Different Modes Of Origin Research Articles

Characterisation by ESI FT-ICR MS of heteroatomic compounds in catalytic hydropyrolysates released from marine crude oil asphaltenes

Aliphatic hydrocarbon biomarkers released from the asphaltene-bound fractions of crude oils have been well studied, whereas attention to released polar non-volatile heteroatomic compounds is lacking. Here, the molecular compounds bound in asphaltenes were released via catalytic hydropyrolysis (HyPy) of four crude oil samples which have two different modes of origin. The heteroatomic compounds (nitrogen, sulfur, and oxygen-bearing) in the asphaltene hydropyrolysates and crude oils were characterised by electrospray ionisation (ESI) with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The groups of heteroatomic compounds in the asphaltene hydropyrolysates were found to be similar to those in the free fractions of the corresponding crude oils. However, the double bond equivalents (DBE) and carbon numbers of the heteroatomic compounds were different. Generally, the composition and distribution of heteroatomic compounds in samples with different origins had different characteristics, which allowed the origins of the samples to be distinguished. However, crude oils originating from the same source rocks, did show some differences in the composition and distribution of heteroatomic compounds, reflecting differences in hydrocarbon accumulation and post-accumulation alteration. These differences were not so evident in the HyPy asphaltene fractions, indicating that the heteroatomic compounds bound in the asphaltenes can preserve original information about kerogen origins (and post diagenetic changes). Their characterisation and comparison has the potential to provide insights into their origins and into the processes of hydrocarbon accumulation and any subsequent alteration.

Evaluation of terrigenous input, diagenetic alteration and depositional conditions of Lower Carboniferous carbonates of Tethys Himalaya, India

Geochemical and isotopic signatures from Lower Carboniferous Limestone of the Lipak Formation of Spiti region, Tethys Himalaya (for the first time) have been studied for palaeo-climatic reconstruction of the region and to evaluate the influence of terrigenous input into the Tethyan Ocean. The principal component analysis (PCA) suggests that CaO exhibits different modes of origin as compared to other elements. The low and relatively constant Al/Si ratio (0.19–0.46) of Lipak limestone suggests that Si has multiple sources besides clay minerals. Higher Al2O3 of the limestone than siliciclastic-contaminated carbonates (1.59%) as well as comparable Y/Ho ratio to terrestrial material suggests terrigenous input into the basin. The Er/Nd ratio ranges from 0.07 to 0.18 which further indicates the influence of detrital input (in normal seawater Er/Nd is 0.27). The Mn/Sr ratio suggests insignificant diagenetic alterations. The lack of correlation between Sr and LREE concentration in the limestone (r = 0.036) lends credence to this conclusion. Geochemical palaeo-redox parameters such as negative Mn and positive Ce anomalies (V/V + Ni) and Th/U ratios indicate that the limestone was deposited in anoxic environmental conditions. δ18O and δ13C isotope composition of whole-rock samples ranges from −10%o to −24%o and +3.34%o to −8.24%o respectively indicating significant climatic change during Carboniferous period. These observations are consistent and match with those of contemporaneous carbonates elsewhere in the world, which can be linked to the alternative occurrences of cold and warm paleoclimates in the Carboniferous. The onset of the Permo-Carboniferous glaciation would have resulted in more positive δ13C and less negative δ18O values for these carbonates. The isotopic values also indicate eustatic sea level changes due to the glacial and interglacial phases during the period. Thus the signatures of Gondwana glaciation events are well preserved in the Lipak limestone of Spiti region.

