The first Cytokinin was discovered by ----(A)------ during...

F. Skoog and his co-workers observed that from the internodal segments of tobacco stems (Nicotiana tabacum), the callus proliferated only if, in addition to auxins, the nutrient medium was supplemented with extracts of vascular tissue, yeast extract, coconut milk or DNA.

Later, Skoog and Miller identified and crystallized the cytokinesis-promoting active substance that they termed kinetin, which was the first discovered cytokinin.

Therefore, A is Skoog and Miller, and B is Nicotiana tabacum.

Answer: A- Skoog and Miller ; B- Nicotiana tobacum