List and describe four classes of plant hormones.

Auxin, cytokinins, ethylene and gibberellins

Explanation:

The IAA that is indole 3 acetic acid is also called auxin. The first plant hormone identified is auxin. The hormone promotes cell growth on the dark side of plant. The cytokinin play role in cell division and thus named cytokinin. The hormone promote mitosis and thus cell division increases.

The ethylene hormone is responsible for shedding of leaves, flower blooming and ripening of fruits. The hormone also inhibits vegetative tissues. The gibberllins regulate development process in plant. The hormone promote dormancy, scenescence, flower development and elongation of stem.