Alleged Carboniferous (Viséan) volcanism at the eastern margin of the Moravo-Silesian Basin, Kraków region, Southern Poland

The volcanic rocks, represented by clasts in the breccias occurring within the Visean Culm sequence at Gluchowki, previously were considered to provide evidence of the earliest record of Variscan volcanism on the eastern margin of Moravo-Silesian Basin in the Krakow area. The breccias have been described as the deposits of submarine slides, accompanying the Visean volcanic activity. This paper provides evidence of a different mode of origin. The present study, based on new field observations, combined with petrological and geochemical data, showed that volcanic rocks are major framework constituents of a breccia and are accompanied by clasts of spotty hornfels and Culm mudstone. Some clasts originated in erosion of the nearby Permian Zalas rhyodacite laccolith and the spotty hornfelses of the contact aureole, while other clasts came from the Culm mudstones. The breccia framework components are not rounded and poorly rounded, which reflects their short distance of transport. Therefore, an alternative scenario for the genesis of the breccia is proposed. The breccias represent material deposited in erosional pockets formed along the bedding of the Culm mudstones. The red iron oxide shells around clasts may indicate weathering in a warm continental climate, thus constraining the breccia formation to either the Permian or the Early or Late Triassic. Thus, the only well documented Visean igneous rock in the study area remains the diabase, known from the Klucze borehole. Conversely, no volcanic rocks of this age have been documented in the area under consideration.

In defense of a fluctuating-interface, particle-accretion origin of folia

Two recent papers have proposed radically different modes of origin for cave folia. Audra et al. (2009) propose subaqueous origin of carbonate folia via hypogenic CO2 bubble trapping, with concurrent condensation-corrosion and evaporative precipitation within individual folia gas pockets. Queen (2009) proposes that at least some folia are analogous to suboceanic tufa-tower "flanges" and may result from subaqueous freshwater mixing into a briny environment. The purpose of this paper is to show that neither of these mechanisms can be the fundamental process responsible for folia morphology in cave deposits, and that accretion from adherent particles at fluctuating interfaces is the only mechanism that has been shown to apply to folia of all compositions and in all cave environments where they are known to occur.

Review: the charnockite problem, a twenty first century perspective

Beginning of the twentieth century was marked by coinage of a new rock name, Charnockite, first described as a hypersthene-bearing granite from Southern India. Since then charnockites have been described from most of the conti-nents and mostly restricted to high-grade belts. Later half of the last century saw a lively debate over an igneous versus metamorphic origin. However, two factors acted as deterrents for the resolution of the debate. First, charnockites and associated rocks occur in a variety of different structural setting and display diverse field rela-tions, attesting to possible different mode of origin. Second and possibly more important is the lack of consensus on the nomenclature of charnockites and associated rocks and this is commonly linked with the metamorphic versus magmatic perspective. Scanning the literature of this period makes one believe that both metamorphic and magmatic hypotheses are valid, but applicable to different field setting only. Before critically evaluating individual cases, it is imperative that a uniform approach in nomenclature should be agreed upon. It is proposed that name charnockite be adopted for any quartzofeldspathic rock with orthopyroxene, irrespective of its mode of occurrence, struc-tural setting and mode of origin. The associated more mafic varieties, be better described as mafic granulite, rather than basic charnockite. For the patchy charnockites of east Gondwana (including parts of Peninsular India, Sri Lanka and Antarctica), metamorphic transformation from amphibolite facies gneiss, by two different mechanisms: CO2 ingress from deep level, and drop in fluid pressure, has been proposed. However, all such patchy occurrence is not amenable to explanation by metamorphic trans- formation. In some instances, migmatisation of older charnockitic rocks is evident. Also pro- gressive charnockitisation relating patchy char-nockite to banded variety could be argued against on two counts: grain-size relation and time-relation. Larger bodies or bands have been explained as magmatic, but in many instances, from geochemical consideration alone. The compositional variation, commonly encoun-tered in many high-grade belts, if not described in terms of field relation, may lead to wrong no-tions of magmatic differentiation of mantle-de- rived melts. Crustal melting of dry granulite fa-cies source rocks has been proposed from geochemical and isotopic data of charnockitic intrusions. This model proposes high-tempera-ture melting of previously dehydrated and dry granulite source rocks. However, tectonic per-turbation subsequent to granulite facies meta-morphism that might have been responsible for such high temperatures, is not well constrained in this model. Finally, with advent of high- pressure dehydration-melting experiments in the nineties, dehydration-melting of mafic to intermediate composition, syn-kinematic with granulite facies metamorphism has been pro-posed.

