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Energy dispersive X-ray microanalysis (XRMA) in a scanning electron microscope (SEM) was used as a method to measure elemental silicon (Si) and phosphorus (P) in dinoflagellate cysts. Cysts were prepared by quick deep freezing and then freeze-drying, thereby avoiding the addition of preservatives. Cysts of Ceratium hirundinella collected from Lake Erken, Sweden and Esthwaite Water, UK, and Ceratium furcoides collected from Esthwaite Water, were analysed and compared. The hypothesis that cysts are able to assimilate P during dormancy was tested in the laboratory by incubating newly collected cysts of C. hirundinella in medium with and without phosphate. The analyses showed that there was no difference in P content between C. hirundinella and C. furcoides, suggesting that P content reflects differences in physiological status rather than species. C. hirundinella had a significantly higher Si content than C. furcoides, which agrees with earlier studies. Comparison of cysts of C. hirundinella from different years – 1995 (stored for 1 year), 1996 and 1997 – showed that the P content in cysts from 1995 was higher than that in cysts from the following 2 years, which indicates either that P was higher during encystment in 1995 or that cysts accumulated P during dormancy. The P uptake experiment showed a very slightly, but significantly, higher, P content in cysts incubated in P-rich medium.

Essay from the introduction to `The Government of the Tongue,' by Seamus Heaney. Thoughts about art and life and the tensions between them; Anecdote of his and guitarist David Hammond's musical collaboration in Belfast (Northern Ireland); Poet Wilfred Owen and World War I; Polish poetry; Heaney's faith in poetry, song and life.

The clinical and radiological state of the hips of a group of children with cerebral palsy treated without operation is compared with that in a group treated by operation to correct adduction and flexion deformity and to obtain balanced action in the hip muscles. In the first group, 11 per cent of hips were dislocated, 28 per cent subluxated, 46 per cent dysplastic and 15 per cent normal. In the second group no hip was dislocated, 13 per cent were subluxated, 35 per cent dysplastic and 52 per cent normal. Surgical intervention is indicated clinically for a range of abduction diminishing to less than 45 degrees and–on radiological criteria–for early dysplastic changes, especially a break in Shenton's line, irrespective of the patient's age, severity of involvement or neurological maturity. Prevention of subluxation or dislocation improves function and diminishes the liability to develop a painful hip in adolescence or early adult life.

A simple separation technique using polycarbonate membrane filters for purifying microalgae is described.

Large populations of the dinoflagellate Ceratium hirundinella occur regularly in a small productive lake and their decline during September and October is normally associated with mass encystment. Evidence for the major role of benthic cysts in providing the inoculum for subsequent growth is given from morphological and quantitative studies over two contrasting years of cyst production, 1980 and 1981.For both years there were two distinct phases of population increase in the plankton. Low winter densities were followed by rapid rates of increase during February and March at the same time as empty cysts appeared in the sediment. These changes occurred when water temperatures rose from approx. 3 to 5°C. After near-stationary periods in April and May 1980 and April to June 1981 there followed phases of exponential growth but at appreciably slower rates of population increase than during recruitment from excystment. That excystment was the major contributor to the rapid vernal increase of planktonic cells is supported by the observation in the plankton of high percentages of preceratium (recently excysted) cells and young vegetative cells with carbohydrate in their posterior halves. Moreover, a calculation of growth rate in situ, from the phasing of cell division when water temperatures were approx. 8°C, indicated that vegetative growth was very slow relative to the earlier observed rate of increase. Growth rates in culture at temperatures below 10°C were also very slow.Instead of the usual encystment in 1980 there was an early mass mortality of cells. This failure to form cysts did not prevent recruitment from benthic cysts in 1981 due to the large reservoir of viable cysts in the sediment from earlier years.

The diurnal vertical migration (DVM) behaviour of three species of cryptophytes of differing size (Rhodomonas minuta var. nannoplanctica and two species of Cryptomonas) was examined in 4 m tall laboratory columns in relation to gradients of light, temperature and nutrients. Differences were found in the DVM behaviour of the three species in relation to these environmental variables. Both species of Cryptomonas were able to cross steep thermal gradients whereas Rhodomonas did not. All three species avoided high levels of irradiance, especially when the cells were phosphorus-depleted. The large species of Cryptomonas made use of vertically separated resources of light and phosphorus by migrating from the illuminated, but phosphorus-depleted, upper layer during daytime to the phosphorus-rich hypolimnion at night. The smaller species of Cryptomonas had a reverse pattern of DVM swimming upwards during darkness, indicating a strong negative geotaxis. Moreover, downward migration of this smaller Cryptomonas ceased abruptly at the thermocline giving rise to well developed mid-water maxima in contrast to the larger species. The migration speeds of the Cryptomonas species were up to 0·7 m h-1 and cells were able to move quickly in response to environmental changes in the water column. The results demonstrate the importance of both the physiological state of the cells and the external physical and chemical conditions, particularly irradiance, as factors regulating the DVM behaviour of cryptophytes.

Eight methods for estimating algal biomass were compared, using the colonial diatom Asterionella formosa as a test organism. They were based on (i) cell counts by visual microscopy and electronic means, (ii) optical properties in vivo of scattering, attenuance and fluorescence and (iii) chemical estimations, on filtered cell-aliquots, of reducing capacity (C-equivalent) and solvent-extracted chlorophyll a. The main criteria were the parameters of precision, sensitivity, limit of detection plus time taken and sample quantity required.Most methods yielded an acceptable precision over wide ranges of algal concentrations although for visual counting and nephelometry the coefficient of variation typically exceeded 10%. The estimations in vivo were the most rapid, but were unsuitable for very low biomass concentrations. The chemical methods and (on undiluted samples) electronic counting generally required the larger quantities of sample - with the notable exception of extract fluorometry. The chemical methods were relatively slow but they allowed batches of samples to be processed together and gave more generalized measures of algal biomass (e.g. C-equivalent, chlorophyll a). Visual cell counts, although relatively slow and fatiguing, were unsurpassed for low limit of detection, economy of sample, and assessment of cell condition.

Growth in relation to CO2-depletion and CO2-enrichment was investigated for the freshwater diatoms Asterionella formosa and Fragilaria crotonensis in batch cultures. Algal concentration and pH were measured during growth cycles, and inorganic carbon quantities determined by potentiometric Gran titrations and from pH-alkalinity relationships. After the primary growth with CO2-depletion and pH increase, successive CO2-enrichments induced further such cycles and produced a final three- to fivefold increase in algal biomass over that of unenriched controls. The extent of CO2-depletion, and pH rise, was greater in later cycles, indicative of some cellular adaptation. Values of pH reached 9·7 for Asterionella and 9·9 for Fragilaria. The lowest residual quantities of free CO2 were 0·1 and 0·03 μmol 1-1 for Asterionella and Fragilaria respectively, which were less than 0·05% of the corresponding residual quantities of total CO2. The primary limitation of CO2-uptake and growth was probably related to the concentration of free CO2, given the relative excess of other major nutrients (N, P, Si) in he media used. Limited of CO2-uptake could be restored without CO2 additions if the CO2 present was redistributed between its several forms (increasing free CO2) by the addition of strong acid, although growth was still restricted.Limitation of CO2-uptake, either by CO2-depletion or the addition of an inhibitor of photo-synthesis (DCMU), increased the sinking rate of Asterionella cells from 0·3 to 1 m day-1. The possible ecological implications of CO2-pH-growth and CO2-pH-buoyancy relationships are discussed, which may contribute to the frequent paucity of diatoms during summer in manv productive lakes.