Final answer:
Lateral meristems are responsible for increasing the girth of plant roots and stems through the secondary growth. The two main types of lateral meristems are vascular cambium, which produces secondary xylem and phloem, and cork cambium, which generates the protective outer bark.
Step-by-step explanation:
The three major types of plant meristems are apical, lateral, and intercalary meristems. Lateral meristems increase the girth of roots and stems as they create new tissue. There are two main types: vascular cambium, which produces secondary xylem and phloem, and cork cambium which produces the outer bark. Secondary meristems like the vascular cambium add to the plant's diameter or girth, a process known as secondary growth. This type of growth is responsible for building the sturdy trunks of trees by producing wood through the formation of secondary xylem and phloem. On the other hand, the cork cambium, another type of lateral meristem, lies between the epidermis and the phloem and generates the protective outer layer of the plant, known as the bark, with one layer being cork.
These secondary meristems are essential for the radial growth of woody plants, which is a stark contrast to the primary growth caused by apical meristems, responsible for lengthening plants. Intercalary meristems, typically found in monocots, contribute to the lengthening of leaf blades and are particularly evident in plants like grass that can regrow after being cut.
Meristematic tissues, therefore, allow plants to grow in different dimensions and aspects, whether it be vertically via apical meristems or horizontally and radially via lateral and intercalary meristems.