A new species of Poly dor a (Polychaeta: Spionidae) from the Indo-West Pacific and first record of host hermit crab egg predation by a commensal polydorid worm

A new spionid polychaete, Polydora robi, is described from intertidal and shallow subtidal areas in the Philippine Islands and Bali, Indonesia. Polydora robi belongs to the Polydora ciliata/ websteri species group and is characterized by a rounded prostomium, triangular occipital tentacle, needlelike posterior notosetae, and a pygidium with digitiform composite cirri surrounding the anus. Adults burrow into empty gastropod shells inhabited by hermit crabs. The burrows of the worms typically extend from an external opening in the apex of the shells to an opening in the central body whorls along the columella. The species was found to ingest the fertilized eggs and developing embryos attached to the pleopods of host hermit crabs. The occurrence of egg predation and the symbiotic relationship between polydorids and hermit crabs is discussed. Known egg predators of hermit crabs are reviewed.     

Biochemical Approaches to Mating Type Expression in Tetrahymena thermophila1

Two-dimensional gel electrophoresis was used to identify the patterns of protein synthesis during initiation, and the patterns of membrane protein expression following initiation, in all of the mating types of the Tetrahymena thermophila B family. In addition, one-dimensional analysis was used to survey ¹²⁵I-Concanavalin A-binding proteins. Although a large number of proteins was identified by each technique, no variation among the mating types was observed.     

Insect pollination of sugar-beet (Beta vulgaris) seed crops

The flowers of sugar-beet crops grown to produce hybrid seed were visited by many species of insects which often carried much sugar-beet pollen on their bodies and could have contributed to pollination.     

Carnation Italian ringspot virus

Carnation Italian ringspot virus (CIRV) was obtained only twice in tests on several thousand carnations in Britain during 15 yr. The two isolates, from cultivars ‘Dusty Sim’ imported from Italy and ‘Orchid Beauty’ from the U.S.A., were indistinguishable serologically and in host reactions. CIRV was cultured in Nicotiana clevelandii and assayed in Chenopodium amaranti-color; it was readily transmitted by leaf-rubbing inoculation to 62 of 104 plant species tested. Virus-free carnations were infected only by injecting purified preparations into the stem, and developed chlorotic spots and oval rings in the younger leaves. CIRV was eliminated from Nicotiana clevelandii plants grown for 8 weeks at 36°C. CIRV presents no threat to carnation growing in Britain. In N. clevelandii sap, CIRV was infective at a dilution of 1/50000 to 1/100000, after heating 10 min at 85 °C (but not 90 °C), and after 16 weeks at 16 °C or 23 weeks at 2 °C. After freeze-drying, the virus survived at least 7 yr storage under vacuum at room temperature. CIRV was still infective and antigenic after treatment for 30 min at 18 °C with ultraviolet radiation (750 μW/cm²), ultrasound, 2% formaldehyde or 0.2% tri-sodium ortho-phosphate (TSP). Infectivity was not wholly abolished in 30 min by 2% TSP. The virus was readily purified by overnight maceration of N. clevelandii leaves extracted in phosphate buffer + butanol, followed by differential centri-fugation. Purified preparations contained abundant isometric particles c. 29 nm diameter, and like other serotypes of the tomato bushy stunt-pelargonium leaf curl group, gave three or four specific bands in density-gradient centri-fugation. The bands corresponded to four Schlieren peaks in analytical centrifugation. Virus from the lower bands was usually less invasive in N. clevelandii than from the upper bands, although the material in the different bands contained similar amounts of nucleic acid. Only one antigenic component was found by Immunoelectrophoresis; different serotypes of the TBSV-PLCV group differed widely in immunoelectrophoretic behaviour. The present cryptogram of CIRV is */*:*/*:S/S:S/*.     

Attempts to eliminate chrysanthemum stunt from chrysanthemum by meristem-tip culture after heat-treatment

‘Mistletoe’ chrysanthemums infected with stunt were grown at 35°C for 14–37 weeks, and meristem-tips cultured from them at intervals. Of 337 meristems, seventy-two survived to plants but their development took 50% longer than did that of stunt-free meristem-tips. All plants were symptomless for at least 5 weeks after planting in 75 mm pots of soil-mix, and only three showed symptoms after 9 weeks. No more plants developed symptoms during the next 5 (winter) months, but between mid-March and late May sixty-seven did so. Only two plants were freed from stunt. ‘Mini-cuttings’ rooted from shoot tips of infected chrysanthemums grown at 35°C for 37 weeks all developed stunt symptoms within 27 weeks.     

