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At the same time the cambium cells are forming new bark, and if examine a section an endogenous stem several years growth find appear similar the section represented next page, in which the asterisk indicates the cambium zone, all within which conventionally spoken as wood while all without bark. If cut a willow twig in spring, during the time rapid growth when the tissues are fresh and soft, choosing a straight, smooth piece and preferably a single in tern ode for the experiment, and then beat the surface gently with custom written term papers the side the knife-handle, bruise and loosen the cambium cells that may slip a tubular outer piece from the solid cylinder wood the tube thus separated the bark.

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If make transverse sections, first, the whole thickness a willow twig, then a piece the bark and another the wood-cylinder from which the bark was removed, as explained, and compare them with each other, obtain a good conception the relation the bark the other parts the planUaxis.

We see that the wood-cylinder consists the pith, the xylem or wood portions the flbrovaaculsr bandies and the medullary rays, as far outward as the fibrovascnlar bundles alternating with the prolongations how do i write a thesis the medullary rays, a layer parenchyma surrounding tbem, and an outer corky layer, while the inner side find also remnants torn After this description almost superfluous add that the arrangement the endogenous plant-axis each that there can no bark in the proper Let now examine pay to write paper this diagram a bark.

A typical bark consists three layers. The outer layer epidermis in young branches a, under which a layer cork or suber soon forms, and in somewhat older barks the epidermis disappears and cork alone remains this layer called the outer bark exophlceum. Next within this corky layer or outer bark a layer parenchyma cells formed the apparent extension, broadening and merging into each other the medullary rays in reality these cells, together with the medullary rays and pith, are fundamental tissue.

This layer extends from the cork inward an imaginary line drawn connect the outer points the bast portions all the fibro-vascular bundles in the transverse section, and this parenchyma constitutes the middle bark mesophloeum.

The third layer consists the bast-portions the fibrovascular bundles and the intermediate medullary rays from the imaginary line just described inward the cambium layer called the inner bark endophloeum or liber and consists alternating wedges bast and parenchyma, the wedges bast having their base or broader ends inward and the points outwards, and the fundamental parenchyma wedges vice versa The bast consists bast-parenchyma, which differs in the shape and size its cells from the fundamental parenchyma and bast-cells also contains sieve-ducts, which, however, are little or no practical importance the pharmacognocist.

The arrangement the bast-parenchyma, bast-cells and medullary rays or fundamental tissue and their relations each other give the peculiar appearances the transverse sections barks which group them. The outer surfaces barks offer several points The Latin technical names are quoted, because some authors use theni in preference the plain and easily-understood English names in these notes the simpler terms are preferred and used. interest which may diagnostic value. Formerly much attention was given the study the parasitic cryptogams, lichens and mosses, which grow the surfaces trees, and which were supposed characteristic features certain barks. At the heed these forms vegetation, although some them are peculiar diagnostic value the accompanying illustration figures a lichen, from its resemblance Chinese writing, which occurs Saigon cinnamon the little black spots the white corky layer Cascarilla are also cryptogamic plants. While possible that a closer study this subject, not only in connection with barks, but also with other plant-parts, might furnish some data value for the identification powdered drugs, yet the former plan use these lower plant-forms identify whole barks about as if some one would suggest that because the thumbmarks no two persons agree in shape, therefore the lines and figures the thumb might used in recognizing our friends. A finger-mark in blood the wall a room in which a murder was committed might lead the conviction a murderer, but recognize our friends face and features other than thumb-marks use other coarser and equally characteristic features identify drugs, rather than a study the cryptogamic parasites.

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The mere presence how to write thesis proposal or absence such growths may, however, sometimes useful in distinguishing between the barks stems with and the barks roots without Cork proper consists true cork-cells suber which may from a few a few hundred or thousand cells in thickness. These cells are practically impervious moisture and serve prevent evaporation moisture Irom the stem while route from the roots the leaves. As the stem grows in thickness this corky layer becomes Assured in a manner which enables the wood-man recognize the varieties trees in the forests or fields their barks, and often enables pharmacognocistB recognize barks these same characteristics. In some barks this corky layer cracks off after awhile, but a thin protecting layer remains, from which thicker layers soon are reproduced meanwhile the middle bark forms new cells adapt the bark the growing help with writing a speech circumference the plant, that while the bark grows in all directions yet retains tbe structure a typical bark with the three layers, the outer, middle and inner barks. In other plants, however, the bark continues grow only or mainly at the cambium zone and in tbis case, as the circumference enlarges and fissures form, these extend into the middle bark or even into the inner bark, until large pieces bark finally fall off. This would leave tbe stem in a denuded condition, somewhat like an open ulcer an animal surface, if nature had not provided a plan prevent this. A layer, or layers, secondary cork rhytidoma dips down from the surface the bark through the middle and later through the inner bark and emerges again sit some little distance each secondary cork layers are shown in this section cornns florida bark. When formed, nourishment or sap cut off from the tissues outside, and the latter are sphacelated or necrosed, cnt oS from the living tree, much like a sphacelus in a spontaneous amputation or slough in an animal, or in the same manner as deciduous leaves are shed in fall. As far as external appearances these masses fissured and necrosed bark tissue resemble the fissured masses true cork previously described, and both formations are called Borke German botanists no better term having been suggested, has also been adopted English writers and the term frequently met with but care should taken that no confusion permitted doctoral thesis the similarity the English terms bork The bork plants sometimes peels off in sheets or leaves when called liber, from a Latin word for book.

 

 

 

 

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