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meristematic-like cells differentiate into parenchyma on one side and into intrusive cells on the other. This, therefore, is the mechanism for increasing the bulk of the haustorium. Old haustoria do not exhibit this cellular differentiation. Unlike S. asiatica and S. hermonthica, the vascularisation of the S. gesnerioides haustorium is not composed of one single vascular strand, but consists of several strands, more or less branched, of which 2 to 4 of the more important ones are located at the periphery in an arc-shaped fashion. This type of vascularization can be compared to that of Aureolaria pedicularia, Seymeria pectinata and Castilleja coccinea, according to Musselman and Dickison (1975). It can also be compared to the vascularization of the haustorium of Alectra vogelii. -
endophyte
The endophyte is composed of intrusive cells and the ends of the tracheids from the vascular axial strand which are in contact with the host root xylem. These elongated cells of the parasite form the front of the invading tissue.
Ultrastructure of the haustorium of Striga gesnernioides Meristematic-like cells have a dense cytoplasm with an abundant endoplasmic reticulum, often laying in rows. They have poorly developed plastids and mitochondria and a long elongated nucleus. They are separated by more or less large, intercellular spaces. -
intrusive cells
These cells are elongated (up to 30 microns) with a cytoplasm containing numerous endoplasmic reticulum lining the length of the cell. There are a few, poorly differentiated plastids and mitochondria. The cells are in an opaque fluid when viewed under the electron microscope. The fluid seems to dissolve the cell walls of the host plant.
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sieve cells
Sieve cells have been reported for the first time to occur in the transition zone between the meristematic-like cells and the parenchyma cells that have no starch grains. The phloem is therefore composed of typical sieve cells, very often associated with companion cells, and typical branched plasmodesmata. Using fluorescence microscopy, it has been possible to observe sieve-tubes in the parenchymatous vascular core and around the xylem strands. It clearly appeared that the phloem of the haustorium is connected to that of the host root. Nevertheless, it has not been possible to distinguish with certainty the relationship between the phloem of the haustorium and that of the host root.
Conclusions This anatomical and ultrastructural study of the haustorium of S. gesnerioides has enabled us to describe histological and cytological features related to the physiology of the haustorium.