The Management of Small Private Woodlands with Special Reference to the Problems of Regeneration and Rotation

The importance of small woodland holdings of 500 acres and less,particularly of those under 100 acres, is stressed. The latter,which are largely unmanaged, add up to one-quarter of the totalarea of private woodland in Great Britain. A more dynamic policy,on the European pattern, is needed. This will necessitate moretrained supervision and more financial aid. Three examples ofmanagement intensity are outlined.     

Expression of Occludin in Testis and Epididymis of Wild Rabbits, Lepus sinensis coreanus

Tight junctions (TJs) in inter-Sertoli junctional areas and epididymal epithelia build up the blood–testis barrier (BTB) and the blood–epididymal barrier (BEB), respectively. In this study, the expression of occludin, an integral member of the TJs, was examined in testis and different regions of epididymis of Lepus sinensis coreanus , an Korean wild rabbit species. In testis, intense occludin immunoreactivity was found in the basally located inter-Sertoli junctional area together with diffused immunoreactivity of occludin in the cytoplasm of Sertoli cells. It can be suggested that occludin is one of the robust elements of BTB in seminiferous tubules of rabbit testis. In proximal and distal caput epididymis, occludin immunoreactivity was found in the lateral as well as apical contacts of epithelial cells. In corpus epididymis, intense occludin immunoreactivity was found in the basolateral as well as apical contacts of epithelial cells together with cytoplasmic signal. In cauda epididymis, occludin immunoreactivity in luminal epithelia was relatively strong but largely found in the cytoplasm. This suggests that intriguing regulatory mechanisms differentially recruit occludin to the TJ in the different regions of epididymal epithelia. The differences in the subcellular localization as well as expression levels of occludin among the epididymal segments may reflect differential paracellular permeability of epithelia along the epididymal tubules and be correlated with sperm maturation in rabbit. In Western blot, a major form of occludin was MW 62 kDa together with small fragments of MW 34–39 kDa in testis and epididymis, suggesting the peptide cleavage of occludin. This is the first report on the molecular nature of TJs in a wild rabbit testis and epididymis.     

Melaena associated with dexamethasone therapy in the dog

A retrospective study of seventeen cases of canine melaena incriminated a mean daily dosage of 3.6 mg/kg (range 1.3–13.8 mg/kg) of dexamethasone. All dogs were afflicted with some central nervous system disorder with intervertebral disc disease present in twelve of the cases. Ten of the the seventeen subjects had concurrently received ampicillin therapy. Causation was linked by the previous finding that ACTH and cortisone impede both gastric epithelial renewal and surface mucus formation.     

NASAL SALT EXCRETION AND THE POSSIBLE FUNCTION OF THE CLOACA IN WATER CONSERVATION

Secretion of concentrated salt solutions from the nasal region was observed in several terrestrial birds and reptiles. In the secreted fluid potassium usually exceeded sodium concentrations, with chloride and bicarbonate as the major anions. It is suggested that the extrarenal excretion of salts is related to the reabsorption of water in the cloaca, that it is necessary for the production of urine with a particularly low water content, and perhaps was prerequisite for the evolution of efficient cloacal water conservation.     

On the relation between number-size distributions and the fractal dimension of aggregates

Number-size distributions (i.e. particle- and aggregate-size distributions) have historically been used as indicators of soil structure, and recent work has aimed to quantify this link using fractals to model the soil fabric. This interpretation of number-size distributions is evaluated, and it is shown that a number-size relation described by a power law does not in itself imply fractal structure as suggested, and a counter example is presented. Where fractal structure is assumed, it is shown that the power-law exponent, φ, describing the number-size distribution cannot be interpreted as the mass-fractal dimension, D_M, of the aggregate. If the probability of fragmentation is independent of fragment diameter, then the exponent may be identified with the boundary dimension, D_B, of the original matrix. If, however, as is likely, this probability is scale-dependent, then φ may over- or under-estimate the boundary dimension depending on whether the fragmentation probability increases or decreases with fragment size. The significance of these conclusions is discussed in terms of the interpretation of number-size distributions, and alternative methods for quantifying and interpreting soil structure are evaluated.     