Osmium isotope and highly siderophile element systematics of the lunar crust

Coupled 187Os/ 188Os and highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, and Re) abundance data are reported for pristine lunar crustal rocks 60025, 62255, 65315 (ferroan anorthosites, FAN) and 76535, 78235, 77215 and a norite clast in 15455 (magnesian-suite rocks, MGS). Osmium isotopes permit more refined discrimination than previously possible of samples that have been contaminated by meteoritic additions and the new results show that some rocks, previously identified as pristine, contain meteorite-derived HSE. Low HSE abundances in FAN and MGS rocks are consistent with derivation from a strongly HSE-depleted lunar mantle. At the time of formation, the lunar floatation crust, represented by FAN, had 1.4 ± 0.3 pg g − 1 Os, 1.5 ± 0.6 pg g − 1 Ir, 6.8 ± 2.7 pg g − 1 Ru, 16 ± 15 pg g − 1 Pt, 33 ± 30 pg g − 1 Pd and 0.29 ± 0.10 pg g − 1 Re (∼ 0.00002 × CI) and Re/Os ratios that were modestly elevated ( 187Re/ 188Os = 0.6 to 1.7) relative to CI chondrites. MGS samples are, on average, characterised by more elevated HSE abundances (∼ 0.00007 × CI) compared with FAN. This either reflects contrasting mantle-source HSE characteristics of FAN and MGS rocks, or different mantle–crust HSE fractionation behaviour during production of these lithologies. Previous studies of lunar impact-melt rocks have identified possible elevated Ru and Pd in lunar crustal target rocks. The new results provide no supporting evidence for such enrichments. If maximum estimates for HSE in the lunar mantle are compared with FAN and MGS averages, crust–mantle concentration ratios ( D-values) must be ≤ 0.3. Such D-values are broadly similar to those estimated for partitioning between the terrestrial crust and upper mantle, with the notable exception of Re. Given the presumably completely different mode of origin for the primary lunar floatation crust and tertiary terrestrial continental crust, the potential similarities in crust–mantle HSE partitioning for the Earth and Moon are somewhat surprising. Low HSE abundances in the lunar crust, coupled with estimates of HSE concentrations in the lunar mantle implies there may be a ‘missing component’ of late-accreted materials (as much as 95%) to the Moon if the Earth/Moon mass-flux estimates are correct and terrestrial mantle HSE abundances were established by late accretion.

Divergence of Recently Duplicated M -Type MADS-Box Genes in Petunia

The MADS-box transcription factor family has expanded considerably in plants via gene and genome duplications and can be subdivided into type I and MIKC-type genes. The two gene classes show a different evolutionary history. Whereas the MIKC-type genes originated during ancient genome duplications, as well as during more recent events, the type I loci appear to experience high turnover with many recent duplications. This different mode of origin also suggests a different fate for the type I duplicates, which are thought to have a higher chance to become silenced or lost from the genome. To get more insight into the evolution of the type I MADS-box genes, we isolated nine type I genes from Petunia, which belong to the Mgamma subclass, and investigated the divergence of their coding and regulatory regions. The isolated genes could be subdivided into two categories: two genes were highly similar to Arabidopsis Mgamma-type genes, whereas the other seven genes showed less similarity to Arabidopsis genes and originated more recently. Two of the recently duplicated genes were found to contain deleterious mutations in their coding regions, and expression analysis revealed that a third paralog was silenced by mutations in its regulatory region. However, in addition to the three genes that were subjected to nonfunctionalization, we also found evidence for neofunctionalization of one of the Petunia Mgamma-type genes. Our study shows a rapid divergence of recently duplicated Mgamma-type MADS-box genes and suggests that redundancy among type I paralogs may be less common than expected.