A study of a subalpine woodland-grassland boundary

Reasons for the absence of trees on flat valley-bottoms in the subalpine regions of south-eastern Australia were studied at Seventeen Flat near Currango and other sites in the Snowy Mountains of New South Wales. Temperature changes with height above terrain were measured at grassland and woodland sites by thermistors attached to a hydrogen-filled balloon. The occurrence of nocturnal temperature inversions above grassland was established. Minimum temperatures at 80 cm above ground were recorded for thirty-one weeks at thirteen stations along a transect across the grassland and extending into the woodland on either side. Minima were lower and frequency of temperatures below—9°C were higher in grassland than in woodland. Seedlings of subalpine woodland species and other eucalypts were planted at both grassland and woodland stations. At grassland stations seedlings of tree-line species showed frost injury within a short time from planting and none survived two winters. The death of planted trees at grassland stations, the high frequency of temperature inversions and the low minima recorded on grassland compared with woodland suggest that temperature is a primary cause of the absence of trees in grasslands below subalpine woodlands.     

A survey of the fauna of streams on Mount Elgon, East Africa, with special reference to the Simuliidae (Diptera)

The stream fauna of Mt Elgon is described from collections taken during a 6-week visit. Collections were mainly made on the cultivated slopes below the belt of montane forest, and although stations were concentrated on the western sides of the mountain sufficient were worked elsewhere to show that there was little or no geographical variation of the fauna. The streams are physically diverse but faunistically rather uniform, with a few genera dominating the fauna throughout the entire range of altitude investigated. Most of the other taxa showed evidence of altitudinal limitation which may be attri-buted to the pronounced temperature gradients of the mountain's streams. As the species of Simuliidae and adult Elminthidae could be reliably distinguished their distributions were studied in greater detail. The Simuliidae showed a pronounced zonation of species, the majority being confined to narrow ranges of altitude below the forest margin. Factors considered to influence their distribution were principally altitude (temperature), current speed and, to a lesser extent, stream size. The influence of these factors on the distribution of adult Elminthids was less marked, although all species showed at least an upper or a lower limit of altitude, and more than half the commoner species a preference for a particular stream type. Taxonomic knowledge of African freshwater faunas allows few groups to be identified beyond the genus, and with this limitation the Elgon stream fauna is found to differ in only minor respects from the faunas of other highland areas in Central Africa.     

Somatic Embryogenesis: Factors Influencing Coordinated Behaviour of Cells as an Embryogenic Group

A number of common features are associated with a great diversityof observations of somatic embryogenesis in vitro. There arefundamental homologies between direct and indirect somatic embryogenesis,and between single-cell and multiple-cell initiation. Many ofthe observed differences can be attributed to whether or notcells require redetermination to the embryogenic state, andto differences in the nearest neighbour relationships of initiatingcells. The observed pattern of morphogenesis depends on whethera group of cells can establish and maintain coordinated behaviouras an embryogenic unit and will be influenced by factors whichaffect intercellular communication. Somatic embryogenesis, tissue culture, cell-cell interactions     

The Nature and Organization of Filaments in the Oral Apparatus of Tetrahymena1

ABSTRACT. Filaments in the oral apparatus of Tetrahymena appear similar, but not identical, to the intermediate filaments of multicellular organisms. The mean diameter of filaments measured in the present study was 16.4 nm, but the range of variation was much greater than has been reported for intermediate filaments. The organization of filaments within the oral apparatus has been studied by indirect immunofluorescence microscopy and immunogold localization at the electron microscopical level using antiserum raised in rabbits against the major subunit protein of the oral filaments (87K). The filaments were found to be organized into cables, networks, and chambers or cages which encase the basal bodies. At the highest level of organization, the filaments connect into a rigid framework capable of maintaining the overall architecture in the absence of microtubules. Like intermediate filaments, the oral filaments are insoluble at high ionic strength, have evolutionarily non-conservative subunit proteins, are probably non-contractile, and serve to stabilize persistent cellular architecture.