They function in conduction. Basically they support the photosynthetic organs, the leaves in a favorable position for exposure to the light. Leaf primordia -young leaves, these develop into the mature leaf. Remember when we talked about the formation of lateral roots last time we mentioned the term endogenous. I.E. the new roots develop on the inside of a mature root and punch their way out through the cortex.
Leaves are different.
They arise surficially on the stem, on the outside . Develop from the leaf primordia. The root apex lacks a root cap. It usually isn't pushing its way through the soil. But the apex is surrounded by the developing leaves.