Anatomy and Histology of the Pineapple Inflorescence and Fruit

Abstract

The collective fruit of the pineapple, Ananas comosus, develops from numerous complete, trimerous, sessile flowers fused to one another, to their subtending bracts, and to the inflorescence axis. The edible tissues consist of the ovaries and fleshy bases of sepals and bracts. 3 large internal nectaries or septal glands in the inferior ovary result ontogenetically from incomplete fusion of adjacent carpels. During anthesis, nectar flows from these glands through flattened, tubular ducts into the blossom cup. The gland cavity is closed after anthesis by expansion of septal parenchyma which forces the formerly secreting epidermal layers into close contact. The ducts remain open as 3 inward extensions of the blossom cup. Lightly cuticularized linings of the duct and blossom cup are modified later into a continuous, brown and horny, impervious layer by lignification, suberization, and wound periderm-like activity. The stylar canals, which are unobstructed passageways from the stigma to the locules before anthesis, are later closed by mucilaginous plugging and tylosis-like cells. Cell division in the fruit parenchyma ends at anthesis, followed by cell enlargement in varying degrees in different tissues. Softening and some disintegration of cell walls occur in overripe fruits. Vascular fusion and anastomosis within the inflorescence axis, within the flower, between the flower and its subtending bract, and between adjoining flowers and bracts indicate extreme adnation and cohesion of various tissues which make up the pineapple fruit.