Incorporating an environmental stock–recruitment relationship in the assessment of Pacific cod (Gadus macrocephalus)

The robustness of a previously described environmentally mediated stock–recruitment relationship for Pacific cod in Hecate Strait, BC, Canada was tested with 10 yr of additional data. The original analysis tested several alternative hypotheses and concluded that water transport through Hecate Strait, as indicated by sea level height, coupled with cod spawning biomass formed the best model. The present analysis indicates the relationship held through the 1990s. The implications of variation in sea level on stock production were investigated with a delay‐difference stock production model that included an environmentally mediated stock–recruitment relationship. The model predicted that the maximum fishery yield would vary between 1750 and 3670 t yr^?1 over the observed range of sea level height, and the estimated unsustainable fishing mortality during periods of low productivity would be only 0.5 times that in periods of high productivity.     

The fractal structure of soil aggregates: its measurement and interpretation

The theory of fractal geometry is presented with reference to soil structure. Recent work on relating fractal structure to pore structure in soils is reviewed. It is suggested that the connection made in previous work between the fractal dimension and soil moisture retention curves is based on simplified assumptions that complicate the interpretation of results. A simple method for estimating the fractal dimension, D, of natural aggregates which circumvents some of these assumptions is presented. Preliminary results of aggregates from soils under different management systems show that, for the soils examined, D ranged from 2.75 to 2.93. The use of D to quantify heterogeneity in soil is explored.     

DIFFUSION COEFFICIENTS FOR TWO TRIAZINE HERBICIDES IN SIX SOILS

Summary. Diffusion of the triazine herbicides propazine and prometryne was studied in six soils. Apparent diffusion coefficients were calculated from the distribution of herbicide in a column of soil after diffusion from one half of the column for a known time. The magnitude of the diffusion coefficients varied from 1·5 × 10^?9 cm² sec^?1 for propazine in a sandy soil to 3·1 × 10^?9 cm² sec^?1 for prometryne in an organic soil. Under the conditions of measurement, the diffusion coefficients decreased in proportion to the extent of adsorption. Calculations were made to determine over what distances diffusion could be of importance in the movement of these herbicides. Coefficients de diffusion de deux triazines herbicides dans six sols Résumé. La diffusion de deux triazines herbicides, la propazine et la prometryne a étéétudiée dans six sols. Les coefficients de diffusion apparente furent calculés selon la distribution de I'herbicide dans une colonne de sol, aprés diffusion à partir de la moitié de la colonne pendant un temps connu. Les coefficients de diffusion variérent de 1,5 × 10^?7cm² see^?1 pour la propazine dans un sol sableux, á 3,1 × 10^?9 cm² sec^?2 pour la prométryne dans un sol organique. Dans les conditions oú les mesures furent effectuées, les coefficients de diffusion diminuérent en proportion de 1′étendue de l'adsorption. Des calculs ont été effectués pour detérminer au-delá de quelles distances la diffusion pouvait presenter une importance dans le mouvement de ces herbicides. Difftisions-KoeffizienUnfur zwei Trtazin-Deriaate in sechs Böden Zusammenfassung. Die Diffusion der beiden Triazin-Derivate Propazin und Prometryn wurde in sechs Böden untersucht. Die Diffusions-Koeffizienten wurden aus der Verteilung des Herbizids in einer Bodensaule nach Diffusion aus der einen Säulenhalfte in einer bestimmten Zeit errechnet. Die Grösse der Diffusions-Koeffizienten variierte von 1,5 × 10^?7 cm²× sec^?1 bei Propazin in einem Sandboden bis 3,1 × 10^?9 cm²× sec^?1 bei Prometryn in einem Humus-Boden. Unter den gegebenen Versuchsbedingungen nahmen die Diffusions-Koeffizienten in Abhángigkeit von der Stärke der Adsorption ab, Es wurden Berechnungen darüber angestellt, über welche Entfernungcn die Diffusion dieser Herbizide im Boden eine Rolle spielen könnte.