Ueber einige von J. Menyhardt in Südafrika gesammelte Süsswasseralgen

Ohne Zusammenfassung     

The cytomorphology of goblet cells of the fetal intestine. Studies of the large intestine of cattle (Bos primigenius taurus)

In the region of the base of the intestinal crypts undifferentiated goblet cells display a configuration and constellation of organelles and membrane structures that are indicative of their importance for function. These images at this stage of development deliver a scenario of the mechanism of secretory granule production: aggregates of protein vesicles from the "transitional elements" (PALADE) of the granular endoplasmic reticulum are, so to speak, rolled up on the trans side of the Golgi apparatus by inversion of peripheral membrane segments of the innermost Golgi lamellae, thereby forming corpuscles. The origin of the capsulated vacuoles, which contain vesicles as single elements or as conglomerates, is well established. Their capsule consists of a trilaminar external and external and internal membrane; between them lies condensed material of the Golgi apparatus. In the opinion of the present author, the development of the ensheathed vacuoles represents a basic, more general mechanism. In contrast, the further steps of synthesis, for the formation of secretory granules, are more heterogeneous. Condensation of the vesicles and the inner capsular membrane results in the formation of a prosecretory granule, which in the basic element in the process of secretory granule production. The prosecretory granules develop singly or by fusion with other granules to give primary secretory granules. The complexity of this mechanism of secretory granule formation, however, becomes evident when considering the apposition of capsulated vacuoles and prosecretory--primary--secondary secretory granules, of prosecretory and primary secretory granules as well as prosecretory granules and secondary secretory granules. Generally, primary granules show a tendency to become secondary secretory granules or to fuse with them. During maturation of the goblet cells the secretory granules fuse to form larger mucous bodies in the theca by fusion of the laminae of the membranes; a final product, there is a homogeneous mucous mass devoid of membranes.     

Replicate plating: does it increase reliability?

K.K. WILLE, B.R. VOWELS, A.N. FOGLIA, C.A. BERGE, B.M. SCHNELL AND F.W. BRIESE. 1996. As a part of a clinical study to evaluate the antibacterial effect of a topically applied erythromycin gel, microbiological specimens were taken from two groups of patients : one group using 2% erythromycin gel and the other group using a placebo gel. These specimens were plated in triplicate using a common source on bacteriological media using standard procedures. After the appropriate incubation times, the numbers of aerobic and anaerobic organisms were counted separately from each of three plates. A comparison of the bacterial colony counts from the replicate plates showed a high degree of similarity for each type of organism. Tests for treatment differences in organism counts were performed based on single, double and triplicate plating. The results obtained were almost identical, suggesting that replicate plating from a common source is no more accurate than single plating. The only apparent advantage of this type of replicate plating is heightened confidence in the reliability of bacterial counts from single plates.     

Pan-Arctic soil moisture control on tundra carbon sequestration and plant productivity

Long-term atmospheric CO₂ concentration records have suggested a reduction in the positive effect of warming on high-latitude carbon uptake since the 1990s. A variety of mechanisms have been proposed to explain the reduced net carbon sink of northern ecosystems with increased air temperature, including water stress on vegetation and increased respiration over recent decades. However, the lack of consistent long-term carbon flux and in situ soil moisture data has severely limited our ability to identify the mechanisms responsible for the recent reduced carbon sink strength. In this study, we used a record of nearly 100 site-years of eddy covariance data from 11 continuous permafrost tundra sites distributed across the circumpolar Arctic to test the temperature (expressed as growing degree days, GDD) responses of gross primary production (GPP), net ecosystem exchange (NEE), and ecosystem respiration (ER) at different periods of the summer (early, peak, and late summer) including dominant tundra vegetation classes (graminoids and mosses, and shrubs). We further tested GPP, NEE, and ER relationships with soil moisture and vapor pressure deficit to identify potential moisture limitations on plant productivity and net carbon exchange. Our results show a decrease in GPP with rising GDD during the peak summer (July) for both vegetation classes, and a significant relationship between the peak summer GPP and soil moisture after statistically controlling for GDD in a partial correlation analysis. These results suggest that tundra ecosystems might not benefit from increased temperature as much as suggested by several terrestrial biosphere models, if decreased soil moisture limits the peak summer plant productivity, reducing the ability of these ecosystems to sequester carbon during the summer.