Q.What is endothelium?

The gynoecium (one or more pistils, each from a carpel) is the flower's female reproductive whorl; each pistil has an ovary (base, bearing ovules on its placenta), style (connecting stalk) and stigma (pollen-receiving tip), and arises as a papillate meristematic outgrowth that differentiates into these three parts. A mature ovule (megasporangium) has a stalk (funiculus/funicle, attaching it to the placenta; its junction with the ovule body is the hilum, and in an inverted ovule the fused funicle forms a ridge called the raphe) and a body - a food-rich parenchymatous nucellus enclosed by one (unitegmic) or two (bitegmic) integuments that leave a tip pore, the micropyle, and meet the funicle at the base in a region called the chalaza (with a hypostase below the embryo sac and an epistase above the micropyle). In some species (e.g. Asteraceae) the inner integument layer specialises into a nutritive endothelium (integumentary tapetum). Ovules are tenuinucellate (hypodermal sporogenous cell, single-layered, small nucellus) or crassinucellate (subhypodermal sporogenous cell, fairly large nucellus), and by orientation fall into six types: orthotropous (micropyle-funicle-chalaza in one line, e.g. Piperaceae), anatropous (fully inverted, the commonest type in dicots and monocots), hemianatropous (body at right angles to the funicle, e.g. Primulaceae), campylotropous (curved, bean-shaped, e.g. Leguminosae), amphitropous (horseshoe-shaped nucellus, e.g. some Alismataceae) and circinotropous (funiculus coiled around the ovule, e.g. Cactaceae). Megas …