<P> The position of vascular bundles relative to each other may vary considerably: see stele . </P> <P> Bundle - sheath cells are photosynthetic cells arranged into tightly packed sheaths around the veins of a leaf . They form a protective covering on leaf veins, and consist of one or more cell layers, usually parenchyma . Loosely arranged mesophyll cells lie between the bundle sheath and the leaf surface . The Calvin cycle is confined to the chloroplasts of these bundle sheath cells in C plants . </P> <Ul> <Li> Campbell, N.A. & Reece, J.B. (2005). Photosynthesis . Biology (7th ed .). San Francisco: Benjamin Cummings . </Li> </Ul> <Li> Campbell, N.A. & Reece, J.B. (2005). Photosynthesis . Biology (7th ed .). San Francisco: Benjamin Cummings . </Li>

What is nature of vascular bundles in dicot stem