ALBERT

Notes: Summary 1. In addition to the earlier published late winter/spring diatom (Asterionella, Stephanodiscus, Fragilaria andCyclotella) succession (1977–1980), data on diatom summer and autumn pulses, and on the occurrence of maxima of other predominant algae (flagellates) in the epilimnion (which was sampled twice a week) are presented. 2. Asterionella andFragilaria also flowered in summer and autumn, irrespective of stagnation and overturn (the lake is completely mixed from December until April). Succession, as in spring, was not observed then; only one population (eitherAsterionella orFragilaria) was encountered, or both species concurred.Cyclotella had a summer maximum concurring with that ofAsterionella. Stephanodiscus only flowered in spring. 3. Dinobryon divergens had pronounced maxima in late spring and (together withcf. Chlamydomonas) in summer. It concurred withAsterionella andFragilaria, respectively withCyclotella. Cryptomonas, distinguished in two size classes, were permanently present. 4. The diatoms andDinobryon showed yearly variation in maximum numbers as well as in periodicity. 5. Simultaneously growing populations of two diatom species (in all seasons) and ofDinobryon with one or two diatom species (in summer) emphasizes the ‘paradox of the plankton’ (HUTCHINSON, 1961).

Notes: Abstract Laboratory and field studies on aphid damage in wheat are described. Both direct and indirect effects of aphids on the behaviour of the crop were studied. In the laboratory a clear effect of honeydew and yeasts on photosynthesis was found. This effect could not be demonstrated under field conditions, since even at yield loss levels of 700 kg ha−1 the size of this effect may be undetectable with crop enclosures reaching an accuracy of 10%. The effect of honeydew on ageing, measured in the laboratory trials was also found in the field and may form a major cause of the yield losses found in the field. Yield losses under field conditions reached 700 kg ha−1 and were for 72% due to direct sucking damage of the 35 aphids, found maximally per culm, and direct and indirect honeydew effects. Saprophytic and possibly also some necrotrophic fungi caused 28% of the yield losses. The exact contribution of each of the damage factors was not revealed but it was demonstrated that direct and indirect effects contribute to the final yield losses.

Notes: Abstract The object of this study is the class of closable Gabor operators. That is the set of operators which map a Gabor function (or ‘note’) into a multiple of a Gabor function. By using the Bargman space (sometimes called Bargman representation) some general properties of these operators are derived. It is shown that the set of Gabor operators whose adjoint is also a Gabor operator establishes a six-dimensional complex manifold with a partial Lie-group structure and with an involution. The corresponding Lie-algebra and the infinitesimal generators are calculated. Further it turns out that, at least locally, a Gabor operator with a Gabor adjoint results from an evolution process. The proofs of the theorems are a hybridization of Hilbert space techniques and classical complex analysis (theorems of Osgood, Montel, etc.). The proofs will be published elsewhere in a wider context.

