File:Herbaceous Dicot Stem Medicago (37141703136).jpg

cross section: Medicago stem common name: Alfalfa magnification: 100x

Like most herbaceous dicots, Medicago is capable of limited amounts of secondary growth.

The uniseriate and cutinized epidermis contains trichomes and occasional stomata.

The narrow cortex consists of an outermost hypodermis of up to four or five layers of chlorenchyma with areas over stem ridges being strengthened with collenchyma.The middle cortical layer consists of a zone of loosely arranged parenchyma and the deepest layer, of a band of endodermis (starch sheath) that follows the contours of the underlying vascular bundles.

Within the stele the vascular bundles are arranged in a ring and separated from each other by wide medullary rays of parenchyma cells.

The collaterally arranged vascular bundles are almost entirely primary phloem and xylem. Each bundle consists of a large outer supportive cap of sclerenchyma fibers (phloem fiber cap), a deeper layer of primary phloem with well-defined sieve tubes and companion cells, and a deepest layer of primary xylem. In between the xylem and phloem, a narrow band of cambium may be seen. In some preparations, the highly lignified cells walls of xylem and mature sclerenchyma are stained red orange. These cells are dead at maturity and can also be distinguished by a heavy cell wall and absence of cytoplasm.