Foraminifera from the Silberberg Formation («Lower Oligocene») at Silberberg,near Helmstedt (Germany)

From the Silberberg Quarry, type locality of the Silberberg Formation (Martini &Ritzkowski 1968), some planktonic foraminifera are described:Globigerina officinalis Subbotina, Globigerina ouachitaensisHowe &Wallace,G. praebulloides leroyi Blow &Banner, G.praebulloides occlusa Blow &Banner which taxa are here suggested to form intergrading morphotypes within the range of variation of a population dominated byG. officinalis. In addition,G. cf.danvillensis Howe &Wallace is found. The planktonic fauna, together with some elements in the benthonic fauna, suggests a possible correlation with the Danville Landing Member of the Jackson Formation, Louisiana, traditionally ascribed to the Upper Eocene. There is some similarity with European Uppermost Eocene — Lower Oligocene faunas described by various authors. The Silberberg Formation was suggested to be a Neostratotype for the Latdorfian Stage of the Lower Oligocene byMartini &Ritzkowski (1968). It is suggested that the Silberberg Formation may well be coeval with the Upper Priabonian as proposed byCita 1969.     

Rapid action of abscisic acid on photosynthesis and stomatal resistance

Summary (RS)-Abscisic acid, a natural plant hormone, has been found to inhibit photosynthesis in both detached and attached primary wheat leaves. The action occurs rapidly and is accompanied by large increases in stomatal diffusive resistance.This research was supported by the Wheat Industry Research Council.     

Apical surface topography of invaginating and noninvaginating cells. A scanning-transmission study of amphibian neurulae

A comparative study on scanning and transmission electron microscopy of apical ultrastructure in epithelia of the axolotl neurula (Ambystoma mexicanum, Cope) is presented. The aim of the work is to determine whether apical surface topography is correlated to other morphological features of the cells, and whether there are any ultrastructural differences between surfaces of invaginating and noninvaginating regions. Scanning specimens are prepared by critical point drying and benzene freeze-drying. Comparisons show that the scanning specimens are comparable to the standard transmission specimens with regard to surface topography.Apical surfaces are sculptured by folds and microvilli-like processes. Assessment of the relative abundance of surface projections shows that these occur in largest numbers on invaginating, bottle-shaped cells in the neural plate and in the notochord rudiment of stage-16 larvae. It is proposed that the surface projections may support apical narrowing in these cells, by facilitating endocytosis, and that they may be lateral attachment organelles. It is suggested that the morphogenesis of the invaginating cells may be the result of coordination between microfilaments, apical endocytosis, microtubules, and “adhesive peripheral surface projections.”     

Mitotic chromosomes of species in the subgenusDrosophila (Diptera:Drosophilidae)

The karyotypes of 17 species in the subgenusDrosophila are compared according to their taxonomical relationships. Although closely related species often possess similar karyotypes, the karyotypes diverge considerably within the subgenus. Thus extensive chromosome rearrangements did occur during the speciation. Species with higher chromosome numbers do not necessarily have higher average of total chromosome length per cell.