Pattern Of Cessation Research Articles

Flexible drought deciduousness in a neotropical understory herb.

PremiseAdaptive divergence across environmental gradients is a key driver of speciation. Precipitation seasonality gradients are common in the tropics, yet drought adaptation is nearly unexplored in neotropical understory herbs. Here, we examined two recently diverged neotropical spiral gingers, one adapted to seasonal drought and one reliant on perennial water, to uncover the basis of drought adaptation.MethodsWe combined ecophysiological trait measurements in the field and greenhouse with experimental and observational assessments of real‐time drought response to determine how Costus villosissimus (Costaceae) differs from C. allenii to achieve drought adaptation.ResultsWe found that drought‐adapted C. villosissimus has several characteristics indicating flexible dehydration avoidance via semi‐drought‐deciduousness and a fast economic strategy. Although the two species do not differ in water‐use efficiency, C. villosissimus has a more rapid growth rate, lower leaf mass per area, lower stem density, higher leaf nitrogen, and a strong trend of greater light‐saturated photosynthetic rates. These fast economic strategy traits align with both field‐based observations and experimental dry‐down results. During drought, C. villosissimus displays facultative drought‐deciduousness, losing lower leaves during the dry season and rapidly growing new leaves in the wet season.ConclusionsWe revealed a drought adaptation strategy that has not, to our knowledge, previously been documented in tropical herbs. This divergent drought adaptation evolved recently and is an important component of reproductive isolation between C. villosissimus and C. allenii, indicating that adaptive shifts to survive seasonal drought may be an underappreciated axis of neotropical understory plant diversification.

RETRACTED ARTICLE: Attributes of smoking cessation in the Egyptian community: dependence matters

Smoking is an avoidable behavioral cause of premature morbidity and mortality. The initiation, continuation, and dependence of smoking is associated with multiple personal, environmental, and sociocultural factors, which vary between age groups and geographical regions. To investigate the pattern of smoking cessation and the extent of the smoking dependence among smokers in urban and rural societies in Egypt. A cross-sectional study was conducted targeting a convenience sample of 552 adult smokers aged 11–75 years. All participants were inquired about their demographic features, lifestyle and behaviors, motives for smoking cessation, and quitting attempts using a predesigned interview questionnaire. Nicotine dependence was assessed using the Fagerstrom Test for Nicotine Dependence (FTND). About 28.1% of the participants reported a motivation to quit smoking and about 61.1% had made at least one attempt. The longest duration of quitting was ≥5 years, as reported by 4.0% of the smokers. The drive to quit smoking was prompted by the advice of a family member (39.9%) or a doctor (30.1%), concerns about smoking hazards (19.7%), or due to financial limitations (12.7%). The most frequently used methods to quit smoking were cold turkey (23.4%), gradual reduction (15.9%), and the use of nicotine replacement therapy (12.5%). Moderate and high nicotine dependence was found in 46.7% and 24.6% of respondents, respectively. Male sex was the single predictor of smoking dependence. Motivation to stop smoking was associated with the presence of social support and having a low dependence score. Nicotine dependence was significant at younger ages. Therefore, smoking cessation programs should be a top priority and targeted to prevent smoking in adolescence. Appropriate interventions addressing individuals’ motives and considering pharmacotherapeutic management are needed to encourage successful quit attempts.

Dual Antiplatelet Therapy Cessation and Adverse Events After Drug-Eluting Stent Implantation in Patients at High Risk for Atherothrombosis (from the PARIS Registry)

