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the varied tribes of this part of Nature's wide domain, is so gradual, and the relation by which many of these tribes are connected together, so intimate, that the difficulty which botanists experience in the arrangement of the objects of their studies frequently consists more in the separation of allied plants and families than in their union with each other into groups.

The structure of the powdery lichen, to which allusion has already been made, and of its allied species, is most simple, consisting of vesicles only, and those scarcely connected together. Other forms of the vast tribe of lichens-those humble individuals of the vegetable race which form the first of Nature's coveringswhich act, as it were, the part of pioneers, and though of small repute, and to the unobservant eye insignificant, are the very instruments which it has pleased the Almighty Creator and Ruler of all to employ as the secondary agents of his power in breaking down the surface of the hard and barren rock, and rendering many a wild and uncultivated region fit for the nourishment of larger tribes of plants, and ultimately adapted to the support of the higher orders of animals, yes, even of man himself. Other forms of this vast, and shall we not say important family of plants, are found, in which these primary vesicles are closely compacted into crusts or films,-crusts of extreme tenuity, but covering the surface of stones and rocks, and the bark of trees. Such are the curious Lecidea geographica, so called from its resemblance to a chart or map; the Graphis elegans, and Opegrapha scripta, a species of mimic writing, &c. The transition from these filmy expansions to the foliaceous lichens, such as the common yellow wall lichen, Parmelia parietina, and its allies, by the splitting up, as it were, of the crust in different directions from the surface to which it is attached into scales or lamina of various thickness, as in Squamaria, and others of the scaly lichens, is well marked; and again from these through the Cetraria Islandicus, or Iceland moss, and others in which these scaly and leafy crusts are gradually lengthened into thongs, to the fibrous or filamentous lichens on the one hand, and into some of the tribe of Alge or sea weeds on the other.

The same gradual development of the cellular structure may be traced in the Alge, a family of plants, the greater number of which are inhabitants of the ocean. This we have already had occasion to observe in their fructification from the simple vesicles of Porphyra and Ulva, to the variously compounded granules of Gracilaria, Rhodomela, and Microcladia, changes accompanied by corresponding variations in the structure and configuration of the entire plants.

The transition from the Alge to the mosses, in which the external form approaches still more to those vegetable tribes where the cells, becoming gradually more elongated, approach more or less to the tubular structure, is well marked by some of the Hepatici, or liverworts. Of these last, the frond or leafy

expansion of the Riccia natans affords a beautiful example of the cellular structure, and its general appearance comes very near to some of the Alga, while, on the other hand, many of the Jungermannie, another genus of the liverworts, are almost as closely allied to the mosses.

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The mosses are universal favourites, and it is impossible, even for the most superficial observer, to have glanced over any of these beautiful plants, without admiring the general elegance of their forms, and the extreme delicacy of their leaves and other parts. The most finished drawing can convey but a faint and imperfect idea of their extreme beauty. We must here have recourse to the microscope for ourselves, and when thus examined, so as to display their internal structure, the modifications of cellular texture as seen in their transparent leaves,— the varied forms and delicacy of these parts, the curious structure of the filmy teeth which encircle the mouth of their capsules, the interest which attaches to these productions is increased ten-fold, and the reflecting mind is lost in the contemplation of the infinitely varied beauties of form and structure which proceed from the Master hand, and which prevail in every department of nature. In the works of the great Creator, there is nothing imperfect-nothing unfinished-whether in simplicity of design, or in the most delicate and refined construction. far as our limited powers will enable us to comprehend it, the same sublime unity of purpose is displayed throughout. We look above us and contemplate the vastness of the heavenly expanse, -its brilliant orbs preserving their prescribed limits, and rolling through space in perpetual harmony, and with never-varying regularity, and we feel lost in the vastness of the power and wisdom of that Divine Intelligence which has called them into being, and which presides over, directs, and regulates the whole. We are ready to exclaim with the Psalmist, "What is man, that thou art mindful of him? and the son of man, that thou visitest him?" But shall we, therefore, infer, with the disciples of a false philosophy, that He regards not the beings whom he has called into existence? that He, having breathed into them the breath of life, there leaves them, and casts them aside as utterly beneath his attention and care? Let us turn to the humble moss which groweth upon the wall, and to the insect flutterer which reveleth its short hour in the setting beams of a summer's sun. We behold the same attention bestowed upon these minute existences, -the same care in the adaptation of the circumstances under which they are placed to the purposes which they are destined to fulfil. Can we then doubt that even the hairs of our heads are all numbered, and that he who so clothed the grass of the field will fulfil all his purposes of love towards that being who, though fallen indeed, and in himself powerless of good, is yet gifted with faculties by which he can investigate, and in a measure comprehend, the mighty works even of the High and June, 1835.--VOL. II. NO. XI.

