Bot. [f. TRI- + Gr. ἀρχή beginning, origin.] Arising from three points of origin, as the woody tissue of a root: cf. DIARCH.
1884. Bower & Scott, De Bary’s Phaner., 354. As a rule the xylem-plates are diarch in Lupinus varius,… triarch in Pisum sativum,… tetrarch in Phaseolus. Ibid., 363. Triarch and tetrarch bundles sometimes occur in thick roots of species which are usually diarch.
1895. [see TETRARCH a.].
