Axis

Axis, in Botany, a term applied to the central portion of the higher plants (higher cryptogams as well as phanerogams), which bears the appendages or lateral members arranged upon it. Those plants in which no distinction of axis and appendages can be made out are termed Thallophytes, and include algae, lichens, and fungi. The stem is called the ascending axis; the root, the descending axis. In the germinating seed, these are distinguished as plumule and radicle. The terminal part of an axis bearing the reproductive organs in flowering plants is called the floral axis. This is usually a very short portion, but may be elongated, broadened, hollowed, &c. The notion of a flowering plant as simply an axis with more or less modified appendages serving different purposes, as scale, leaf, petal, stamen, carpel, &c., is older than Linnaeus, but was first clearly grasped by the embryologist Wolff, and even more systematically at a later date (1790) by the many-sided poet Goethe. In describing animal forms it is customary to define the disposition of the parts in reference to certain axes, lateral, dorso-ventral, radial, &c. (see MORPHOLOGY).—The term axis is specially applied in human anatomy to the second vertebra of the neck (see SPINAL COLUMN).