That is to say, the roots of some plants are not directly or indirectly formed by radicles, but grow from stems, leaves or other parts, and there is no fixed growth site, so they are called adventitious roots. Adventitious roots can enlarge the absorption area of plants and strengthen the fixation or support of plants. In tissue culture, the roots from callus are also called adventitious roots. The occurrence of adventitious roots is due to the damage of plant organs or the stimulation of external factors such as hormones and pathogenic microorganisms, so it shows the regeneration reaction of plants. Especially when subjected to mechanical trauma and anaerobic stress of water, plants will form a large number of adventitious roots at the lower end of the form or at the injured part of the flooded land-water junction. For example, take a weeping willow branch and insert it in wet soil, and soon a root will grow on the stem inserted in the mud, which is an adventitious root. A narcissus head, put in water for a few days, densely produces a ring root at the bottom, which is also an adventitious root. In forestry and horticulture, the vegetative propagation of willow, grape, rose and begonia can produce a large number of adventitious roots.