Although the leaf structure is reasonably intact and recognizable (e.g, you can see vein patterns) some degradation has occurred over time. There has been a stripping-away some of the cuticular layers that comprise the thickened protective surfaces of the leaf, leaving a delicately translucent leaf fossil behind that actually reveals some of the cellular substructure of the original (approximate magnification 2x; see higher magnification below).
Amber is the fossilized resin of ancient trees and often, along with insects, plant material is trapped by dripping resin and thereby preserved intact over millenia by the gradual process of amberization. In the above photomicrograph, an ancient leaf from an unknown (at least by me) plant is seen embedded within a golden matrix of Dominican amber; the leaf is at least 20 million years old and may actually belong to the tree that produced the resin that trapped it.
In this enlarged (approx. 10x) view of an area of the fossil leaf, the complex process of amberization reveals some of the substructural components of the leaf. The delicate patterns of the microveins are preserved, as are the large circular structures of pores (stomata) that occur in the leaf which controls the rate that water vapor and gases are transpired from the leaf surface to the air. Even tinier cellular detail is apparent in some cases, where individual guard cells that make up stomata can be observed. These basic structures used in ancient plant leaves to control gas exchange are essentially identical to those found in leaves today.
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