There are many parts within a leaf and each part has a special function in order to keep everything functioning smoothly. First, the top layer of the leaf, the cuticle as you can see in the diagram above is a fatty/waxy coating on the outer surface of a leaf in order to protect is and prevent the evaporation of water from the plant's tissues. Next, underneath the cuticle there is the epidermal tissue which also serves as the plant's skin and another layer of protection that produce the cuticle. As we make our way down the leaf structure more, we run into the mesophyll which is the middle of the leaf which includes the vascular tissue in the palisade layer; in other words, this area is considered the leaf's veins. This area consists of tubes that are within the vascular bundle which transport water through the xylem tube and sugar through the phloem tube. In order for this all to take place the cells need to be packed closely together however, some air spaces are what allow gas exchanges. Last but not least, we make our way to the bottom of the leaf structure which contain the guard cells and the stoma. Guard cells boarder the stoma and regulate the opening and closing of it. The stoma however, is a pore in the leaf in which gases and water vapor leave and enter the cell. This is what the guard cells assist with. The stoma also allows oxygen to be transported through the leaf. These are the basic, but most important structures within a leaf.