Populations ofR Research Articles

Molecular systematics of Australian rhinolophid bats (Chiroptera : Rhinolophidae)

Genetic variation in two morphologically distinct species of Australian Rhinolophus, R. megaphyllus, and R. philippinensis, and a third putative species (‘the intermediate’) were examined using allozyme electrophoresis and sequencing of the mitochondrial DNA (mtDNA) control region with the aim of resolving their taxonomic status. The surprising result was that no fixed allozymic differences and low allozyme divergence existed among these three taxa over 45 loci examined. In contrast, levels of intra-generic divergence among eight species of Rhinolophus showed up to 50% fixed allozyme differences between species, indicating that low allozyme divergence was not a common feature of the genus and that the three Australian taxa are likely to be monophyletic and recently diverged. Phylogenetic analyses of mtDNA sequence data revealed that populations of R. megaphyllus and R. philippinensis from Sabah, New Guinea, and Australia were represented by distinct mtDNA clades and that the two species are polyphyletic. These data suggest a reclassification of the different geographic populations of R. megaphyllus and R. philippinensis as separate species on the basis of a phylogenetic species concept. Within Australia, three distinct mtDNA clades were found, one of which showed ‘the intermediate’ in paraphyly with R. philippinensis from Queensland, but does not resolve the taxonomic status of ‘the intermediate’. Two mtDNA clades were also found representing R. megaphyllus from Queensland and R. megaphyllus from Victoria and New South Wales respectively. The finding of genetic subdivision along the east coast of Australia in an apparently continuously distributed bat species raises questions of the origin and historical biogeography of these bats in Australia.

Rhizobium as a factor in the re-establishment of legume-based pastures on clay soils of the wheat belt of north-western New South Wales

Summary. Populations of Rhizobium meliloti in self-mulching clay soils (Vertisols) at 48 sites on 27 properties in north-western New South Wales were classified according to number and ability to fix nitrogen with several species of Medicago. Rhizobia were counted using serial dilution, nodulation frequency, plant infection tests. Abilities of the soil populations to fix nitrogen were determined in the laboratory with whole-soil inoculation of Medicago seedlings in test tubes with shoots exposed to the atmosphere and roots within the tubes under bacteriological control, and in the field using a technique based on the natural abundance of 15N in the soil. The majority of soils contained >1000 cells of R. meliloti per gram. The major component of those populations fixed nitrogen with lucerne (Medicago sativa) and some components of some soils also fixed nitrogen with M. polymorpha, M. scutellata, M. littoralis, M. tornata, M. laciniata and Trigonella suavissima. However, a number of soils were located which contained few if any rhizobia effective in nitrogen fixation with M. polymorpha. Overall, the effectiveness of nitrogen fixation of the naturally occurring populations of R. meliloti in association with M. polymorpha, M. scutellata, M. littoralis and M. tornata was only 46% of the effectiveness of standard strains. At one particular site, where 10 lines of annual Medicago spp. were growing experimentally, fixed nitrogen as a proportion of shoot nitrogen averaged only 28%. At that site, there were no effective rhizobia for M. scutellata and it was wholly dependent on the soil as the source of its nitrogen. The results are discussed in relation to the need for a substantial input of legume nitrogen for restoring the natural fertility of self-mulching clay soils in degraded wheat lands of north-western New South Wales. It is suggested that lucerne, or perhaps other perennial Medicago spp., might fill this role better than annual medics such as M. polymorpha and M. scutellata that are more dependent than lucerne on specific strains of R. meliloti to meet their requirements for symbiotic nitrogen fixation.

