New Methods of Chromatographic Separation of Gibberellins A1 and A3

Biologia Plantarum - New Chromatographic methods, chromatography in centrifugal field and thin-layer chromatography on alumina, were used for separating physiologically active gibberellins A1 and...     

Changes in the anatomical structure of the shoot apex ofSenecio vulgaris L. during ontogenis in relation to the formation of leaves and inflorescence

An investigation was made of the anatomical structure of the shoot apex ofSenecio vulgaris L. a photoperiodically neutral plant, and compared with the formation of successive leaf primordia along the axis up to the initiation of the terminal inflorescence. In the shoot apex of a germinating plant a central zone can first be distinguished from the peripheral zone which is composed of small and intensely stained cells. Later, a rib meristem appears. At the time of the initiation of the middle (the largest) leaves, the shoot apex has a distinct small central zone and a well developed peripheral zone and rib meristem. Between these zones there is a group of cells dividing in all directions, the subcentral zone. At the time of initiation of the last leaves, the central zone extends to the flanks and gradually ceases to be distinguishable. At the same time, the subcentral zone increases in size. This is caused first by cell division and later, with the initiation of the last, most reduced leaves, by enlargement of the cells. Vacuolization in the inner part of the apex and the arrangement of the superficial cells in rows parallel to the surface of the apex, is a preparatory step to the initiation of the inflorescence.     

A method of rapid examination of meiosis in fruit-trees

Vypracování nové metody rychlého vy?et?ování meiose u jádrového ovoce bylo vynuceno rozsáhlostí materiálu, který bylo nutno zpracovat p?i cytologickém zhodnocení 40 soret ?eskoslovenského základního hru?ňového sortimentu. Metoda umo?ňuje během t?í dn? získat trvalé ?ezané preparáty p?ibli?né z 1800 pra?ník?. Této metody je mo?no pou?ít u v?ech rostlin, které mají v době pr?běhu reduk?ního dělení v pylovýeh mate?ských buěkách dostate?ně velké pra?níky k extirpaci.     

Fine structure of ureteric duct epithelium in the North Atlantic hagfish (Myxine glutinosa L.)

Summary The epithelial cells lining the ureteric duct in the cyclostome, Myxine glutinosa, have a brush border and show specializations of their apical cytoplasm similar to those observed in absorptive proximal tubule cells in higher vertebrate species. These features and the presence of large and numerous cytosomes, presumed to contain lysosomal enzymes, indicate that the ureteric epithelium has taken over some of the functions of the proximal tubule in the atubular kidney of Myxine. Sparsity of basal cytoplasmic processes and mitochondria in the ureteric duct cells appears to correlate with an inability for active, energy-dependent secretory and ion transport functions.This study has been supported by a grant from the Karolinska Institutet Medical School, Stockholm, Sweden (Therese och Johan Anderssons Minne). The author is indebted to Doctor Bertil Swedmark for permission to use the facilities of Kristineberg Marine Biology Station, Fiskebäckskil, Sweden, where hagfish were caught.     

Some features of oscillatory flow in a model bifurcation

Oscillatory flow in the lung is studied using an order-of-magnitude analysis and flow visualization experiments in a single bifurcation with lung-like geometry. The results are used to obtain a classification scheme that identifies three major flow regimes, distinguished on the basis of whether the flow is dominated by unsteadiness, viscous effects, or the effects of convective acceleration. The unsteady regime is found to exist for values of a dimensionless stroke length (L/a, i.e., stroke volume/local cross-sectional area) less than or equal to 3 and for values of a dimensionless frequency (alpha 2 = alpha 2 omega/nu, where alpha is airway radius, omega the oscillatory frequency, and nu the kinematic viscosity) less than or equal to 10 in basic agreement with previous studies. The viscous regime is found when alpha 2(L/a)(a/R)1/2 less than 10 and alpha 2 less than 10 where R is the local radius of curvature in the bifurcation; the convective regime is found when alpha 2(L/a)(a/R)1/2 greater than 10 and L/a greater than 3. This same approach yields scaling laws for the magnitude of secondary flow velocities and shows that the ratio of secondary-to-axial velocity is small everywhere outside of the convective regime where it scales with (a/R)1/2. Comparison of these results to related simple flows shows that many of the features observed can be attributed to the effects of curvature, suggesting that the influence of the flow divider and of area change may be of lesser importance than previously thought.