BOTANY

the common designation of the scienoe which treats of the vegetable kingdom, is a Greek term, from Inxtanif an herb or gra . A designation more in accordance with the names of the other physical sciences would be Phytclogy, iiom the two Greek words phyton, a plant, and logoSf a discourse. Phttoloot, or the history of plants, in its general range embraces — 1, the structure and composition of all vegetable bodies; 2, the physiology or laws which regulate the living plant; 3, the cla ification of the various specific forms of plants; 4, geoeraphical relations of plants; and, 5, fo il botany, or the history of extinct species. A plant or vegetable forms the first and simplest stage of an ganized being — it is a precursor of the more highly endowed animal, and forms an intermediate link tween inorganic matter and sensitive existence. plant may be defined as a living organism, non-sensitive— ^generally rooted or fixed in the soil, though always — ^po e ing a certain amount of motion from the stimulus of mechanical causes, but not the muscular self -produced motion of animals. A plant, opposition to mineral or inorganic bodies, may considered as a living centre or individual, actuated by special vital laws, which empower it to take external inorganic matters and a imilate these into its substance, whereby peculiar organic compounds are produced from simple elements. A plant, then, in the first instance, performs what no animal can do — ^it directly a imilates simple oiganic matter into organic compounds, and thus is the preparer of the proper f o bab tree is said to attain a circumference of 90 feet, some chestnut-trees are 60 feet in girth. The will continue to grow for 500 years; the olive-tree for 1000 years. A chestnut tree on Mount Etna supposed to be 1000 years old, and the great dragon tree of Teneriffe, shattered by a storm in 1868, said to be over 5000 years of age. The character of the stem differs materially three great divisions of plants. The acrogenoue as in the tree-fern, is composed of bundles of cellular and vascular structure which shoot up simultaneously, and the farther elongation takes place by additions to the summit, hence the name summit growers. stem is formed by the union of the stalks fronds or leaves, which expand upon the summit. The stem forms no branches, but is marked surface by the scars of the leaves which have off. A section of the stem exhibits, near the circumference, a series of waved, irregular, dark lines, is the condensed vascular ti ue, while the consists of a uniform ma of psJer dotted ve els. The section of the root stem of the common fern exhibit this appearance. The endogenous stem, the palm, ia also composed of bundles of ve els, more compact than the other. The growth proceeds by the new matter from below elevating the central matter, and thus the elongation and breadth are increased from a pushing out of the matter within; hence the term inward growers, A section of an endogenous stem (PL XVII. XVIII., figs. 30, 31) exhibits a similarity of the cellular structure throughout, without any central pith medullary or annual layers (as are exhibited exogenous sections, figs. 18, 19, 27, .), and out any true bark, but only a thicker and more densed condition of the cellular structure on outer circumference. The exogenous stem, such the oak and elm, exhibits a section composed various cellular and vascular bundles, arranged succe ive circles, from the central pith outwards the circumference. The growth in this case place by an annual succe ion of rings of new externally, and hence the tenn outside growers. fig. 28 A is the centre of such a section, where medullary cellular structure lb seen; g U the medulatema | lary skeathf consisting chiefly of spiral ve els; m iB a medullary ray, formed chiefly of condensed spiivl ve els radiating from the central pith; / ia the woody per ti ue, a layer of which is deposited each year, thus forming a number of concentric rings, by counting her which the age of the tree may be Imown; e is the there camhium layer of mucilaginous semi-fluid matter between the wood and the bark, oonstitutiiig the active the in and formative ti ue of dicotyledonous stems, by soiL means of which they are enlarged. The bark consists of two or thi«e layers, an inner green and leaves succulent, the liber or endopMcBum, d; a middle cellular portion, forming cork in the cork oak, 6, c; and root, an external epidermis or outer bark, a, which is be- Jeruquentiy colourle , as in the beech, and semi-trans col parent or white, as in the birch. The extent of the bulb a, annual circle varies in size in the same tree, aoocrding to its age, state of vigour, exposure, and the and nature of the season — cold, nngenial summefs often are retarding the growth of the tree. The oenteal woody have circles become hardened and condensed by age, so exthat the si^ flows most copiously through the outer and newer circles. Beferring again to PL XVTI. 311