Radiation Damage in Shoot Apices of Concord Grape

P ratt , C harlotte . (N. Y. State Agri. Expt. Sta., Geneva.) Radiation damage in shoot apices of Concord Grape. Amer. Jour. Bot. 46(2) : 103‐109. Illus. 1959.—Dormant rooted cuttings of ‘Concord’ grape were exposed either to 200‐6000 r of X rays or to 2‐6 hr. of thermal neutrons (average total dose of 4.80 × 10 11 to 1:59 × 10 13 neutrons/cm. 2 ). Percentage of plants surviving in the field tended to decrease with dosage beginning with 2000 r of X rays or 2 hr. of thremal neutrons. It showed a sharp drop in lots which had received doses of 4000 r of X rays or 4 hr. of thermal neutrons. Frequency of hudless shoots (shoots lacking a terminal bud after the first leaves emerged) increased with dosage, beginning with groups which had received 2000 r of X rays or 2 hr. of thermal neutrons. Microscopic examination of radiation‐damaged shoot apices showed one or more of the following characteristics: (1) shape and organization of the apical meristem different from that of the untreated shoot apex, which is described; (2) no young primordia; (3) acropetal advance of maturation of cells; in 4 cases cells with spirally thickened, lignified walls were found 1‐4 cells deep in the meristem; (4) collapse of cells in the tunica and corpus; formation of periderm and deeper, cambium‐like divisions below the wound; (5) site of the former apical meristem either carried up on the base of a single terminal leaf or remaining a flat area between terminal leaves. Aspects of radiation sensitivity of the shoot and theories of shoot organization with reference to natural and induced chimeras are discussed.