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Lofty One, who sitteth upon the circle of the Heavens and inhabiteth Eternity.

The various species of the fern tribe, those leafy expansions, some of while rival even the mosses in elegance of form and delicacy of structure, while others vie with the loftiest denizens of the tropical forests, are among those forms of vegetation, in the internal texture of which tubes or vessels, as well as cells, are found to exist. They constitute, as it were, the transition link between the cellular and vascular plants, being allied to the latter in internal structure, while in external configuration, and more especially in their fructification, they are intimately connected with the former. In that covering of herbage, the verdure and freshness of which gives such a charm to the rich scenery of the valleys and plains of our native country, we find many different species of plants. These are called gramina or grasses, and resemble each other very closely in their general structure and appearance, constituting one of the most natural groups with which we are acquainted. They have for the most part fibrous roots, a tubular jointed stem, narrow ribbed leaves, and an elongated spike or panicle of flowers, in all which parts, whether root, stem, leaves, or flowers, we find the cellular structure to be combined with the vascular,-vessels or tubes traversing in a longitudinal direction the general cellular texture of the plant. The same combination of vascular and cellular structure is found in the sedges and rushes-in the numerous species of iris-in the lilies-the Orchidea, and others, constituting the first division of the flowering plants. To trace the connections between the several families of the Vasculares, or to examine the gradations by which they insensibly pass into each other, is not necessary for our present purpose, since in these more complex and highly organized forms of vegetation there is a unity of structure prevailing, with certain modifications, throughout the whole. It will be sufficient if we examine the several parts or organs of which these plants consist separately and in detail, pointing out as we proceed the modifications in the development of these several parts as they occur in plants of a higher or lower degree of organization.

The more important divisions of the vegetable organization, as it exists in the more highly developed families of plants, are the root-the stem and branches--the leaves-the flowers-the fruit, including the seed-and lastly, bulbs and buds.

The external characters of the root vary considerably. In grasses, as we have just observed, it is generally fibrous, sometimes creeping, rarely bulbous; whereas, in many others of the monocotyledonous plants, the tulip for instance, it is bulbbous. In every true root, however, a fibrous portion will be found to exist, and it is the ultimate fibrils or divisions of the fibrous part of the root, with the minute vesicular bodies at their extremities, which constitute the essential part of this organ. It is by

these little vesicular terminations of the fibrils of the roots that plants obtain their nourishment from the soil in which they grow. They are found equally in the lofty forest tree and the herb which grows beneath its shade, and are equally necessary to the existence of both; for if by accident or design the fibrils are materially injured, the plant withers and dies. In their internal structure, roots, with some exceptions, will be found to resemble the stem; in fact, in many instances, they consist of a main descending trunk, branches, and twigs, the organization of which is precisely conformable to the ascending stem and its divisions, as it is found above ground.

