Citrus in West Africa,with special reference to Liberia

Although ample evidence has been gathered to show that citrus can be grown in many parts of West Africa, relatively little of it is cultivated there at present because of difficulties in transportation and communication. Shifting agriculture is still characteristic of the region, and tradition makes the growing of any introduced tree crop difficult.     

Ethnogenesis of South Asia with special reference to India

An attempt has been made to illustrate the quite complicated process of ethnogenesis in South Asia from the viewpoint of physical anthropology. The numerous invading waves which reached the Indian subcontinent from the northwest played an important role in this process. Most important for the ethnogenesis of South Asia was the invasion of Indo-Aryan groups in the middle of the 2nd millenium B.C. known from historical sources. In large parts of the Indo-Pakistan region they assimilated the aboriginal population in ethnic, cultural and linguistic respects in the course of time. Furthermore, the ethnogenesis of the Indian region is determined by the caste system of Hinduism which, however, is not as rigid as generally assumed. There are numerous evidences that since more than 2000 years a slow but steady process of assimilation and integration of tribal groups, living in the forest areas of Central India, into the Hindu caste system took place, a process which is still going on. It is intended to demonstrate to what degree the ethnogenetic processes in South Asia, known from prehistoric and historical sources, can be traced in human skeletal findings of different time periods as well as in the anthropological structure of the living population. Finally, hypotheses and theories, especially those of Risley and von Eickstedt are discussed, who attempted to interpret the great variability of anthropological and morphological traits in the Indian subcontinent by taking into consideration the existence of different old population substrata and their mixing and assimilation.     

The characteristics of certain varieties of potato with special reference to their suitability for drying

There is considerable varietal variation in the characteristics of the potato. The characteristics of any one variety of potato may be very greatly modified by environmental conditions. Rainfall and percentage dry matter may be inversely correlated, as may rainfall and yield in localities with a medium or high precipitation. There is an apparent correlation between time of maturity, percentage dry matter, and texture when cooked, late varieties having a higher percentage dry matter and a more floury texture than early varieties. It is a fundamental requirement of potatoes for drying purposes that they should not discolour on cooking. In addition the texture of the cooked potato should be suitable for the method of drying employed, and for the type of reconstituted product desired, and the percentage dry matter should be as high as is compatible with the foregoing conditions.     

Phylogeny of certain biocontrol agents with special reference to nematophagous fungi based on RAPd

A number of phylogenetic studies have been carried out on biocontrol agents having similar biological control activity. However, no work has been carried out to determine the phylogenetic relationship amongst various groups of biological control agents with varied biocontrol properties. Our aim was to derive a phylogenetic relationship between diverse biocontrol agents belonging to the deuteromycetes and determine its correlation with their spore morphology and their biocontrol activity. RAPD was used to assess genomic variability in fungi used as biological control agents which included ten isolates of nematophagous fungi such as Arthrobotrys sp., Duddingtonia sp., Paecilomyces sp. and Verticillium sp., along with two isolates of fungal biocontrol agents such as Trichoderma sp. and two isolates of entomopathogenic fungi including Beauveria sp. A plant pathogenic fungus, Verticillium alboatrum was also included to increase the diversity of Deuteromycetes used. A similarity matrix was created using Jaccard's similarity coefficient & clustering was done using unweighted pair group arithmetic mean method (UPGMA). The final dendogram was created using a combination of two programs, Freetree and TreeExplorer. The phylogenetic tree constructed from the RAPD data showed marked genetic variability among different strains of the same species. The spore morphologies of all these fungi were also studied. The phylogenetic pattern could be correlated with the conidial and conidiophore morphology, a criterion commonly used for the classification of fungi in general and Deuteromycetes in particular. Interestingly, the inferred phylogeny showed no significant grouping based on either their biological control properties or the trapping structures amongst the nematophagous fungi as reported earlier by other workers. The phylogenetic pattern was also similar to the tree obtained by comparing the 18S rRNA sequences from the database. The result clearly indicates that the classical method of classification of these deuteromycete members on the basis of their spore morphology is reliable and could be used for identification of these fungi at species level. The PCR fragment pattern polymorphism exhibited by the various species of a genus and different strains of a species indicates that construction of probes from one or more of these fragments will prove to be useful as a rapid tool for identification of species and strains of nematophagous fungi in future.     

