On ecological conceptualizations of perceptual systems and action systems

This article examines Gibson's concept of perceptual system and Reed's concept of action system. After discussing several assumptions underlying these concepts, the ontological status of these systems is considered. It is argued that perceptual systems and action systems should be conceptualized neither as parts of an animal's body nor as softly (temporarily) assembled devices; rather, they are best understood as animals' abilities to achieve functional relationships, that is, as dispositional properties. This conceptualization entails that these systems are relatively permanent properties of the animal that are causally supported by, though not identical to, anatomical substrates. Further, it entails that it is the animal that perceives and acts, not its perceptual and action systems

Val en worp : een bijdrage tot de geschiedenis der mechanica van aristoteles tot newton/ Dijksterhuis

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Antibiosis plays a role in the context of direct interaction during antagonism of Paenibacillus polymyxa towards Fusarium oxysporum

Interaction of Fusarium oxysporum and Paenibacillus polymyxa starts with polar attachment of bacteria to the fungal hyphae followed by the formation of a large cluster of non-motile cells embedded in an extracellular matrix in which the bacteria develop endospores. Enumeration of fungal viable counts showed that less than one of 36 000 colony-forming units survived in paired cultures for 71 h. Effective antagonism was not observed below pH 5 and was specific for the bacterial species. Development of F. oxysporum was inhibited in cell-free filtrates derived from cultures of P. polymyxa, but was much more strongly repressed in the presence of living bacteria. Furthermore, recovery of fungal growth started immediately after addition of antibiotics to paired cultures. Restoration of fungal growth was enhanced in filtrates that were supplemented with MgCl2, which suggests that anti-fungal compounds produced by the bacteria were counteracted by magnesium ions. In paired cultures, fungal counts remained very low, even in the presence of the magnesium salt. This study clearly showed that P. polymyxa antagonizes the plant pathogenic fungus F. oxysporum in liquid medium by means of an interaction process in which the presence of living bacteria is a prerequisite for continuous suppression of fungal growth