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The objective of this study of hybridization between H. mantegazzianum Somm. & Lev. and H. sphondylium L. in Britain was to provide evidence for the existence of hybrids from field observations and experimental crosses. H. sphondylium is native to the British Isles; H. mantegazzianum was introduced to Europe from the Caucasus in 1895. During the nineteenth century several species of Heracleum were cultivated in Britain, but only H. mantegazzianum is now widely naturalized along rivers and on waste ground in south-east Scotland. In 1976 and 1977 several sites in south-east Scotland were surveyed for hybrids. Mass collections and morphometric measurements were made in the field. Principal components analysis and summary statistics were used to demonstrate the existence of an intermediate group of low fertility. A detailed comparison of plants at one site showed that for the putative hybrids the length of pollen grains and of leaf hairs on the lower epidermis of the leaf was discrete. The H. sphondylium x H. manteqazzianum cross set 23% seed which was 73% viable. Attempts to synthesize hybrids on H. mantegazzianum failed on six of nine plants, and gave an average 1% seed set. Both species set more seed on intraspecific crosses between plants, but on selfing H. sphondylium set only 16% seed, and H. mantegazzianum proved to be fully protandric within the primary umbel. Pollen transferred from secondary to primary umbels of the same H. manteqazzianum plant set 69. seed; there was no evidence of a self-incompatibility system, or inbreeding depression. In the field the flowering time of both parents and hybrids overlap. A single backcross on H. sphondylium with hybrid pollen gave 14% seed set which was 77% viable, but from the survey there was no noticeable increase in variation between pure and mixed populations of either species that might indicate introgression. Putative hybrids were rare, and only found where populations of both species grew interspersed.

The Alpine Lady-fern, <I>Athyrium distentifolium </I>Tausch ex Opiz is found throughout the northern hemisphere. In Scotland, there is a smaller endemic form which was discovered in 1852 and has been named Newman's Lady-fern, <I>Athyrium flexile </I>(Newman) Druce. <I>A. flexile</I> is usually found with <I>A. distentifolium.</I> Although morphologically distinct, the taxonomic status of <I>A. flexile</I> has been the subject of continuing debate. This thesis aims to clarify the relationship between the two taxa. A morphometric analysis showed little overlap between the taxa for wild grown specimens. Comparisons between the spores and stomatal density showed small differences. The chromosome number was confirmed as being the same for both taxa. Gametophytes and sporophytes of both taxa grown at low nutrient levels demonstrated that the smaller <I>A. flexile</I> matured faster and became fertile while <I>A. distentifolium,</I> which is usually larger and more vigorous, remained small and infertile. The <I>flexile</I> taxon may therefore be an ecotype which is specially adapted to stressful environments. <I>A. flexile</I> is only found in a limited number of sites in the Central Highlands of Scotland which have a low-nutrient substrate. It appears it can only survive in habitats where the competition from <I>A. distentifolium</I> is reduced. The most significant discovery from the cultivation of spores from individuals of <I>A. distentifolium </I>was that some plants, when self-fertilised, produced both the <I>flexile </I>and <I>distentifolium</I> type of sporophyte. <I>A. flexile</I> plants always bred true when selfed. When gametophytes of <I>A. distentifolium</I> and <I>flexile</I> were given the opportunity to cross fertilise, some <I>A. flexile</I> gametophytes produced an <I>A. distentifolium</I> sporophyte. This suggests that <I>A. flexile</I> might be a homozygous recessive and does not justify species status.

