Just as animals have vessels that carry materials throughout their bodies, plants have veins for the transportation of nutrients, including water. Plant veins are also sturdy enough to act as a support system and keep leaves open for photosynthesis -- the process through which plants make food. Plants have a vascular system throughout their roots and stems, but the system's veins are most visible in leaves.
Veins are distributed either in a netlike or parallel formation. Narrow and needle leaves typically have a parallel vein structure with a main vein or veins extending from each leaf's base to its tip. Leaves of broad-leaf plants have one of two types of netlike veins. A pinnate leaf, for example, has a dominant, central vein with other vessels branching to the vein's sides. A palmate leaf, however, has several large veins originating from the leaf's base.