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One-year-old cherry trees were fumigated with propene and gas-phase hydrogen peroxide, singly and in combination, in controlled-environment chambers for an 8-week period during the summer season. A UV light source was included with the combined propene and hydrogen peroxide regime to provide a source of hydroxyl radicals and ozone, and thus all the constituents of a photochemical smog. Measurements were made of soluble protein concentration and of glutathione reductase activity in leaf extracts from two or three leaf classes in plants from each treatment regime at the end of each fumigation period. Significant increases in soluble protein concentration with respect to the controls were found in plants fumigated with propene and hydrogen peroxide. The occurrence and extent of these differences depended on the leaf class and on the timing of the fumigation period over the summer with respect to bud break. The activity of glutathione reductase was found to be significantly increased in mature lower leaves of plants which had been fumigated with hydrogen peroxide. This effect was independent of the timing of fumigation with respect to bud break. Enzyme activity was also increased in propene and in propene plus hydrogen peroxide treatments, but only when plants were fumigated early in the growth season.

Orang-utans (Pongo pygmaeus) at the Singapore Zoological Gardens were presented with two thick-shelled edible seeds, Mezzettia parviflora (Annonaceae) and Macadamia ternifolia (Proteaceae) in order to estimate their maximum bite forces. The orang-utans could break the Macadamia seeds in one bite, while those of Mezzettia required repeated attempts. Examination of shell fragments showed that many had scratches and some had clear, but small (ca. 1-2 mm diameter), impressions on them. Building upon this information, semi-imitative tests were performed on the seeds in a universal testing machine by loading them in compression with either flat plates or metal casts of orang-utan cheek teeth. The maximum forces required to break the seeds were similar with both the flat plates and the metal teeth; the average for the Macadamia seeds being about 2,000 N (which forms a minimum estimate for the maximum bite forces in orang-utans) and for the Mezzettia seeds, 6,000 N. The work done with the metal teeth was much greater than with the plates. A mechanical analysis showed that this extra work went into producing permanent impressions ("bite marks") in the shell with the tooth cusps. These impressions were larger than those found on the shells of seeds bitten by the orang-utans. Nevertheless, it is shown theoretically that the size of these indentations can given an estimate of the bite forces used. The maximum force developed in the machine tests with the metal teeth was correlated with the force calculated from analysis of the bite marks. The method is suitable for use in field studies where the marks left on remnants of hard foods eaten by primates may be used to estimate, very roughly, the forces used to produce them.

Elevated levels of total glutathione and enhanced activities of glutathione reductase and ascorbate peroxidase were found in needles of red spruce which had been exposed to acidic mists. Reduced levels of ascorbate were also detected. Such observations suggest that oxidative stress is involved in processes which resist foliar injury caused by acidic misting. Different ionic compositions of the acidic mists applied had pronounced effects on the levels of these antioxidants and the activities of related enzymes. Sulphate was found to be most effective in causing increases in glutathione, while additions of ammonium and/or nitrate mitigated the effects of sulphuric acid. Moreover, it is the composition of ions in the applied mists, rather than the levels of acidity, that determines the extent of the overall response of red spruce. By contrast, although acidic mists caused similar increases in glutathione content of Norway spruce needles, no statistically significant changes of ascorbate or related enzymic activities were found.

Simultaneous recordings of the activity of the masseter and anterior temporalis and of jaw movement were made on 10 healthy dentate volunteers while they chewed roasted peanuts in their habitual manner. The quantity of food taken was altered by varying (a) its total weight (mouthful) between 8 and 1 g, but with a fixed initial particle size and (b) by varying its initial particle size between median sizes of 9.2 and 2.4 mm, but keeping the mouthful constant. Significant differences were found in the peak and mean (r.m.s.) estimates of muscle activity (particularly in the masseter), and the dimensions of jaw movements. These differences were associated with the variation in both the size of the mouthful and of the initial particles but were much greater with changes in the mouthful. A dimensional argument treating both the weight of food in the mouth and initial particle size as volumes showed that initial particle volume had been varied by approximately 50 times as much as mouthful volume and therefore that the mouthful was a far more critical factor in masticatory physiology than was the particle size of the food. The reasons for this probably lie in an understanding of mechanisms of food comminution.

