This thesis presents the results of a four year study from 1986 to 1990 on the biology of the leguminous tree Prosopis Cineraria (L.) Druce in the Sharqiya region of the Sultanate of Oman. Descriptive studies were performed on both the woodland habitat and the species. The suitability and methodology of utilising P.cineraria in future forestry programmes in Oman were also examined. Field studies have shown that this drought-tolerant indigenous phreatophyte forms large mono-culture relic woodlands in the sandy deserts of the Sharqiya. It is well adapted to the harsh environment of shifting sand dunes, growing vegetatively through accumulated sand to form tree clumps. Ecological studies have shown that the Prosopis woodland micro-environment supports wildlife not necessarily adapted to arid conditions. P.cineraria is an excellent multi-purpose tree for local people, particularly in providing fodder, fuel wood and shade protection. Over-exploitation and the general absence of natural reproductive regeneration has resulted in the decline in the condition of some Prosopis woodlands in Oman. To ensure their continued survival several methods of conservation were recommended. Studies on the mature trees have shown that the morphological variability of this species in the Sharqiya was high, which contributed to its multi-purpose potential. This variability was both phenotypic and genotype in origin. Glasshouse trials of P.cineraria in Durham have shown that seeds sampled from individual trees produced seedlings that were morphologically variable and were particularly tolerant to high salinities. Variation in morphology and salinity tolerance were related to both their geographical and parental origin. Three P.cineraria field trials in Oman have shown that the climate and soil environment greatly affected seedling growth and morphology. Silvicultural recommendations derived from these trials have been proposed for the propagation of this species in Oman.

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Axenic cultures of Peridermium pini have been established on modified Shenk &'38 Hilderbrandt's and Harvey &'38 Grasham's media from naturally infected cortex tissues and aeciospore-infected calluses of P. sylvestris and from aeciospores collected from NE Scotland and East Anglia. The cultures occasionally produced immature smooth-surfaced, binucleate spores. Actively growing cultures infected P. sylvestris calluses but not seedlings or trees. In the experiment of fungal nutrition, (NH4)2SO4 appeared essential, sucrose, D-glucose, raffinose and D-sorbitol supported good growth while D-xylose, cellobinose and L-arabinose did not. Opt. medium pH proved to be 5.0-6.0. Axenic cultures were also obtained from 30-40&'37 of single sporelings of some East Anglia spore sources but not from NE Scotland sporelings. When inoculated at a high density, however, all spore sources from both East Anglia and NE Scotland readily formed colonies. Colonies from East Anglia spores mostly appeared smooth at the surface and distinct around margin while those from NE Scotland sources had fluffy surface and irregularly extended periphery. Rapidly expanding hyphal layers developed from both of the colony forms 3 months after inoculation. Callus tissue cultures of P. sylvestris, P. nigra var. maritima and P. mugo vars mughus, rostrata and pumilio were infected by inoculation with aeciospores from NE Scotland. Infections were characterized by formation of aerial hyphae on the callus surface and intercellular hyphae and typical haustoria in the callus tissue. Hyphae from some of the infected calluses penetrated the medium. Seedlings of the pines as above were infected at their cotyledon stage by inoculation with NE Scotland spores. Infections resulted in swelling, death of the seedlings and formation of spermogonia after a year and aecia after two years. Infections of young seedlings of 7 seed sources of P. sylvestris and the UK were examined 6 weeks after inoculation. Discolouration and necrosis of cotyledons were not always related to stem infection.

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Digitized by Kansas Correctional Industries

One of the restrictions used in all of the works done on phylogenetic invariants for group based models has been that the group be abelian. In my thesis, I aim to generalize the method of invariants for group-based models of DNA sequence evolution to include nonabelian groups. By using a nonabelian group to act one the nucleotides, one could capture the structure of the symmetric model for DNA sequence evolution. If successful, this line of research would unify the two separated strands of active research in the area today: Allman and Rhodes’s invariants for the symmetric model and Strumfels and Sullivant’s toric ideals of phylogenetic invariants. Furthermore, I want to look at the statistical properties of polynomial invariants to get a better understanding of how they behave when used with real, “noisy” data.

Phylogenetic trees represent theoretical evolutionary relationships among various species. Mathematically they can be described as weighted binary trees and the leaves represent the taxa being compared. One major problem in mathematical biology is the reconstruction of these trees. We already know that trees on the leaf set X can be uniquely constructed from splits, which are bipartitions of X. The question I explore in this thesis is whether reconstruction of a tree is possible from subsplits, or partial split information. The major result of this work is a constructive algorithm which allows us to determine whether a given set of subsplits will realize a tree and, if so, what the tree looks like.

Relational information visualisation concerns viewing relational data, where the underlying data model is a graph. Hierarchical visualisation is one of hot topics in graph visualisation in which the data is organised in a hierarchical structure. As the amount of information, that we want to visualise, becomes larger and the relations become more complex, classical visualisation techniques and hierarchical drawing methods tend to be inadequate.Traditional hierarchical visualisation algorithms are more concerned with the readability of the layouts. They usually do not consider the efficient utilisation of the geometrical plane for the drawings. Therefore, for most hierarchical layouts, a large portion of display space is wasted as background. The aim of this research is to investigate a space-efficient approach to handle the visualisation of large hierarchies in two-dimensional spaces. This thesis introduces a new graph visualisation approach called enclosure+ connection for visualizing large hierarchies. This approach maximises the space utilisation by taking advantages of the traditional enclosure partitioning approach, while it retains the display of a traditional node-link diagram to hopefully provide users a direct perception of relational structures. The main contribution of this thesis is layout and navigation algorithms for visualising large hierarchies. Two layout algorithms, the space-optimised tree and the EncCon tree, have been developed to achieve the space-efficient visualisation. Both algorithms use the enclosure concept to define layout of hierarchies, which ensure the efficient utilisation of display space. Two focus+context navigation and interaction methods have been proposed to cooperate with the visualization of large hierarchies. Several advanced computer graphics approaches, such as graphic distortion and transparency, are used for the development of these navigation methods. Two case studies have been implemented to evaluate the layout algorithms and the associated navigation methods. The first case study is an application of a shared collaborative workspace which aims to provide users with a better assistance for visual manipulation and navigation of knowledge-based information. The second case study is a visual browser for navigating large-scale online product catalogues. Although the case studies have provided some useful evaluation, formal usability studies would be required to justify fully the effectiveness of these layout and navigation methods. Although this task has not carried out in this research, the author has presented his usability study's plan as a future work.