In the bark and in the pith of some trees, vessels are noticed very different from those we have hitherto spoken of. They are remarkable at once for their structure and their contents. They are tubes simple or ramified, sometimes completely independent sometimes attaching themselves one to the other in a continuous length. While the vessels traceable in the woody fibres are formed of cells which can be separated one from the other by the use of proper means, the cells constituting the | taticgforos. vessels are, 08 the contrary, so intimately blended together tl nor chemical action can separate them.

The laticiferous vessels contain a juice, generally coloured. It is easily proved, under the microscope, that this liquid is composed

of an uncoloured serum, holding in suspension numerous and very small globules, to which it owes its colouration. This liquid is called latex. But what strikes the observer as above all remarkable, is the circulating movement which is the property of latex. The transparency of the vascular walls, and the presence of the granules, render this movement very perceptible in some plants.

The /atex is very abundant in certain vegetables. Place on the object-glass of a microscope, and under a thin plate of glass, for instance, a young leaf of Chelidonium laciniatum,—better known as 2 celandine, which is said to be so named from its being in flower when the swallows arrive, (Fig. 50), still attached to the branch, or a sepal of the same plant, of which the latex is an orange yellow; or a petal of the Poppy, of which the latex is white; or a stipule of Ficus elastica (one of the Caoutchouc trees); we shall see in all these cases the latex descending in one branch of the net-work of the laticiferous vessels, and ascending im another, returning sometimes to its point of departure, and, in one word, circulating with ‘ a rapidity greater in proportion as the temperature is warmer and vegetation more active. Gutta-percha, caoutchouc, and opium proceed from the latex of certain plants. composition The elements entering into the of the trunks of forest trees are, as we S€@; rather complex. Having described each m

Wig: 60.—Lactiferons veseeia in their turn, it will be instructive to bring”the whole of them under the eyes of the reader.

Fig. 51 represents a section, both horizontal and vertical, of @ _ trunk of the Maple (Acer campestre). The substances embraced by the lines marked No. 1 represent the wood of the first yeat, those in No. 2 the wood formed during the second year, and those in No. 3 the substances forming the corticle, or bark. In the centre of the stem, M represents the pith, the cells of which are polyhedric. The trachea, or medullary sheath, coming next to the pith and enveloping it on all sides, are represented by the letters

4 t, EM. Then follow three groups of Ligneous fibres, FB; the wood vessels, vp, are placed alternately with three groups of woody fibres. The bark, enclosed by the line marked 3, succeeds these substances, the fibres of the /iser being represented by the letters Fc (cortical fibres), and the elements of the suber by the letters Es, the laticiferous vessels by the letters vx, and the herbaceous layer by the letters nc, the epidermis, EP, bristling with hairs, forming the external surface of the trunk. The medullary rays are plainly enough observable on the horizontal edge; they commence with the pith, and stop with that part of the wood which belongs to the

EP &S “Ee” EC vp RE VP RN VP PB| ae 4 . Fig. 51.—Transverse sectiou of the trunk of the Maple, fax

second year’s growth, as indicated in the vertical section by the letteks RM. Having reviewed all the constituting elements belonging to the trunks of forest trees with membranous leaves, we have now to speak of the structure of the stems of evergreen trees. Evergreen trees (Pines, Firs) are at once easily distinguished from the trees we have been considering by the structure of their wood, which is exclusively formed of large fibres, without any appearance of thick vessels. These woody fibres (Fig. 52) present besides the singular peculiarity of exhibiting on each of their lateral faces—namely, those which | look towards the medullary rays—a row of dots or punctations, each —

_ 46 THE VEGETABLE WORLD.

surrounded with a very remarkable cavity (alveola). The wood is traversed by resiniferous ducts, which are a kind of interstice in which the resin produced by the peculiar cells surrounding it is deposited and accumulates. Fig. 53 represents the transverse section of the stem of Fir-tree. We see that evergreen trees, like forest, trees, present a central medullary canal, concentric woody layers, and cortical layers. But the wood-vessels have no existence in these stems, and the medullary rays are scarcely visible. The stem thus formed is said to be exogenous, from eG, “without,” and yevvaw, “I produce.” All indigenous trees, and a vast number of’ our smaller shrubs and plants, have this form of stem. The general appearance of palm-trees 1s very different from that of our indigenous trees,—their long and drawn out stem (Lat. =

stipa), perceptibly equal in thickness from the base to the summit, and completely bare, that is, not divided by boughs and branches, making them like some tall column surmounted with a thick tuft of leaves. What is the interior structure of this stipa? To give an idea of its formation, we must first understand that the growth of the Palm-tree differs from that of any group of trees we have hitherto considered. Palm-trees do not, like our evergreen and forest trees, increase their growth by concentric layers, deposited between the wood and the bark. The interior structure, therefore, must show arrangements very different from those we have been describing. Here there is no single central canal destined to hold the pith, no concentric layers distinctly separating the pith, the wood, and the bark; no medullary rays diverging from the centre to the circumference. If we cut the stem of a Palm across, we shall immediately see that it differs as much from the trunk of our trees in its inmost organisation as it does in its outward appearance. We look

Fig. 54.—Section of the stem of a Palm.