Biochemical mechanisms of organophosphate resistance inRhyzopertha dominica(Coleoptera: Bostrichidae) populations from the United States and Brazil

AbstractFour possible biochemical mechanisms of organophosphate resistance were examined in populations ofRhyzopertha dominica(Fabricius) collected from eight locations in the states of Minas Gerais and São Paulo in Brazil and from seven locations in northeast Kansas, United States. Results from insecticide bioassays with synergists (triphenyl phosphate, diethylmaleate, and piperonyl butoxide) suggested that metabolic detoxification mechanisms might be involved in organophosphate resistance in some of the populations ofR. dominica. However, overall low synergism, non-synergism or even antagonism presented by these synergists in all 15 resistant populations suggested that carboxylesterases, cytochrome P450 monooxygenases and glutathioneS-transferases were not likely to play a major role conferring organophosphate resistance inR. dominica. This hypothesis was strongly supported by our biochemical studies showing no significant difference in these enzyme activities, as well as cytochrome b5, P420, and P450 levels between the susceptible and resistant populations. In contrast, all resistant populations ofR. dominicashowed higher acetylcholinesterase activity than the susceptible population both in the presence and absence of malaoxon. Furthermore, acetylcholinesterase from the resistant populations was less sensitive to inhibition by malaoxon than that from the susceptible. These results suggested that quantitative and qualitative changes in acetylcholinesterase might contribute to organophosphate resistance in these populations ofR. dominica.

Effect ofMethanobrevibactersp MF1 Inoculation on Glycoside Hydrolase and Polysaccharide Depolymerase Activities, Wheat Straw Degradation and Volatile Fatty Acid Concentrations in the Rumen of Gnotobiotically-reared Lambs

Four naturally born lambs were placed in sterile isolators 24 h after birth before the natural establishment of cellulolytic microorganisms and archaea methanogens. At the age of 6 weeks they were inoculated with pure cultures of the strains FD1 and 007 ofRuminococcus flavefaciensand at the age of 4 months with a pure culture ofMethanobrevibactersp. MF1. Following the establishment of MF1, the population ofR. flavefaciensslightly increased in the rumen of the four lambs, there was also an increase in straw degradation, in the activity of some glycoside and polysaccharide hydrolases of the adherent microbial populations and in the concentration of acetate in ruminal contents.

Exploring Phenotypic Plasticity in the LichenRamalina capitata: Morphology, Water Relations and Chlorophyll Content in North- and South-facing Populations

The present work analyses the morphology, anatomy, water relations and chlorophyll content of thalli of the lichenRamalina capitatavar.protectafrom two different populations exposed to contrasting microclimatic conditions due to differences in the orientation of the rock surface. The population on the north-facing rock surface (NFS) was exposed to lower photosynthetic photon flux densities (PPFD), remained at high relative humidities for longer periods of time and was exposed to lower temperatures than the population on the south-facing surface (SFS). We proposed the hypothesis that the shadier the habitat the greater the ecological advantage for enhanced light harvesting. Thalli from the SFS had shorter and wider lacinia, thicker thalli, mostly due to increased medulla thickness, a higher water-retention capacity, a higher percentage of thallus volume occupied by the algal cells and a higher chlorophyll content than thalli from NFS. The phenotypic plastic response of the traits studied inR. capitatavar.protectawas not directly related to differences in the light availability, at least for the range of PPFD experienced by the two populations studied, since the population exposed to higher PPFD exhibited larger amounts of light harvesting pigments. Both populations exhibited the same intrathalline distribution of algal cells and chlorophylls, which were more abundant in the apical than in the basal zones of all thalli studied. Periods of water-induced metabolic activity were shorter in the SFS than in the NFS, and structural and chlorophyll data indicated that thalli from the SFS were better prepared for the photosynthetic exploitation of these briefer periods and for maintaining thallus hydration into dry periods. These results suggest that differences in selective pressure between the two populations ofR. capitatavar.protectastudied involved maximization of the photosynthetic exploitation of the periods of metabolic activity when they are brief, as has been described for certain vascular plants from xeric environments.

