Abstract/Summary:
Prior to attachment of the adhesive disk, epidermal cells of the stem develop into a secretory epithelium of unicellular trichomes which upon attachment produce finger-like projections from the apical end in Cuscuta reflexa Roxb, and Cassytha pubescens R.Br. Viscum minimum Harvey, develops an epithelium of uni- or bicellular trichomes with blunt tips from the apex of the radicle. The development of epithelial trichomes and the ultrastructure, development, disintegration, and partial reorganization of the cuticular membrane of these secretory cells have been investigated before and after attachment to the host. On young epithelial cells the cuticular membrane is composed of a cuticle proper with alternating electron dense and electron translucent lamellae and a cuticular layer of the reticulate type. Pockets of granular and fibrillar secretory products are located within the lamellar system of C. pubescens and V. minimum. Cutin cystoliths occur most frequently in V. minimum. In all three species the lamellar system and most of the cuticular layer break up during secretion and flow towards the surface of the host as part of the adhesive secrete. After host contact has been established most of the translucent lamellae are still intact but reorientated. In V. minimum the secrete is predominantly cutinaceous according to its positive reaction with Sudan IV and auramin-0. Although mixed with fragments of the cuticular menbrane the secrete in the two twining species is PAS-positive and most likely pectinaceous. V. minimum fills the space between the adhesive disk and the host with enormous quantities of secrete while Cassytha and Cuscuta only secrete small quantities, and their finger-like projections fill the space in question. The cuticular menbrane of three different host species predominantly showed a reticulate ultrastructure.