Monocot StemMonocot Stem
In most monocots the vascular bundles are arranged throughout the ground tissue rather than in a ring; thus it is not possible to distinguish pith and cortex regions.
Along with leaves the stems are the main organ that make up the shoot system. Along the stem, nodes, the points at which leaves are attached, alternate with inner nodes, the stem segments between them, modified stems of some plants are sometimes mistaken for roots. Stolons, horizontal stems, grow along the surface of the ground, bermuda grass is an example. Rhizomes are horisontal stems that grow along the ground. Some rhizomes end in enlarged tubers where food is stored as in white potatoes. Bulbs, such as those as tulips and onions are vertical, underground shoots with leaves modified for food storage.
The stems and roots of most vascular plants grow in girth as well as length. This increase in diameter is called secondary growth. These two lateral meristems are the vascular cambium, and the cork cambium. The formation of secondary tissues not only increases the thickness of a stem or a root but also changes its structure. Secondary growth does not occur in most monocots but the increase in size is solely based on primary growth.
Vascular tissue runs the length of the stem in several strands called vascular bundles. Each vascular bundle of the stem is surrounded by ground tissue. The ground tissue is mostly parenchyma cells but many stems are strengthened by collenchyma cells, located just beneath the epidermis.