methoxone) or of sodium 2:4-dichlorophenoxyacetate (Fernoxone) would kill most of the angiospermous water-weeds found in the Gezira area.
Small-scale field experiments, using channels of known water capacity, have shown that not only leaves and stems but also seeds and underground rhizomes were killed in treated stagnant water, provided that the weed-killers were applied as dusts. The water remained toxic to crop plants for approximately 7 weeks after treatment.
In a large-scale experiment in 1950, treating normal irrigation canals, temporary weed clearance was attained, re-infestation was delayed, and one major canal, 4.5 km. long, remained weed-free 12 months after treatment.     

Nebela tuberculata comb. nov. (Arcellinida), its History and Ultrastructure

SYNOPSIS. The name Nebela tuberculata comb. nov. is proposed for the testate ameba formerly known as Difflugia tuberculata (Wallich, 1864) Archer, 1867. The generic reassignment is based upon the test construction material which is shown, by electronmicrographs and X-ray diffraction, to be autogenous regular and irregular silicious rods. A brief history of the animal is recounted utilizing works of several authors who have encountered the ameba over the last century.     

The infrastructure of aesthetes in Tonicella marmorea (Polyplacophora; Ischnochitonina) and a new functional hypothesis

The valve surface morphology and aesthete ultrastructure of Tonicella marmorea is described. The possible functions of these very numerous organs are considered with particular reference to the ecological needs of the animal and their similarity to other invertebrate organs. A periostracum-secreting function is proposed as an alternative to the more commonly postulated light receptor theory.     

Association of a phytoplasma with a yellow leaf syndrome of sugarcane in Africa

Evidence is presented for the association of a phytoplasma, provisionally named sugarcane yellows phytoplasma (ScYP), in sugarcane affected by a yellow leaf syndrome. The phytoplasma was consistently detected in leaves of more than 40 varieties from eight African countries. It was present in all symptomatic as well as some asymptomatic field grown cane samples but not in plants grown from true seed, and it was also observed in phloem sieve tubes by transmission electron microscopy. Phytoplasma 16S rDNA was confirmed by PCR, and restriction fragment analysis using Rsal and Haelll confirmed that PCR-amplified products were of phytoplasma rather than of plant or of other pathogen origin. Sequences obtained from the intergenic spacer region, between the 16S and 23S rDNA genes, confirmed the identity of the phytoplasma as belonging to the western X group of phytoplasmas.     

Evidence for Genetic Change in the Antirrhinum Rust (Puccinia antirrhini)

The available data on the resistance of Antirrhinum majus L.to rust, Puccinia antirrhini Dietel and Holway, are reviewed.There is evidence for one or more genetic changes in the pathogen.In one instance it can be demonstrated that this change is likelyto have been by mutation. The chronology of the changes is:in the U.S.A., east of the Rockies between 1921 and 1935 andin California during 1936; in Europe between 1936 and 1954 andin Britain between 1958 and 1962. A virulent race was presentin Australia by 1954. Puccinia antirrhini Dietel and Holway, rust, Antirrhinum majus L., mutation, virulence, resistance     

Increased sensitivity in the measurement of ATP in freshwater samples with a comment on the adverse effect of membrane filtration

SUMMARY. Increased sensitivity in the determination of ATP in fresh water and sediment samples was achieved by incorporating protein, EDTA and extra luciferin in the reconstruction of the firefly lantern preparation. Maximum recovery was only obtained when samples were extracted in actively boiling Tris buffer. The method was sufficiently sensitive for the determination of ATP in 1 ml water samples injected directly into the boiling buffer. Concentration of water samples on membrane filters, even volumes as small as 1 ml, caused a significant drop in the ATP recovered. This was thought to be due, at least in part, to cell lysis and the concentration of interfering detrital material on the membrane. Further interference was observed when sediment samples were analysed. This was only partly overcome by dilution of the sample and the importance of the inclusion of internal standards (bacterial cultures) is emphasized.     

A Study of Fatty Acids as a Taxonomic Tool for Dermatophyte Fungi

The fatty acid composition of 64 strains from 15 species of dermatophyte fungi was studied by gas-liquid chromatography. The percentage amounts of palmitic, palmitoleic, stearic, oleic and linoleic acids were measured. These proved to be very similar for all species, with considerable intraspecific variation. As a group, Epidermophyton floccosum strains could be distinguished but individual strains could not be assigned reliably to any species or genus. No significant changes due to age or formaldehyde treatment were noted.     

The relationship between wound-induced proteinase inhibitors and hydraulic signals in tomato seedlings

Localized wounding is known to induce systemic proteinase inhibitors (PI) in seedlings of tomato (Lycopersicon esculentum L.). Inhibitors of elastase (EC 3.4.21.36) were shown here to be among those systemically induced by wounding, and a simple rapid assay for PI based on elastase was developed. Using this assay, the nature of the systemic signalling system (‘PIIF’) was investigated. Hydraulic signals were shown to be induced in tomato by localized wounds. These signals travelled throughout the plant well within the lag time before appearance of systemic wound-induced PI. A number of correlations were drawn between the occurrence of the hydraulic signals and induction of systemic PI, suggesting that hydraulic signals might be the PIIF, or a component of it. It was shown that systemic hydraulic signals could be triggered, without significant wounding, by excision of a single leaflet through the submerged petiole. These hydraulic signals were similar in both kinetics and magnitude to those induced by localized wounding. However, they did not induce systemic PI. In addition, it was shown that systemic events almost as rapid as wound-induced hydraulic signals could be induced without wounding, under certain environmental conditions. This indicates that rapid hydraulic signals do not provide a specific signal of wounding. These findings demonstrate that hydraulic signals per se are not the PIIF.     

Habitat Value of Intensively Established Pine Plantations for Northern Bobwhite

ABSTRACT Declines in northern bobwhite (Colinus virginianus; bobwhite) populations in the southeastern United States may be partially attributable to loss of early successional plant cover associated with greater use of herbicides in forest management. We tested effects of 5 levels of operational plantation establishment intensity on vegetation communities and structure important for bobwhite in 1–5-year-old loblolly pine (Pinus taeda) plantations (n = 4) in the Outer Coastal Plain Mixed Forest of Mississippi. We compared results with values reported in the literature to calculate usable space for winter food, loafing, nesting, and brood-rearing at 2 levels of spatial resolution. Treatments (k = 5) reflected a range of management intensities and were combinations of mechanical site preparation, chemical site preparation (CSP), and herbaceous weed control (HWC). Coverage of winter food plants in the least intensive treatment was more than double that in the most intensive; however, differences in usable space of winter food cover were negligible due to improved accessibility in more intensive treatments. Although CSP reduced coverage of nonpine woody plants across all years, loafing cover reached adequate levels by year 3 in all treatments. Usable nesting cover was <4% across all years and treatments and was nearly eliminated by the reduction in herbaceous cover and visual screening cover following broadcast HWC. Optimal brood-rearing habitat was virtually absent in all treatments and years due to the lack of conjoint occurrence of bare ground and forb canopy. Although bobwhite habitat may have been promoted by formerly widespread plantation establishment methods that involved wide-scale soil disturbance, those established using newer methods with less soil disturbance are likely inadequate for most bobwhite habitat requirements. Efforts to provide bobwhite habitat in plantation-dominated landscapes may have to rely on management of thinned mid-rotation stands and permanent landscape features such as rights-of-way. The value of young plantations for bobwhite may be increased by reducing management intensity or increasing spacing between planting rows, thus increasing time before crown closure and providing opportunity for understory manipulations.