Tridax procumbers is a common dicotyledon plant whose stems are taken for anatomical studies. The transverse section of this stem shows the following features:
The outer boundary is more or less circular having a single layered epidermis. The epidermal cells are rectangular without chlorophyll. A number of multicellular epidermal hairs are found in this layer. Cuticle is thin.
It is the outer zone of cortex and lies below the epidermis. It consists of a few layers of collenchymatous cells with distinct thickened intercellular spaces.
It is inner to hypodermis and consists of several layers of thin walled parenchymatous cells. The outer layers contain chlorophyll within the cells.
It is the inner layer of cortex and consists of only one layer of barrel shaped cells. This layer possesses abundant starch and hence, called starch sheath.
It is the outer layer of stele. It is sclerenchymatous in nature and continuous. However, there are more layers of sclerenchyma opposite to vascular bundles.
Several vascular bundles are arranged in one ring and very close to the pericycle. Each vascular bundle is a conjoint, collateral and open type with few layers of cambium in between xylem and phloem patches. The phloem is outer and xylem is inner in position. Xylem is endarch in nature. Xylem contains all vessels, tracheids, parenchyma and fibres. Protoxylem elements are smaller than metaxylem elements.
Pith (Medulla) The centre of the stem is occupied by a well developed parenchymatous pith. Pith is broad and has intercellular spaces.