The impact of dual antiplatelet therapy (DAPT) cessation after percutaneous coronary intervention with drug eluting stent implantation in patients at high atherothrombotic risk remains unclear. We aimed to characterize the risk for adverse events, and its relation with the mode of DAPT cessation in patients at high atherothrombotic risk (HATR). Considering patients treated with drug-eluting stents among those enrolled in the Patterns of Non-Adherence to Anti-Platelet Regimens in Stented Patients registry, we defined subjects with prior myocardial infarction (MI), prior stroke or peripheral vascular disease at HATR, while patients without any of these conditions were classified as atherothrombotic risk (LATR). DAPT cessation-modes were defined as physician-recommended discontinuation, temporary interruption, and disruption due to bleeding or poor compliance. Compared to patients with LATR (n = 2867; 68.2%), patients with HATR (n = 1340; 31.8%) were older with a higher prevalence of cardiovascular risk factors. Over 2 years, HATR patients had lower rates of physician-recommended discontinuation (32.5% vs 39.4%; p = 0.002) and trend for disruption (11.5% vs 13.7%, p = 0.051), though no significant difference in the rate of DAPT interruption. Patients with HATR had higher 2-year rates of cardiac death, MI, or stent thrombosis compared with those at LATR (8.7% vs 4.0%; adjusted hazard ratio [aHR]: 1.80; 95% confidence interval [CI]: 1.36-2.39; p < 0.0001). Disruption of DAPT was associated with greater risk for cardiac death, MI, or stent thrombosis in both HATR (aHR: 1.86; 95% CI: 1.05 to 3.46) and LATR (aHR: 2.84; 95% CI: 1.68 to 4.80) patients (pinteraction = 0.40). The degree of atherothrombotic risk influences the pattern and mode of DAPT cessation with less discontinuation among patients considered HATR. Atherothrombotic risk status does not influence the association between DAPT cessation and cardiac risk.

Causes, Timing, and Impact of Dual Antiplatelet Therapy Interruption for Surgery (from the Patterns of Non-adherence to Anti-platelet Regimens In Stented Patients Registry)

Temporary interruption of dual antiplatelet therapy (DAPT) is not infrequently required in patients undergoing percutaneous coronary intervention (PCI). We sought to describe the procedures and outcomes associated with DAPT interruption in patients treated with DAPT following successful PCI from the Patterns of non-adherence to anti-platelet regimens in stented patients registry (n = 5018). DAPT interruption was prespecified as physician recommended cessation for <14 days. Of the study cohort, 490 patients (9.8%) experienced 594 DAPT interruptions over 2 years following PCI. Only 1 antiplatelet agent was interrupted in 57.2% cases and interruption was frequently recommended by noncardiologists (51.3%). Where type of surgery was reported, majority of DAPT interruptions occurred for minor surgery (68.4% vs 31.6%) and a similar cessation pattern of single versus dual antiplatelet cessation was observed regardless of minor or major surgery. Subsequent to DAPT interruption, 12 patients (2.4%) experienced 1 thrombotic event each, of which 5(1.0%) occurred during the interruption period. All events occurred in patients who either stopped both agents (8 of 12) or clopidogrel-only (4 of 12), with no events occurring due to aspirin cessation alone. In conclusion, in the Patterns of Non-adherence to Anti-platelet Regiments in Stented Patients registry, 1 in 10 patients were recommended DAPT interruption for surgery within 2 years of PCI. Interruption was more common for a single agent rather than both antiplatelet agents regardless of severity of surgery, and was frequently recommended by noncardiologists. Only 1% of patients with DAPT interruption experienced a subsequent thrombotic event during the interruption period, which mainly occurred in patients stopping both antiplatelet agents.

Perception and experience regarding menopause among menopaused women attending teaching hospitals in Erbil City.

Background and Objectives:The timing of menopause, perception as well as menopausal symptoms varies between populations and within populations. The main objective of the present study was to assess women’s perception and experience regarding menopause, to find out symptoms and mean age of menopause and to study socio-demographic characteristics of menopaused women and to find out its relationship with their age at menopause and their knowledge about menopause.Methods:Over a period of eight months a descriptive cross sectional study were carried out at the outpatient departments of four teaching hospitals in Erbil city. A total of 500 menopaused women their age ranged from 40-60 years were interviewed using a close ended self administered questionnaire.Results:Mean age of menopause was 47.44 years with median age was 48 years, 4.4% had premature menopause and 23.6% had early menopause. The only factors that significantly associated with age at menopause were education and pattern of menstrual cessation and 93.4% of menopaused women were heard about menopause, 56.6% had prior knowledge of menopausal symptoms, cessation of menstruation was positive in 47.0% and 85.8% of women perceive menopause as natural condition and the most common menopausal symptoms were tiredness occurring in 83.2%.Conclusion:Most of menopaused women perceive menopause as natural condition and not aware about hormone replacement therapy and the mean age of menopause is comparable to that mean reported in other part of Iraq. Among menopaused women tiredness was the most common complaint was followed by hot flushes and night sweats.

