Mida

The only other members of the Santalaceae occurring in New Zealand are the two species of the endemic genus Mida, both of which are confined to the North Island. Formerly this genus was united with Eucarya (Fusanus), a genus which

Fig. 1.—Mida salicifolia, haustorium in longitudinal section X 8. Between the roots of the parasite (p) and of the host (h) is the haustorium with three cortical folds, each with a layer of collapsed cells (c). Down the centre of the haustorium runs a massive vascular cylinder, which becomes distended by a core of parenchyma (m) before it enters the host root.

has been shown to possess haustorial connections with neighbouring roots (Herbert, 1921, 1925). But Skottsberg (1930) has confirmed that the New Zealand species are not very closely related to any other members of the Santalaceae. It was interesting, therefore, to determine whether the genus Mida exhibited parasitism.

Dr. J. A. Rattenbury, of the University of Auckland, very kindly obtained roots of Mida salicifolia for me which had developed haustoria in contact with roots which he thought might be kauri (Agathis australis). Sections passing through these haustoria (Fig. 1) show a structure similar to those of other Santalaceae figured by Rao (1942). The structure is much more complex than the simple swellings of Exocarpus bidwillii, and the contact with the vascular tissue of the host is more complete. The cortex of the larger haustoria is thrown into a series of collars or folds which are traversed by strands which Rao (1942) interprets as collapsed cells caused by differential growth rates in the outer and inner tissues of the haustorium. Towards the host root the vascular cylinder becomes distended by a mass of dense parenchyma cells. This feature was recorded in the material examined by Benson (1910) and Rao (1942).

In the roots examined the parasitic tissue did not extend beyond the outer xylem of the host. It seems probable, however, that if the haustoria persist from one year to the next that they will become more deeply embedded in the xylem.

Anatomical investigation confirmed that the host roots were Agathis australis, but it seems probable that Mida will prove to resemble many other Santalaceae and parasitise a number of hosts.