Breeding biology of the Barn Owl Tyto alba in central Mali

Data were obtained on 178 clutches of African Barn Owls in central Mali from four breeding seasons during 1979–1983. Significantly more clutches were laid in 1979–1980 and significantly fewer in 1980– 1981 than the average for the 4 years and there were significantly more clutches laid in the middle period of the annual breeding season. The egg volume was significantly smaller at the beginning of the breeding season and significantly larger in the middle than the overall mean with eggs of second clutches being larger than those of first clutches. The clutch size was 605 eggs of which 479 hatched. The number of young fledged per successful nest was 319 and was 1 83 for all nesting attempts. The month was the only variable shown to affect significantly the clutch size, eggs hatched and fledging rate, the highest success rates being associated with the middle of the breeding period. The average interval between the hatching of eggs was 2–31 days. Survival rates (47'1%) to fledging were significantly affected by year (1981–1982 being the least) and month (mid-season birds the best). The order of hatching significantly affected age at death or disappearance, the first-hatched birds surviving the longest. The year significantly affected age at fledging, the young from the year in which most clutches were laid leaving the nest at the youngest age and those associated with the year having the least number of clutches remaining in the nest the longest. The month of hatching also affected fledging age, birds at the extremes of the breeding season fledging at older ages. The discussion compares these data with those from elsewhere.     

Ultrastructural features of chilling-injury in Episcia reptans

Abstract. Chilling the leaves of the extremely chill-sensitive plant Episcia reptans for only a few hours at 5°C causes ultrastructural changes such as swelling and disorganization of chloroplasts and mitochondria, and vesiculation of cytoplasmic membranes. Rewarming plants after 5–6 h chilling causes further deterioration in chloroplast and mitochondrial structure and the appearance of fibrous material in the cytoplasm of epidermal, mesophyll and vascular cells. The nature of the deposit is not known but it may be the cause of the rapid development of chilling-injury on return of plants to the warmth.     

Control of Drag-Line Spinning in Certain Spiders

Araneomorph spiders from many different families show some regionaldifferentiation of the duct which carries the drag-line silk,but only in the orb-web spiders is there a well-defined controlvalve. This valve, and its associated muscles, is described for Araneusdiadematus (Argiopidae), an ecribellate spider, and is comparedwith that found in Uloborus octonarius (Uloboridae), a cribellatespider. It is suggested that the remarkable similarity betweenthe valves in these two groups implies evolutionary convergence. Some evidence is presented which suggests that variations inbody pressure are used to control the drag-line spinning, atleast in the more primitive Araneomorphs.     

Confirmation by Chemical Synthesis of the Structure of 4-Ipomeanol,a Lung-toxic Metabolite of the Sweet Potato, <Emphasis Type="Italic">Ipomoea batatas</Emphasis>

WE have described the lung and liver toxicity of mould-damaged sweet potatoes and characterized briefly some abnormal metabolites responsible for these phenomena^1–4. The respiratory tract toxin, 4-ipomeanol (1-[3-furyl]-4-hydroxy-1-pentanone) (VI), may be responsible for the typical lung oedema of cattle that are fed mouldy sweet potatoes as well as a similar pathological state in mice fed or injected with the pure compound.     

Studies on the Growth in Culture of Plant Cells: XII. A VERSATILE SYSTEM FOR THE LARGE SCALE BATCH OR CONTINUOUS CULTURE OF PLANT CELL SUSPENSIONS

A versatile large-scale batch culture unit has been developedfor the growth of plant cell suspension cultures. This unithas been modified to permit of intermittent or continuous renewalof culture medium and, in a modified form, incorporated intoopen continuous culture systems of the chemostat and turbidostattype. A fully automatic culture sampler has been incorporatedinto the basic culture unit. The culture systems described havebeen successfully operated using a cell suspension derived fromAcer pseudoplatanus and results are presented demonstratingsynchronous growth in batch culture, prolonged logarithmic increassein cell number under conditions of high aeration and culturemedium renewal, and steady states of growth resulting from automaticregulation of the optical density of the cell suspension andfrom fixed rates of displacement of cell suspension by new medium.The potentialities of the culture systems are discussed in thelight of the experimental results presented.     

Physiological and Ecological Studies in the Analysis of Plant Environment: VI. The Constancy for Different Species of a Logarithmic Relationship between Net Assimilation Rate and Light Intensity and its Ecological Significance

In this further study of light as an environmental factor theeffects of shading on the growth of Helianthus annuus, Fagopyrumesculentum, Trifolium subterraneum, Tropaeolum majus, Lycopersicumesculentum, Vicia faba, Pisum sativum, Hordeum vulgare, Solanumdulcamara, and Geum urbanum have been investigated. It has been established that the reductions in the net assimilationcaused by shading are similar for all ten species. The net assimilationrate during the season of active growth is linearly relatedto the logarithm of the light intensity. When similar experimentsare conducted late in the autumn and the relative growth rateis very low, the logarithmic relationship no longer holds. From the data it is possible to obtain precise estimates ofthe compensation point. The mean values of the compensationpoint ranged from 0·06 to 0·09 of daylight foreight species, while for V. faba and H. vulgare somewhat higherfigures were obtained—0·14 and 0·18 of daylight. Flctuations in the net assimilation rate in full daylight showedno correlation with variations in the value of the compensationpoint. From these results it is concluded that species cannot be groupedinto ‘sun’ or ‘shade’ plants, eitheron the basis of differences in the value of the compensationpoint or on the grounds that there are large variations in theeffects of shading on net assimilation rate.     

