a) Gibberellins- These are plant hormones that regulate growth and influence various developmental processes, including stem elongation.

b) Auxin- 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.

c) Cytokinin- They are a class of plant growth substances (phytohorm-ones) that promote cell division. They are the positive regulators of cell division in shoot apical meristem. They are presenting in greater concentration in areas of rapid cell division, such as in fruits and seeds.

d) Abscisic Acid (ABA)- It is the growth inhibitory hormone or the stress hormone. It restrains the growth and causes the falling of old leaves.