Please correct me if my understanding is incorrect; I understandbranch/stem, and root are composed of different types of cells. Yetin some plants (e.g. rose, bougainvillea) a cutting from the stemis capable of developing and taking root.

How does this transformation from stem to root come about?

As an aside - I believe such root-generation happens only inplant cuttings, and not in a tree branch. Why? Is it a matter ofthe volume of nutrition required?