An anatomical arrangement in which the smallest veinlets of a leaf span the upper and lower surfaces of the leaf blade and project as ribs onto the leaf surface, forming a network of fine translucent lines. Found in many tree species and in some herbaceous plants, such as sunflower and broad bean, these projections are bundle sheath extensions (BSEs) arising from the bundle sheath cells. They form a network of barriers within the leaf, separating the mesophyll into numerous compartments (areoles) and inhibiting transverse movements of air. The function of heterobaric anatomy is uncertain. One suggestion is that the translucent nature of BSEs enables them to act as light guides, transferring light to deeper layers of photosynthetic cells within the leaf, thereby permitting a thicker leaf as an adaptation to dry conditions. Compare homobaric leaf anatomy.
Subjects: Biological Sciences.