Final answer:
When the top of a forage legume or dicot is removed, the apical meristem is lost, preventing further vertical growth of the stem. Monocots, like grasses, can regrow from intercalary meristems after damage. Dicots may respond by growing lateral buds leading to a bushier plant.
Step-by-step explanation:
When the top of a forage legume (or other dicot) is removed, the apical meristem is lost, leaving no other active above-ground meristems on the plant. The apical meristem is a critical plant structure involved in vertical growth and development of the plant's organs. Found at the tip of shoots, it enables the plant stem and leaves to grow longer and differentiate. However, when this meristem is damaged or removed, plants like dicots cannot continue their growth upward as there is no substitute meristem available above ground to take over this role.
In contrast, plants like monocots, particularly grasses, have evolved to withstand damage to their shoot tips. Monocots have intercalary meristems located at the stem nodes and the base of leaf blades which enable them to regrow after being grazed or cut. This adaptation can be attributed to the evolutionary pressure from herbivores and involves meristematic zones that can be activated when upper parts are grazed or removed.
In the absence of the apical meristem, some dicots may still continue to grow through the activation of lateral buds. These buds are initially dormant and are stimulated to grow once the dominant influence of the apical meristem is gone. This results in a more bushy growth pattern as opposed to the single, dominant main stem usually seen in a plant's natural growth habit.