Answer: Some plants need to callous over before their internal cells trigger the development of shoots and roots. Cactus and geraniums are good examples. But not all plants need, or should, develop callouses before they can root and develop shoots. When you look up the propagation technique for each plant, there will be a note as to whether the cut end needs to dry before proceeding. If there is no notation, don't let the cut part dry out.
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