Zur anatomischen Struktur der aus Schuppenblättern hervorgegangenen Kontaktorgane von Hyobanche (Scrophulariaceae)

Abstract

In a previous report by M arloth (1932) on Hyobanche (a root parsite on various hosts e. g. Hermannia dissermifolia, Pteronia incana and others), host roots have mistakenly been interpreted as roots that originate on the rhizome of Hyobanche . No such roots could be observed on older Hyobanche plants. The first phase in the development of the haustorium is characterised by enlargement of the vascular bundle of the scale leaf that is about to engage in haustorial formation, followed by cell division to give rise to a slight swelling on the surface of the scale leaf. In the course of subsequent development of the haustorium the entire scale leaf is transformed into a massive haustorium. While mesophyll cells of the scale leaf penetrate into the cortex of the host root, procambium strands differentiate simultaneously in the haustorium, continuing into the host root. Subsequent differentiation into xylem and phloem elements results in a massive vascular bundle which may act as a bridge between the enlarged vascular tissue and the central cylinder of the root, thus establishing a firm connection between parasite and host. Although phloem elements were identified within the intrusive organ the nature of the contact between the two phloem systems is still obscure. In older haustoria the intrusive organ consists for its greater part of xylem elements that have differentiated out of the procambium strands after dissolution of the host xylem vessels. Associated with consideratle swelling of the host roots, haustorial penetration stimulates lateral root development in the area of contact. Apart from the increase in the number of cortical cells mainly xylem elements are subsequently differentiated from the central cylinder. No differences were observed between the leaf haustoria of Hyobanche glabrata H iern and Hyobanche sanguinea L.