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In glasshouse and laboratory conditions, death of root cortices of cereal and tomato plants was followed by nuclear and cytoplasmic staining methods. Various treatments were applied to whole plants or sterile root pieces on agar, to study factors that influence root tissue senescence and its relationship to invasion by the parasitic fungi <i>Microdochium bolleyi, Pyrenochaeta lycopersici</i> and <i>Gaeumannomyces graminis</i> var. <i>tritici (Ggt)</i>. Other experiments involved growth and sporulation of <i>M.bolleyi</i> in culture, and the ability of this fungus to spread on roots by spores produced on seeds or roots, to facilitate development of <i>M.bolleyi</i> as a seed-applied biocontrol agent of plant pathogens. Nuclear staining with acridine orange was satisfactory for assessing root cell viability in cereals but not in tomato, for which neutral red/plasmolysis was used; no other cytochemical method was suitable for routine work with either plant. Sterile detached root pieces of wheat and tomato senesced rapidly on media without sucrose, but tomato root cells remained alive on media of low sucrose concentration (0.1&37), whereas wheat root cortical death (RCD) was delayed but not inhibited by even high sucrose levels. RCD was also delayed by removal of the shoot, root tip or seed from sterile wheat seedlings; supply of sucrose or minerals to only part of a root piece did not affect the pattern of RCD. Indolylacetic acid, Ag<SUP>+</SUP> or Co<SUP>2+</SUP> delayed RCD in wheat root pieces on agar, but other growth regulators accelerated RCD. The results suggest that RCD in cereals is programmed and internally regulated, being only slightly modified by external factors. <i>M.bolleyi</i> invaded senescing cereal root cortices mainly intercellularly. It accelerated RCD of detached roots but had little effect on attached roots; it invaded tomato roots only poorly. <i>P. lycopersici</i> invaded cereal and tomato roots mainly intracellularly and killed the tissues, indicative of a different growth habit. Wheat, barley, oats and rye showed different rates of RCD in root pieces on agar, and oats had a different pattern of RCD from that in other cereals. <i>Ggt</i> killed roots of all four cereals, attached and detached from seedlings, but it penetrated poorly into oat roots even when their cells died. An attempt was made to relate these events to patterns of induced lignification in root cells.

No description available.

The 8(-9) annual species of <i>Bromus</i> generally placed in sect <i>Genea</i> were investigated taxonomically and biologically with the aim of improving their classification and giving a better understanding of their morphology and relationships. The species are widely distributed in the Mediterranean countries, SW Asia and also in northern Europe; some are important introduced weeds in other regions of the world, mainly with a Mediterranean-type climate. None has previously been investigated throughout their total areas. In this multi-disciplinary approach, material falling into the following existing taxa were studied: <i>B.diandrus</i>, <i>fasciculatus</i>, (<i>Haussknechtii</i>), <i>madritensis</i>, <i>rigidus</i>, <i>rubens</i>, <i>sericeus</i>, <i>sterilis</i> and <i>tectorum</i>. The investigation was based on: herbarium resources, field-work, an experimental plasticity study, geography/ecology, a computer analysis, anatomy, SEM studies, serology and cytology. For reasons of convenience, the species were considered in 3 groups. In each of these, varying degrees of emphasis were given to the results of the different investigations listed above. In the <i>B.tectorum-sericeus</i> group, a computer analysis, based on information from a very large number of herbarium specimens supported the recognition of one species with 2 subspecies (<i>B.tectorum</i> subsp. <i>tectorum</i> and subsp. <i>lucidus</i> Sales). In this group, the taxonomic and evolutionary significance of the features of dispersal biology was stressed. In the <i>B.sterilis</i>-<i>diandrus</i>-<i>rigidus</i> group, it is shown that the existing typification of <i>B.sterilis</i> is incorrect. <i>B.diandrus</i> and <i>rigidus</i>, so often recognized as independent species are here regarded as varieties of one species. In the last group (<i>B.madritensis</i> (<i>haussknechtii</i>), <i>rubens</i>, <i>fasciculatus</i>), particular attention was given to <i>B.fasciculatus</i>. Its uniform morphology is stressed; no infra-specific taxa are recognized within it. Leaf anatomy was studied and described; no major or significant differences were revealed in the species studied. Micromorphology was investigated for many vegetative and floral parts of the plant. These showed, inter alia, that certain characters, such as the shape of the callus scar have previously been given undue emphasis. SEM studies provided a new insight into some characters of biological importance, including stomata on the awns and the incomplete development of callus at floret base on chorispermous plants. A chapter on cytology confirms previous records of chromosome number and describes an improved technique. Serological studies of double diffusion confirmed the close relation of <i>Genea</i> species and supported, in general, the recognition of the three groups based on morphology. <i>B.sterilis</i> and <i>B.madritensis</i> are probably at the core of sect. <i>Genea</i> from which 2 evolutionary lines towards <i>B.diandrus</i> var. <i>rigidus</i> and <i>B.fasciculatus</i> developed. <i>B.tectorum</i> may represent a link between sect. <i>Genea</i> and the <i>B.pectinatus</i> complex (sect. <i>Bromus</i>). These aspects are discussed in the chapter on adaptive radiation.