Temporary patterns in the embryonic development of the beluga]

The data concerning the absolute and relative duration of different periods of the beluga embryogenesis are obtained and the relative durations of the same periods of embryogenesis in beluga, sevryuga (Acipenser stellatus) and sturgeon (Acipenser güldenst?dti) were compared. The relative durations of cleavage, gastrulation and early organogenesis in beluga are rather stable within the zone of optimal temperatures and similar to those in sturgeon and sevryuga. In beluga the relative duration of the period between the insemination and the appearance of the 1st cleavage furrow on the egg surface and the relative duration of the second half of embryogenesis (from the formation of heart rudiment till the hatching of single larvae) are somewhat less.     

Temporary immersion systems in plant micropropagation

Temporary immersion systems for plant micropropagation have been described and grouped into 4 categories according to operation: tilting and rocker machines; complete immersion of plant material and renewal of the nutrient medium; partial immersion and a liquid nutrient renewal mechanism; complete immersion by pneumatic driven transfer of liquid medium and without nutrient medium renewal. The positive effects of temporary immersion on micropropagation are indicated for shoot proliferation and microcuttings, microtuberization and somatic embryogenesis. Immersion time, i.e. duration or frequency, is the most decisive parameter for system efficiency. Optimizing the volume of nutrient medium and the volume of the culture container also substantially improves efficacy, especially for shoot proliferation. Temporary immersion also generally improves plant material quality. It results in increased shoot vigour and in the frequency of morphologically normal somatic embryos. Hyperhydricity, which seriously affects cultures in liquid medium, can be eliminated with these culture systems or controlled by adjusting the immersion times. Plant material propagated by temporary immersion can perform better during the acclimatization phase than material obtained on semi-solid or in liquid media. Successful regeneration of plants, after direct sowing on soil of Solanum tuberosum microtubers and Coffea arabica somatic embryos produced in temporary immersion bioreactors, has been demonstrated. As could be expected when using liquid medium for micropropagation, several estimations confirm large gains in efficacy from temporary immersion. The parameters most involved in reducing production costs include: (1) the drastic reduction in work; (2) reduction in shelving area; (3) reduction in the number of containers used; (4) better biological yields. Scaling-up somatic embryogenesis and shoot proliferation procedures involving temporary immersion systems in order to commercialize this process are now taking place.     

The Ecology of Temporary Streams III. Temporary Stream Fishes in Southern Ontario,Canada

The 12 fish species living in three temporary streams in Southern Ontario, Canada, during 1973–1974, are listed. Environmental parameters are recorded together with details of the abundance, distribution, age structure, growth, reproduction and food of the more common species. These species are thought to be either physiologically very tolerant, or to be capable of temporal or spatial migrations. Colonization of temporary streams bestows benefits in terms of plentiful invertebrate food, although resource sharing may occur, earlier spring breeding and reduced predation.