Pattern of smoking cessation and its associated factors in Vietnam

Background: Even though the number of research on tobacco in Vietnam has recently increased rapidly, there remains a lack of reporting on the pattern of quit smoking and its correlates. It is necessary to have scientific evidence on this issue to help the policy makers and the Public Health sector to have appropriate intervention program to enhance the smoke cessation smoke program and improve the health status of the smokers. This study aims to: (1) Describe the pattern of smoking cessation in Vietnam 2010. (2) Examine the association between smoking cessation with some associated factors in Vietnam 2010. Methods: Data used in this paper were obtained from the Global Adult Tobacco Survey (GATS) conducted in Vietnam in 2010. A total of 11,142 households were selected for this survey using a two-phase sampling design analogous to a three-stage stratified cluster sampling. Both descriptive and analytical statistical analyses were carried out. Multivariate logistic regression modeling was performed to examine the association between the patterns of quit daily; quit smoke; attempt to quit and intend to quit among smokers with relevant factors. Results: The prevalence of the different type of cessation among male and female were 23.3% and 28.6% for quit daily; 19.1% and 1.0% for quit; 55.6% and 44.4% for attempt to quit and 29.6% and 19.3% for intend to quit respectively. The prevalence of quit daily and quit increased with age whereas attempt to quit decreased with age. Prevalence of cessation was highest among the group who were asked about smoking tobacco by health care providers. Some determinants of quit daily and quit include age, area, and knowledge of illnesses caused by smoking. There was no association between attempt and intend to quit with any socio-characteristic except for area. People in rural area were 2.1 and 1.7 times more likely attempt to quit and intend to quit than those in urban area, respectively. Conclusion: The GATS Vietnam 2010 showed that the prevalence of cessation in Vietnam was low. Quit daily and quit had association with age, area, knowledge about the top three consequences of smoke. People in rural area were 2.1 and 1.7 times more likely attempt to quit and intend to quit than those in urban area, respectively.

Time trends and educational differences in the incidence of quitting smoking in Spain (1965–2000)

Background To analyze the pattern in the incidence of quitting smoking in Spain from 1965 to 2000 according to gender, age and educational level. Methods We used data from 5 Spanish National Health Interview Surveys including 33532 ever smokers ≥ 20 years old. We reconstructed the history of smoking and the age at smoking cessation. We calculated the biannual incidence of quitting smoking according to sex, age and educational level. We fitted joinpoint regression to identify significant changes in trends. Results The incidence of quitting smoking at ages 20–50 years has increased from 0.5% in 1965–1966 to 4.9% in 1999–2000 for males and from 1.1% in 1965–1966 to 5.0% in 1999–2000 in females. For those aged > 50 years old, the incidence of quitting smoking has increased from 0.4% in 1965–1966 to 8.7% in 1999–2000 for males and from 7.9% in 1973–1974 to 8.8% in 1999–2000 in females. A level-off in cessation rates is observed both in men and women aged 20–50 years old with lower educational level in the last decade, while cessation among those with higher educational level continue to increase. Conclusions The different pattern of smoking cessation according to gender, age, and level of education suggests that health promotion actions and tobacco control policies might have had a different effect among different population subgroups.

Role of Oleoresin Flow in Initial Colonization of Loblolly Pine by Southern Pine Beetle (Coleoptera: Scolytidae)

The influence of total resin flow in loblolly pine, Pinus taeda L., on initial colonization by the southern pine beetle, Dendroctonus frontalis Zimmermann (Coleoptera: Scolytidae), was investigated. Resin flow of trees was manipulated mechanically so that it followed the same pattern of decrease and near cessation as seen in trees successfully attacked by southern pine beetle. There were also intermediate treatments where resin flow was allowed to recover after near cessation. Beetles were introduced by means of mesh cages attached to the mid-bole of trees and left until the end of the longest wounding treatment. In trees where resin flow was reduced, significant increases in number of attacks, total gallery length, and length of gallery free of resin occurred.

