Bracken (Pteridium aquilinum (L. ) Kuhn) is considered a problem plant in many countries, so an understanding of its method of reproduction is important to those trying to control it, prevent its spread or to manage rangelands sustainably. It is commonly believed that in the UK, bracken mainly reproduces asexually via its rhizome system. However, spores are produced in many locations in some years and in some places apparently every year. What stimulates the production of these spores and whether they contribute to the spread of the plant is unknown. The spores as allergens are hazardous to the health of animals including humans, and may be carcinogenic when ingested in sufficient dosage. The aims of this study were therefore to identify both the conditions conducive to spore production, and the conditions that may promote the growth and survival of gametophytes and sporelings. To test what conditions were associated with spore production, three experiments using bracken sporophytes of different genotypes grown in pots in controlled environment growth chambers were carried out. The experiments differed in their designs and the range of variables tested, but all were multifactorial. The environmental variables were: two different levels of photosynthetically active radiation (PAR) and light quality (simulated broad-leaf canopy shade versus simulated full sun), two temperature regimes (each resembling one of those at the sites inhabited by the source plants), two nutrient addition rates, two water addition treatments, and rhizome disturbance. A novel quantitative method of scoring sporangial development was developed and used to assess the effects of these factors. Genotypeh ad a significant effect on sporangial development, but not on the rate of that development. Nutrient and water additions affected vegetative growth, but had no significant effects on sporangial development. The higher of the two rates of PAR and temperature increased both the rate and the maximum sporangial development attained. Rhizomes that were excavated and cut to length immediately before the experiment produced fronds with sporangia that developed at a slower rate and attained a lower degree of maturity than those rhizomes that had been excavated and cut prior to the previous growing season. There was no correlation of biomass of the sporophyte with sporangial development, or development of sporangial tissue on fronds from rhizomes in a second experiment, with sporangial development of the same rhizomes in the previous year. This shows that environmental factors influence sporangial development in bracken, with genotype having an influence on maximum spore output, but that the rate of development depends entirely on some environmental variables. Spores of bracken were cultured in a wide range of different conditions. The variables included temperature, PAR; state of media; calcium content; pH; soil water content, and relative humidity. Of these, only temperature significantly affected germination, with 20°C producing the highest germination of 5,10,15,18,20,25 and 30°C. Gametophytes were more likely to reach a state of 2-dimensional growth (transition) at 20 or 25°C than at 18 or 30°C. Lower levels of PAR decreased the likelihood of gametophytes reaching transition. Of the calcium levels tested, only complete lack of added calcium had a significant effect on gametophytes, with increased gametophyte mortality and a decrease in numbers reaching transition. Media at pH 4 and 8 reduced numbers of gametophytes reaching transition compared to pH 6.25. There was increased mortality at pH3 Water content of the substratum outwith the range 50 - 150% field capacity, significantly reduced the number of cordate gametophytes. Humidities in the range 10 - 100% relative humidity did not have any significant effect on gametophyte growth. This may have been due to the constant availability of water from the substratum. Conditions conducive to gametophyte development to transition were; a temperature above 8°C, the presence of calcium, the absence of deep shade, a pH near to 6.25 and adequate soil moisture. Data from the growth chamber and spore culture experiments involving temperature were used to create a model of bracken sporulation and spread in the British Isles. Resultant maps show that the south east is at the highest risk of bracken spread by spores, however, when climate change predictions are used in conjunction with the model, it can be seen that northerly areas may be at risk in the future. This research shows that while genotype does play a part in determining spore production of bracken, environment plays the bigger role. It is likely that with the predicted increase in temperatures in the UK, more bracken plants will begin to spore in more areas of the country, putting more animals and people at risk from health problems and potentially further degrading susceptible land. This work does not explain why bracken gametophytes are rarely encountered in field situations. Since the conditions that were found to be conducive to gametophyte establishment are often found in the UK, either one or more factors that were not included in these experiments play a key role in determining the success of sporal regeneration, or colonisation by spores occurs more frequently than is widely believed.

A taxonomic revision of the species of the genus Selaginella Beauv. has been undertaken. The study was concentrated on the species of the subgenus Stachygynandrum (Beauv-) Bak. found in West Africa and Madagascar. On the basis of the examination of the morphological features - vegetative and reproductive -a total of 29 species have been recognized to be present in West Africa and Madagascar. Twenty species occur in West Africa, 11 species are found in Madagascar while two species are common to both areas. All the 29 species have been described, illustrated and keys for their identification given. A new species - S. serrato-squarrosa Quansah - from West Africa has been identified. A proposed scheme of classification for the genus Selaginella. is given. In this scheme, the genus is divided into two subgenera. - Selaginella Bak. and Stachygynandrum - while subgenus Stacchygynandrum is subdivided into two sections - Ibmiostachys (Bak. ) Quansah and Heterostachys (Bak. ) Quansah

No description available.

No description available.

No description available.

No description available.

