Some Physiological Aspects of the Relationship between Cocoa, Theobroma cacao, and the Mistletoe Tapinanthus bangwensis (Engl. and K. Krause)

The anatomy and development of a typical Tapinanthus bangwensis-cocoaassociation is described, and it is shown how the mistletoehaustorium grows obliquely through the xylem of its host, causingthe cocoa distal to it to die gradually from desiccation. Inearly development the mistletoe haustorium forms a plate oftissue between the host xylem and phloem, having roughly equalareas of contact with both. Later the ratio of phloem: xylemhaustorial contact decreases. Two experiments using ¹⁴C showed that the mistletoe took productsof photosynthesis from its hosts, in one case against the expecteddirection of flow in the host phloem. A third experiment showedthat no labelled photosynthates produced by the mistletoe weretranslocated into cocoa. It is suggested that in this case hosthypertrophication is stimulated by the stresses set up by haustorialgrowth, rather than by mistletoe-produced hormones.