Studies of the growth and water relations of the grass Phleum pratense L. (Timothy) were made after simultaneous exposure to SO(2) and NO(2) at concentrations ranging from 80 + 57.4 microg m(-3) to 240 + 172.2 microg m(-3) (SO(2) + NO(2)). Decreased partitioning to the roots was evident during exposure to the pollutants, but when the plants were returned to clean air restrictions in root growth did not persist. Shoot to root partitioning was, however, complicated by the additional factor of changes in the nutritional status of the soil after additional columns of fresh soil were attached to the original tubes. The rate of use of soil water was nevertheless substantially increased by the pollution treatment and after a period of 23 days in which water was withheld, a clear pollution x water stress interaction was seen. The ability of polluted leaves to conserve water under severe water stress was tested by excising the leaves and measuring their water loss over time. The results from this second experiment showed that conservation of water by the leaves was appreciably affected after exposure to 80 + 57.4 microg m(-3) or 133.3 + 95.6 microg m(-3) SO(2) + NO(2). It seems likely that damage to the cells in the epidermal layer, leading to malfunctioning of stomata, is mainly responsible for the reduced ability to conserve water under conditions of extreme stress.

A method is described for measuring the rate at which carrot particles are broken down in chewing. In 10 subjects, this rate declined progressively throughout mastication. This was analysed in terms of two variables: (a) the intra-oral selection of particles for fracture, (b) the size distribution of fractured pieces of those particles. When intra-oral selection was measured by different methods, it depended mainly upon particle size. The selection of small particles might depend on the number of chews taken after the food was placed in the mouth. The size distribution of fractured pieces was obtained from one chew on three different particle sizes. These distributions were partially described by two different equations whose characteristics suggest that carrot particles are subjected to only one breakage per chew and that the number of fragments formed per breakage is small. It is suggested that the cusps present on the post-canines were important in determining this breakage pattern, and that the dependence of selection on particle size was primarily responsible for the decline in the rate of breakdown with increasing numbers of chews.

An analysis of the reduction of food particle sizes during human mastication is presented in terms of the probability of a particle being broken (selection function) and the distribution of fragment sizes produced when it fails (breakage function). Both selection and breakage functions are defined and a general equation produced. Several feasible behaviours for these two variables that have been suggested in the literature are modelled by computer simulation and the results are compared to published breakdown patterns. The conclusions are that selection and breakage functions probably behave very simply with respect to particle size, and that these behaviours could be deduced from an analysis of food particle size distributions and the rate at which particle sizes are reduced per chew.

There are two separable aspects of the mastication of food particles. One aspect describes the probability of the selection of particles for fracture (selection); the other describes the manner of fragmentation of the particles (breakage). Definitions of these concepts were used to produce an approximate equation for food breakdown, which can be solved by iteration in a computer. Values for the selection and breakage functions, obtained from 10 human subjects using carrot as a test food, were used in a computer program which modelled mastication. The model assumed (1) that selection depended only on particle size (2) that fragmentation (range of fractions or sub-particles produced) was similar for all particles, whatever their size. Good agreement was found between the actual particle-size distributions produced by mastication and those distributions generated by the computer. Simulations predicted that the initial particle size of the carrot before mastication could be varied substantially, so producing similar particle-size distributions after 15 chews.

Canine crown heights, measured from the cement-enamel junction to the cusp tip, were directly proportional to mandible length for 37 species of catarrhines (males and females plotted separately). The ratio canine height/mandible length was much greater for males than females. An allometric analysis revealed close relationships between canine size and body weight in males when the sample was split into hominoid, cercopithecine and colobine groups but not close for females. It is suggested that canine size in males is controlled by differences in mandibular form. Reasons for the variability of canine size in females remain unresolved.

The effect of varying the portion of food offered for chewing (termed the mouthful) on aspects of the oral comminution of salted peanuts was investigated on six human subjects. Particle-size distributions, assessed from a sieving analysis, were similar for different mouthfuls, and could be characterized by a sieve size that would pass 80 per cent of the particles by volume in a distribution. As the food weight was increased, (a) the rate of particle-size reduction of the food declined exponentially, (b) the rate of food surface area production increased, (c) the number of chews to swallow the food increased, (d) the number of chews per unit gram to swallow the food decreased, (e) the food-particle sizes that were swallowed increased. It is hypothesized that the volume of food between the teeth at any chewing stroke depends more on food-particle size than on the weight of food in the mouth. The swallowing of small mouthfuls of peanuts may have depended more on the time to wet particles with saliva than particle size.

A local Singaporean study of the presence of incremental lines in the cement of extracted teeth of 41 identity card-holding subjects is reported. The undecalcified roots of these teeth were sectioned transversely, some of which were stained with alizarin red. The lines observed were counted by one observer while blind to the actual ages of the subjects. A previous suggestion that these lines are deposited annually could not be supported in this sample, the number of lines tending to produce a lower estimated age than that registered on the identity card. The Pearson correlation coefficient for the line counts between two observers on 26 teeth was 0.73 (r2 = 0.535) which reflected difficulties in visualising the lines.