A deciduous leaf's structure is divided into two categories, internal and external, with external structures including the blade, the petiole and the stipules and internal structures including the epidermis, the palisade layer, the spongy mesophyll, the vascular bundle, the stomata and the guard cells. Leaf composition differs from tree to tree but adheres generally to these overarching categories.
Leaves absorb light to facilitate photosynthesis, the process by which trees turn light into energy for growth. They also exchange moisture and gas with the atmosphere to keep trees healthy.
A leaf's internal features perform the following functions:
- Cuticles are waxy layers of the epidermis that regulate water loss.
- Chloroplasts are sub-cellular parts of the palisade layer that perform much of the photosynthetic process.
- Guard cells open and close the stomata to facilitate water and gas release.
Internal structures have to do primarily with the functions of the leaf and its part as a component of the tree's larger system.
A leaf's external features are organized in the following ways:
- Spiral clusters called rosettes
- Rings called catalpas
- Staggered distributions called alternates
Leaves are vital to the health of deciduous trees and are an important part of forest ecology. Decomposing, they reintroduce nutrients to the forest's soil and allow for the growth of their parent trees and of new vegetation and growth.