ANGIOSPERMS
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atmosphere and may readily be overshadowed by other of trees, for instance Ficus religiosa, whose years must be plants. Herbaceous growth makes a carpet of vegetation counted by thousands. On the other hand many Angioupon all areas of the earth’s surface, but is essentially a sperms are pronouncedly short-lived, passing through feature of temperate regions. Trees, on the other hand, birth, vegetation, reproduction, and death within a few have a persistent aerial trunk with copious shoots, and they months. For an account of the internal organization of Angiosperms, see are therefore woody and may be evergreen or have deciduous leaves. Their growth brings them into atmospheric Anatomy of Plants. The primary disposition of the permanent in an Angiosperm is determined by the necessity of prostrata drier than those near the soil, where they are tissues viding an ample mechanism for carrying water from the absorbmore exposed during the whole year to air currents and ing ends of the roots to the other seat of absorption of foodto every change of temperature, and where they are not material in the leaves, and to all growing points for the maintenof turgidity ; the carrying system therefore dominates the liable to be overshadowed except by their fellows. Tree- ance its position and form in each organ haying relation to growth then may be said to affect moist sheltered areas; anatomy, the strain to which the organ is liable. In Dicotyledones the cold dry wind-swept regions, for instance the polar and monostelic system admits of an indefinite extension of the area of alpine, are treeless. As the intermediate form between the carrying system to keep pace with the growth and extension the often ample perennating shoot-system, and this has conherbs and trees the shrub merges into both, and is found of tributed largely to the establishment of the group as the dominant along with or replacing them in all areas. The liane may vegetation of our day. The polystelic condition so common in partake of the character of each of the preceding forms, Pteridophytes is occasionally found, but only in forms which are but its special feature is that rooting in the soil it makes not progressive. The absence of this capacity of increase of the use of the support of other plants to secure an extension carrying system in Monocotyledones is probably one of the factors have led to their insignificant development as tree-forms as and exposure in the atmosphere, and in this way may which compared with Dicotyledones. attain a length of many yards. To this end it may adopt Though the geophyte responds in some degree in the the habit of a twining stem, or it may climb by means of modifications of its organs such as prickles, hooks, leaf- configuration of its vegetative organs to all the physical tendrils of various degrees of conversion, and stem-tendrils and chemical conditions of its environment, we ^nv/ron. and of kinds. Liane-growth is found in all areas of vegeta- have as yet but little certain knowledge of the cmeatlgura ' tion, except, and for obvious reasons, in polar and alpine effect to be ascribed to some of these or of the °"* on manner of their operation. Nor are we able as yet, ” regions, but it reaches its maximum development in the tropics where woody twining stems and stem-tendrils are even in the case of those factors of which we know.most, to determine clearly in every instance how far their influence specially developed. A fundamental character of Angiosperms, as indeed is controlled by intrinsic causes, expressed for instance in it is of all plants excepting the unicellular Protophytes, correlation, or is modified in combined action with, other but one which is too often lost sight of in the factors. We know that the direction and disposition of Colonial study of their economy, is their colonial organiza- the parts of the root and shoot are directly influenced by the stimulus of gravity, and also that radial and dorsiventral °tionniZa' tion- The livin£ plurinucleated protoplasm of constructions are often conditioned by light which also the plant-body is spread over the skeletal support furnished by the cells of the root and shoot, and in may induce anisophylly and the flattening of organs; light the more highly differentiated forms occupies but a small also may be a direct cause in provoking a difference in area of the whole body of the plant. Each living cell form between the juvenile and adult foliage, with the.result encloses an energid (a portion of the protoplasm dominated that the organs concerned in carbon-dioxide-assimilation by a nucleus) which is connected by protoplasmic threads and in the absorption of energy are exposed in the most piercing the cell-membrane with the adjacent energids, and favourable manner to illumination. The direct influence thus the protoplasmic body forms one continuous whole in of light in formation of chlorophyll is well known. Conappears to be but little directly influenced by the plant. (See Cytology.) According to their position in figuration the organism, the primary cells become devoted to the temperature excepting perhaps by extreme cold, and we formation of special tissues building up the organs required can seldom say by consideration of its outside whether a for the discharge of the several life-functions of the plant, plant inhabits a warm or a cold climate, notwithstanding but nevertheless each living cell must be regarded as a the paramount influence temperature exerts in the distripotential protophyte, whilst its actual destiny is determined bution of specific forms. The most influential environfactor in relation to form and structure is unby its relations to the other cells. This colonial organiza- mental questionably Water-carriage within the plant tion of the Angiosperm enables it to have growth pro- determines itswater. anatomy, and the safeguarding of the longed in one direction whilst this is arrested in another, water-supply alike at its intake in the root-system and at to throw off effete and old parts of its body without mutila- its outgo by transpiration and by transudation in the tion, and to renew or replace them as required; all tissues shoot, is a prime concern of the vegetative organization which pass out of the sphere of active life are not, however, thrown off, for it is a marked feature of Angiosperms that of geophytes, and is modified in relation to the amount water available for the functional purposes of the such tissues, and many excreta also, may be enclosed by the of plant. This does not always correspond with the actual living ones and remain unchanged so long as they are unex- amount of water in the physical environment, and a. plant posed to the putrefactive influences of the atmoDuration Sppere_ qpe fixed organism as a whole is endowed may be in a condition of physiological drought in the of an abundance of water. When there is a risk of of tlte ‘ with what we may term potential immortality—a midst physiological drought—as in areas where the xeropblly. character in sharp contrast with the relatively short period absorption of water from the soil is hindered, of life of the motile individuals of the higher members of by a scant amount of water, by too much dissolved the animal kingdom. We have but little accurate infor- e.g., salt, by humus, or by low temperature, as well as where mation bearing upon the actual longevity .of Angiosperms transpiration and transudation are facilitated, e.g., by the by which to judge whether their theoretical expectation dryness or high temperature of the atmosphere, by low of life may come to realization. Perennating herbs and barometric pressure, and by intense light the . plant under shrubs probably approach most nearly to its ml - responds and means are developed to promote the intake ment. Shrubs and trees expose themselves by their aerial and check the outgo. For the former there may be an growth to many accidents which militate against great increase of the whole root-system and of the absorbing length of life; nevertheless there are authentic instances
