From investigations of two life stages of the green seaweed Urospora wormskioldii (U. wormskioldii and Codiolum pusilium) it was found that both weeds synthesise the following ethanol soluble carbohydrates: glucose, fructose, sucrose, myo-inositol, glycericacid and a number of glucose containing oligosaccharides. Both weeds also synthesise starches comprising amylose and amylopectin as well as highly branched 1,3-linked glucans. Evidence for a1.4-linked homoxylan with C-2 branch points was found in U. wormskioldii and indications of a homoxylan both 1,3- and 1,4-linked was found in Codiolum. Small amounts of an a-1,3-linked mannan and large amounts of a B-1,4-linked mannan branched at C-6 and sulphated at C-2 were found in Codiolum, although U.wormskioldii contained only trace quantities of a mannan. Polydisperse heteropolysaccharides ("rhamnans") containing L-rhamnose, D-xylose and D-glucuronic acid and half ester sulphate linked to the rhamnose were found in both weeds. The glucuronic acid was found to be 1,4linked and end group and the xylose to be 1,4-linked and end group and in U. wormskioldii it was also 1,2,4-linked. The rhamnose residues were mainly 1,3-linked and sulphated at C-2 or C-4 and to a lesser extent 1,4-linked with sulphate groups at C-2 or C-3. A small amount of 1,2-linked and end group rhamnose units was also found. The "rhamnans" metabolised by Codiolum appear to be basically linear while those from U. wormskioldii appear to be highly branched with possibly 1,3,4- or 1,2,4-linked rhamnose branch points. The structural cell-wall polysaccharide in both weeds was found to be cellulose admixed with protein and "rhamnan". A "rhamnan" from the green seaweed Ulva lactuca was found to be a linear polysaccharide consisting of 1,4- (major), 1,3-linked and end group rhamnose, 1,4-linked xylose and 1,4-linked and end group glucuronic acid. The "fucans" (polydisperse heteropolysaccharides) from the brown seaweeds Himanthalia lorea and Padina pavonia were found to consist of fucose, glucuronic acid, xylose and traces of galactose (H. lorea). The xylose and glucuronic acid were found to be1,4-linked and end group while the fucose was found to be 1,3-linked with sulphate groups at C-2 or C-4 and 1,4-linked with sulphate groups at C-3. Indications were obtained for a linear fucose backbone for these "fucans". The two brown seaweeds Desmarestia ligulata and Desmarestia firma were both found to have a high content of free sulphuric acid in the vacuolar sap. The free sulphuric acid in D. firma was found to be 6% of the dry weight of the weed. Consequently new methods to avoid degradation of the polysaccharides had to be devised. Both weeds were found to synthesise inannitol as their main ethanol soluble material though oligosaccharides containing xylose and galactose (D. firma) and xylose, galactose and mannose (D. ligulata) as well as myo-inositol (D. ligulata) and indications of glucose-mannitol di- and trimers (D. firma) were also found in this extract. Both weeds were found to synthesise laminaran, D. firma in comparativelylarge amounts. The "fucans" extracted from the two species were found to contain fucose, xylose, galactose, and glucuronic acid and mannose was also found in the "fucans" from D. ligulata. The alginic acid from D. ligulata was found to contain 33% of mannuronic acid and the mannuronic acid in both alginic acids was found to be more easily degraded and hydrolysed than the guluronic acid. The structural polysaccharide in D. ligulata was found to be cellulose.

Development and decline of phytoplankton populations was investigated in Wraysbury Reservoir between October 1971 and December 1974. This reservoir is the second to be supplied by the River Thames via a choice of jet or low velocity inlets. Substantial periods of artificial mixing have supplemented natural wind-induced turbulence, thus usually preventing thermal and chemical stratification and creating a high mixed depth/euphotic depth ratio. Input of eutrophic River Thames water provides a more or less constant supply of nutrients: a phytoplankton succession characteristic of enriched waters developed although the species were not those typical of the river Diatom growths predominated, in particular the centric diatoms Steuhanodiecus astraea (Ehr) Grun and Melosira granulata Ehr. Blue-green algae were conspicuous during the summer months. A similar seasonal distribution of phytoplankton at different stations resulted from the mixing process. Inverted microscope, counts of Stephanodiscus populations and the use of the Coulter Counter suggested near homogeneity with depth when the diatom cells were healthy: increased heterogeneity through the water column accompanied decline of populations and cell sedimentation. Ageing of Stephanodiscus cells was accompanied by changes in pigment composition; large growths (800 cells per ml) could substantially modify the vertical attenuation coefficient. Consideration of the silica budget has suggested that 100 cells per ml "require" approximately 1.5 pgm S10. Primary productivity experiments in the field suggested that reduced illumination restricted growth at and near the bottom of the reservoir for much of the year. Laboratory cultures of mud samples shoved the presence of numerous algae. Whereas the centric diatom Cyclotella ref. meneghiniana Kutz. was maintained relatively easily in laboratory cultures, similar attempts to grow Stephanodiecus astraea were unsuccessful.