The role of oleoresin flow in the induced response of loblolly pine to a southern pine beetle associated fungus

The influence of total resin flow in loblolly pine, Pinus taeda L., on initial inoculation of the blue stain fungus Ophiostoma minus (Hedgc.) Syd. &amp; P. Syd., a fungal associate of southern pine beetle (Dendroctonus frontalis Zimmermann (Coleoptera:Scolytidae)), was investigated. Resin flow of trees was mechanically manipulated so that it followed the same pattern of decrease and near cessation as seen in trees successfully attacked by southern pine beetle. There were also intermediate treatments where resin flow was allowed to recover. The fungus was inoculated into holes drilled to the xylem surface and allowed to grow for a specified time period. The lesion that formed as a result of the induced reaction was then measured and compared with lesions formed in trees for which resin flow was not manipulated. The experiment was conducted three times in 1993 and 1994 and twice in 1995. It was hypothesized that with decreased resin flow, O. minus would be less inhibited and that growth would be greater before being stopped by the induced reaction. It was found that longer lesions occurred in trees where wounding was prolonged and resin flow was decreased below that of control trees. Mixed results were obtained for trees in intermediate wounding treatments.Key words: oleoresin, blue stain fungus, defenses, bark beetles, induced reaction, Dendroctonus.

Widening social inequalities in smoking cessation in Spain, 1987–1997

In southern Europe, the prevalence of smoking among women has been lower than in northern Europe, with a wider gender and socioeconomic gap compared with most other developed countries. In...

The relation between growth cessation and frost hardening in Scots pines of different origins

The cessation of shoot elongation, diameter growth and needle elongation were compared with the initiation of frost hardening of the stems and needles in an 8-year-old provenance trial of Scots pine (Pinus sylvestris L.) established in central Finland. The saplings were of six different origins ranging from Estonia to northern Finland, forming a latitudinal gradient of ca. 10°N. The frost hardiness of the stems of current-year shoots was assessed by electrical impedance analysis and that of current-year needles by electrolyte leakage and visual scoring of damage. Artificial freezing tests were used in the assessments. The pattern of growth cessation (shoot and needle elongation, diameter growth) tended to follow the latitude of origin, i.e. growth ceased in the northernmost provenance first and in the southernmost one last. Both stems and needles of the northern provenances hardened earlier than the southern ones, but the differences in hardiness disappeared as hardening progressed. Growth cessation and initial hardening to –15°C were clearly correlated at the provenance level, indicating that growth must cease prior to hardening, and that earlier cessation of growth predicts earlier frost hardening of stems and needles. No differences in frost hardiness of stems were found at the provenance level at the end of the growing period in August. At that time, the frost hardiness of needles of the northernmost provenance was higher than that of other origins. Within the provenance, the stems were less hardy than the needles.

Correlates of age at natural menopause: a community-based study in Alexandria

Differences in the age at natural menopause were examined using a retrospective population sample of 289 naturally menopausal women. The mean age at natural menopause was 46.70 +/- 5.44 years. Earlier menopause occurred in women living in semiurban areas, divorced/separated and less educated women, and women who were younger at: first marriage, widowhood, divorce/separation and first or last full-term pregnancy. Later menopause occurred in women who had: irregular menstrual periods before 25 years, dysmenorrhoea and mid-cycle spotting. Duration of oral contraceptives use, weight and body mass index were significantly positively correlated with age at natural menopause. Multiple regression analyses indicated that age at last full-term pregnancy, residence, pattern of menstrual cessation and duration of oral contraceptive use were the significant predictors of the end of menstrual activity.

Photoperiodic induction of dormancy and freezing tolerance in Betula pubescens. Involvement of ABA and dehydrins

In many woody plants photoperiod signals the initiation of dormancy and cold acclimation. The photoperiod‐specific physiological and molecular mechanisms have remained uncharacterised. The role of abscisic acid (ABA) and dehydrins in photope‐riod‐induced dormancy and freezing tolerance was investigated in birch, Betula pubescens Ehrh. The experiments were designed to investigate if development of dormancy and freezing tolerance under long‐day (LD) and short‐day (SD) conditions could be affected by manipulation of the endogenous ABA content, and if accumulation of dehydrin‐like proteins was correlated with SD and/or the water content of the buds. Experimentally, the internal ABA content was increased by ABA application and by water stress treatment under LD, and decreased by blocking the synthesis of ABA with fluridone under SD. Additionally, high humidity (95% RH) was applied to establish if accidental water stress was involved in SD. ABA content was monitored by gas chromatography‐mass spectrometry with selective ion monitoring (SIM). Short days induced a transient increase in ABA content, which was absent in 95% RH, whereas fluridone treatment decreased ABA. Short days induced a typical pattern of bud desiccation and growth cessation regardless of the treatment, and improved freezing tolerance except in the fluridone treatment. ABA content of the buds was significantly increased after spraying ABA on leaves and after water stress, treatments that did not induce cessation of growth and dormancy, but improved freezing tolerance. In addition to several constitutively produced dehydrins, two SD‐specific proteins of molecular masses 34 and 36 kDa were found. Photoperiod‐ and experimentally‐induced alterations in ABA contents affected freezing tolerance but not cessation of growth and dormancy. Therefore, involvement of ABA in the photoperiodic control of cold acclimation is more direct than in growth cessation and dormancy. As the typical desiccation pattern of the buds was found in all SD plants, and was not directly related to ABA content or to freezing tolerance, this pattern characterises the onset of photo‐period‐induced growth cessation and dormancy. The results provide evidence for the existence of various constitutively and two photoperiod‐induced dehydrins in buds of birch, and reveal characteristics of dormancy and freezing tolerance that may facilitate further investigations of photoperiodic control of growth in trees.

