. The anatomy of woody plants. Botany -- Anatomy. 260 THE ANATOMY OF WOODY PLANTS secondary growth. In the Lepidodendraceae in the narrower sense the secondary wood is distinguished from the primary struc- tures only by the presence, exclusively, of radial parenchyma and by the radial seriation of its tracheary elements (Fig. 185). The organization of the tracheids of the secondary wood is, in fact, identical with that found in the primary region. In the higher lepidodendroid forms assembled under the appellation Sigillariae very frequently, particularly in the region of the secondary wood mor
. The anatomy of woody plants. Botany -- Anatomy. 260 THE ANATOMY OF WOODY PLANTS secondary growth. In the Lepidodendraceae in the narrower sense the secondary wood is distinguished from the primary struc- tures only by the presence, exclusively, of radial parenchyma and by the radial seriation of its tracheary elements (Fig. 185). The organization of the tracheids of the secondary wood is, in fact, identical with that found in the primary region. In the higher lepidodendroid forms assembled under the appellation Sigillariae very frequently, particularly in the region of the secondary wood more remote from the pith, the tra- cheids cease to be scalariform and assume the pitted type characteristic of the gymno- sperms and other higher representa- tives of the Vascu- lares. The vascular strands of leaves in the lepidodendrids are characterized, as are those of the Lycopodiales in general, by mesarch organiza- tion. This condition is clearly shown in Fig. 186. It is appar- ent that the foliar trace is surrounded by secondary wood. It has been stated by Scott that true transfusion tissue is present in the leaf of the lepidodendrids, but this statement, in view of the situation present in the Lycopodiales in general and in the Lepido- dendraceae in particular, seems open to some question, and certainly the subject seems to require further investigation. The foliar organs of the lepidodendroid stock were characterized by the presence of two aerating strands on either side of the foliar trace; these were in communication below with the external air through the agency. FIG. 185.—Longitudinal section through primary and secondary wood of Lepidodendron 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. , The University of Chicago Press
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