AP BIOLOGY

Detailed explanation-1: -The outer cortex is chlorenchymatous, while the inner cortex is made up of thin-walled parenchymatous cells. There is a large air cavity in the inner cortex corresponding to each furrow and alternating with the ridges, known as vallecular canal.

Detailed explanation-2: -The leaves of horsetails are arranged in whorls fused into nodal sheaths. The stems are usually green and photosynthetic, and are distinctive in being hollow, jointed and ridged (with sometimes 3 but usually 6–40 ridges). There may or may not be whorls of branches at the nodes.

Detailed explanation-3: -The outer layer of the rhizome possesses a thick brown cuticle, and its cells have dark, thick walls. The next layer consists of smaller cells, the walls of which are also strongly sclerized. This marked thickening extends to a third layer of cells, especially to their outer walls.

Detailed explanation-4: -Just below each groove is present a large air canal in the parenchymatous cortex. It is known as vallecular canal.