This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1887 Excerpt: ... of fibro-vascular bundles are distinguished, the collateral, the concentric, and the radial. (a) The Collateral Bundle is characterized by having the xylem and phloem masses arranged side by side, and usually in such a manner that the former faces interiorly, and the latter exteriorly, as regards the organ that bears it. In leaves, the xylem faces the upper or ventral surface, while the phloem faces the lower or dorsal surface. In Fig. 385,/ is the phloem, and x the xylem. Bundles of this kind are characteristic of the stems and foliage leaves of nearly all flowering plants, but they seldom occur in roots. Two varieties are distinguished, the ordinary form, in which there is one mass each of xylem and phloem, and the bi-collateral bundle, in which there is one mass of xylem between two of phloem. The latter variety is found only in the stems of members of the gourd family, and in a few other plants. Some collateral bundles continue to grow during the life of the organ which contains them, and the growing layer is located at the junction of the xylem with the phloem. Such bundles are called open bundles, while those which soon cease to grow or form new tissues are called closed bundles. The former are characteristic of the stems of woody dicotyledons. In this case, the bundles being radially arranged, with the phloem masses pointing outward, the growing layer constitutes a continuous zone, which forms the line of junction of the wood with the bark. This is called the cambium zone, Fig. 385, c. The bundles found in the stems of most monocotyledons are of the closed collateral variety. (b) The Concentric Bundle. This differs from the last in having one of the two elements of the bundle (xylem or phloem) placed centrally, and surrounded by the other. In most f...
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