Voisin (1959) aptly stated that "A pasture plant must be capable of growing again after it has been cut either by a tooth of the animal or by the blade of the mower." Proper harvest management, matching timing and intensity of defoliation with the plant's readiness to regrow, affects both the yield and quality of harvestable forage.

Growth, as well as regrowth following defoliation, depends upon cell division and cell expansion. Cell division and growth areas are called meristem systems or formative tissue. In as much as these meristems are the sole mechanisms for regrowth, their location and specific function merit close attention in forage grass management. Unfavorable consequences result when these meristem systems are destroyed. The three main tissues involved in growth and regrowth are: apical meristems, intercalary meristem in leaf bases, tillers (also called shoots), rhizomes, stolons, and buds.

Within a seed, when conditions are right to begin germination, specific cells within the germ tissue divide and expand, pushing the apical meristem contained in the seed out of the seed. A tube-like organ called the coleoptile protects the first leaf blade by pushing through the soil eventually breaking through the crust of the soil. Then the first leaf unfurls. Many will follow.

A node at the base of the coleoptile is also pushed up towards within a few centimeters of the soil surface by the elongation of an internode called the mesocotyl. The node that is pushed upward becomes the crown tissue from which roots and additional tillers arise. Seedling roots develop through branching into an efficient seminal (seed) root system capable of supplying water and inorganic nutrients. Later, an adventitious root system forms.

A crown of a grass plant is where the stem projects upward and the roots extend below and serve as a base for the plant's growth. The crown is actually a contracted stem with its nodes stacked closely on each other. These nodes will be pushed upward with internodes between nodes as the stem elongates. The crown is the organ that produces leaves, roots, tillers, and elongated stems. It is also a storage organ for carbohydrates which fuel new plant parts.

People think of stems as growing upright but grasses have stems that can also grow horizontally. Rhizomes and stolons are elongated and horizontal stems. They emerge or branch outward which is called extravaginal branching. Bunchgrasses have extravaginal branching growth.

Grasses can tolerate defoliation because during their vegetative phase, leaves continue to form after defoliation. During the vegetative phase almost all cells capable of dividing into new cells (meristem) remain at or near the surface of the ground although each new leaf forms higher on the stem than the previous leaf. They are too low for mowing blades and biting teeth of grazing animals until stems elongate, pushing the meristem cells upward. This growth is fueled by storage reserves and other leaves.

  • Apical meristem: contains cells which eventually produce leaves, stems, and floral structures. An apical meristem is also called a shoot apex, shoot primordium, or growing point.
  • Leaves: are comprised of two separate organs, the sheath and the blade. The sheath is the part of the leaf that wraps around the stem. The blade of a leaf arches away from the stem. A narrow band of intercalary meristem is found in the basal zone of both the sheath and the blade. This meristem accounts for the increasing length of the sheath and blade. The narrow band of meristem at the base of the blade is designated as the collar.
  • Tillers: are cylindrical bundles of relatively immature leaf blades enclosed by mature leaf sheaths. The apical meristem cells in the base of the tillers develop leaves.
  • Basal buds: are capable of developing new tillers and will do so when the apical meristem is removed. Grasses can develop new tillers from basal buds on stem bases, rhizomes, or stolons.