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THORN (O. Eng. porn, cf. Du. doorn, G...

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Originally appearing in Volume V26, Page 880 of the 1911 Encyclopedia Britannica.
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THORN (O. Eng. porn, cf. Du. doorn, Ger. Dorn, &c)  , in See also:botany, a hard pointed structure; also termed a " spine," generally representing a small See also:branch, as in See also:hawthorn, where a normal branch arising in the axil of a See also:leaf is replaced by a sharply pointed See also:thorn; See also:accessory buds on each See also:side of the thorn and See also:developed in the same leaf-axil will grow in the next See also:season into See also:ordinary branches . The similarly developed thorns of the See also:honey-See also:locust (Gleditschia) are branched . In other cases, as the sloe or the See also:wild See also:pear, branches become spiny at the See also:apex tapering into a stiff leafless point . On a cultivated See also:tree these branches disappear owing to their more vigorous growth . Leaves may be modified into spines, as in See also:barberry, the leaves of which show every gradation between a leaf with a spiny-toothed edge and those which have been reduced to See also:simple or multiple spines . In some See also:species of Astrdgalus the petiole of the pinnately See also:compound leaf persists after the fall of the leaflets as a See also:sharp spine . In the false See also:acacia (See also:Robinia) the stipules are represented by spines . The reduction of the leaf-See also:surface, of which the spinous See also:habit is often an expression, is associated with growth in dry or exposed windy places . Thus, in the gorse, a characteristic plant of exposed localities such as open See also:commons, the smaller branches, instead of being leaf-bearing shoots, are reduced to slender See also:green spines, while the leaves on the See also:main shoots are also more or less spinous in See also:character . As the giving off of See also:water from its surface is one of the See also:chief functions of a leaf, this See also:process is thus reduced to a minimum in situations where water is scarce or would be liable to be given off too rapidly . An extreme See also:case is afforded by the cacti and See also:cactus-like euphorbias, which are a characteristic type of See also:desert vegetation where water is extremely scarce . The whole plant is reduced to a simple or branching succulent, leafless, columnar or flattened See also:stem, the branches of which are represented by small clusters of thorns .

Incidentally the thorns protect the plant which bears them from the attacks of animals seeking See also:

food . Prickles are structures of less importance from the morphological point of view, being See also:mere superficial outgrowths which may occur anywhere on stem or leaf, or even See also:fruit . THORNABY-ON-See also:TEES, a municipal See also:borough in the See also:North See also:Riding of See also:Yorkshire, See also:England, 3 m . S.W. of See also:Middlesbrough, on the North-Eastern railway . Pop . (1901), 16,054 . It lies opposite See also:Stockton-on-Tees, with which it is connected by a See also:bridge, on the See also:river Tees . There are blast furnaces, See also:iron foundries, See also:engineering See also:works, iron See also:ship-See also:building yards, extensive saw-See also:mills, See also:flour-mills and a manufactory of " See also:blue and See also:white " pottery . The See also:town was formerly known as See also:South Stockton, and is still included in the See also:parliamentary borough of Stockton (it is within the See also:Cleveland See also:division of the See also:county), but was incorporated as a See also:separate municipal borough in 1892 . It is under a See also:mayor, 6 aldermen and 18 councillors . See also:Area, 1927 acres .

End of Article: THORN (O. Eng. porn, cf. Du. doorn, Ger. Dorn, &c)
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