In a foundational experiment on plant growth regulators, F. Skoog observed that a mass of undifferentiated cells (callus) proliferated when the nutrient medium was supplemented with auxin along with extracts of vascular tissues, yeast extract, or coconut milk. Which specific plant tissue was used in this observation?

Step-by-step solution

F. Skoog and his co-workers observed that from the internodal segments of tobacco stems, the callus proliferated only if, in addition to auxins, the nutrient medium was supplemented with extracts of vascular tissues, yeast extract, coconut milk or DNA. Coleoptile tips of oat seedlings were used by F.W. Went for the discovery of auxin. Uninfected rice seedlings were used by E. Kurosawa in the discovery of gibberellic acid. Coleoptiles of canary grass were used by Charles Darwin and Francis Darwin for observing photo