Cirrus

In botany, a Cirrus is a specialized stem, leaf or petiole with a threadlike shape that is used by climbing plants for support, attachment and cellular invasion by parasitic plants, generally by twining around suitable hosts. They do not have a lamina or blade, but they can photosynthesize. They can be formed from modified shoots, modified leaves, or auxiliary branches and are sensitive to airborne chemicals, often determining the direction of growth, as in species of Cuscuta.

In the garden pea, it is only the terminal leaflets that are modified to become cirrus. In other plants such as the yellow vetch (Lathyrus aphaca) the whole leaf is modified to become cirrus while the stipules become enlarged and carry out photosynthesis. Still others use the rachis of a compound leaf as a cirrus, such as members of the genus Clematis.

The specialised pitcher traps of Nepenthes plants form on the end of cirrus. The cirrus of aerial pitchers are usually coiled in the middle. If the cirrus comes into contact with an object for long enough it will usually curl around it, forming a strong anchor point for the pitcher. In this way, the cirrus help to support the growing stem of the plant.

Source: en.wikipedia.org/wiki/Cirrus - 19.03.2012