Phylogeography of the longnose dace (Rhinichthys cataractae) species group in northwestern North America — the origin and evolution of the Umpqua and Millicoma dace

The Umpqua and Millicoma dace are small cyprinid fishes endemic, respectively, to the Umpqua and Coos rivers on the central coast of Oregon. The origins and relationships of these dace are unclear; however, two hypotheses have been postulated that assume these dace had evolved from a longnose dace ( Rhinichthys cataractae (Valenciennes, 1842)) like ancestor, but from different modes of origin. The direct origin hypothesis postulates that each of these dace originated directly, but independently, from a common ancestor. In contrast, the indirect origin hypothesis postulates that the Umpqua dace originated from a R. cataractae like ancestor and that the Millicoma dace evolved from the Umpqua dace. We used mitochondrial (cytochrome b and control region) sequences to test the two hypotheses. Our maximum likelihood analysis supports the indirect origin hypothesis and argues that together the Umpqua and Millicoma dace form a distinctive Oregon coastal clade within the R. cataractae species group. We also attempt to reconcile this result with the observation that the geographic distribution of the morphologically divergent Umpqua dace is sandwiched between the geographic ranges of the morphologically similar Millicoma dace and longnose dace.

Geochemistry of bedded barite of the Mesoproterozoic Aggeneys-Gamsberg Broken Hill-type district, South Africa

Stratiform and stratabound barite ± magnetite beds are intimately associated with the polymetallic Broken Hill-type (BHT) massive sulfide deposits of the Aggeneys-Gamsberg Pb–Zn–Cu ± Ag–Ba district in the Northern Cape Province, South Africa. Barite samples were collected and studied from four localities in the district. Although metamorphic water–rock interaction processes have partially altered the chemical and to a lesser degree the isotopic composition of barite, samples identified as being the least altered display distinctly different isotopic compositions that are thought to reflect different modes of origin. All barite samples are marked by low concentrations of SrO (0.5 ± 0.2 wt%), highly radiogenic 87Sr/86Sr ratios, elevated δ 34S and δ 18O values compared to contemporaneous Mesoproterozoic seawater. Radiogenic 87Sr/86Sr signatures (0.7164 ± 0.0028) point to an evolved continental crustal source for Sr and Ba, while elevated δ 34S values (27.3 ± 4.9‰) indicate that contemporaneous seawater sulfate, modified by bacterial sulfate reduction, was the single most important sulfur reservoir for barite deposition. Most importantly, δ 18O values suggest a lower temperature of formation for the Gamsberg deposit compared with the occurrences in the Aggeneys area, i.e. Swartberg-Tank Hill and Big Syncline. The obvious differences in temperature of formation are in good agreement with the Cu-rich, Ba-poor nature of the sulfide mineralization of the Aggeneys deposits vs the Cu-poor, Ba-rich character of the Gamsberg deposit. In conjunction with this, isotopic and petrographic arguments favor a sub-seafloor replacement model for the stratabound barite occurrences of the Aggeneys deposits, while at Gamsberg, deposition at the sediment–water interface as a true sedimentary exhalite appears more likely.

Geochemical evidence for a subducted infant arc in Franciscan high-grade-metamorphic tectonic blocks

Some of the evidence of tectonic and chemical processes that occur in subduction zones is preserved in blueschists and eclogites, as validated by the geochemical data presented from high-grade-metamorphic tectonic blocks from the Franciscan Complex in central California. Combining major elements, compatible and incompatible trace element concentrations and ratios, and Sr-Nd-Pb isotopic data, we conclude that the protoliths of these high-grade Franciscan blocks were arc lavas with no continental crust–derived components. Although the protoliths underwent high-grade metamorphism at the inception of subduction, the tectonic affi nity of the protoliths can be distinguished by our geochemical study. Our geochemical data are signifi cant in that (1) the protoliths of these high-grade blocks have a different mode of origin than the protoliths of the lower-grade Franciscan basalts that were incorporated later in the subduction complex, as the latter generally are considered to be oceanic-island basalts (OIB) and derived from mid-oceanicridge basalt (MORB); and (2) the protoliths of the high-grade blocks were formed over a pre-Franciscan subduction zone. Based on the geochemical evidence for an arc origin and the available geochronological data, we suggest that protoliths of the highgrade tectonic blocks of the Franciscan Complex and the Coast Range Ophiolite formed in the same infant-arc setting. Initiation of Franciscan subduction in this arc crust led to the formation of the high-grade blocks beneath the young Coast Range Ophiolite. Continued subduction resulted in subduction of older oceanic crust of MORB and OIB origin, some of which was scraped off to form lower-grade metabasites within the Franciscan Complex.

