Secondary Growth In Stem ||Spring Wood - Autmn Wood || Anatomy of Angiosperms ||+3 3rd Sem || Lec-09

Secondary growth in stems is a process that increases the girth or thickness of the stem in vascular plants. It occurs in woody plants, including many angiosperms (flowering plants). The primary meristems involved in secondary growth are the vascular cambium and cork cambium.

Vascular Cambium:

The vascular cambium is a lateral meristem located between the xylem and phloem in the vascular bundles of stems and roots.
It produces secondary xylem (wood) towards the inside and secondary phloem towards the outside.
The activity of the vascular cambium leads to the formation of annual rings in the stem.
Annual Rings:

In temperate regions, where there are distinct seasons, the vascular cambium produces wood with varying characteristics during different times of the year.
The wood formed in the spring is called "springwood," and the wood formed in the autumn is called "autumnwood" or "latewood."
Springwood is characterized by large, thin-walled cells, while autumnwood has smaller, thicker-walled cells.
This variation results in the formation of concentric rings in the stem, with each pair of springwood and autumnwood representing one year's growth.
Anatomy of Angiosperms:

Angiosperms, or flowering plants, are the most diverse group of plants on Earth.
The basic anatomy of angiosperms includes roots, stems, and leaves.
In the context of secondary growth, the stem anatomy is crucial.
The stem typically consists of epidermis, cortex, vascular bundles, pith, and a cylindrical arrangement of tissues called the vascular cambium.
Springwood and Autumnwood Characteristics:

Springwood:

Formed during the early part of the growing season.
Cells are larger, have thinner cell walls, and are less dense.
Typically lighter in color.
Shows higher water-conducting efficiency.
Autumnwood:

Formed during the later part of the growing season.
Cells are smaller, have thicker cell walls, and are more dense.
Typically darker in color.
Provides more structural support.
Understanding the patterns of springwood and autumnwood in annual rings can be useful in dendrochronology (the study of tree rings) for dating and environmental analysis. The distinct characteristics of these wood types are related to the changing environmental conditions and the plant's growth dynamics during different seasons.