Plant xylem of the less developed to developed, juicy stems, and more flexible. Herbaceous plants by the length of the life cycle can be divided into:
1. Annual herb: growth in a season could be completed within the life cycle, that is, when flowering, seed after the death of plants, such as rice, beans, tomatoes and so on.
2. Biennial herb: in the first year growing season (autumn) only organs Nutrition long, the second year of the growing season (spring) flowering, seed after the death of plants, such as winter wheat, sugar beet, broad bean and so on.
3. Perennial herb: can live more than two years of herbaceous plants. Some of the underground part of the plant for the perennial, or ratoon, such as roots, bulbs, root, and other abnormal organs, and each year some of the dead on the ground until the spring of the following year from the underground sections of the new branches grow, flower seed, such as lotus root, onion, lines, sweet potato, Dahlia, and so on; there are a number of other plants on the ground and the underground sections for the perennial, flowers, fruit, is not part of the ground dead, and many solid, such as evergreen,and so on.