On the reconstruction of phylogenetic transformations. The origin of the arthropods

The conditions are outlined under which the body construction of annelids could have been transformed into that of arthropods. As an adaptation to a vagile life and an uptake of food by filtering particles from the sediment, the body was more and more flattened. Thus lateral protrusions, the subsequent pleurotergites, developed, and the parapodia were shifted to a more ventral position and could differentiate into the branched limbs typical for arthropods. This is the condition under which parts of the body wall were kept immobile, so that they could become sclerotized in the form of rigid plates.     

Viruspartikel im Siebröhrensaft von Cucumis sativus L. nach Infektion durch das Cucumisvirus 2 A

Summary Sieve tube sap obtained from cucumber plants infected by Cucumis Virus 2 A induced the typical mosaic disease when it was inoculated into healthy plants of the same species. The infectious factor could not be removed by dialysis or by treatment with phosphodiesterase. Therefore it is improbable that the virus is transported in the sieve tubes as low molecular units or as an unprotected RNA. Rod shaped particles (345×23 m) were found in the infectious sieve tube sap when it was investigated by electron microscopy. The same particles could be found in the sap extracted from infected leaves, but never in sieve tube sap obtained from healthy plants. There is reason to suppose that the Cucumis Virus 2 A is transported in the sieve tubes as complete particles.

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Einige Ergebnisse dieser Arbeit sind Teil einer Dissertation der Technischen Hochschule Darmstadt (D 17, 1964).     

The xylem sap of maple (Acer platanoides) trees--sap obtained by a novel method shows changes with season and height

Xylem sap of log pieces of maple trees was collected by a novelpressure/decompression method developed recently for the mechanicaldrying of timber. Seasonal changes and spatial distributionsof the osmotic potential, the pH and the concentrations of majorsolutes and of the plant stress-hormone abscisic acid (ABA)were investigated. Sucrose and quebrachitol were the main components of the xylemsap. The sucrose concentration varied between 10 mM and 25 mMduring the winter months and declined to a minimum during theperiod of bud burst. Quebrachitol was found in concentrationsof up to 7 mM with a high variability throughout the year. Highconcentrations of ABA were measured during the summer seasonand in mid-winter. Rainfall caused an increase of ABA in somesamples. The osmotic potential of the xylem sap increased with the heightof the collection site. The pH of the sap decreased by approximatelyone unit between the base of the trunk and the crown. The increaseof the osmotic potential was mainly due to sucrose, quebrachitoland potassium. Malate contributed to the decrease of the pH.ABA of the xylem sap increased with decreasing moisture contentof the wood. Key words: Pressure/decompression method, xylem sap, abscisic acid, sucrose, quebrachitol, Acer platanoides     

Statistics of RNA melting kinetics

We present and study the behavior of a simple kinetic model for the melting of RNA secondary structures, given that those structures are known. The model is then used as a map that. assigns structure dependent overall rate constants of melting (or refolding) to a sequence. This induces a landscape of reaction rates, or activation energies, over the space of sequences with fixed length. We study the distribution and the correlation structure of these activation energies. Correspondence to: P. Schuster