ROOT MODIFICATIONS INDUCED IN VICIA FABA BY IRRADIATING DRY SEEDS WITH SOFT X-RAYS

Abstract

The radiations were supplied by a gas x-ray tube having a Cu target and a window of aluminum foil and cellophane, operated at 30 peak kv. and 10 ma. Unsoaked Vicia faba seeds were arranged 8 cm. from the focal spot of the tube and exposed for 20 min. Seedlings grown from these seeds showed the following external modifications in their primary roots: absence of lateral roots; poor development of the root tip; and occurrence of "delayed killing" after a germination period of 8 days. These roots displayed foreshortening of the meristem, elongation and mature regions as compared with the primary roots of control plants; appearance of the primary xylem, in the upper limits of the primary root, as a continuous band surrounded by a region of poorly differentiated cells which have a position comparable to that occupied by the phloem, pericyclar, cambial and endodermal areas in control primary roots; a slight indication of cambial activity opposite the primary xylem arcs; degeneration of cells which normally retain their ability to divide as observed in the root tip meristem, the probable cambium and the pericycle; absence of secondary xylem in the hypocotyl; the characteristic occurrence of a schizogenous cavity in the pith region of the hypocotyl when the "delayed killing" effect is evident.