Genetic Origin of Malignant Trophoblastic Neoplasms Analyzed by Sequence Tag Site Polymorphic Markers

Objective. To study the causative conception of malignant gestational trophoblastic neoplasms (GTNs), we analyzed malignant GTNs by microsatellite PCR markers.Method. DNAs extracted from 12 malignant GTNs were subjected to PCR for five different chromosomal locations.Result. Of the 7 cases after a complete mole (CM), 5 were derived from androgenesis, but the remaining 2 were from normal fertilization. Of the 5 cases after nonmolar pregnancies, 2 placental site trophoblastic tumors had alleles from both parents. Of the other 3 choriocarcinomas, 1 was from normal fertilization after spontaneous abortion but 2 originated from androgenesis, suggesting that 1 was from a CM prior to the antecedent abortion, transforming after a long interval.Conclusion. By combining the previous cases with these, our analysis of 39 cases demonstrated that trophoblastic neoplasms can arise from at least three different modes of origin (androgenesis, normal fertilization, and parthenogenesis), and antecedent pregnancy is not always identical to the causative conception. Placental site trophoblastic tumors might have different machinery for carcinogenesis because of the predominance of paternal and maternal contributions. In addition, a long dormancy of trophoblasts before malignant transformation, especially for those originating from normal fertilization, was also suggested.

Geochemical comparison between Archaean and Proterozoic orthogneisses from the Nagssugtoqidian orogen, West Greenland

In the Palaeoproterozoic Nagssugtoqidian orogen of West Greenland reworked Archaean and juvenile Proterozoic orthogneisses occur side by side and are difficult to differentiate in the field. Archaean gneisses have tonalitic to trondhjemitic compositions with relatively low Al 2O 3 and Sr, and may have been derived from magmas formed by melting of basaltic or amphibolitic rocks at moderate pressures. The Proterozoic rocks are on average more mafic, and it is likely that they crystallised from mantle-derived magmas. Felsic varieties of the Proterozoic igneous suite probably formed from the original magma by fractional crystallisation, in which hornblende played an important role, and at SiO 2 > 65% Archaean and Proterozoic rocks have very similar major and trace element compositions (including REE), illustrating that different modes of origin may lead to very similar results.

NGC 4622 versus NGC 3081 Disks: Encounter versus Intrinsic Rings

AbstractStar formation processes in galaxies are far from being understood. Resonance rings of star formation are a common phenomenon of early-type barred spiral galaxies. Most rings are regions of enhanced star formation via gas cloud collisions near resonances, under the action of a gravitational bar perturbation. A small number of rings may form in response to a mild tidal interaction with a nearby companion. In either case, resonance rings are natural dynamical experiments in star formation stellar association time evolution. We study star formation in two galaxies where resonance rings probably have these two different modes of origin. NGC 3081 has four bi-symmetric star-forming rings that are probably connected to bar-driven gas dynamics, while NGC 4622 is a non-barred spiral where a strong one-sided ring may be connected to a past tidal interaction. We model the young clusters in the rings as two-fold and one-fold periodic orbits, respectively. We show that age indicators, Hα emission and the color index B – I, vary with position angle around the rings in a two-fold and one-fold sense as predicted by our models. The success of these models shows that future high resolution observations can be used to separate the individual associations from the underlying disk light so as to study their evolution and luminosity function.

