. The anatomy of woody plants. Botany -- Anatomy. FIBROVASCULAR TISSUES: WOOD length. Elements in the aggregation belonging to this category are known as the metaxylem or, more specifically, as the primary metaxylem. In the preceding paragraph, for the sake of convenience it has been assumed that the order of development of the primary wood is always in the same direction. As a matter of fact the time and the order of appear- ance of the elements in this, from the evolutionary stand- point, highly signifi- cant tissue vary within certain im- portant limits. We may first consider the most ancie
. The anatomy of woody plants. Botany -- Anatomy. FIBROVASCULAR TISSUES: WOOD length. Elements in the aggregation belonging to this category are known as the metaxylem or, more specifically, as the primary metaxylem. In the preceding paragraph, for the sake of convenience it has been assumed that the order of development of the primary wood is always in the same direction. As a matter of fact the time and the order of appear- ance of the elements in this, from the evolutionary stand- point, highly signifi- cant tissue vary within certain im- portant limits. We may first consider the most ancient order of seriation of the constituents of the primary wood- that found in the stems of the most antique plants and in the roots of all vascular organisms from the lowest to the highest. Fig. 15 illustrates the organization of the wood in a stem of the common club moss, Lycopodium. The tissues of the xylem constitute a sort of star, the points of which are occupied by the small-sized elements of the protoxylem. As the rays of the star broaden inwardly, there is a transition from protoxylem to metaxylem. The situation becomes more clear by reference to transverse sections of the root in a fern shown in Fig. i6a. Spiral sculpture marks the small elements on the outside, while toward the center of the organ the typical sculp- ture of the metaxylem becomes more and more conspicuous. In the club mosses and their allies, as well as in all roots, the seriation in the development of the elements of the primary wood is very. FIG. 15.—Transverse section of the upright stem of Lycopodium clavatiim, showing centripetal or centrad development of the primary wood; the smaller elements represent the Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Jeffrey, Edward C. (Edward Charles), b. 1866. Chicago, Ill.
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