Phorbaketal A (I) and phorone A (II) are members of a growing family of biologically active sesterterpenoid natural products, derived from marine sponges. These compounds possess potent biological activities and intriguing molecular architectures, which have inspired efforts towards their total synthesis. Early work in this thesis describes how new methodology is developed aimed at the synthesis of phorbaketal A (I). The synthesis and subsequent treatment of the model hydroxyphenol III with PhI(OAc)2 led to the development of a new method for spiroketal synthesis via cascade oxidative dearomatisation. This new spiroketalisation method was then further elaborated for the total synthesis of phorbaketal A (I). This required the construction of the noralotane carbon skeleton IV, employing the union of the aryl aldehyde V and the propargylated geraniol VI. Treatment of the noralotane IV with PhI(OAc)2 gave the spiroketal VIII as a complex mixture of labile diastereomers. This new method for spiroketalisation ultimately proved unsuitable for the total synthesis of these spiroketal natural products. Following this, attempts at expanding the substrate scope for this new oxidative dearomatisation method were explored for the formation of a range of saturated spiroketals. v The second part of this thesis describes efforts towards the total synthesis of the related sesterterpenoid natural product phorone A (II). Considerable synthetic effort led to synthesis of the novel (Z)-bromoalkene IX and the drimane aldehyde X, which were coupled to give the ansellane alcohol XI, in a total of 17 steps. This work represents the first ever synthesis of the ansellane skeleton. Efforts to oxidise and cyclise the alcohol XI were initiated; however difficulties with eliminative dehydration prevented its conversion to phorone A (2). The final work in this thesis describes alternate coupling methods aimed at circumventing these unforeseen issues.

Two species of Euglena, Euglena gracilis and Eug1ena mutabilis, were cultured with the object of finding the conditions which would give the highest mitotic index at a predictable time. This was done, and the cell-cycle time under controlled conditions was found. Following this, mitosis was investigated by ordinary cytological methods and with the electron microscope. Using the microdensitometer, it was found that DNA replication occurred during interphase and in other organisms. Evidence for the presence of separated chromatids was found at the end of interphase (G2). Counting sectioned chromatin masses in sections photographed under the electron microscope showed the presence of separated chromatids at metaphase. It was found that irradiation made metaphase and particularly anaphase stages easily spread, and from these stages it was seen that the chromatid is characteristically V-shaped with the point of the V directed to the poles. At metaphase however the point was predominantly on the equator. Detailed study of the ultrastructure of the mitotic figures showed that microtubules are connected by arms or bridges; they are also attached laterally to the endosome and probably to the chromatin; in addition they pass through the chromatin. The relationship between chromosomes and microtubules has been followed by means of aerial transverse sections and in 1ongitudinal sections. Models for mitosis in Euglena have been devised. The ultrastructure of the endosome has been investigated and observations suggesting the presence within it a nucleolar-organising chromosomal region, have been made. The effects of irradiation have been investigated using gamma radiation in doses from 4Kr to 350Kr. A dose-tolerance curve has been plotted. LD.50 is 35Kr. The effects of radiation on the ultrastructure of the nucleus are described.

