ANATOMY DIFFERS FOR ABORTING AND NONABORTING PISTILLATE FLOWERS IN PECAN

Comparative anatomical features of nonaborting (normal) and aborting p istillate flowers were examined with light and scanning electron micro scopy during the first of four physiological drops characteristic of p ecan [Carya illinoensis (Wangenh.) C. Koch]. Flowers sampled over a 3- year period from a protandrous and a protogynous cultivar (Desirable a nd Wichita, respectively) did not have any tissue necrosis. Diameter, length, and weight of aborting intact flowers were significantly less at 65 %, 55 %, and 30 %, respectively, in aborting than nonaborting in tact flowers. A common anatomical deviation in aborting flowers was th at the integument was less extended over the nucellus of the ovule tha n in nonaborting flowers. The number of parenchymal nucellus cell laye rs lateral to the embryo sac often was less in aborting than nonaborti ng flowers. Embryo sacs were inflated in nonaborting flowers, but appe ared deflated in aborting flowers. Both sacs had a conspicuous central nucleus, egg, and synergid, with a second synergid evident in the emb ryo sacs of some nonaborting flowers. Thus, aborting pecan flowers had incompletely developed ovules with no evidence of necrosis.