BARIDIUS. 



BARK. 



390 



has been introduced by means of clover and other seeds used for 

 agricultural purposes. 



(Koch, Flora Germanica ; Babington, Manual of British Botany ; 

 Phytologiit, vol. i.) 



BARI'DIUS, a genus of Insects of the order Coleoptera and family 

 Curciil ionidce. These are cylindrical little beetles which feed upon 

 aquatic plants. They are generally of a black colour, and more or 

 less covered with a whitish down. 



BARIS, a genus of Insects belonging to the order Coleoptera 

 and family Curculionidee. The species of this genus feed upon the 

 dead parts of trees. One of the species, Baris liynarius, feeds upon 

 the elm tree, both in the larva state and that of the perfect insect. 

 When the little beetle is about to lay its eggs it generally selects the 

 interior of a hollow tree for that purpose, and bores a hole with its 

 short snout in the dead wood where it is still tolerably sound ; this 

 being accomplished it enters the hole, hinder part first, deposits its 

 eggs, and dies : the hole being only just the size of its cylindrical body, 

 it thus forms a protection for its young by stopping the hole so that 

 no other insect can enter. It is not known that it ever attacks any 

 other wood but that part where the sap has ceased to flow, and conse- 

 quently the tree can receive no injury from this little weevil. 



BARI'TA, the name given by Cuvier to a genus of Birds which he 

 places among the Shrikes, but which Vigors considers to belong to the 

 family of Crows. 



The following are the characters of Barita : Bill hard, long, and 

 strong, convex above, slightly hooked at the extremity, near which 

 both mandibles are notched ; nostrils lateral, and longitudinal near 

 the base ; legs stout ; outer toe joined to the middle one as far as the 

 first joint ; inner toe entirely free ; hind toe elongated ; claws strong 

 and curved. 



Barita Tibicen, the Piping Crow, common in New South Wales, 

 where Quoy and Gaunard, the able naturalists attached to Freycinet's 

 Expedition, saw numbers of them on the Blue Mountains, living gre- 

 gariously in small troops, will serve as an illustration of the genus. 



Piping Crow (litirita Tibiccn}. 



The bird brought home by Freycinet reached France alive, and by 

 its good-natured and amusing manners became a great favourite wliilt: 

 on ship-board. It was a skilful mimic, and clucked and cackled like 

 a hen ; but its imitation of a young cock was complete. It had been 

 trained to whistle airs at Port Jackson, and some of these it appeared 

 to forget, but recollected them on being prompted. 



BARK, in Vegetable Physiology, is the external coating of the stem 

 and branches of plants, ensheathing the wood. In woody Exogm it 

 separates spontaneously from the wood in spring and summer, and in 

 herbaceous plants of the same class it may be easily removed with a 

 little care ; but in Endogen* and Acrogmt it is so continuous with the 

 central part of the stem that it can never be divided except by 

 violence, and by lacerating the tissue which lies immediately below 

 it. This difference arises from the manner in which the plants of 

 these three great natural classes respectively grow. Exogens add 

 annually new matter to the inside of their bark and the outside of 

 their wood, which renders it necessary that a spontaneous separation 

 of wood and bark should take place in order to make room for the 

 newly-generated substance ; but Endogens, which grow by addition to 

 their centre, and Acrogens, by elongation of their point, require no 

 such separation. [KXOOKNS; ENDOGENS ; ACROOENS.] 



Bark may be considered to originate thus : When a plant is in the 



state of embryo, that part which finally develops into a stem and 

 root, or, as botanists say, into the axis of growth, is something like 

 two cones applied to each other by their bases, but it will simplify 

 our ideas if we consider it as a cylinder. In a dormant state it con- 

 sists of nothing but cellular substance ; but in Exogens, as soon as the 

 cotyledons, or seed-leaves, are roused into growth, woody matter is 

 generated in the form of a number of little bundles, which are 

 arranged in a circle (a a) about half 

 way from the centre to the circum- 

 ference, thus forming a sort of hollow 

 cylinder within the first. The cylinder 

 so commenced cuts off the cellular sub- 

 stance into two parts : one central (V), 

 which finally becomes pith, and the 

 other external (c), which becomes bark ; 

