When did the first plants on earth begin to grow on land and what were they called? July 18, 2014 by Karen Hill | Filed Under: Earth The first plants to begin growing on land were bacteria, or microscopic plants, in the Ordovician period, 505 to 438 million years ago. Lichens, mosses, and liverworts followed the bacteria onto land. Before the Ordovician period ended, a varied plant population, including ferns and trees, extended all over Earthâs land masses. Related
The iris (plural: irides or irises) is a thin, circular structure in the eye, responsible for controlling the diameter and size of the pupils and thus the amount of light reaching the retina. Eye color is the color of the iris, which can be green, blue, or brown.
The Iris and Pupil. The pupil is the black hole in the center of the colored iris. It contracts when exposed to bright light and expands in darkness to allow more light into the eye. The iris is the colored part of the eye. This coloring is due to pigment cells in the tissue. People with blue eyes have less pigment in their iris than those who have brown eyes. The iris contains the sphincter pupillae, the muscle used to narrow the pupil, and the dilator pupillae, the muscle used to widen it.