Symplasmic Sieve Element Continuity between Orobanche and its Host*

Electron microscopical investigations of primary haustoria of Orobanche crenata parasitizing the roots of the highly compatible host, Vicia narbonensis, reveal an uninterrupted phloem system connecting both partners. Individual sieve elements belonging to the host and parasite could be identified by the cell markers: plastids, mitochondria and P‐protein, which in the present system turned out to have species‐specific fine structure. Sieve pores of normal structure interconnect the sieve elements of host and parasite. They originate from interspecific plasmodesmata.