Modes of union and interaction between parasite and host in the Loranthaceae. III. Further observations on Viscum and Korthalsella

Abstract

The sinkers of Viscum cruciatum , V. album and V. rotundifolium influence the direction of the host xylem elements, so that vessels meet them end on. In the case of V. rotundifolium on Gymnosporia laurina the course of the vessels may become in part transverse. It is otherwise with V. capense and V. obscurum , the sinkers of which are by-passed by the host vessels, communication being established with those in lateral contact. The haustorium of Korthalsella dichotoma on Ochrosia vieillardii spreads against the host wood as in other species; in the nodal region it also penetrates through leaf gaps to the inner side of a wood sector, between it and the internal phloem. Korthalsella aoraiensis differs from other species; the haustorium extends longitudinally up and down against the wood, but not tangentially except by growth in thickness of the haustorial strand, which splits the cambium. In the galls formed by K. opuntia on Altingia excelsa the haustorium forms a girdle round the host wood and perforates the host cambium by numerous papillae, so that the gall-wood covering the girdle is riddled with parasite tissue like coarse medullary rays. Haustorial flanges also penetrate between cambium and gall-wood at various levels, starting mostly from the primary axis of the haustorium.