single-cell or multicell outgrowths of the epidermal cells of plants. Plant hairs are similar to other outgrowths, or so-called emergences; deeper layers of plant tissue participate in the formation of these emergences. Single-cell hairs appear as outgrowths, making the petals of many flowers velvety, or cylindrical processes in the shape of tubes, primarily on the roots. Sometimes they curve and take on a stellate shape or another shape. Multicellular hairs are often large and shaped like long appendages or scales.
Hairs fulfill various functions. Often covering leaves and stem with a dense feltlike fuzz, the hairs that are dead and puffed with air protect the plant from temperature variations and loss of moisture; this phenomenon is found mostly among high mountain and desert plants. In some desert plants the hairs take the form of bubbles or receptacles that store water, which is absorbed later during droughts. Hairs can also protect plants from natural enemies. They are stiff, woolly, prickly, or toxic (for example, the stinging hairs of nettles). Sometimes they play a role in the distribution of fruits or seeds—the hairs on the fruit attach themselves to the coats of animals or are easily picked up by the wind. (Various adaptations of parachute or wing forms are found on such plants as the dandelion, cotton, and poplar.) Hooklike hairs on stems help to support climbing plants such as hops and beans. Root hairs on all plants and special hairs and squamellae on epiphytes absorb water and nutrients dissolved in the soil. Glandular hairs are organs of secretion for essential oils or even digestive juices (in insectivorous plants).
REFERENCEAleksandrov, V. G. Anatomiia rastenii, 3rd ed. Moscow, 1954.
M. S. NAVASHIN