These are roots of parasites which suck nutrients from the host plant.
Example: Loranthus and Dodder
Loranthus is a a partial stem parasite. It has sucking roots which establish connection with the xylem of the host plant for absorbing water and mineral nutrients. It has chlorophyll in its leaves and it can prepare its own food.
Cuscuta is total stem parasite. It has no leaves. Its haustoria penetrate both xylem and phloem. They absorb both water and prepared food from the host plant.
