This allowed them to attain great heights and compete for sunlight vertically. Secondary growth also provided protection for plant organs so that they could persist over a long time span. The Basic Steps in the formation of Secondary Vascular Tissues are illustrated below. The tissue between the Primary Xylem and Phloem may remain meristematic . This is called Vascular Cambium.
Meristematic activity can spread between the bundles so that the cambia become united.
This produces concentric rings of secondary vascular tissues with the Vascular Cambium between them. Note the two growth rings in the Secondary Xylem. Also note the presence of Periderm in the right-hand image. It is important to realize that the same process occurs in Roots. We will use Coleus as a Model plant to study the early stages of Secondary Growth in Angiosperms.