Define/Explain: Cytokinins.

(N/A) Cytokinins are a class of plant growth substances (phytohormones) that promote cell division,or cytokinesis,in plant roots and shoots. They were discovered by Miller et al. during the investigation of cell division-promoting activity in degraded $DNA$ preparations. They help in producing new leaves,lateral shoot growth,and adventitious shoot formation. They also help in delaying leaf senescence.