Genetic markers distinguishing between the two subspecies of the rosy bitterling,Rhodeus ocellatus (Cyprinidae)

Eleven populations of the rosy bitterling,Rhodeus ocellatus, from different localities in Japan, were genetically compared at 16 protein-coding loci using starch-gel electrophoresis. Two loci,Ldh-2 andPgdh, were demonstrated as diagnostic markers for the identification of two subspecies;R. ocellatus kurumeus, which is native to Japan, andR. ocellatus ocellatus, which was introduced from China. The two subspecies were distinguished by the complete substitution of different alleles between them. Population ofR. ocellatus kurumeus occurring in Yao City, Osaka, and in Kanzaki, Saga Prefecture were genetically closely related to each other (genetic distance: D=0.056) but distantly so toR. ocellatus ocellatus from Saitama Prefecture (D=0.202 or 0.265). Electrophoretic analyses also elucidated the existence of hybrid populations of the two subspecies. The populations ofR. ocellatus kurumeus in Yao City had lower genetic variability and a lower incidence of white coloration on the ventral fins than populations of the same in Saga Prefecture. The present study strongly implies that the introduction of the foreign freshwater fishes with subspecific differentiation, into the original range of indigenous subspecies, should be averted not to bring the genetic pollution.

Structure, chirality, and field testing of a male-produced aggregation pheromone of Asian palm weevilRhynchophorus bilineatus (Montr.) (Coleoptera: Curculionidae)

4-Methyl-5-nonanol is a male-produced aggregation pheromone of the Asian palm weevil,Rhynchophorus bilineatus (Montr.). The pheromone was identified by coupled gas chromatographic-electroantennographic detection (GC-EAD) and coupled GC-mass spectrometric (MS) analyses of male-and female-produced volatiles. Analyses by GC-EAD and GC-MS of weevil-produced and stereoselectively synthesized isomers of 4-methyl-5-nonanol on a Cyclodex B column, which separated isomers with baseline resolution, revealed that only (4S,5S)-4-methyl-5-nonanol is EAD active and produced by the males. In field experiments in Papua New Guinea, (4S,5S)-4-methyl-5-nonanol and a racemic mixture of disatereoisomers of it enhanced attraction of male and female weevils to sugarcane-baited traps. (4S,5S)-4-Methyl-5-nonanol is also an aggregation pheromone of two other Asian palm weevils.R. ferrugineus (Oliv.) andR. vulneratus (Panz.). The stereoisomeric mixture of 4-methyl-5-nonanol is currently used to manage populations ofR. bilineatus in Papua New Guinea.

Life history variation and infraspecific heterochrony inRhinanthus glacialis (Scrophulariaceae)

Comparative cultivation experiments were made with 14 populations of the annual, hemiparasitic speciesRhinanthus glacialis from seven different habitat types. Phenological data were recorded and plants from field samples and from corresponding experimental samples were morphologically analysed. There are up to ten weeks difference in the start of flowering between means of the extreme experimental populations. Flowering time variation correlates with the number of internodes and also with most of the other morphological characters. Flowering time also shows close relationships to different grassland types and the examined populations appear to be well-adapted to the environmental conditions in natural or man-influenced grassland types as far as flowering time is concerned. The number of internodes is mostly insensitive to the applied experimental influences. The rate of internode production is constant. Trade-offs are suggested for some morphological traits (i.e., few internodes with few branches and thus few flowers as trade-off for early flowering). — Previous studies of life history variation based on population data have not been incorporated into the theory of heterochrony. The pattern of life history variation of populations ofR. glacialis together with information about morphology, ecology, and phylogeny suggests that some variants have evolved from ancestors via heterochronic processes. Earlier flowering populations from montane hay meadows, litter meadows, and dry meadows belong to paedomorphic variants. These have fewer internodes and branches as well as reduced height in comparison with the suggested ancestor. Later flowering populations from subalpine limestone grassland belong to a peramorphic variant with more internodes, more branches, and taller stems in comparison with the suggested ancestor.