 the two maintaining their connection 

 by means of the passages (d d) between 

 the woody bundles (a a). These pas- 

 sages ultimately become the medullary 

 processes. The direction thus given in 

 the beginning to the several parts in the 

 interior of an exogenous stem is never afterwards departed from, but 

 all the additions which are subsequently made are moulded, as it 

 were, upon this original form. The woody bundles (a a) increase in 

 size by growing outwards, and consequently the medullary, processes 

 are extended ; the bark continues to grow and give way to the pressure 

 of the wood from within, till at last a year's increase has been accom- 

 plished. Up to this time no separation between the wood and the 

 bark has taken place ; but in a second year, as it is necessary for the 

 new matter to be added to the outside of the wood and to the inside 

 of the bark (at d d), a spontaneous separation of the two takes place 

 over the whole surface of the wood, the medullary processes softening, 

 stretching, and growing externally, hi order to admit of such a sepa- 

 ration. But Endogens and Acrogens always retain their bark in the 

 same connection with the wood as it is in Exogens at the end of the 

 first year, there being no necessity for a separation between the two 

 in order to admit of subsequent growth. 



In its anatomical structure bark consists of a mass of cellular tissue 

 pierced longitudinally by woody matter, which is composed entirely of 

 woody tubes without any trace of vessels, but which is sometimes 

 accompanied by long fistular cavities, in which resinous, or milky, or 

 juicy, or other secretions are lodged. 



In the first year of its existence bark is a cylinder, the woody 

 matter of which is a continuation of that of the wood itself. In 

 Endogens and Acrogens it undergoes no material increase or alteration 

 subsequently, unless it be that the parts are increased in quantity 

 without shifting their position. But in Exogens, in consequence of 

 their wood being annually augmented by external additions, as before 

 stated, the bark undergoes annual changes. Corresponding with the 

 annual additions to the wood are annual additions to the inside of the 

 bark, consisting of a cellular layer overspreading the whole of the 

 inside, and then a layer of woody matter, which answers to the spaces 

 of wood included between the medullary pi-ocesses. These annual 

 additions, which are called the liber (whence books which were written 

 upon such layers, properly prepared, were called librf), must therefore 

 be exactly the same in number as the annual layers of wood, and 

 would be arranged with equal regularity if the bark were not affected 

 by any disturbing cause. But in consequence of the wood's perpetual 

 increase in diameter there is an incessant lateral strain upon the 

 liber, so that after the first year there is little trace of regularity to be 

 discovered in the structure of the bark. It soon becomes a mere 

 confused mass of woody tubes and cellular tissue, in which all trace 

 of annual concentric formation has disappeared. The manner in 

 which it was originally generated is however said to be detected in 

 some plants by the facility with which the bark will peel into layer 

 after layer ; but it may be doubted whether this phenomenon is not 

 more connected with the original arrangement of the tissue of which 

 the bark is composed than with the annual formations. These layers 

 are sometimes so numerous that as many as 150 have been separated 

 on a single tree. 



When the bark of an Exogenous tree is examined, it will be found 

 to consist of four parts or layers, which to a greater or less extent can 

 be made out in every tree. These layers have been technically called 

 the Epidermis, the Epiphl&wn, the MesopUrfum, and the Endophlaum. 



The Efidermis is but a continuation of that layer of condensed 

 cellular tissue which is found on the external surface of every part or 

 organ of the plant. It varies in thickness as well as compactness in 

 almost every tree. It is frequently split up by the growth of the 

 layers which lie beneath it, and with the next layer is separated from 

 the stem in large pieces, as is the case in the common Birch (Betula 

 alba). Like the epidermis on the leaves, it possesses stomates, which 

 in the case of plants, as the Caclacete, seem to possess the power of 

 performing the functions of the same organs on the leaf. The epi- 

 dermis is variously coloured as well as affected by the colour of the 

 layer immediately beneath it. 



The Kpiiihlaum is the outermost layer of bark ; it is composed of 

 cellular tissue, and when cut through presents under the microscope 

 a tabular appearance indicative of pressure above and below. This 



