STUDIES ON WEED SPECIES OF THE GENUS POLYGONUM L.     

J. L. HAMMERTON 《Weed Research》1965,5(1):13-26

Summary. Seeds of Polygonam persiaria were collected from seven localities during 1962. In 1963 plants of these seven populations were grown in the field and sampled at regular intervals over the period 21st June to 13th August. At all samplings there were differences between populations in total dry weight, in leaf area index and in total nitrogen content, and populations also differed in the date of flowering. The populations also differed significantly in relative growth rate, leaf area ratio, net assimilation rate and relative nitrogen absorption rate. The variations in net assimilation rate did not appear to be closely associated with variations in leaf area index. Certain growth attributes were correlated with the latitude of origin, and it is tentatively suggested that the populations may represent genetically distinct latitudinal ecotypes.
Études sur des espèces de mauvaises herbes du genre Polygonum L.  相似文献   

Shoot culture dynamics of six Populus clones   总被引：1，自引：0，他引：1  

Sellmer JC  McCown BH  Haissig BE 《Tree physiology》1989,5(2):219-227

Shoot tips of five genotypically diverse Populus clones, P. alba x P. grandidentata 'Crandon,' P. nigra 'Betulifolia' x P. trichocarpa, P. nigra x P. laurifolia 'Strathglass,' P. maximowiczii x P. trichocarpa 'Androscoggin' and P. deltoides x P. nigra 'Eugenei,' were collected from hardwood cuttings, sterilized,and established in vitro. Stable shoot cultures were obtained from all clones except P. deltoides x P. nigra 'Eugenei'. The four poplar clones that formed stable shoot cultures together with a previously established P. tremula 'Erecta' clone were placed as two-node explants on either Murashige and Skoog medium or Woody Plant Medium containing benzyladenine to determine the rate of shoot multiplication, shoot growth and other responses of the clones. All five poplar clones showed rapid shoot multiplication when cultured in the presence of 0.4-1.0 microM benzyladenine on Murashige and Skoog medium, although P. tremula 'Erecta' produced a greater number of healthy shoots when grown on Woody Plant Medium. Individual shoot growth of all clones was more vigorous when the medium contained 0-0.1 microM benzyladenine, and 100% of such shoots rooted ex vitro.  相似文献   

Ultrasound emission after cycles of water stress in Picea abies     

Borghetti M  Raschi A  Grace J 《Tree physiology》1989,5(2):229-237

The relationships among rate of ultrasound acoustic emission (AE), xylem water potential and transpiration rate were investigated in 5-year-old potted saplings of Picea abies Karst. after cycles of water stress. Water-stressed plants displayed minimum xylem water potentials of -3.9 MPa, near-zero transpiration rates and up to 45 AE counts per minute. After rewatering, water-stressed plants no longer produced AEs. Well-watered control plants produced only a small number of ultrasonic AEs. After three cycles of water stress (lasting 24 days in total), it was estimated that about two-thirds of the functional tracheids were embolized. The concomitant reduction in hydraulic conductance was about 70%.  相似文献   

CRADAs Raise Conflict Issues     

Culliton BJ 《Science (New York, N.Y.)》1989,245(4922):1035

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Giant radiation-induced color halos in quartz: solution to a riddle     

Odom AL  Rink WJ 《Science (New York, N.Y.)》1989,246(4926):107-109

The radii of radiation-induced color halos(RICHs) surrounding radioactive mineral inclusions in mica generally correspond closely to the calculated range of common uranogenic and thorogenic alpha particles in mica. Many exceptions are known, however, and these variants have led investigators to some rather exotic interpretations. Three RICHs found in quartz are identified as aluminum hole-trapping centers. Whereas the inner radii of these RICHs closely match the predicted range of the most energetic common alphas(39 micrometers), the color centers observed extend to 100 micrometers. Migration of valence-band holes down a radiation-induced charge potential might account for enigmatic RICHs. Such RICHs provide natural experiments in ultraslow charge diffusion.  相似文献   

What's in a Name?     

Benditt J 《Science (New York, N.Y.)》1989,246(4935):1252-1253

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Jeane dixon, call your office!     

Benditt J 《Science (New York, N.Y.)》1989,246(4935):1252

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Combining cognitive and statistical approaches to survey design     

Fienberg SE  Tanur JM 《Science (New York, N.Y.)》1989,243(4894):1017-1022

Sample surveys provide data for academic research, government policy-making, the media, and business. Statistical research aims to improve survey data by reducing extraneous sources of variability and thus increasing accuracy. Researchers have begun to use paradigms adapted from the cognitive sciences to study those sources of variability associated with the processes that the respondent undertakes in understanding questions, remembering, judging and estimating, and formulating answers. To generalize laboratory-based findings, researchers must begin to embed designed experiments that vary the questionnaire content into sample surveys of broad population. Issues associated with the design of and statistical inference from such embedded experiments are examined and illustrated with an example on the effects of context questions on responses in attitude surveys.  相似文献   

Broad training for social scientists     

Barkow JH 《Science (New York, N.Y.)》1989,243(4894):992

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A biomedical pioneer: otto folin     

Edsall JT 《Science (New York, N.Y.)》1989,244(4905):719-720

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