Rays

Abstract

The term medullary ray is derived from the fact that the pith was for many years called the medulla. Consequently, the parenchymatous tissue extending from pith to cortex between primary vascular bundles became known as a medullary ray or pith ray. According to Hartig (1855a), the term “Markstrahl”, or pith ray, was applied not only to the parenchymatous tissue occurring between vascular bundles in woody plants, but also to the cellular tissue that occupied the same position in the growing shoot. Because of this relationship, many early workers assumed that the rays of woody plants arose by compression of the originally separated fiber bundles. Conversely, new fiber bundles were thought to arise by the intervention of new ray cells. That is, when new ray cells were initiated in the “cambial layer”, they split a vascular bundle, thus forming two bundles in the place of one (Göppert 1842, Hartig 1854a).