Malignant trophoblastic neoplasms with different modes of origin

The genetic origin of 24 trophoblastic neoplasms was determined using PCR polymorphisms. Based on pregnancy history, these tumors included nine postmolar trophoblastic tumors, 12 tumors preceded by live birth or abortion, and three nongestational tumors. Androgenetic origin was defined in eight post-molar trophoblastic tumors, and the remaining one might have arisen from a normal fertilization. Six tumors retained genetic features carried by the homozygous complete mole. Two tumors showed PCR polymorphism compatible with that of the heterozygous complete mole. All 12 tumors in the second class had alleles of both paternal and maternal contribution. However, discordance of sex between the antecedent pregnancy product and the tumor was recognized in three choriocarcinomas. The absence of paternal contribution suggested a parthenogenetic origin of three nongestational choriocarcinomas. The findings that PCR polymorphisms were either homozygous in certain loci or heterozygous in others may mean that the tumor was derived from a germ cell after meiosis I. As a result, at least three subtypes with different modes of origin were demonstrated in the 24 trophoblastic tumors. These findings underscore the importance of precise genetic marker analyses in a large series to clearly identify clinical and biologic characteristics of each subset of tumors.

Character, mass, distribution, and origin of tephra-fall deposits of the 1989–1990 eruption of redoubt volcano, south-central Alaska

The 1989–1990 eruption of Redoubt Volcano spawned about 20 areally significant tephra-fall deposits between December 14, 1989 and April 26, 1990. Tephra plumes rose to altitudes of 7 to more than 10 km and were carried mainly northward and eastward by prevailing winds, where they substantially impacted air travel, commerce, and other activities. In comparison to notable eruptions of the recent past, the Redoubt events produced a modest amount of tephra-fall deposits − 6 × 10 7 to 5 × 10 10 kg for individual events and a total volume (dense-rock equivalent) of about 3–5 × 10 7 m 3 of andesite and dacite. Two contrasting tephra types were generated by these events. Pumiceous tephra-fall deposits of December 14 and 15 were followed on December 16 and all later events by fine-grained lithic-crystal tephra deposits, much of which fell as particle aggregates. The change in the character of the tephra-fall deposits reflects their fundamentally different modes of origin. The pumiceous deposits were produced by magmatically driven explosions. The finegrained lithic-crystal deposits were generated by two processes. Hydrovolcanic vent explosions generated tephrafall deposits of December 16 and 19. Such explosions continued as a tephra source, but apparently with diminishing importance, during events of January and February. Ash clouds of lithic pyroclastic flows generated by collapse of actively growing lava domes probably contributed to tephra-fall deposits of all events from January 2 to April 26, and were the sole source of tephra fall for at least the last 4 deposits.

Crypt Cell Proliferative Micronests in Rectal Carcinoids

Gastrointestinal endocrine cells are situated both in the epithelium as well as in the subepithelium, especially in relation to enteric nerves. This has complicated efforts at delineating the histogenesis of gastrointestinal carcinoids. However, gastrointestinal carcinoids themselves are a heterogeneous group made up of various subsets, and as such may have different modes of origin. The present study investigated the histogenesis of rectal carcinoids because this has not been adequately addressed. Nine rectal carcinoids together with sex- and age-matched controls were stained with silver stains and various immunoreagents. The number of intraepithelial endocrine cells per unit length of mucosa in the carcinoid group was compared with the controls using the Student t test. Our results showed that there was no evidence of diffuse intraepithelial endocrine cell hyperplasia associated with these carcinoids. In six of the cases, however, there were focal areas where the carcinoids abutted onto the mucosal epithelium, and in another two cases there were focal areas depicting crypt cell proliferative micronests. These findings suggest that most conventional rectal carcinoids arise from localized areas of crypt cell proliferation rather than from diffuse areas of intraepithelial endocrine cell hyperplasia. Furthermore, rectal carcinoids appear to be constituted of a heterogenous population of endocrine cells rather than a monoclonal population of cells with each cell expressing a multiplicity of hormones.

