(i) Auxin- It is a growth promoting hormone.

● The primary function of the auxin hormones is to elongate plant cells in the stem. Auxin by some mechanism breaks the bonds holding its cellulose fibers together. These broken bonds give the cell wall greater flexibility and expandability so that more water can enter the cell by diffusion, causing the cell itself to elongate.

● Auxins are also responsible for adventitious root development, secondary growth in the vascular cambium,

● Inhibition of lateral branching, and fruit development. In fact, seedless fruits can be artificially created by applying synthetic auxin to plants; this causes fruit to develop even though fertilization (and thus seed formation) has not occurred.

(ii) Abscisic acid- It is the growth inhibitory hormone or the stress hormone.

● It restrains the growth and causes the falling of old leaves.

● It maintains the period of dormancy in seeds and buds.

● It also causes the guard cells of the stomata to close when the plant is losing too much water.