Genetic Structure of Rhizobium leguminosarum biovar trifolii and viciae Populations Found in Two Oregon Soils under Different Plant Communities

An investigation was carried out to determine the genetic structure in soil populations of Rhizobium leguminosarum bv. trifolii and viciae at each of two Oregon sites (A and C) that were 1 km apart. Although the soils were similar, the plant communities were quite different because grazing by domestic animals had been allowed (site A) or prevented (site C). Analysis of allelic variation at 13 enzyme-encoding loci by multilocus enzyme electrophoresis delineated 202 chromosomal types (ETs) among a total of 456 isolates representing two populations of R. leguminosarum bv. trifolii (AT and CT) and two populations of R. leguminosarum bv. viciae (AV and CV). Regardless of their site of origin or biovar affiliation, isolates of the same ET were confirmed to be more closely related to each other than to isolates of other ETs by repetitive extragenic palindromic and enterobacterial repetitive intergeneric consensus sequences and the PCR technique. Despite the wide range in densities of the Rhizobium populations (<10 to >10/g of soil), their overall genetic diversities were similar (mean genetic diversity, 0.45 to 0.51), indicating that low-density populations of soil-borne bacterial species are not necessarily of little genetic diversity. Linkage disequilibrium analysis revealed significant multilocus structure (nonrandom associations of alleles) within each of the four populations. From a combination of cluster and linkage disequilibrium analyses, a total of eight distinct groups of ETs were defined in the four populations. Two groups (I and III) contributed significant numbers of ETs and isolates to each population. The two populations of R. leguminosarum bv. viciae (AV and CV) exhibited similar genetic structures despite existing at different densities, in different plant communities, and in the presence (CV) or absence (AV) of their local Vicia hosts. In contrast, total linkage disequilibrium was partitioned differently in two biovar populations occupying the same soil (AV and AT), with disequilibrium in the latter being due entirely to the presence of group V.

Effect of space on the multiplication of the reniform nematode,Rotylenchulus reniformis Lin. &amp; Ol. on cowpea,Vigna sinensis

The effect of space on the multiplication of the reniform nematode,Rotylenchulus reniformis on cowpea was determined under green house conditions. Both plant growth as estimated by root and shoot weights as well as its lengths and multiplication of the reniform nematode were greatly affected by the amount of space (soil). The population ofR. reniformis increased with an increase in the amount of space (soil) around seedling; highest being observed at 1,250 g of soil. The growth pattern of cowpea was attaining highest growth in 1,000 g of soil. Population ofR. reniformis increased with an increase in soil up to 1,250 g with 5 seedlings. The growth of cowpea was highest in 500 g of soil with 2 seedlings.

Serological and Ecological Characteristics of a Nodule-Dominant Serotype from an Indigenous Soil Population of Rhizobium leguminosarum bv. trifolii

Although at least 13 antigenically distinct serotypes of Rhizobium leguminosarum bv. trifolii exist in an Abiqua silty clay loam soil, one serotype, AS6, occupies >/=50% of the root nodules formed on field-grown subclover and between 33 and 78% of the nodules formed on five annual clover species grown in the same soil under laboratory conditions. The dominance of subclover nodules by serotype AS6 was reproducible over a 4-year sampling period and throughout the entire 200- by 100-m pasture examined. Serotype AS6 was composed of three antigenically distinct subtypes (AS6-a, AS6-b, and AS6-c). Each subtype contributed about one-third of the AS6 isolates recovered from nodules of field-grown subclover plants and maintained similar population densities in nonrhizosphere and rhizosphere soil. Rhizobia with the AS6 antigenic signature accounted for from 20 to 100% of the soil populations of R. leguminosarum in arable and pasture soils under legumes throughout the state of Oregon. Over a 12-month period, the population densities of the serotype AS6 complex and three minor nodule-occupying serotypes (AG4, AP17, and AS21) were measured in the rhizospheres of field-grown subclover and orchard grass and in nonrhizosphere Abiqua soil. Regardless of season or serotype, the orchard grass rhizosphere effect was minimal, with the ratio between rhizosphere and nonrhizosphere serotype population densities ranging between 2.5 (midsummer) and 10.5 (spring). In contrast, the magnitude of the subclover rhizosphere effect varied seasonally and among serotypes. Between October and December the ratios for all serotypes were similar (12.5 to 25.5). However, in the spring (April and May), the magnitude of the rhizosphere effect varied among the indigenous serotypes (ratios, 10.5 to 442) and for minor nodule-occupying serotypes AS21 (ratio, 442) and AP17 (ratio, 47) was as great as, or even greater than, the magnitude of the rhizosphere effect observed with the AS6 complex (ratio, 65.5).