Isotopic evidence for UK Upper Permian mineralization by bacterial reduction of evaporites

The dolomites (Ca Mg (CO3)2) of the Lower Magnesian Limestone (or Cadeby Formation, Upper Permian age) are believed to have been formed by evaporation of seawater and include sulphate also associated with that environment. Mineralization in the formation includes baryte (BaSO4) and galena (PbS) together with other sulphides and has been ascribed to many different modes of origin. Sulphur isotope analyses have now shown that the sulphates were derived from seawater of Upper Permian age and that sulphides in sites of former anhydrite (CaSO4) nodules were formed by bacterial reduction of sulphate. This latter point is confirmed by the carbon isotope composition of the carbonates whose oxygen isotope values indicate the possibility of admixture of meteoric water to the system. Other baryte mineralization directly involves Upper Permian seawater or evaporite sulphate, whereas smaller baryte occurrences and epigenetic galena mineralization show no such direct involvement.

Morphologie und Morphogenese des Bodenciliaten Oxytricha granulifera sp.n. (CiIiophora, Oxytrichidae)

Oxytricha granulifera sp.n. differs from other members of the genus by its subpellicular granules and the strongly shortened dorsal kinety 4. The overall pattern of the morphogenetic events is similar to that known from other Oxytrichidae. However, the oral primordium evolves de novo between the left marginal cirral row and the postoral cirri. The six anlagen of the frontoventral cirri are of different origin. Two anlagen of the proter evolve from parental frontal cirri, two from the opisthe, and one includes basal bodies of the proter and opisthe. Two anlagen of the opisthe evolve from the oral primordium, and three primordia originate from the postoral cirri. Frontal cirrus 1 evolves from the paroral membrane in the proter, and from the oral primordium and the anlagen of the frontoventral cirri in the opisthe. The genus Oxytricha can be subdivided into several groups with regard to the origin of its oral primordium and the development of the frontoventral cirri. The morphogenesis of the dorsal kineties in the Hypotrichida is reviewed. Seven different modes of origin are distinguished. We conclude that morphogenetic features cannot be used in the classification of the Hypotrichida at the generic level, because we have too little information to decide whether special morphogenetic features are important at the generic or species level.

THE DEVELOPMENT OF MYCORRHIZAL POPULATIONS ON POT‐GROWN SEEDLINGS OF EUCALYPTUS ST‐JOHNII R.T. BAK

SummaryThe development of a population of mycorrhizas on the root system of a pot‐grown Eucalyptus seedling has many of the characteristics of a disease epidemic. For example, the number of mycorrhizal apices tends to increase exponentially in the early stages. The disposition of these mycorrhizal apices is non‐random, a fact which should engender care when sampling during field surveys. The final pattern of distribution of mycorrhizal apices within the root system reflects the degree of pre‐infective ectotrophic spread, the frequency and location of primary infection events, the perpetuation of mycorrhizal apices by forward growth, the extent to which they proliferate by branching, and the contribution of later secondary infections from mycorrhiza‐derived inoculum. The relative importance of these different processes is determined, as in a plant disease, by interaction between prevailing fungal, plant and environmental factors. The importance of inoculum availability and the capabilities of the fungus with respect to different regions of the root surface are stressed. The different modes of origin of mycorrhizal apices must be taken into account in any studies which seek to understand the mechanisms involved in conversion of normal root apices into mycorrhizas.

Allende meteorite—old age but normal isotopic composition of potassium

The extensive investigation of the Allende meteorite has provided much new information on the early history of our Solar System. The findings include small but significant anomalies of the isotopic composition for several elements which are clearly not due to any of the processes hitherto known to cause such variations (see ref. 1 for review). These anomalies seem to confirm the reality of astrophysical concepts developed since the classical paper of Burbidge et al.2 on the different modes of origin of the nuclei. Evidence has also been found which points to the possible presence in Allende of pre-solar condensates. Jessberger and Dominik3 have presented data to support an earlier result4 according to which the 40Ar gas retention ages of some white inclusions from Allende exceed the canonical age of the Solar System. These gas retention ages were obtained by 40Ar–39Ar dating, however, and are therefore based on the assumption that the 39K/40K ratio in the inclusions is identical to that used in the reference standard. In view of the far-reaching implications of finding in meteorites solid matter pre-dating by roughly 500 Myr the condensation of the Solar System we have attempted to verify this assumption. This is especially important because the Allende inclusions contain elements with an anomalous isotopic composition.