Notes: Summary In this article the results of a study of a couple of quaking bogs in the Netherlands have been published. The author has tried to give a picture of the composition of the microbiocoenoses as detailed as is possible for one investigator. Apart from the micro-organisms the physical and chemical conditions in the bogs have been studied also. The bogs show a very sharply marked zonation, which is the result of the successive development of the bogs from infra-aquatic peat-bog, via transitional peat towards peat-moor formation. This succession is mirrored in the macrophyte-vegetation, in the chemical composition of the biotope water and in the composition of the micro-biocoenoses. The environment in which the microorganisms live changes from mesotrophic in the infra-aquatic peat-bog and initional quaking bog formations to oligotrophic and very acid in the real quaking bog and initional peat-moor formations. Optimal conditions are reached for a very large number of species in the initional stages of the quaking bog formation, c.q. in the Scorpidium zone. This zone harbours a total of 426 identified micro-organisms. Among the Microphyta the Bacillariophyceae and the Desmidiales are best represented and dominate in the entire biocoenosis. The genus Trachelomonas among the Euglenophyceae is highly characteristic for the community. Among the Microzoa high numbers of Rhizopoda and Rotatoria are characteristic for this zone. Chemically the Scorpidium zone is characterized by a pH around the neutral: 6,0–7,2. The food standard is mesotrophic. An other highly important factor is the rather high concentration of iron. Many desmids and flagellates and even some rhizopods show incrustated iron, in membranes and theca. The next zone of the quaking bog shows a reduced biocoenosis with regard to the Scorpidium zone. An abundant Sphagnum vegetation mirrors the more acid conditions. The total population drops to 236 species. All groups of microorganisms have diminished in numbers. The Rhizopoda have replaced the Desmidiales and Bacilla-riophyceae as dominating organisms in the entire biocoenosis. Chemically this first Sphagnum zone is characterized by a lower pH viz. 4,9–6,0, with an average value of 5,4. The food standard is of the oligotrophic type. The environment becomes more and more extreme. An important conclusion can be drawn in connection with the observed distribution of the micro-organisms. The pH 7,0 is not the real dividing line between alkaliphilous and acidophilous organisms, but pH 6,0. Most alkaliphilous species can thrive very well in the interval 6,0–7,0. But below pH 6,0 conditions become too extreme. Minimum conditions are reached in the last or second Sphagnum zone. The total population drops to 123 species. Only the most specialised organisms and the truly indifferent ones are able to live in this environment. The Rhizopoda, best adapted to live under very acid conditions, dominate in the entire biocoenosis. The dinoflagellate Gloeodinium montanum is highly characteristic. Chemically the second Sphagnum zone is characterized by a very low food standard and a pH of 3,8–5,5, with a average value of 4,6. Throughout the article reference has been specially made to the influence of the pH on the distribution of the micro-organisms. Although no causal connection could be clearly detected, the hydrogenion concentration is of the utmost importance for the ecology of micro-organisms, according to the observations made during this study. It is clear that a characterization for the quaking bogs as such can not be given. Each of he three zones, which form together the transitional peat series, has its own characteristic community and set of milieu factors. For a summary of the succession in which a characterization of each zone is given, see the chapter on the succession of the microbiocoenoses. Table 21 gives a survey of the distribution of the observed micro-organisms from which easily is seen the community of each zone. From this table it is clear, that the first Sphagnum zone borrows its character from the fact that it is the meeting place for organisms from the Scorpidium zone and the second Sphagnum zone; it harbours only 6 characteristic species. These species are moreover doubtful as far as their worth as characterizing species is concerned. In the three zones together a total of 482 micro-organisms was discovered: 271 microphytes and 211 microzoa (See table 20). The real, total, population of the bogs is estimated at about 600 species.

Notes: Summary The propagation of electromagnetic waves is investigated theoretically for a round wave guide, containing a gyroelectrie-gyromagnetic medium with gyroaxis parallel to the guide in the form of a cylindrical shell of thicknessδ, adjacent to the wall of the guide. An equation is set up, permitting to compute the change in the propagation constantγ due to the presence of the shell, including terms proportional toδ 2. Assuming only the presence of gyromagnetism, the changeΔ 1γ of first order inδ for TE-waves is determined and is found to be the same fpr right- and left-circular polarization. The second order differenceΔ 2 + γ —Δ 2 - γ for the two senses of polarization, however, appears to have a non-vanishing value which, just likeΔ 1γ can be expressed in terms of the radius of the guide, the frequency, the dielectric constant and the elements of the gyromagnetic permeability tensor which characterize the medium of the shell.

Notes: Abstract In gram-negative bacteria only few proteins are exported across both the cytoplasmic membrane and the outer membrane which forms an extra barrier for protein excretion. In this review we describe the mechanisms of production and export of two types of plasmid-encoded proteins inEscherichia coli. These proteins are the bacteriocin cloacin DF13 and the K88ab and K99 fimbrial subunits. Specific so-called helper proteins located at different positions in the cell envelope play an essential role in the export of these proteins. The genetic organization, subcellular location and functions of these helper proteins, as well as the effects of mutations and culture conditions on the export of the proteins are described. Models for the export mechanisms are presented and future application possibilities for engineering foreign protein excretion inE. coli with these export systems are discussed.