Effects of moldboard plowing, chisel plowing and rotation crops on the Rhizoctonia disease of white potato

Two tillage practices, chisel plowing (30 cm) and deep moldboard plowing (22 cm), and five rotation crops (oats, lupine, buckwheat, broccoli and peas) were studied for their effects on the soil population ofRhizoctonia solani AG-3 and on Rhizoctonia disease on potato. All rotation crops were harvested except buckwheat, which was treated as a green manure crop. Chisel plowing significantly reduced (p = 0.05) the incidence and severity of stem lesions on potato caused byR. solani AG-3. In 1990, oats after moldboard plowing significantly increased disease when compared to other crops and broccoli after chisel plowing decreased disease severity. Soil populations ofR. solani AG-3 were significantly lower with chisel plowing. No interactions between tillage and rotation crops were observed.

Inoculation of pea by application of Rhizobium in the planting furrow

Selected streptomycin resistant strains ofRhizobium leguminosarum suspended in nutrient broth were added to the planting furrow immediately before the sowing of pea. The nodule occupancy by a strain isolated from Riso soil (Riso la) was increased from 74 to 90%, when the inoculum rate was increased from 3.7×106 to 3.7×108 cells per cm row. The experimental soil contained 103 to 104 cells ofR. leguminosarum per gram. An almost inefficient strain isolated from Riso soil (SV10) was less competitive with respect to nodulation on two pea cultivars than an efficient Riso strain (SV15) and an efficient non-Riso strain (R1045). The nodule occupancy by the introduced strains varied between pea cultivars. Irrespective of the generally high nodulation by the efficient strains introduced to the soil, the pea seed yield, compared to pea nodulated by the indigenous population, was not significantly increased. Neither were two commercial inoculants, applied in rates corresponding to 3 times the recommended rate, able to increase the yield. This suggests that the indigenous populations ofR. leguminosarum were sufficient in number and nitrogen fixing capacity to ensure an optimal pea crop. However, some inoculation treatments slightly increased the seed N concentration and total N accumulation, indicating that it may be possible to select or develop bacterial strains that may increase the yield.

Influence of Location, Host Cultivar, and Inoculation on the Composition of Naturalized Populations of Rhizobium meliloti in Medicago sativa Nodules

A phage typing system was used to evaluate the composition of indigenous populations of Rhizobium meliloti inhabiting nodules of Medicago sativa cultivars grown with and without inoculation at two field sites during 1983 and 1984. Soil at both locations contained established populations of R. meliloti at planting. Analysis of 1,920 nodule isolates revealed 55 unique phage types of indigenous R. meliloti at one site and 65 indigenous types at the other location. The distributions of phage types differed markedly between locations. At one site, the nodule population was dominated by two phage types; seven others occurred consistently but at lower frequency, and the remainder were encountered infrequently. No indigenous types predominated at the other location, although nine occurred more frequently than the remaining types. Indigenous R. meliloti predominated in nodules from inoculated plots at both sites, with inoculant recovery varying between 10 and 38% in each of two years. The frequency of occurrence of particular phage types at one location was significantly influenced by both M. sativa cultivar and inoculation. At this location, the interaction of cultivar and inoculation on the incidence of phage types suggests that the presence of an inoculant strain differentially affected nodule occupancy of M. sativa cultivars by members of the indigenous R. meliloti population. At both sites, the frequency of specific phage types differed between years. The data emphasize the importance of understanding the ecology and characteristics of indigenous Rhizobium populations as a prerequisite for elucidating problems of inoculant establishment and persistence in competitive situations.

