No abstract

No abstract

In The Netherlands, the majority of heathlands and dry, unproductive grasslands have been brought into cultivation or afforested since the end of the 19th century. As a result, the original landscape has become highly fragmented. Nowadays, the heath habitat occurs in more or less isolated patches only. Many of these fragments show a small spatial variation in conditions. Ground-dwelling arthropods, with a low dispersal power and a specific preference for poor, sandy, open habitats, could disappear from such small fragments under the influence of temporarally unfavourable conditions. As recolonization from other fragments is often very difficult because of hostile surrounding areas, isolated small fragments that have lost their populations will remain unoccupied. The absence of some carabid species in such small, isolated fragments is thought to be the result of this situation. By introducing heathy corridors between such fragments, animals might be enabled to pass a hostile environment. This study shows that heathy road-side verges can possibly function as such a corridor. On the studied road-side verges, carabid species of poor sandy, open habitats were present, including the more rare species. Some species even found a better habitat at road-side verges than in adjacent poor sandy open areas. For other species the road-side verge seemed to be a more marginal habitat in which they occur only because of the presence of a suitable adjacent area. The distance to such an area, as well as the width of the poor sandy, open stripon the road-side verge seem to be important conditions for the occurrence of the latter species. In order to increase the survival chance in such a corridor, it is suggested that some wider strips or patches be created at the road-side verges, suitable for reproduction. In this way, road-side verges might contribute to a metapopulation structure by which species are better protected against regional extinction.

No abstract

SYNOPSIS. A description is given of a disease of Coffea liberica Bull ex Hiern. occurring in Surinam, British Guiana and, according to previous investigations by Stahel, also in Brazil, San Salvador, and Colombia. The symptoms and spreading of the disease are described and its relation to a fungus disease of coffee with very similar wilting symptoms. Special attention has been paid to the concurrence of the observed flagellate Phytomonas leptovasorum Stahel and the multiple division of the phloem vessels on account of the scepticism with which Stahel's discovery of the flagellates in sieve tubes of wilting coffee trees was met by other research workers. Moreover a short description is given of experiments to transmit the disease to healthy coffee trees by grafting, with special reference to the successful root grafting. Furthermore it could be ascertained that no viruses or nematodes are involved as pathogens. The possible relation between the disease and insects is still unsettled; observations of flagellates in the midgut of certain bugs, found on the roots of coffee trees, seem to indicate that the vector of the phloem necrosis disease is a Hemipteran insect. Although no final proof of the pathogenicity of the flagellate can be given, secondary indications support the theory that the flagellate Phytomonas leptovasorum is the cause of the phloem necrosis disease of Coffea liberica in Surinam.