The correct answer is Option C: Tumor inducing plasmid.

The "Ti plasmid" is a type of plasmid (a small DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently) found in the bacterium Agrobacterium tumefaciens. This bacterium is known for its ability to transfer a segment of its DNA to a plant, integrating this DNA into the plant's genome, causing the plant to develop tumors, known as crown gall disease.

The term "Ti plasmid" stands for "Tumor inducing plasmid" because of its role in this process. When Agrobacterium tumefaciens infects a plant, the Ti plasmid transfers a portion of its DNA-known as T-DNA (transfer DNA)-into a random site in the plant's genome. The expression of genes in the T-DNA leads to the overproduction of certain growth hormones (auxins and cytokinins), which results in the formation of tumors on the plant.

Thus, Option C "Tumor inducing plasmid" most accurately describes the Ti plasmid's function of inducing tumor formation in infected plants. Options A, B, and D do not correctly describe the properties or functions of the Ti plasmid.