The sociodemographic pattern of tobacco cessation in the 1980s: results from a panel study of living condition surveys in Sweden.

To analyse the factors that determined whether or not people were successful in quitting tobacco during the 1980s in Sweden. A logistic regression model was used for the analyses and included: education, marital status, socioeconomic group, social network, physical activities, cigarette consumption, and years spent smoking as independent variables. Men and women were analysed separately for smoking. A specific univariate analysis was also performed for men who used snuff. Sweden. A panel of 5104 randomised people aged 16-84 years was interviewed in 1980-81 and followed up in 1988-89 in the survey of living conditions undertaken by Statistics Sweden. The participation rate was 86%. The panel included 1546 men and women who were daily smokers. There were 418 daily users of snuff among the men, and 129 men both smoked and used snuff. Together 26% of women and 23% of men had quit smoking. Five percent in both groups were new smokers. Among men, 26% had quit using snuff and 5% had begun smoking. New snuff users among men were 5%. In the multivariate analysis, unmarried men kept smoking at significantly higher rates (OR 2.1; 95% CI 1.2,3.6), as did those men who smoked 11-20 cigarettes/day (OR 2.2; 95% CI 1.5, 3.4), or more than 20 cigarettes/day (OR 2.8; 95% CI 1.4,5.7). Among women, smoking 11-20 cigarettes/day was also a significant factor (OR 3.3; 95% CI 2.1,5.0). Men and women aged 25-44 were significantly more likely to continue smoking (OR = 2.1; 95% CI 1.1,3.7, and 2.2; 95% CI 1.2,4.4) as were those who had smoked for 20 years or more (OR 4.7; 95% CI 2.0,10.8 and OR 2.5; 95% CI 1.1,5.5, respectively). For women, low education (up to grade 9) was also a significant factor (OR = 2.5; 95% CI 1.2,5.1). Among men who had quit using snuff we did not find any values of significance. One in four smokers had quit during the 1980s and a few started smoking (5%). Some men quit smoking and started using snuff instead. For both sexes, the daily consumption of cigarettes, years spent smoking, and age were the most important determinants of successful quitting. In men, being married/ cohabiting was an important factor as was higher education in women.

The effect of melatonin implantation in the middle of the breeding season on the subsequent reproductive activity of Scottish Blackface ewes

The aim of this study was to determine if melatonin administration after the winter solstice affected the duration of the current and/or the onset or duration of the subsequent breeding season of ewes. Thirty-one cyclic Scottish Blackface ewes were randomly allocated to two treatments: (i) control, and (ii) implanted subcutaneously with a 350-mg sachet of melatonin on 17 January. Ovarian activity was monitored by use of vasectomised rams and strategically timed examinations of the ovaries by laparoscopy. Blood samples were collected from all ewes on 21 June (the summer solstice), 21 December (the winter solstice), and the following 7 July, and melatonin concentrations determined by radioimmunoassay (RIA) to confirm the presence of functional implants. The mean dates of last oestrus were 21 and 24 March for control and treated animals, respectively (s.e.=6.3 days). There was no difference between the control and implanted ewes in the pattern of cessation of ovulations, as observed by laparoscopy. Ovulation rate of ewes for the two cycles following implantation was not affected by treatment. Daytime concentrations of melatonin on 21 June were 25 ± 1.9 pg/ml and 138 ± 13 pg/ml for control and implanted ewes, respectively ( P<0.01), and these concentrations were maintained at the other two bleeding dates. Ovarian activity, as determined by laparoscopy, was observed in treated animals significantly earlier than in control animals at the start of the second breeding season ( P<0.02). Mean date of onset of the first oestrus of this breeding season was not significantly different in treated (8 October) and control ewes (16 October, s.e.=3.6). Mean duration of anoestrus was 206 and 193 days for control and implanted ewes, respectively (s.e.=9.3). The mean ovulation rate was significantly lower in implanted than in control ewes in October and November ( P<0.025). The mean date of the last oestrus of the second breeding season was 12 March for control ewes and 7 March for melatonin-implanted ewes (s.e.=7.5). The mean duration of this breeding season was 147 and 150 days for control and implanted ewes, respectively (s.e.=9.0). It is concluded that (i) melatonin implantation in the mid-breeding season is ineffective in extending the current breeding season of Scottish Blackface ewes; (ii) prolonged exposure to high circulating levels of melatonin significantly advanced the time of first ovulation of the following breeding season, and (iii) ovulation rate during much of the following breeding season was significantly depressed in treated animals.

