Anatomy of Dicot Stem - Sunflower

A sunflower stem - the textbook's dicot stem example - again reads outside-in as a clear sequence, but with more internal zoning than the corresponding root. Its epidermis is a single layer of compactly-arranged, cutin-covered, rectangular parenchyma cells bearing numerous multicellular hairs, with chloroplasts normally absent. Its cortex is not homogeneous like the root's - it splits into three distinct functional zones: an outer, few-layered hypodermis of living, corner-thickened collenchyma cells giving mechanical strength to the still-elongating stem; a middle zone of chlorenchyma with conspicuous intercellular spaces (carrying out photosynthesis, and sometimes housing resin ducts); and an inner zone of ordinary parenchyma dedicated to food storage. The cortex's innermost layer is again an endodermis, but here it usually shows no true casparian strips - instead its starch-rich cells earn it the alternative name starch sheath, homologous to (but not identical in function to) the root's true endodermis. Everything inside the endodermis makes up the stele: a pericycle, and - arranged in a ring around a large central parenchymatous pith - the vascular bundles, an organisation given the specific name ** …