An intensive study was undertaken in order to isolate and identify bioactive compounds in bracken, Pteridium aquilinum (L.) Kuhn (Dennstaedtiaceae). A systematic phytochemical investigations of the underground rhizomes of this plant afforded thirty-five pterosins and pterosides along with the main carcinogen in bracken, ptaquiloside, 5-hydroxyisocalamene and 5-(β-hydroxy)ethyl-2, 2, 4, 6-tetramethyl-1, 3-indandione. By detailed analysis of one- and two-dimensional nuclear magnetic resonance spectroscopy, circular dichroism and highresolution mass spectrometric data, thirteen previously undescribed pterosins and pterosides have been identified. Interestingly, for the first time 12-O-β-D-glucopyranoside substituted pterosins, rhedynosides C and D, and the sulfate-containing pterosin, rhedynosin H, alongside the two known compounds, trans-histiopterosin A and (2S)-pteroside A2, were isolated from the rhizomes of subsp. aquilinum of bracken. In addition, the six-membered cyclic ether pterosins and pterosides rhedynosin A and rhedynoside A are the first examples of this type of pterosin-sesquiterpenoids. Additionally, the three previously reported compounds [(2S)- rhedynosin I, (2S)-2-hydroxymethylpterosin E and (2S)-12-hydroxypterosin A] were obtained for the first time from plant source as opposed to mammalian metabolic products. Single crystal X-ray diffraction analysis was applied to the previously undescribed compounds (2R)- rhedynoside B, (2R)-pteroside B and (2S)-pteroside K, yielding the first crystal structures for pterosides, and three known pterosins, (2S)-pterosin A, trans-pterosin C and cis-pterosin C. Rhedynosin C is the only example of the cyclic lactone pterosin with a keto group at position C-14. Six selected pterosins ((2S)-pterosin A, (2R)-pterosin B and trans-pterosin C) and associated glycosides ((2S)-pteroside A, (2R)-pteroside B and pteroside Z) were assessed for their anti-diabetic activity using an intestinal glucose uptake assay; all were found to be inactive at 300 μM. A simple, reproducible and rapid reverse phase high performance liquid chromatography (RP-HPLC) method was developed which was linked to the UV detection source. The method validated for quantification of pterosin B and pteroside B in different plant matrices, soil and water samples. A new solid phase extraction (SPE) method was developed and established for sample preparation based on using 500 mg Supelco-SPE cartridges. The RP-HPLC was performed with mobile phase containing 0.1% formic acid (FA) in water and 0.1% FA in acetonitrile with an appropriate gradient and a flow rate of 1 mL/min. Detection of the analyte peaks was performed at 254 nm. The method showed good linearity (correlation coefficient (r) > 0.99), and appropriate limit of detection (LOD) and limit of quantification (LOQ). The proposed RP-HPLC-UV method has a retention time of 20 min (3 samples/h). Overall, this work focuses on the application of SPE–HPLC-UV analysis to quantify pterosin B and pteroside B in different matrices including soil, water and bracken samples. The method involves pre-concentration and clean-up by SPE cartridges. Final analysis of the selected compounds was carried out by the developed HPLC-UV method. The extraction efficiency was checked by recovery experiment while the accuracy of the method was tested by relative standard deviation (% RSD). Recoveries were ranged from 90.29 to 96.23 % (pterosin B) and 93.64 to 101.03 % (pteroside B). The RSD (%) for both target analytes (pterosin B and pteroside B) was less than 2.5 % for all the analysed bracken stem samples. Preliminary results demonstrated that the present method was suitable for determination of pterosin B and pteroside B in bracken tissues, soil and water samples. The simplicity, accuracy and sensitivity of the developed SPE-HPLC-UV method, recommending that the method is also convenient and useful for quick check and detection of trace amounts of pterosin B and pteroside B in water, soil and plant samples. The quantification of pterosin B and pteroside B was applied to bracken, divided into rhizomes, stems and fronds, the top soil of the sample cores and a set of water samples. The rhizome contained the largest concentration of pteroside B through the completed bracken growth period (750-2950 mg/kg). Its concentration was approximately one order of magnitude above pterosin B (10-245 mg/kg). The above ground stems and fronds showed distinct increases in concentrations of pterosin B (ca. 500 mg/kg) and pteroside B (ca. 250 mg/kg) at the time of crosier emergence, that were about one order of magnitude higher than the other samples collected during the growth periods. The soil sampled reflected the increased mobilisation of pterosin B during the onset of above ground growth (May to June) while no pteroside B was detected. The absolute pterosin B concentrations determined were about three orders of magnitudes lower (0.02-0.3 mg/kg). Water samples that drain bracken covered areas were found to contain pterosin B between 9-47 ng/L and pteroside B in range of 16-85 ng/L. Overall, the seasonal variation of pterosin B and pteroside B showed that the compounds are stored in the rhizome, preferably as the glycoside, and are mobilised to protect the early tissue as a means of chemical defence. The stability of pterosin B was exemplified by its environmental presence in plant, soil and water.

No description available.

No description available.

This thesis examines a wide range of domestic novels, from Bram Stoker's Dracula (1897) to Woolf's Mrs Dallowa~ (1925), in order to explore their intensified concern with the aesthetlc value of domestic scene. The representation of the house in these works is viewed as an ideological strategy of containment, effected not only by narrative exclusions but also by the literary mode of the narrative. The domestic novel at the turn of the century does not necessarily produce an image of the house but presents a writing of space which interacts with architectural aesthetics in a discourse of the house beautiful. Critical analysis of the cultural and economic contradictions of this discourse indicates the way that the domestic novel is shaped by the colonial situation and at the same time opens out the complexity of its construction of feminine subjectivity. The late 19th century produced simplified spacious design in a reaction to the Victorian concept of the civilised house. The fictional and architectural ideal of a unified house form is, however, an assertion of identity and, in this sense, a renegotiation of the opposition between the E~gl~sh home and foreign or colonial 'otherness ' • This mapping is effected w~th~n the ideological imperative of the question of colonial trade. The flctl0nal emphasis on woman's relation to the house deals with her displacement in the commodity world of the aestheticised house. Yet the privilege given to the English word home lends to woman's sensual appreciation of the house, or creation of setting for herself, an importance which limits th~ ~mplied critique. Furthermore, feminine experience of habitation is relfled by the authoritive definition of the house in the interacting aesthetics of architecture and literature. The domestic novel thus mystifies new feminine roles, particularly the role of entertainment and even the attempt to demystify such ideals of habitation to . some extent colludes with the mystique by seeking the truth of woman's unspoken experience of the house