Cambium layer

As a tree grows, the cells are produced in concentric lamella in the cambium layer, which is between the bark and the wood. In the spring, when moisture is plentiful and the tree is growing rapidly, the tracheid cell wall is thin (3—4 -lm) and the hoUow center or lumen is relatively large (26—43 p.m). 

Pectin and pectic substances are sometimes removed prior to xylan extraction. This is especially desirable when dealing with plant material containing large amounts of pectic substances such as the cambium layer of wood28 or the leaves and stems of plants.29-80 Extraction for one or more separate periods with 0.5% solutions of ammonium oxalate at 90-100° removes water-insoluble pectin substances3182 83 that are not mechanically trapped or chemically bound in the plant struc-... 

Figure 1. Outer part of a tree stem. New cells are formed in the cambium layer and differentiate either to wood or bark tissue.

There are several kinds of plant tissues. Undifferentiated, embryonic cells found in rapidly growing regions of shoots and roots form the meristematic tissue. By differentiation, the latter yields the simple tissues, the parenchyma, collenchyma, and scleren-chyma. Parenchyma cells are among the most abundant and least specialized in plants. They give rise through further differentiation to the cambium layer, the growing layer of roots and stems. They also... 

Figure 1-16 shows a section from a stem of a typical angiosperm. Note the thin cambium layer between the phloem and the xylem. Its cells continuously... 

Calvin, Melvin 84 Cambium layer 29 Cambrian explosion 9 cAMP 536,544,544s, 556,557 second messenger 557 Cancer 573-575... 

The cambium layer of plant stems (Fig. 1-16) differentiates continuously to form phloem on the outside of the cambium and xylem on the inside. At the same time, cambium cells are retained. Thus, at each cell division one daughter cell becomes a differentiated cell, while another remains the less differentiated cambium. This pattern of continuous differentiation from a line of stem cells with constant properties is found in animals as well as in plants. In the differentiation of cambium it appears that chemical signals obtained from the surrounding cells on either the inside or the outside of the cambium layer determine whether the differentiated cell becomes phloem or xylem. Sucrose, auxin, and cytokinins are all involved. 

In the isolation of hemicelluloses from plant materials containing a relatively large amount of pectic substances, such as the cambium layer of a wood or the leaves and stems of plants, the water-soluble materials and insoluble pectic substances are first removed. The hemicelluloses are then extracted by an alkaline solution. Sodium hydroxide solutions at concentrations varying from 2 to 17% have been used for this purpose. Norman recommends a 2% solution of sodium carbonate when high purity is more desirable than completeness of extraction. Most investigators have used a cold sodium hydroxide solution of approximately 4% concentration. " ... 

Interfacic ular.—Applied to a cambium layer which extends from one fibro-vascular bundle to another in the stems of Dicotyledons and Gymnosperms. 

Retting takes place first in the cambium layer where is quite soluble and where because of the very thin cell layers of pectin or cementing substance are correspond When flax stems are sterilized in water at 115 degrees C. xx pectin in the cambium layer is dissolved, and the cortex loosened from the wooden core that the loose-core test is c at all as a positive indicator that retting is completed. Tlx the tissues of the cortex is less soluble than that in the cam and is not much affected by the solvent action of the hot w not entirely because of a difference in accessibility that till retted after the cambium layer, aB at the exposed surfaces o. where all.tissues are equally exposed to the attack of tlx. retting is not materially hastened in the cortex. 

It is true, however, that the cambium layer, located oxx of the stem, is somewhat more accessible to the attack of til... 

FIGURE 8.5 The five zones in the cross section of the flax plant stems A, layer of cuticular cells B, intermediate layer of cortical parenchyma C, the bast layer containing the flax fibers D, cambium layer E, woody tissue. (From Mauersberger H.R., ed., Mathews Textile Fibers, 5th ed., John Wiley and Sons, New York, 1947 J. Adhes. Sci. Tech., 18(9), 1063-1076, 2004.)... 

Since the j3-glucosidases have been demonstrated in the cambium layer of conifer stems and the dehydrogenating enzymes have been found in an inner layer, an increase in the lignification progressing from the outer layers to the inner layers may be explained. 

Arabinogalactan is found in small amounts in the wood of other trees. It occurs in the cambium layer and sapwood of hemlock. Minor amounts are also pre-... 

Latex is obtained from the tree by a process called tapping. Near the cambium layer in the bark are the latex vessels, a network of capillary tubes that occur in all parts of the tree but are concentrated in the bark. Here the plant food is changed into rubber hydrocarbon. A cut is made into the thin lay of lactiferous vessels, the cambium lay being carefully avoided. Latex exudes from this cut and is collected. 

In the stem of dicotyledons, the xylem and phloem tubes are usually found in a ring near the outside of the stem with phloem on the outside and xylem on the inside, separated by a cambium layer. In monocotyledons the vascular bundles are more randomly arranged within the stem. In the root, the xylem and phloem tubes form separate bundles and are found near the centre. 

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