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A hydathode is a type of pore, commonly found in
hydathode physiology
Plant anatomy {{botany-stub
A hydathode is a type of pore, commonly found in vascular plant
Vascular plants (), also called tracheophytes (, ) or collectively tracheophyta (; ), are plants that have lignin, lignified tissues (the xylem) for conducting water and minerals throughout the plant. They also have a specialized non-lignified Ti ...
s, that secretes water through pores in the epidermis
The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and Subcutaneous tissue, hypodermis. The epidermal layer provides a barrier to infection from environmental pathogens and regulates the ...
or leaf margin, typically at the tip of a marginal tooth or serration. Hydathodes occur in the leaves of submerged aquatic plants such as '' Ranunculus fluitans'' as well as herbaceous plants of drier habitats such as '' Campanula rotundifolia''. They are connected to the plant vascular system by a vascular bundle. Hydathodes are commonly seen in water lettuce
''Pistia'' is a genus of aquatic plants in the arum family, Araceae. It is the sole genus in the tribe ''Pistieae'' which reflects its systematic isolation within the family. The single species it comprises, ''Pistia stratiotes'', is often call ...
, water hyacinth
''Pontederia crassipes'' (formerly ''Eichhornia crassipes''), commonly known as common water hyacinth, is an aquatic plant native to South America, naturalized throughout the world, and often invasive species, invasive outside its native rang ...
, rose
A rose is either a woody perennial plant, perennial flowering plant of the genus ''Rosa'' (), in the family Rosaceae (), or the flower it bears. There are over three hundred Rose species, species and Garden roses, tens of thousands of cultivar ...
, balsam, and many other species.
Hydathodes are made of a group of living cells with numerous intercellular spaces filled with water, but few or no chloroplasts
A chloroplast () is a type of membrane-bound organelle, organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. Chloroplasts have a high concentration of chlorophyll pigments which captur ...
, and represent modified bundle-ends. These cells (called ''epithem cells'') open out into one or more sub-epidermal chambers. These, in turn, communicate with the exterior through an open water stoma or open pore. The water stoma structurally resembles an ordinary stoma
In botany, a stoma (: stomata, from Greek language, Greek ''στόμα'', "mouth"), also called a stomate (: stomates), is a pore found in the Epidermis (botany), epidermis of leaves, stems, and other organs, that controls the rate of gas exc ...
, but is usually larger and has lost the power of movement.
Hydathodes are involved in the process of guttation
Guttation is the exudation of drops of internal liquid out of the tips or edges of leaves of some vascular plants, and also a number of fungi. Ancient Latin gutta means "a drop of fluid", whence modern botany formed the word guttation to designa ...
, in which positive xylem
Xylem is one of the two types of transport tissue (biology), tissue in vascular plants, the other being phloem; both of these are part of the vascular bundle. The basic function of the xylem is to transport water upward from the roots to parts o ...
pressure (due to root pressure) causes liquid to exude from the pores. Some halophyte
A halophyte is a salt-tolerant plant that grows in soil or waters of high salinity, coming into contact with saline water through its roots or by salt spray, such as in saline semi-deserts, mangrove swamps, marshes and sloughs, and seashores. ...
s possess gland
A gland is a Cell (biology), cell or an Organ (biology), organ in an animal's body that produces and secretes different substances that the organism needs, either into the bloodstream or into a body cavity or outer surface. A gland may also funct ...
ular trichome
Trichomes (; ) are fine outgrowths or appendages on plants, algae, lichens, and certain protists. They are of diverse structure and function. Examples are hairs, glandular hairs, scales, and papillae. A covering of any kind of hair on a plant ...
s that actively secrete salt in order to reduce the concentration of cytotoxic inorganic ions in their cytoplasm; this may lead to the formation of a white powdery substance on the surface of the leaf.
Hydathodes are of two types:
# passive hydathodes, formed when a leaf vein terminates in an epithem (an area of thin-walled parenchyma
upright=1.6, Lung parenchyma showing damage due to large subpleural bullae.
Parenchyma () is the bulk of functional substance in an animal organ such as the brain or lungs, or a structure such as a tumour. In zoology, it is the tissue that ...
).
# active hydathodes, formed when epidermal cells lose water actively.
See also
*Transpiration
Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers. It is a passive process that requires no energy expense by the plant. Transpiration also cools plants, c ...
*Vascular plants
Vascular plants (), also called tracheophytes (, ) or collectively tracheophyta (; ), are plants that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They also have a specialized non-lignified tissue ( ...
*Xylem
Xylem is one of the two types of transport tissue (biology), tissue in vascular plants, the other being phloem; both of these are part of the vascular bundle. The basic function of the xylem is to transport water upward from the roots to parts o ...
References
External links
hydathode physiology
Plant anatomy {{botany-stub