Das Phloem der Haustorien vonCuscuta

Summary Haustoria ofCuscuta odorata R. & P. andC. grandiflora H.B.K. show continuous traces of sieve elements, connecting the phloem of the host with that of theCuscuta shoot. The continuity of this haustorial phloem is discernible by callose fluorescence after staining with aniline blue. The fine structural criteria for sieve tubes are analyzed electronmicroscopically, with special respect to sieve pores, P-protein, and a distinct wall-standing smooth surfaced ER. Within the central part of the haustorium sieve tubes are elongated, while the elements abutting the phloem of theCuscuta shoot are nearly isodiametric in shape. Both elements are associated with rather large companion cells, derived from an unequal division.