Population Dynamics of Sugar Beets, Rhizoctonia solani , and Laetisaria arvalis : Responses of a Host, Plant Pathogen, and Hyperparasite to Perturbation in the Field

Rhizoctonia solani causes crown rot of sugar beets, a severe disease that has destroyed up to 60% of the plants in a test field in western Nebraska. Laetisaria arvalis, a natural hyperparasite of Rhizoctonia spp., was isolated from fields in western Nebraska. To test for the potential for biological control of R. solani, in November 1980 (following harvest) we applied various combinations of a nematicide (Telone II; Dow Chemical Co.), a nutrition source (sugar beet pulp), and an inoculum of L. arvalis in a randomized block design. Populations of R. solani, L. arvalis, and sugar beets were monitored monthly through October 1981 (just after harvest). In control and nematicide plots, the R. solani population did not change significantly through time. In plots inoculated with L. arvalis, the R. solani populations declined through March, concomitant with an increase in L. arvalis. L. arvalis then declined with a corresponding increase in the R. solani populations. Beet plant numbers declined significantly in all treatments. We suggest that reduction of the R. solani populations with the hyperparasite L. arvalis is possible but that a stable equilibrium naturally exists.

Population Changes and Persistence of Rhizobium phaseoli in Soil and Rhizospheres

The impact of legume cultivation on the establishment and persistence of an inoculant strain of Rhizobium phaseoli and its ability to compete with a resident population of R. phaseoli for nodule occupancy was examined utilizing strain-specific fluorescent antibodies. The soil (Hubbard loamy sand) was inoculated homogeneously with 5 x 10 cells per g of soil and confined in plastic cylinders kept in field plots. Inoculated and uninoculated cylinders were either left fallow or planted to two seeds of legumes. Two hosts, navy bean (Phaseolus vulgaris L.) cv. Seafarer and snap bean cv. Picker, as well as a nonhost, soybean (Glycine max (L.) Merr.) cv. Wilkin, were used. Inoculant Viking 1 was highly stimulated in all three rhizospheres sampled at 6 (flowering), 10 (podfill), and 17 (decay) weeks and in the following spring, whereas counts in fallow soil decreased rapidly. Although the overwintering population remained highest in the vicinity of decaying host roots, Viking 1 persisted, even in fallow soil, to produce abundant nodulation of host plants the following spring. Viking 1 was an excellent competitor for nodulation sites on the roots of the hosts; it thoroughly outcompeted the resident population of R. phaseoli, occupying virtually 100% of the nodules under inoculated conditions in all experiments.

Competitive Abilities of Rhizobium meliloti Strains Considered to Have Potential as Inoculants

Twenty four strains of Rhizobium meliloti considered to have potential for inoculant production were grouped in pairs and tested for their ability to compete for nodulation on Medicago sativa, Medicago truncatula, and Medicago littoralis. At the outset, each pair of strains, which consisted of a wild type and a selected streptomycin-resistant mutant of another strain, was tested in an autoclaved soil. Six strain pairs, each consisting of a good and a poor competitor, reacted consistently when tested in each of five other autoclaved soils; eight pairs consisting of strains with comparable competitive abilities varied in their reactions in some of the soils, or even in the same soil when retested. An effect of soil pH on competitive ability was observed with some of these strains. Not all of the strains identified as good competitors on one or more of the Medicago spp. in the autoclaved soils were able to nodulate these plants satisfactorily in a field soil containing an established population of R. meliloti. Strain RF24, which seemed to be the best competitor on each of the three Medicago spp., grouped among the less effective strains on two of the legumes. Two strains of R. meliloti frequently used for inoculant production differed markedly with regard to competitive ability; this places some doubt on the relevancy of singling out competitive ability for special attention when selecting a strain for inoculant production.