The physical and, chemical factors which affect sporulation, and the growth and survival of vegetative populations of blue-green algae were examined in two eutrophic kataglacial lakes of the Ellesmere (North Salop) group of meres. The importance of individual factors were examined under controlled conditions using natural populations or uni-algal isolates from the meres. The induction of akinete formation, which, in all the cases examined, proceeds once the alga forms a surface bloom, is thought to be due to the extreme conditions, particularly of solar radiation, which prevail at the surface during the summer. Winter blooms did not sporulate. Nutrient deficiency, particularly of orthophosphate, is not considered to be a critical factor. This is supported by the finding that blooming algal material is not depleted of phosphorus, that alkaline phosphate activity was low, and that nutrient deficiency under controlled conditions did not induce sporulation of the species predominant in the meres. Nitrogenase activity (acetylene reduction) and the photosynthetic rate (oxygen evolution) were observed to fall in the period subsequent to bloom formation. The reduction of measured net photosynthesis may be correlated with the increase of bacterial numbers. The activity of light-damaged material was lower than that of unaffected populations. It appears that there must be a low cellular carbon to nitrogen ratio before akinete differentiation can begin, indicating that a reduction of photosynthetic activity relative to that of nitrogon assimilation is required. Akinetes probably do not form a significant overwintering mechanism in the lakes investigated. Numbers of akinetes found during the winter were low. The bloom populations probably develop from growth of the overwintering planktonic vegetative populations during the spring and early summer. Cornparisons of planktonic, sedimenting and benthic algal material indicates that germination of akinetes shortly after their maturation may give rise to the greater part of the overwintering vegetative populations. Physical rather than chemical facters appear to control the population sizes and life cycles in the environments studied.

An investigation which has tended to be extensive rather than intensive, of the survival of fresh water algae during dry periods has been carried out. From April 1953 to June 1955, five small ponds, two in Hertfordshire, two in Middlesex and one in Surrey, have been visited regularly. At these ponds, water levels, water temperatures and the pH of the water and marginal litter or mud were recorded. Litter and mud samples were taken for the estimation of moisture content. Water samples and samples of litter and mud exposed above the water level were collected and examined for algae. In addition, throughout the period of the whole investigation, samples of water, litter and mud have been taken from various other habitats at irregular intervals. A series of large- and small-scale drying experiments have been carried out to investigate the reactions of various algae to drought and the survival of species through drought periods. Some investigation was made of the stratification of algae in pond margin litter and mud. Two methods were employed, a buried-slide technique and a micro-sampling technique. The observations made suggest that certain algae are capable of surviving dry periods by methods other than by the existence of resistant spores. It has been found that more or less obviously modified vegetative cells of a number of algae will survive drought. Further, certain algae, both motile and non-motile, have been found to survive in the deeper layers of litter and mud at pond margins during exposure and drying. While an attempt has been made to cover an extensive field, more detailed observations have been made on a number of individual species of algae.

The thesis describes the first extensive study of the carbohydrates of the brown seaweed Lessonia nigrescens, harvested in Chile. It was hoped to discover a different metabolic pattern for the stems and for the fronds of this seaweed. In the initial studies sequential extraction with water, acid and alkali and a direct alkaline extraction were applied separately to stems and fronds. Each of the extracts was hydrolysed and the hydrolysates were analysed by paper and by gas liquid chromatography allied to mass spectrometry. Crystalline mannitol was separated from both parts of the s eaweed. "Fucans" were present in all the extracts together with, in the alkaline extracts, alginic acid. Fractionation of the aqueous extract failed to reveal any laminaran, a typical (1,3)-B-linked glucan of brown seaweeds. Each of the "fucan" contained varying proportions of fucose (major), galactose, mannose, xylose, glucuronic acid and half ester sulphate. Varying proportions of protein were present in all the extracts. Molecular weights determinations revealedpolydispersity with high proportion of the molecules equal to orlarger than M of 6.7 x 10.The only significant difference between stems and fronds was the higher proportion of glucuronic acid in the former. Investigation of the alginic acids revealed that theyconsisted of mannuronic to guluronic acid in the ratio of 0.54. Viscosity and C n.m.r. measurements were carried out. Large scale partial acid hydrolysis of water soluble "fucan" from a mixture of stems and fronds led to the separation of neutral and acidic oligosaccharides, an insoluble and a soluble polymer. The neutral oligosaccharides which contained only galactose were separated into six entities and characterised by methylation and the anomeric linkage determined for two of them by enzymic and n.m.r. studies. The eight acidic oligosaccharides proved to be very complex mixtures. However, two were characterised as 3-0-(D-glucopyranosyluronic acid)-L-fucose and 3-0-(D-glucopyranosyluronic acid)-D-glucuronic acid. The insoluble residue, 10% of the starting material was mainly inorganic and protein. The soluble polymeric material, 20% of the initial material (contained 80% carbohydrate) was shown by hydrolysis, 13 molecular weight determination and C n.m.r. to consist of approximately 44 alternating units of glucuronic acid and mannose.