Fig. 55.—Theoretic figure showing the internal structure of the Palm.

in vain for the central pith, the concentric zones, the radiating lines, which so plainly characterise the wood of our indigenous trees. We should see, on a groundwork of palish colour, little spots of a deeper tint, formed by a more solid tissue. These little rounded or half-moon shaped spots are more numerous, more crowded, higher coloured, and in general larger towards the circumference of the stem than they are in the central part. This stem is called Endogenous, from evdov, “within,” and yevvaw, “I produce.” This stem, therefore, appears at first-sight formed of two descriptions of tissue, one rather soft and pulpy, forming the bulk, so to speak, the other very solid, forming little islets in the interior of the former.

Microscopic examination has shown us that the first of these tissues is exclusively formed of cells, and may be compared to the pith of our indigenous trees. It is traversed also by vascular bundles or very tough fibres, the tortuous course of which may be traced theoretically by the help of Fig. 55, in which letters a, B, ©? represent the different interlacings of these fillets in the middle of the pith. The fibrous bundles which traverse the stem of the — Palm and other trees belonging to the same natural group, present arrangements which are very interesting to understand. The anatomical structure of each of them does not appear to be alike — through their whole length; it seems to become more simple the — farther they are distant from the point where they leave the ste™ to pass into the leaves. In this higher part, at the end of its | course, the fibrous bundle of which we speak is invested with the characteristic structure of the stems of our indigenous trees including the medullary sheath; presenting, in fact, trache®, punctated and striated vessels of a greater or less size, ligneous-fibres, and other peculiarities of indigenous stems.

The Tree ferns of warm climates approach in their appearance much nearer to Palms than to our indigenous trees. Their slendet trunks, simple and branchless, and of nearly equal thickness from the base to the summit, support at a great height a tuft of leaves Nevertheless, Ferns differ much from Palms in their internal structure. Round an abundant pith voluminous vascular bundles - are drawn out, showing in the transverse section of the stem4 winding form, more or less irregular and hieroglyphic, and groul e

in circles towards the circumference of the trunk. This is shown in Fig. 56, representing the horizontal section of the stem of a Tree Fern. The reed-like bundles tra- ] verse the stem of the Tree Fern § from top to bottom, presenting a dark edge, formed of very tough fibres, impregnated with | adark browncolour, containing cellular tissue and a few vessels of different sorts. Among these vessels we shall particularly notice some prismatic tubes, which show on each of their faces horizontal clefts very close to each other, and at equal distances, called scalariform vessels. Fig. 57 shows the structure and relative arrangement of the scalariform vessels in the trunk of a Fern-tree. These vessels are represented under the microscope. “Here,” says Mr. Dresser, “the woody matter contained in the stalks of some leaves is transmitted into the stem, retaming the same disposition it did in the leaf stalks, in which case it surrounds the central cellular axis (Fig. 56); and the cellular apex of the stem grows and develops new leaves, the new portion of the stem being formed at the summit. Hence plants with this form of stem are said to be acrogenous, from axpa,a “summit,” and yevvad, ‘‘ produce,” or summit growers. All ferns have stems of this form. Although the Tree Fern has no close resemblance to the stem of either exogenous or endogenous plants, it seems to be more closely allied to the latter. Thus the rind or bark consists of layers of cellular tissue only, marked by the cicatrices of leaves or J=qESY fronds, showing that its leaves are produced at the Fiz. 51.—Seuleform ° veasels of the summit only. Fern-tree. E

Fig. 56.—Section of the stem of a Tree Fern.

ern 3 ern-t l eform 3 of the ern Fern-tree,

Fig. 58.—Pollard Willows in blossom.

Or Bups.

We have studied the tortuous and deformed roots, and denuded trunks of trees; before considering the branches, the boughs, the leaves, and the flowers which decorate them, we pause at the organ from which emanate all these elements. We speak of the bud, which hides under its delicate green envelope the source of these brilliant ornaments of nature of which every year witnesses the birth and death. The bud is, in fact, the cradle of the youBs plant. This organ alone is capable of reproducing a new individual, and the horticulturist is familiar with many wonderful of species through its means. In ordinary circu multiplications stances, however, the bud is not intended to be separated from the mother plant: its function is to nourish, strengthen, and increase

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