Verticillium wilt of the hop: fluctuating outbreaks in wilt-resistant varieties

New varieties of hop resistant to progressive Verticillium wilt are now widely grown and generally give acceptable disease control in commercial plantations, but on a few farms their normal high level of resistance is not maintained. The incidence of wilt on one such farm is analysed in detail. At this site wilt was not directly associated with plant death, as it is in a sensitive variety. In a discussion on etiological aspects of wilt in resistant varieties it is concluded that while seasonal fluctuations in disease incidence are influenced by climatic conditions, high mean incidence is related to undefined, intrinsic soil factors. Attention is directed to the analogous forms of disease resulting from host/pathogen interactions in which resistance and virulence are either both high or both low.     

Patterns of Tracheary Differentiation in Lettuce Pith Explants: Positional Control and Temperature Effects

When lettuce pith explants were cultured for 14 d on a xylogenicmedium, tracheary elements differentiated in greatest numbersbetween 25 and 30 °C. Numbers were depressed at lower temperaturesby slower development and at higher temperatures by adverseprocesses. The data did not support previous suggestions ofa great stimulation of xylogenesis above 30 °C and of aspecial sensitivity to low temperatures. Tracheary elements differentiated in various spatial patterns:as clumps in the peripheral callus, as strands which extendedradially and longitudinally from some of these clumps, as individuallarge tracheids especially at the more extreme temperatures,and as short strands associated with nodules and roots thatformed at favourable temperatures. We suggest that indoleacetic acid (IAA) has various roles inthe positional control of these tracheary patterns: (1) IAAdestruction at the explant surface leads to concentration gradientsthat inhibit tracheary induction close to the surface; (2) IAAtransport from the source in the culture medium to sinks especiallyat the explant surface, coupled with autocatalytic flow facilitation,leads to canalization along pathways that become meristematicand then trachcary strands; (3) the IAA flux (and associatedproton flux) along these pathways tend to orient cortical microtubulesat right angles to the flow, by some mechanism as yet unknown,and hence to control the orientation of tracheary element elongationand secondary wall banding. These suggestions, supported bymorphometric studies of tracheary element dimensions and orientations,and by experiments with localized IAA application, lead to ageneral interpretation of the development of polarity in plants. IAA, Lactuca sativa, lettuce, pith explants, positional control, temperature effects, tracheary element differentiation     

Effects of Auxin Concentration on the Dimensions and Patterns of Tracheary Elements Differentiating in Pith Explants

The optimal concentration of IAA (0.03 mM) for tracheary elementdifferentiation in lettuce pith explants was about ten timesgreater than the optimal concentration for callus proliferation.Related to this, the mean volume per tracheary element increasedwith increasing IAA concentration, 18-fold between 0.001 mMand 0.3 mM IAA. At the highest concentrations, some pith cellsappeared to differentiate directly into tracheary elements,without cell division, resulting in especially large trachearyelements. Tracheary strands developed at intermediate concentrationsof IAA, and led to a small increase in the mean length/breadthratio of tracheary elements. For tracheary elements differentiating from stem cambial derivatives,a reassessment of previous studies indicates that increase inauxin concentration brings greater tracheary element size atconcentrations up to the 0.03 mM optimum. Above this optimum,however, further increase in auxin concentration brings progressivelysmaller tracheary elements, as the high auxin curtails enlargementof the differentiating cells. This contrasts with the pith explants,in which tracheary element size increases with IAA concentrationmost markedly above the optimum concentration. The interpretationof these relations requires an understanding of the effectsof auxin concentration on interacting quantities such as initialsize of cells, rate of enlargement, and rate of differentiation. Lactuca sativa, lettuce, IAA concentration, pith explants, tracheary element dimensions     

The Foraging Ecology of Migratory Shorebirds in Marine Soft-sediment Communities: The Effects of Episodic Predation on Prey Populations

This paper explores the extent to which life histories of infaunalprey have been molded and maintained by predation. It is arguedsuch relationships should be most evident for episodic predation,where the predation is predictable, intense and short-lived.Migratory shorebirds are used herein as model episodic predators.Four stop-over areas in North America, for which experimentaldata exist, are compared. Evidence exists that SemipalmatedSandpipers in the upper Bay of Fundy maintain the observed lifehistory of their major prey, the amphipod Corophium volutator.In southeastern Massachusetts, shorebirds significantly reducethe abundance of their prey but in a frequency-dependent fashion,precluding life history responses of the prey. For Grays Harbor,Washington and Delaware Bay, there is no detectable effect ofshorebird predation on the infauna. In three of the four studies,there is no apparent effect of early shorebird migrants in significantlyincreasing the required stop-over of later migrants by depressionof prey densities. The data support the characterization ofsoft-sediment communities as loosely organized assemblages whosespecific constitution is determined more by ecological combiningability than by specific evolutionary responses to associatedspecies.