An investigation over a period of more than two years of phytoplankton, and physical and chemical conditions of the River Thames and the Wraysbury Reservoir in Southern England, has indicated seasonal occurrence of phytoplankton populations with diatoms (chiefly Stephanodiscus ref. hantzschii Grun.) forming a large percentage of the populations. During 1984, 1985 and 1986, phytoplankton populations occurred most abundantly during the spring (mainly diatom populations) and during the summer (diatoms and green algae in the River Thames, and blue-green algae in the Wraysbury Reservoir). Selected algal taxa were isolated and grown in culture in the laboratory and experiments carried out in which culture conditions have been manipulated in various ways. Such experiments included those involving suspected nutrient limiting factors (e.g. phosphate) as well as physical factors especially those of temperature and light. Ecological records and experimental cultures indicate that the occurrence and growth of diatoms is encouraged by the increasing water temperatures and light intensity during the spring, and by higher levels of nutrient concentrations (i.e. nitrate-nitrogen, phosphate-phosphorus and silica) at all times. On the other hand, the growth of green algae (Chlorophyceae) and blue-green algae (Cyanophyceae) was influenced by the maximum water temperatures and light intensity of the summer period and despite lower nutrient concentrations. Thus, differences in physical and nutrient requirements by phytoplankton populations help to explain the presence of diatoms during the spring and green algae (in the River Thames) and blue-green algae (in the Wraysbury Reservoir) during the summer. Simple investigation of the growth responses of the River Thames and Wraysbury Reservoir phytoplankton populations to River Thames and Wraysbury Reservoir water as natural culture media were performed. The results indicated that the River Thames and Wraysbury Reservoir are potentially able to support considerable crops of phytoplankton populations, and that the potential is present throughout the year.

Phytoplankton distribution and periodicity patterns were investigated in a series of four intermittently linked ponds during the period January 1984 to December 1987. The ponds, each with an area of less than one hectare, are located within the boundaries of Windsor Great Park, Berkshire. During the middle two of the four field seasons studied the ponds were subjected to mechanical disturbances which involved the dredging and enlargement of all basins. Inverted microscope counts of the algae in sedimented water samples indicated a phytoplankton succession characteristic of eutrophic bodies of water. The vernal increase was consistently dominated by the Bacillariophyceae mainly Asterionella formosa and Stephanodiscus ref hantzschii. Asterionella formosa is normally associated with larger more open water areas and may have been living at the limit of its ecological range. Diatoms were succeeded largely by species from the Chlorophyceae, Cryptophyceae and Euglenophyceae. Cyanobacteria were conspicuous only occasionally during the summer months. Changes in phytoplankton distribution and composition were observed following dredging operations, these changes suggested a reversion to less eutrophic conditions in ponds one, two and three; this was not apparent in pond four. Additionally, Stephanodiscus ref hantzschii was succeeded by Asterionella formosa as the dominant diatom during spring growth, a factor possibly associated with basin enlargement. Flagellates rather than other species were more apparent in the turbid conditions which obtained after dredging. Algae collected from the benthos indicated the presence of planktonic and bottom living species such as Caloneis silicula and Gyrosigma spencerii. These typically benthic species were not observed in sedimented samples.

An investigation has been carried out on the algal flora of slow sand filter beds. Ecological field studies were made from August 1963 until December 1965 and experimental work was continued until June 1966. The filter beds studied were located at the Ashford Common works of the Metropolitan Water Board, London. The major chemical nutrients, and pH were determined throughout the period together with temperature and penetration of light into the water. Biomass, interpreted from calculated cell volumes, of the major species of algae encountered was used to express the results of cell concentrations. The periodicity end distribution of the algae in the filter beds was investigated. The algal populations present were sub-divided into planktonic, epipelic and attached bottom living species and each one was found to have a distinct seasonal periodicity. Observations suggested that the filter bed algal populations were not often limited by nutrient concentrations but the algae on the sand surface may on several occasions have been limited by low light levels. Experiments to determine the toxicity of copper sulphate to certain species of algae were carried out. The ability of algae to penetrate the sand and to survive was also investigated experimentally. These experiments showed that cells could stay alive in the filter bed sand after cleaning and act as population innocula when the bed was refilled. The flora of the sand surface was compared with that of an in-situ polythene bag to ascertain the effects of nutrient limitation. The variation in cell sizes of Stephanodiscus astraea and Asterionella formosa were investigated together with the relative growth rate, k', of S. astraea, and seasonal variations in both were found.