Secondary Growth
Secondary growth is an increase in diameter/girth/circumference due to the addition of secondary tissue(secondary cortex, secondary phloem, and secondary xylem) formed by the activity of vascular cambium in stelar region(region inside pericycle) and cork cambium (phellogen) in extrastelar region (the region outside pericycle i.e., cortex). It is found in the dicot stem, dicot roots, and gymnosperms. Herbs, shrubs, and hydrophytes do not show secondary growth. Monocots rarely show secondary growth(e.g., Aloe, Dracaena, Agave).
Vascular cambium and cork cambium are lateral meristems. Secondary tissues are formed in secondary growth to provide Protection (by cork), mechanical strength (by secondary xylem), conduction of water, and nutrients ( by secondary xylem and secondary phloem). Secondary growth is characterized by an increase in the thickness or girth of the plant. It is caused by cell division in the lateral meristem.
Secondary Growth
Term tissue ( French word meaning woven ) was used by N.Grew (1682) the father of plant anatomy. Nageli is regarded as the father of Modern Anatomy. A cell is the functional and structural unit of life. A tissue is a group of cells having a common origin, the same method of development, and function. Anatomy deals with the internal organization of plants. In plants, the terms anatomy and histology have the same meaning. Different organs in plants show differences in their internal structure. Within angiosperms, the monocots and dicots are also seen to be anatomically different. The internal structures show adaptations to diverse environments.