EXTERNAL MORPHOLOGICAL-CHARACTERISTICS FOR HISTOGENESIS IN PECAN ANTHERS

External morphological characteristics of catkins from one protogynous ('Stuart') and one protandrous ('Desirable') cultivar of pecan [Carya illinoensis (Wangenh.) C. Koch] were examined to define markers of cellular differentiation in the anthers. The angle between the catkin rachis and the bract, visibility of the bracteole, rachis, and anther, and anther color proved to be markers by which development could be categorized into five stages. 'Stuart' catkins with bracts as the only externally visible portion of the floret (Stage I) commonly had two locules in each anther lobe. When bracteoles became externally visible (Stage II), cellular specialization had occurred to form a central core containing reproductive cells and tapetal cells differentiated and separated from the exterior layers of the anther wall. Disintegration of tapetal cells and thickening of endothecium cell walls occurred as the angle between the rachis and bract increased to 45-degrees (Stage III). The anther wall was reduced to only two cell layers, epidermis and endothecium, as the anthers became visible (Stage IV). The pollen grains were mature when the anthers developed a yellowish tinge (Stage V) just before anther dehiscence. Tapetal cells had developed distinguishing traits in anthers of Stage I 'Desirable' catkins and endothecial cells of Stage 11. Internal anther development was similar for both cultivars from Stages III-V. Trichomes, a common feature on the surface of the staminate floral parts, became less dense with proximity of the floral parts to the interior of the floret and with catkin maturity.