The effects of land use on freshwater fish in South Africa,with particular reference to Natal

Summary Freshwater fish live in an environment that is liable to modification by human activities. Instability of South African rivers makes them particularly vulnerable to changes brought about by settlement of the land.Indigenous species number 89, of which 47 belong to the Cyprinidae; eight exotic species are also established in South African natural fresh waters. These fish vary considerably in their tolerances, but the habitat of most species has undergone deterioration as a result of agriculture, pollution or water abstraction.Agricultural land-use effects are mainly (i) an increase in soil erosion leading to higher silt loads, which adversely affect the habitat, both for fish and for fish food and (ii) reduced low flows and higher flood-crests.Domestic and industrial pollution are liable to have disastrous effects, but fortunately serious pollution has so far been of localized occurrence and has affected mainly smaller streams.Dam building has had a major impact on fish populations. Below the dams some natural habitats have been impaired and migratory movements curtailed. The impoundments themselves on the other hand, have provided an enlarged and stable environment leading to population increases. Many of the larger impoundments carry indigenous fish, other dams have provided a habitat for exotic species.Progressive development of the land makes changes in natural waterways inevitable but conservation of mountain catchments and the building of dams are likely to prevent decimation of the more economically important species. Special steps may be needed to maintain the habitats of certain rare endemic species.Progressive development of the land makes changes in natural waterways inevitable but conservation of mountain catchments and the building of dams are likely to prevent decimation of the more economically important species. Special steps may be needed to maintain the habitats of certain rare endemic species.

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Zusammenfassung Süwasserfische leben in einer Umwelt, die infolge menschlicher Tätigkeiten leicht geändert werden kann. Die südafrikanischen Flüsse sind im allgemeinen unbeständig und daher besonders empfindlich gegen die Veränderungen, die die Besiedlung des Landes mit sich bringt.Es gibt 89 einheimische Fischarten, wovon 47 zu den Cypriniden gehören; 8 exotische Arten sind auch in natürlichen Gewässern eingebürgert worden. Trotz der ganz verschiedenen Toleranzen dieser Arten haben die Umweltsbedingungen für die meisten jedoch infolge von Landwirtschaft, Wasserverunreinigung oder Wasserabstraktion eine Verschlechterung erfahren.Die hauptsächlichsten Folgen landwirtschaftlicher Bodennutzung sind (i) eine Zunahme der Bodenerosion und die damit verbundene Verschlammung, die auf das Habitat ungünstig einwirkt, sowohl für die Fische als auch für das Fischfutter, und (ii) verringerter Durchflu bei niedrigem Wasserstand und höhere Wasserstände zu Flutzeiten.Die Verunreinigung, sei sie haushältlicher oder industrieller Herkunft, hat gewöhnlich katastrophale Auswirkungen. Glücklicherweise sind ernsthafte Verunreinigungen bis jetzt örtlich beschränkt geblieben und haben hauptsächlich kleinere Flüsse betroffen.Der Bau von Talsperren hat einen besonderen Einflu auf die Fischpopulationen gehabt. Unterhalb der Talsperren sind die Lebensbedingugen zu Ungunsten einiger Arten geändert worden, und Zugbewegungen sind eingeschränkt worden. Die entstandenen Stauseen an sich haben anderseits eine vergröerter und stabile Umgebung beschafft, die zu Populationszunahmen führte. Viele der gröeren Staussen sind von einheimischen Fischen bevölkert, andere beschaffen Lebensbedingugen für exotische Arten.Die fortschreitende Entwicklung der Bodennutzung bringt unvermeidliche Veränderungen der natürlichen Wasserwege mit sich. Der Schutz der Wasserauffangsgebiete in den Bergen und der Bau von Talsperren werden jedoch wahrscheinlich das Fortbestehen der wirtschaftlich wichtigen Fischarten sichern. Besondere Vorkehrungen mögen jedoch nötig sein, um die Lebensbedingugen seltener einheimischer Arten zu erhalten.

     

Mechanics of gliding in birds with special reference to the influence of the ground effect

A model of the mechanics of gliding without loss of altitude (horizontal gliding) is developed. The model can be employed to assess the influence of the principal drag components (induced, profile and parasite drag), choice of initial and final glide velocities and height above the ground on glide distance. For birds gliding near to the ground the ground effect acts to decrease the induced drag and increase the lift to drag ratio of the wings. Minimum drag speed is reduced for birds gliding near to the ground. The model is applied to the gliding flight of the black skimmer (Rhyncops nigra). Glide distances for given initial and final velocities are significantly increased in the influence of the ground effect over out of ground effect values.