STELLA 



STEM 



715 



Among his works are Der Unprung der Spracht 

 <1851); Klattificatitm der Sprachen (1850), worked 

 up later into the important book, Charakteristik 

 der hauptiachlichiten 1'ypen del Sprachbaues (1860); 

 Die Entwickelung der Sprache ( 1852 ) ; Grammatik, 

 Loffik, Psychotoyie (1855); Oeschichte der sprachwiaeu- 

 tchaft bti den OHechen u. Ramern (1863) ; Die Mande- 

 NegerprMhen (1867); Allyemeine Ethik (1885), &c. 

 With Lazarus he edited from its foundation in I860 the 

 JSeitschriftfiir V>lkerpiycholaijie und Sprachwissenichaft. 



Stella. See SIDNEY ( PHILIP ), and SWIFT. 



Stellaland, a short-lived South African repub- 

 lic, formed in 1882 by the Boer adventurers who 

 supported Massouw, a chief of the Batlapins, 

 against his rival Mankoroane, who relied upon 

 the British. In 1884 the British government 

 assumed the administration of the country, and 

 in the following year annexed it and incorporated 

 it in the new colony of Bechuanaland (q.v.). The 

 chief town is Vryburg, which is connected by rail 

 with Kimherley. 



Stelleilbosch, a South African town (pop. 

 4000), in a fertile vine-clad valley, 25 miles K. of 

 Cape Town by rail, with an important college 

 affiliated to Cape Town University. 



Stellerine. See KHYTINA. 



Stelvio Pass (Ger. Stilfserjoch), the highest 

 carriage-road across the Alps (9042 feet), leads 

 from Bormio in the Valtelline for over 30 miles to 

 the Vintschgau in Tyrol. It was completed by the 

 Austrian government in 1825. 



Stem, the ascending axis of a plant, which 

 usually bears leaves and flowers, and maintains 

 communication between the roots and the leaves. 

 In the Thallophytes seaweeds, liverworts, &c. no 

 stem is differentiated ; it begins among the mosses, 

 grows stronger in the ferns, horsetails, and club- 

 mosses, and attains its highest development in 

 such trees as pine, palm, and oak. In these trees 

 and in all other Phanerogams the stem results 

 from the growth of the embryonic plumule. 



Stems vary greatly in general habit ; they may 

 lie upright and unbranched as in palms, or upright 

 and mnch branched as in the oak ; they may be 

 scramblers as in the bramble, or twiners as in the 

 hop, or climbers as in the ivy and Virginian 

 creeper ; they may be prostrate as in the straw- 

 berry, or underground root-like 'rhizomes' as in the 

 Iris. Their usual function of lifting the leaves and 

 flowers off the ground into the fresh air and sun- 

 light may thus be lost, or sulx>rdinated to some 

 other function, such as storage of nutritive material, 

 as in the ' conns ' of the crocus and ' tubers ' of the 

 potato, or storage of water, as in some succulents. 

 When the rind is green it may assimilate as leaves 

 <lo, and this is very important in such stems as 

 those of cactuses, whose leaves are reduced to 

 spines. It may also happen that branches of the 

 stem are modified into flattened, leaf-like phyllodes 

 as in Unsciis, into thorns as in the hawthorn, into 

 tendrils as in the vine. 



The stem is in many ways markedly contrasted 

 with the descending axis or root, but few of the 

 distinctions are rigid. Thus, moat stems have some 

 chlorophyll, which is absent from roots except 

 perhaps in the case of one or two of aerial habit. 

 Stems usually bear leaves, which roots never do. 

 The tip of a stem is almost invariably a naked- 

 growing point, while that of a root is usually pro- 

 tected by a root-cap. The branches of a stem arise 

 as superficial outgrowths (exogenous buds), while 

 rootlets arise endogenously from rudiments which 

 develop in an internal layer known as the pericycle. 

 The stem has a persistent tendency to grow up- 

 wards, while the root seeks the centre of the earth, 

 and in regard to other forces than that of gravity, 

 stem and root usually behave in opposite ways (see 

 PLANTS, MOVEMENTS OF). 



In describing aerial stems we distinguish the 

 nodes from which the leaves arise from the inter- 

 vening internodes, the buds which appear in the 

 axils of leaves from that whicli forms the apex, or 

 from those which appear arbitrarily or adven- 

 titiously, the leaf -bearing branches from the flower- 

 stalks, and so on. The branching of the stem is 

 usually lateral, but there are divergent forms, such 

 as false dichotomy in the mistletoe, false axis in 

 the vine, or true dichotomy in some Lycopods (see 

 BRANCH ). 



In order to present a clear picture of the internal 

 structure of a stem, it will be convenient to restrict 

 our attention in the first place to the young twigs 

 of some Dicotyledonous tree, such as the oak. 



Fig. 1. Diagrammatic cross sections of a young 



Dicotyledonous Stem : 



A, a two-year old stem ; B. a three-year old stem : o, pith ; 6, 

 primary medullary rays ; c, wood, in two layers in A, in three 

 layers in B ; </, cambium ring ; e, bast ; /, cambium (interfas- 

 cicular) between the bundles; g, secondary medullary rays. 



Every one knows that it is easy to peel off the 

 ' bark ' and to leave the white wood bare. This is 

 possible because the region known as the bark is 

 separated from the internal wood by a cylinder of 

 delicate, readily ruptured, actively dividing cells 

 the ' cambium. When a ring of bark is cut off a 

 tree, the leaves do not wither ; therefore we con- 

 clude that the water which ascends from the roots 

 passes up by the wood. But if in the ' ringing ' 

 the young wood be also cut, the leaves wither 

 rapidly ; therefore it is by the young wood that the 

 water ascends a conclusion corroborated by the 

 fact that a tree may flourish well although its heart- 

 wood has rotted away. But the wood includes 

 many different kinds of elements long vessels, 

 tracheide cells, wood-parenchyma, and wood- fibres. 

 It is certain that the younger tracheides and vessels 

 are the paths for the ascent of the water. Again, 

 if we tie a string very tightly around a stem so as to 

 compress the bark, the stem sometimes swells just 

 alx>ve the stricture ; and if there be a fruit grow ing 

 from the stem on that region, it will increase 

 greatly in weight. This suggests that the nutritive 

 materials elaborated in the leaves pass down out- 

 side the wood. But the tissue outside the wood 

 and the cambium cylinder includes many different 

 kinds of elements an external epidermis, perhaps 

 some cork, some softer rind or cortex, a set of hard 

 bast-fibres, and, most internally, what is called soft- 

 bast, including long ' sieve-tubes ' and also ' cambi- 

 form-cells.' It is certain that this soft-bast is very 

 important in the downward passage of elaborated 

 sap. 



If we examine by means of thin sections the 

 delicate growing point of the stem, we find that 

 it consists of an external epidermis and of an 

 almost homogeneous 'fundamental tissue.' As 

 we pass in our examination from the tip down- 

 wards that is, to slightly older parts we notice 

 that within the fundamental tissue there gradually 

 appear certain firm strands. These differentia- 

 tions of the fundamental tissue are known as fibro- 

 vascular bundles. Thus in the stem we distinguish 



