The leaves of plants have been used as food and for medicinal purposes for centuries. Records indicate that plants have been cultivated as early as 2000 BC. In the 5th century BC Hippocrates listed 400 herbs in common use and by the 1st century AD Dioscorides recorded 600 plants in medicinal remedies.
Leaves can be used in a variety of ways for both herbal supplements and culinary enjoyment. They can be chewed by themselves, dried and steeped in a tea, dried and powdered, chopped up into a meal or blended into a beverage. A wonderful way to enjoy the many delicious tastes leave can offer is to tear them up into a salad. You tossed salad will never be the same, with fresh mint, oregano, basil, parsley or rosemary.
Parts of Leaves
Leaves have a variety of different parts. See the diagram on the left to identify what each part of the leaf is.
Cuticle: Is a waxy layer that covers the epidermis. It is impermeable to liquids and water vapor.
Epidermis: Covers the top and bottom of the leaf. The epidermis has many functions. It guards against water loss, regulates the exchange of gases, secretes metabolic compounds and can sometimes absorb water depending on the type of plant.
Mesophyll Tissue: All the parts inside the leaf. This is where the chloroplasts (chlorenchyma) are found.
Palisade Layer: Contains the Chloroplasts. Chloroplast cells are the engine of the leaf, this is where photosynthesis occurs.
Spongy Layer: The cells in this layer are space further apart from each other. This allows carbon dioxide to diffuse into the leaf and oxygen to diffuse out of the leaf during the photosynthesis process. Leaf veins are also located in the spongy layer. The veins are comprised of two types of vascular tissues - Xylem cells that bring water and minerals from the roots to the leaves and Phloem cells that move sap and sugars produced by photosynthesis out of the leaf.
Stoma: Are pores found in the epidermis. They connect to chambers that art connected the air spaces in the spongy layer.
Guard Cells: Located in the epidermis, control the exchange of gases in and out of the leaf.
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https://en.wikipedia.org/wiki/Leaf , also the image source – found in a search for a image with a free to use license 3/28/2016