The internodal and nodal vessel elements and certain aspects of their ontogeny in the stem ofDioscorea alataL., the common cultivated yam of Gujarat State, India, are described. The internodal vessel elements are unusually long with foraminate, scalariform, reticulate, or rarely simple perforation plates. The nodal vessel elements are comparatively short with two to five perforation plates. They generally differ from internodal vessel elements in characters such as (i) size and shape and (ii) nature, number, inclination, and distribution of perforation plates. The ontogenetic study of the vessel element revealed that the coenocytic condition is a result of frequent mitotic divisions of the mother nucleus. The formation of the perforation plate occurs after the vessel element has reached final length. The protoplast persists after the formation of the perforation plate. InD. alatathe cell wall in the region of the perforation shows primordial pits.
展开▼