Tillering behavior in Oryza sativa L. VI. The tillering behavior at late tillering stage.

孤独状態で育てた水稲の, 分げつ期終期の分げつ性について検討した。まず, 個体内全茎で葉齢の進み方が同調している生長 (同周期生長) を仮定して再構築した茎数増加曲線 (同周期生長曲線) と, 実測値の茎数増加曲線との増加停止パターンを比較し, 両曲線の性質を検討した。解析には, 典型的なシグモイド曲線を示したササニシキの茎数増加曲線と, 第2報で全茎が出現すると仮定してシミュレートした茎数増加曲線とを用いた。現実には茎数増加が急激に停止する場合でも, それまでに蓄積した相対葉齢差 (主茎と各分げつとの葉齢の速度の差) により, 同周期生長曲線では緩やかな停止となった。また, ササニシキの同周期生長曲線の終期は2次曲線で, その相対分げつ増加率 (Rt) は直線で近似できた。次に, ある母茎から出現した最後の嬢分げつ (最終分げつ) について, 分げつ期後期の成長と関連させて調べた。最終分げつの分げつ次位が高いほど, 相対分げつ位 (個体内で, 分げつを同伸分げつごとにまとめて, 出現順に位置付けた分げつ位は大きかった。これは最終分げつ出現時の相対葉齢差に基づくものであった。Rt算出の対象茎を, 分げつ生産能力を持つ茎だけに絞る方法が提案されているが, 最終分げつの出現時期や, 3葉を持たない分げつには分げつ生産能力がないことなどから, 分げつ生産能力を持つ茎の特定は困難で, この方法は現実的でないと考えた。従って, Rtは全生存茎を対象とし, 各茎の分げつ生産能力の変動をも含めて考えることが, 水稲の生長解析上有効と考察した。

Within-tree variation in wood production and wood quality in sycamore (Acerpseudoplatanus): its relation to crown characteristics

To quantify patterns of wood formation in sycamore (Acerpseudoplatanus L.), the seasonal progress of wood production and structure was followed systematically throughout the outer growth sheath of the main stem and major branches. These data were considered in relation to the profile of leaf dry weight down through the crown in 8- and 12-year-old trees at stages before and after canopy closure, respectively. Mature fibre production was earliest towards the tips of the branches of the midcrown, and spread basipetally along the branches. In the main stem, mature fibre production was earliest at the tip and spread down the tree, taking about 10 days to reach the base of both pre- and post-canopy closure trees. In the stem, later fibre production down the tree was offset by later cessation of fibre maturation basally. Branch data suggested that the pattern of cessation may depend on the branch position, because cessation was latest at the base of the upper branches and at the tip of the lower branches. The maximum rate of fibre production was in the upper stem, several internodes higher than the internode bearing maximum leaf dry weight. Despite this, ring width increased down the stem, presumably as a result of the increased duration of fibre production and increased cell size. Within growth rings, vessel size remained nearly constant before declining sharply towards the end of the ring. Trees with narrower growth rings tended to have more of their ring occupied by declining vessel size suggesting a slight inverse relationship between ring width and specific gravity. Specific gravity increased down the outer growth sheath of the stem, and this increase was associated with systematic trends in fibre and vessel dimensions, together with changes in the relative proportions by area of the different tissues. Although some anatomical characters appeared to vary with the profile of the crown, others appeared to be independent of crown profile.