Survival and multiplication ofRhizobium japonicum strains in silt loam

Antibiotic resistant mutants 8-0 StrR, 110 TetR and 138 KanR derived from wild typeRhizobium japonicum strains were inoculated into silt loam soil to cell concentrations greater than 2×108/g of soil. Population changes were monitored using antibiotic media and strain identification was done using immunodiffusion assay on microcores of soil. Immunodiffusion bands formed by the mutant strains with homologous antisera essentially duplicated bands formed by the parent strain. Strains 110 TetR and 8-0 StrR had cross reacting antigens whereas antigens of strain 138 KanR reacted only with the homologous antiserum. Populations ofR. japonicum strains introduced into sterile soil increased over a period of four weeks under both single and mixed culture inoculations. All populations decreased by the end of six weeks and thereafter remained constant. When theseR. japonicum strains were introduced into non-sterile soil, the population did not increase over the initial population added. Population decreased gradually for two weeks and then maintained thereafter. It was possible to recover very low populations of antibiotic resistantR. japonicum strains from both sterile and unsterile soils using media containing specific antibiotics. Detection ofR. japonicum strains by immunodiffusion was accomplished only when the population was ≥109 cells/g of soil. The method using antibiotic resistant mutants permitted an evaluation of the interactions of variousR. japonicum strains in soil with respect to their survival and multiplication.

Zum Energieumsatz phytophager insekten im Buchenwald. I

Die Bestimmung des Energieumsatzes der Curculioniden-Populationen vonRhynchaenus fagi L.,Strophosomus (Schonherr) undOtiorrhynchus singularis L. wurde in folgenden Schritten vorgenommen:

Accretion and electrostatic interaction of interstellar dust grains; Interstellar grit

This work is divided into 13 sections and 2 appendices, and aims to elucidate the accretion mechanism, which operates via image-theory forces, whenever two interstellar dust grains come close together. Section 1 is an introduction. Section 2 proposes that the distribution of interstellar grains be taken asn(r) ∝r−4 to avoid distortion of the 3K microwave background by radiation from spinning grains. Section 3 examines each of three types of image force accretion processes, finding them to be dominant compared to radiation or gravitational forces by at least a factor of 1019. Section 4 states that only grains made of conducting material (e.g., graphite, ice, iron) are involved in image theory. Section 5 presents reasons for believing that two grains should coalesce on impact. Section 6 examines the motion of charged interstellar grains in Hi and Hii regions. Section 7 demonstrates, by way of four examples involving dust grains ofr=10−7 cm up tor=10−4 cm, that the image effects on conducting grains are not trivial, and that the dynamics involved is not to be compared at all with elementary Coulomb interaction of two changes. Section 8 concludes that accretion with not take place in Hi clouds if thermal (equipartition) velocities prevail among the dust particles. section 9 examines grain interactions in Hii regions: here, following an argument due to Spitzer, consideration is given to the case of a population of dust grains all streaming in the direction of the local magnetic field B at velocities of order 0.1 km s−1. It is shown that accretion takes place effectively, leading to the formation of interstellar ‘grit’, meaning grains of mass 10−8 to 10−7 gm, radius ≃ 0.1 mm; and leaving also a population ofr≳10−6 cm grains, which are observed in polarization and extinction measurements. The existence of the latter is now a deduction and not an ad hoc postulate, as previously, and implies a distribution of the general formn(r) ∝r mean −3 , in approximate agreement with that of Section 2. Section 10 considers the accretion mechanism as a cascade process. Section 11 shows that the existence of grains in space ofr ≃ 10−6 cm rules out an origin in supernova or galactic explosions, and supports a passive origin, perhaps in red giants or Mira variables. Section 12 discusses the implications of the results found for polarization observations and cosmogony, the latter being given a new foundation in which planets of different composition form automatically from a solar nebula. Section 13 is a conclusion.