Exposed water ice deposits on the surface of comet 9P/Tempel 1

We report the direct detection of solid water ice deposits exposed on the surface of comet 9P/Tempel 1, as observed by the Deep Impact mission. Three anomalously colored areas are shown to include water ice on the basis of their near-infrared spectra, which include diagnostic water ice absorptions at wavelengths of 1.5 and 2.0 micrometers. These absorptions are well modeled as a mixture of nearby non-ice regions and 3 to 6% water ice particles 10 to 50 micrometers in diameter. These particle sizes are larger than those ejected during the impact experiment, which suggests that the surface deposits are loose aggregates. The total area of exposed water ice is substantially less than that required to support the observed ambient outgassing from the comet, which likely has additional source regions below the surface.     

On the ethics of biological control of insect pests

Of the four types of biological control, (1) natural, (2) conservation, (3) augmentation, and (4) importation), ethical concerns have been raised almost exclusively about only one type: importation. These concerns rest largely on fears of extinction of animal species. Importation biological control is a cost-effective alternative to chemical control for basic food crops of resource-poor farmers. Regarding the other types of biological control, natural biological control is not consciously manipulated by humans. Augmentation has some technical concerns, but is generally an environmentally-sound, viable alternative to chemicals and offers local employment. Conservation can help empower farmers to preserve native species, while saving labor and money and reducing chemical insecticides.     

Mobile point defects and atomic basis for structural transformations of a crystal surface

Structural transformations on elemental semiconductor surfaces typically occur above several hundred degrees Celsius, and the atomic motions involved are extremely rapid and difficult to observe. However, on the (111) surface of germanium, a few lead atoms catalyze atomic motions so that they can be observed with a tunneling microscope at temperatures below 80 degrees C. Mass transport and structural changes are caused by the creation and propagation of both vacancy-like and interstitial-like point defects within the crystal surface. The availability of dangling bonds on the surface is critical. A detailed atomic model for the observed motions has been developed and is used to explain the structural phase transition Ge(111)-c(2x8) <--> 1x1, which occurs near 300 degrees C.     

The application of Mahalanobis's generalized distance to measure genetic divergence in Durum wheat

Summary Mahalanobis's generalized distance analysis of days to flowering, days to physiological maturity, height, lodging, and grain yield data pertaining to ten cultivars of durum wheat (Triticum turgidum L. var. durum) revealed no association between genetic divergence and geographic origin. The analysis, however, succeeded in differentiating between those cultivars of tropical origin adapted to short daylength and those of temperate origin requiring longer days. The influence of the characters studied in assigning cultivars to particular groups varied from cultivar to cultivar.Contribution No 304 of the Plant Science Department, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada.     

Normal and abnormal meiosis in a partially male-sterile sugar-beet (Beta vulgaris L.)

Summary The duration of meiosis at 20°C was about 24 hours in Beta vulgaris L. cv. Sharpes Klein monogerm. While timing meiosis some plants were found with aberrant meiotic and tapetal development. The abnormalities are described and compared with abnormal anther development in B. vulgaris previously noted by other workers.     

Methods of evaluating strawberry plants as sources of field resistance to Phytophthora fragariae Hickman

Summary Nine cultivars and four unnamed seedlings were assessed for their potency as parents in breeding for red core resistance. Field resistance was assessed by scoring the plants for survival on a site heavily infected with Phytophthora fragariae. As a generalisation it was found that the field resistance of the parents was closely related to that of their progenies.The information gained from analysis of data obtained from families raised in routine breeding was at least as useful as that obtained from a diallel cross or from a selfing experiment designed specifically to test the parents.Two unnamed Fragaria virginiana I derivatives (53Q13 and 60BQ8) and a Siletz derivative (60CE5) were the most resistant and proved to be the most potent sources of resistance, but their fruit quality was poor. Cambridge Favourite, despite its lack of vertical resistance, was at least as potent as Redgauntlet.General combining ability for red core resistance was more important than specific combining ability though the latter was evident with a few of the crosses.     

Some evidence for genetically controlled variation in photosynthetic rate of oil palm seedlings

Summary The rate of uptake of ¹⁴CO₂ by oil palm seedlings in relation to light intensity was studied in a complete diallel cross. Analysis showed heritable differences in both light saturated and light limited photosynthesis, and in leaf chlorophyll content. The potential importance of this in a breeding programme is discussed.     

The effect of temperature during growth and flowering on the seed set of tetraploid freesia

Summary Phytotron experiments have been carried out to study the effect of different temperatures on the seed set of tetraploid freesias during the raising of the plants and at the time of flowering and pollination.The effect of a relatively low temperature during the growth period is reflected in a comperatively greater number of flowers as a result of an increase in number of ramifications of the peduncle. This sometimes promotes the seed yield notwithstanding that the lower temperature reduces the fertility of each seperate flower. It is clearly proved that the temperature during flowering and pollination affects the fertility of the flower and the ultimate seed yield of the plant. Experiments in our phytotron showed 14°C during the growth period and 20°C at the time of pollination to be the optimum combination for a good seed yield.The effect of a lower night temperature was generally favourable, particularly so when measured by the number of seeds per pollinated flower.     

Nonmethylated transposable elements and methylated genes in a chordate genome

The genome of the invertebrate chordate Ciona intestinalis was found to be a stable mosaic of methylated and nonmethylated domains. Multiple copies of an apparently active long terminal repeat retrotransposon and a long interspersed element are nonmethylated and a large fraction of abundant short interspersed elements are also methylation free. Genes, by contrast, are predominantly methylated. These data are incompatible with the genome defense model, which proposes that DNA methylation in animals is primarily targeted to endogenous transposable elements. Cytosine methylation in this urochordate may be preferentially directed to genes.