The topography of cytogenesis in the developing retina of the cat

We have studied the pattern of cytogenesis in the developing retina of the cat, by observing mitotic cells in sections and whole mounts of the retinae of animals between the ages of E (embryonic day) 29 and P (postnatal day) 20. The whole mounts were prepared with the mitotic or ventricular layer uppermost; all of the mitotic cells in this layer could then be surveyed. In retinae from animals up to E46, mitotic cells were present in the ventricular layer at densities of 1000 to 3000 cells/mm2, and their density did not vary consistently with position in the retina. Thus cell division occurs throughout the retina at these ages, with an approximately constant spatial density. By E50, cytogenesis begins to cease and there is a significant pattern to the cessation. Initially, mitotic activity ceases over a small region of retina at the site of the developing area centralis. The nonmitotic area then increases with age, comprising the central 30 to 50% of the retina at birth and the whole of the retina by P10. The pattern of cessation of cytogenesis is closely coincident in space and time with the development of the outer plexiform layer and the maturation of the ganglion cell layer described in previous studies. These patterns presumably contribute to the regional variations in structure apparent in the adult retina.

The origin of hotspot traces: Evidence from eastern Australia

Interpretation of available isotopic ages and of published geologic maps of igneous rocks in eastern Australia indicates a north‐south time transgressive pattern of cessation of igneous activity along a curvilinear trace, beginning about 35 Ma at 20°S and extending to the present, near 37°S. However, volcanic activity began 70–60 Ma over the length of the Highlands and persisted through the early Cenozoic until progressive cessation began. The latitudinal rate of termination is compatible with that predicted by plate reconstructions relative to the Hawaiian ‘hotspot’, but the trend of the trace is incompatible with that predicted unless the Hawaiian‐Emperor bend is somewhat greater than 50 m.y. in age relative to the LaBrecque et al. [1977] time scale. The volcanic pattern appears to be incompatible with a hotspot or plume hypothesis. Paleostress and contemporary stress indicators as well as the volcanic pattern support a model in which the trace forms, due to intraplate extension normal to the trend of the trace, resulting in pressure release and melting at the base of the lithosphere, beginning in the Late Cretaceous. This stress field persisted until 35 Ma when progressive reorientation of the stress field occurred. Cessation of igneous activity reflected onset of compression normal to the trend of the trace. As a consequence, a migrating stress node is recorded in the progressive pattern of extinction of volcanic activity along the trace. Evidence from other ‘hotspot’ traces suggests that they too represent intraplate stress controls. It is not necessary to postulate deep sources (mantle plumes) for the origin of hotspot traces; intraplate stress due to drag, plate margin forces, thermal contraction, and nonsphericity of the earth can also reflect ‘absolute’ motion.

Observations with scanning and transmission electron microscopy on the structure of human surface enamel

The approximal surfaces of 71 partially erupted and unerupted molars and premolars were examined by scanning electron microscopy (SEM) and ultrasections of enamel specimens taken from the 16 approximal surfaces of eight teeth were examined by transmission electron microscopy (TEM). By SEM, bands of prism-end depressions most commonly alternated with bands of smooth enamel, although perikymata-spacing varied and areas occurred where the enamel was all smooth or all pitted and where perikymata were weak or absent. Many teeth showed other pits and outcrops, 5–60 μm dia, particularly near the enamel-cementum junction, which was contrarily sometimes completely smooth, and on marginal ridges and occlusal surfaces. By TEM, smooth surfaces consisted of crystals perpendicular to the outer enamel contour. Small pits were associated with the ends of prisms reaching the enamel surface. Striae of Retzius, varying from simple gaps between rows of crystals to more severe disturbances of structure, could be followed from within the enamel to the surface; sometimes a row of small outcrops, decreasing in size, was seen on the surface. Within these semi-spherical, or possibly cylindrical, structures, crystals were radially orientated. The variation in surface structure is accounted for by variations in the pattern of cessation of amcloblastic activity. Attention is drawn to the diurnal rhythm of enamel formation indicated by prism cross-striations and to the approximately 8-day periodicity of the striae of Retzius. A possible explanation of the striae is an imperfect synchronization of two or more circadian rhythms, ameloblast activity and general body activity for example, only one of which is exactly 24 hr. If separation of the two rhythms became too great, an incremental deposit would be delayed for the remainder of the cycle, possibly up to one day. until synchrony was restored. Such a mechanism has an electronic analogue in the cyclic “slipping” which can occur when an oscillator is imperfectly synchronized with a trigger signal.