The stem or trunk varies much in different families of plants. In those among the acotyledonous plants in which it occurs it consists of a thin epidermis or cuticle, surrounding a pulpy matter, the texture of both which parts is almost entirely cellular; a few fibres or vessels are, however, found in the stem of the fern tribe, forming an exception to the general internal organization of this division of the vegetable kingdom. In the monocotyledonous plants, the stem consists also of a cuticular envelope and internal cellular substance, but the cuticular portion is more dense and firm, and the cellular texture of the internal part of the stem is traversed by longitudinal fibres or vessels, several of which are arranged together in bundles. In the dicotyledons, the stem is composed of bark, wood, and pith. The bark, which corresponds to the cuticular part of the stems of the acotyledonous and monocotyledonous plants, is formed of several layers of cellular and fibrous texture; the wood or fibrous portion of cellular texture, and closely compacted vessels traversing the cells in a longitudinal direction, and symmetrically arranged so as to form concentric and divergent layers; and the pith, which occupies the central portion of the stem, of a light spongy cellular tissue.

The development of this apparently intricate organization from the simple elements of cell and vessel, according to the principles already laid down, may be conceived to take place in the following manner. Let us suppose a complete circular range of secondary vesicles becoming dilated by the process of growth in the interior of a primary or generating cell. It is evident that the envelope of this cell, pressed at all points of the circumference by similar parts which are growing at once in length and breadth, will take the form of a cylinder; but it is also evident that the secondary vesicles will be more compressed towards the centre than at the circumference, and that, consequently, a transverse section will exhibit each of these secondary cells under the form of a wedge. If the eight vesicles grow in a longitudinal direction, without giving rise to other vesicles within them, we shall then have an organization similar to that of the long stalk which supports the flower of the Nymphea alba, or white water lily, a monocotyledonous plant. Each of these vesicles will form an empty canal, of

which a longitudinal section will present a three-sided prism, and which will extend from the base to the summit of the flowerstalk. But if within each secondary cell a certain number of tertiary vesicles be developed, so as to form cells of considerable size and nearly empty, we shall then have the structure of the central part of certain trunks of the monocotyledons, and also that of the pith, as it occurs in the stems of some of the dicotyledons. Now if, instead of vesicles thus developed, parallel and concentric cells are formed, we shall have a commencement of concentric layers, and other vesicles being developed in their interstitial spaces in a longitudinal direction, so as to form tubes or vessels, a transverse section will exhibit the perfect development of the concentric vascular tissue. If the cells, instead of loose hexagonal cells, give rise to other vesicles pressed one against another, and developed on the coats of more internal cells which are incased in and line completely the cavity of those in which they are formed, then we shall have the most complicated organization of the stem of a dicotyledonous plant, with its incased and concentric layers, and its medullary rays, or divergent layers, which are nothing else than the interstices of the secondary cells, or rather the junctions of their sides, in which vesicles have been developed in a horizontal direction, forming tubes or vessels running from the centre of the stem towards the circumference.*

Branches are nothing more than the divisions of the stem, and may be conceived to be formed by the progressive development of cells and tubes in a manner altogether similar,generating vesicle gradually developing other vesicles upon its internal membrane, and the growth taking place as in the former

instance.

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Leaves consist of a cuticle or transparent film of cellular texture, enclosing a parenchyma or pulp, also of cellular tissue, and usually of a green colour, and fibres of which the nerves and veins of the leaf are chiefly composed. These fibres communicate with each other, and are ramifications from the central nerve or midrib. In the monocotyledonous plants, the nerves are for the most part parallel, or nearly so, extending from the leafstalk to the apex of the leaf in a longitudinal direction, and rarely branched, but communicating with each other by short transverse ribs, which gives the appearance of a tesselated or rectangular network to the vascular structure. In the acotyledons, the leaves or leafy expansions are destitute of ribs or veins, and consist merely of a pulpy cellular tissue, enveloped by a cuticular expansion. The development of these parts from the simple vesicle or cell may be thus supposed to arise. Upon the internal surface of the envelope of a primary cell, two secondary vesicles may follow the growth of the generating or primary cell, and stretch out longitudinally; they will thus form two lateral lobes

* Raspail. Elements of Organic Chemistry, by Henderson, p. - (?)

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