716 



STEM 



STKNO 



tin- epidermis, the fibre- vascular bundles, and lint 

 remains of tin- fundamental tissue, in the form <if 

 central pith and superficial cortex, and radiating 

 plates or medullary rays extending between these. 

 In Dicotyledons the fibro- vascular bundles are 

 radially arranged, and each consists of an internal 

 wood or xy lein part, an external bant or phloem part, 

 and between these a persistent young layer of 

 cambium, which, by the division of its cells, adds 

 internally to the wood, externally to the bast, 

 and enables the stem to grow in girth. These 

 libro-vascular bundles are continued out into the 

 leaves, or, to state the fact in another way, each 

 leaf contributes to the stem a ' leaf-trace' of libro- 

 vascular bundles which extend vertically down the 

 stem, and eventually unite in a connected system. 

 In the lower or older parte of the twig or stem 

 there are necessarily very many libro-vascular 

 bundles, and these are intimately fused with one 

 another. Thus we have from without inwards, 



S 9 



Fig. 2. Longitudinal section of a portion of a woody 



Stem (after Kerner). 



a, epidermis; ft, cork; r, cortical parenchyma; <?, bundle- 

 sheath ; e, hard-bast. ; / bast-parenchyma ; g, sieve-tubes ; 

 A, cambium ; i, vessel with bordered pits ; k, wood-paren- 

 chyma ; 1, vessels ; m, medullary sheath ; n, pith. 



beneath the cortex, a sheath of bast, a cylinder of 

 cambium, and the central wood. The fundamental 

 tissue remains undiflerentiated in the cambium, and 

 slightly modified in the central pith (if that be 

 present), in the radial medullary plates which 

 traverse the wood and bast, and in the superficial 

 cortex. 



The fibro-vascular bundles in the stem of Dico- 

 tyledons have a radial arrangement ; in their 

 vertical course they run parallel to one another, 

 and are united into a connected system. Almost 

 always they are 'collateral' Le. the bast lies in 

 the same radius as the wood and they are ' inde- 

 finite,' for the cambium persists. In Monocotyle- 

 dons the lilirn -vascular bundles which enter from 

 the leaves pursue a curved course first inwards 

 and then nut \v ;l nls again in the stem. In cross 

 section* they therefore appear scattered in the 

 fundamental tissue ; they are also collateral but 

 'definite,' for the cambium is at an early stage 

 used up. This lost peculiarity explains the gener- 

 ally uniform thickness of a Monocotyledonous 

 stem and the fact that the liark in not usually 

 separable. In Ferns the Imst surrounds the wood 

 in each strand, forming 'concentric' bundles. So 

 too there are structural peculiarities in the stems 

 of Lycopods and Horsetails, while those of Mosses 

 are, as we would expect, almost wholly cellular 

 without differentiated bundles. 



It is not easy to form an accurate conception of 

 the internal structure of stems, but we must bear 

 in mind the following physiological considerations. 

 ( 1 ) A the stem is a supporting axis, often bearing 



heavy weight* and resisting great strains, there is 

 usually much skeletal tissue e.g. the bast-fibres, 

 the wood-fibres, and the haul wood which forms the 

 heart of most trees. Schwendencr ami others have 

 shown that the tiliro-vascular bundles are always 

 disposed to mechanical advantage. (2) As tiie 

 outside of the stem is exposed to the weather and 

 is often subjected to considerable strains, there is 

 usually more or less protective tissue e.g. the 

 tough skin and a layer of cork. (3) As the stem 

 mediates physiologically between the roots and the 

 leaves, it contains condueting tissue (a) the young 

 tracheides and wood-vessels by which water and 

 dissolved salts ascend; and (I/) the sieve-tubes, 

 cambiform cells, and conducting parenchyma by . 

 which elaborated materials descend. In the pith, 

 medullary rays, &c. these materials are often 

 stored. 



The most practically important sterna are those 

 of timber- trees, but their uses are manifold. Thus, 

 the bark of oaks (containing tannin) is used in 

 tanning, and several kinds of bark are used in 

 medicine ; the bast-fibres of jute, hemp, iVc. are 

 used in making textile fabrics, ropes, and the 

 like; the farinaceous pith of one of the palms is 

 well known as sago, and many other kinds of pith 

 are nutritious ; the juices of some stems furnish 

 india-rubber, oil, wine, &c. ; the potato is the most 

 important of the edible stem-tubers. 



See BCD, BRANCH, LEAF, ROOT, VEOETABLI PHTBI- 

 OLOGT ; H. Marshall Ward, The Oak ( ' Modern Science ' 

 aeries. Loud. 1892 ), for best English account of internal 

 structure of stem, and Timber and its Diseases ( ' Nature ' 

 series, Lond. 1889 ), for theories of ascent of sap ; Kerner' s 

 fytanitnlebrn (vol. i., Leip. and Wien, 1889), for adapta- 

 tions of stems ; also text-books of Sachs, Van Tieghem, 

 Asa Gray, Wiesner, and others. 



Stencilling, a method of printing letters or 

 designs. The process consists in cutting out the 

 pattern in a thin plate, usually of metal ; this is 

 then laid on the surface intended to receive it, and 

 the colour is rubbed into the cut space with a 

 brush, the plate preventing the contact of the 

 colour, except on the space cut out. It is much 

 used for wall and other surface-decoration, as it is 

 a rapid and cheap process. 



StciHlill. a town of Prussian Saxony, 36 miles 

 by rail N. by E. of Magdeburg, was the former 

 capital of the Altnmrk, and has a Gothic cathedral 

 (1420-24), a Roland pillar, two old gateways, and 

 a statue of Winckelmann, a native of the place. 

 There are here large railway workshops and some 

 textile industries. Pop. 16,184. 



SI riullial. See BEYLE ; and add two recent. 

 French works on him bv E. Hod (1891) and (on 

 his diplomatic career) L. Farges ( 1892). 



Stennis. See STONE CIRCLES. 



Si rim. NICHOLAS, anatomist and geologist, was 

 born at Copenhagen in Mi.'iS. He was brought up 

 a strict Lutheran, and was trained to medicine, 

 winning great fame as an inquirer into the anatomy 

 of the glands, the heart, ami the bruin. For many 

 years he led a wandering life in Holland. France. 

 Austria, Hungary, Italy, but in 16(37 settled in 

 Florence, and was converted to the Koman Catholic 

 faith through the eloquence and earnestness of 

 Bossuet. AiMMit this same period he turned his 

 attention to geology. He was the first to point 

 out the true origin of fossil animals ; he treated 

 of the structure of the earth's crust, clearly 

 portraying the prevalent stratification of rocks, 

 and discriminating between their volcanic, chemi- 

 cal, and mechanical modes of origination. Soon 

 after settling in Florence he was appointed 

 physician to the Grand-duke Ferdinand II., and 

 later lidded thereto the office of tutor to the son ot 

 Grand-duke Cosimo III. But his conversion grdu- 



