Hydathodes 

Hydathodes are structures that release water with some substances from the interior of the leaf to its surface. This process is called guttation and occurs by water pressure coming from the root.

Hydathodes are modifications of some parts of the leaves and are located along the margins or at the tip of the leaf. Structurally, hydathodes consist of a) terminal tracheids of leaf nerves, b) the epithem, which consists of thin-walled and few chloroplasts parenchyma cells located at the leaf nerve endings, c) a sheath or envelope that is continuous with the epidermis (the sheath cells may be suberized and may even have Caspary bands), d) an watery opening or pore (watery pores are small nonfunctional stomata who have lost the ability to regulate opening and closing). Although this is the general organization, there may be variations, such as lack the sheath, or the epithem, or may even have an opening which is not a stoma.

Although hydathodes are normally found at the margins and tips of leaves, in some species, they also appear on the surface and are called laminar hydathodes. Hydathodes are generally associated with the release of water from the plant tissues, but in many xerophytic species they are specialized in the absorption of condensed fog or dew water, i.e., the opposite process. Some authors have described the active hydathodes, also known as trichome-hydathodes, as glandular trichomes that release water. These structures would release water without being influenced by the osmotic pressure, hence they are considered active as opposed to the others that would be passive.