(c) : $Ti$ plasmid (tumor inducing) from the soil bacterium Agrobacterium tumefaciens is effectively used as vector for gene transfer to plant cells. The part of $Ti$ plasmid transferred into plant cell $DNA$, is called the $T-­DNA$. This $T-­DNA$ with desired $DNA$ spliced into it, is inserted into the chromosomes of the host plant where it produces copies of itself, by migrating from one chromosomal position to another at random. Such plant cells are then cultured, induced to multiply and differentiate to form plantlets. Transferred into soil, the plantlets grow into mature plants, carrying the foreign gene, expressed throughout the new plant.