Ethylene production and plantlet formation by Nicotiana anthers cultured in the presence and absence of charcoal

Anthers of Nicotiana tabacum produce ethylene when cultured for plantlet production. The rate is at a maximum 1–2 weeks after the onset of culture. Charcoal in the medium increases the proportion of androgenic anthers in N. tabacum and several other Nicotiana species. The level of ethylene in culture vessels is reduced by charcoal. However, complete removal of ethylene does not significantly alter the incidence of androgenesis, nor does continuous flushing of cultures with air. It is concluded that although charcoal reduces ethylene in the gas phase of the cultures its effect on androgenesis is exerted through some other mechanism

Geomagnetic Observations for Main Field Studies:from Ground to Space

Direct measurements of the geomagnetic field have been made for more than 400 years, beginning with individual determinations of the angle between geographic and magnetic North. This was followed by the start of continuous time series of full vector measurements at geomagnetic observatories and the beginning of geomagnetic repeat stations surveys in the 19th century. In the second half of the 20th century, true global coverage with geomagnetic field measurements was accomplished by magnetometer payloads on low-Earth-orbiting satellites. This article describes the procedures and instruments for magnetic field measurements on ground and in space and covers geomagnetic observatories, repeat stations, automatic observatories, satellites and historic observations. Special emphasis is laid on the global network of geomagnetic observatories