A new annual species, Juncus maroccanus, of the section Tenageia, closely allied to Juncus foliosus Desf., is described from N Morocco. It differs from the latter in having smooth, glossy seeds, capsule shorter than perianth and shortly mucronate. The new species is known from a macrolocality in the Ksar-el-Kebir region, where it grows in non-saline sandy seepage sites. Another, much older specimen was collected in 1835 by W. Schimper in the Sinai Peninsula, Egypt. Syntype specimens of Juncus rhiphaenus Pau et Font Quer were examined and found to be conspecific with Juncus foliosus.
The effects of condensed tannins (CTs) extracted from pine bark on egg hatching, larval development and the viability of infective L3 larvae of Trichostrongylus colubriformis (Giles, 1892) and Teladorsagia circumcincta (Stadelmann, 1894) (syn. Ostertagia circumcincta) were evaluated using in vitro bioassays. Significant inhibitory effects of CTs were obtained on the viability of the infective larvae, egg hatching and larval development of both nematodes. In all bioassays, the larval stages of Te. circumcincta were significantly (P < 0.05) more susceptible to the inhibitory effects of CT than those of Tr. colubriformis. At 1 000 µg/ml, CTs from pine bark inhibited 48% and 69% of the infective larvae of Tr. colubriformis and Te. circumcincta, respectively, from passing through the sieve relative to the control incubations (no CT added; P < 0.0001). At the same concentration, CTs were able to inhibit 36% and 47% of the eggs of the two parasites, respectively, from hatching relative to the control incubations without CTs. Moreover, at 150 µg/ml, the CTs were able to inhibit 88% and 95% (P < 0.0001 relative to control incubation) of L1 larvae of the two nematodes, respectively, from attaining the full development to L3 larvae in comparison with the control incubations without CTs. At 200 µg/ml, CTs were able to inhibit completely the larval development in both nematodes. Addition of 2 µg polyethylene glycol (PEG; tannin inhibitor) per µg CT eliminated up to 87% of the CT activity (P < 0.0001) compared to incubations without PEG. In conclusion, this study shows that CTs are able to disrupt the life cycle of nematodes and their effects varied according to the parasite species and stage.
The ecophysiological function(s) and consequences of guttation, a phenomenon by which water is exuded by and accumulated as droplets along the leaf margins under high humidity in many plants that grow in wet soil, has been poorly studied and remains largely unknown. Thus, leaf gas exchange and chlorophyll fluorescence were examined, using two experimental approaches, in Alchemilla mollis plants under conditions that promoted guttation and those that prevented this phenomenon. Although results were variable, depending on the experimental approach, prevention of guttation effected reductions in photosynthesis and transpiration, as well as photochemical activity measured with fluorescence techniques. These findings lend partial support for a previously hypothesized function of guttation: prevention of excess water in leaves, yet they contradict those of several other studies. More work is required in order to adequately understand the function of guttation., Y.-C. Chen, T.-C. Lin, C. E. Martin., and Obsahuje bibliografii
The Czech immigrants to Southeast Europe contributed to general progress of all regions they came to - particularly in agriculture, trade, arts and crafts.
This article is dealing with the activities of Czech organ-builder Václav Holub from Požega (Middle East Croatia) since he moved from Bohemia to Croatia and with his remarkable work he have done.
We related leaf physiological traits of four grassland species (Poa pratensis, Lolium perenne, Festuca valida, and Taraxacum officinale), dominant in a Mediterranean grassland, to their origin and success at community level. From early May to mid-June 1999, four leaf samplings were done. Species originating from poor environments (P. pratensis, F. valida) had low carbon isotope discrimination (Δ), specific leaf area (SLA), leaf water and mineral contents, and net photosynthetic rate on mass basis (Pmass) but high chlorophyll content. The reverse traits were evident for the fast-growing species (L. perenne, T. officinale). Under the resource-limiting conditions (soil nitrogen and water) of the Mediterranean grassland, the physiological traits of P. pratensis and F. valida showed to be more adapted to these conditions leading to high species abundance and dominance. and J. T. Tsialtas, T. S. Pritsa, D. S. Veresoglou.
Příspěvek pojednává o úloze reálných, modelových i počítačových experimentů ve výuce fyziky jak obecně, tak z hlediska teoretického vyučování. Závěry dokumentuje na zajímavých experimentálních úlohách z fyzikálních soutěží., The paper describes the role of a realistic, model, as well as computer experiments in teaching physics in general, but especially from the point of view of theoretical physics education. The conclusions are illustrated with help of interesting examples of experimental problems solved during Physics Olympiad., Bohumil Vybíral., and Obsahuje seznam literatury