. The anatomy of woody plants. Botany -- Anatomy. 278 THE ANATOMY OF WOODY PLANTS The stem as the most plastic of the organs in vascular plants presents the greatest variety of structure in the Filicales. The leaf, and particularly the root, offer little diversity of organization and may consequently be dismissed with relatively slight con- sideration. Anatomically the stem presents itself in the case of the Filicales under two main conditions: the protostelic, in which there is no medulla present in the fibrovascular system, and the siphonostelic, characterized by the existence of a central m
. The anatomy of woody plants. Botany -- Anatomy. 278 THE ANATOMY OF WOODY PLANTS The stem as the most plastic of the organs in vascular plants presents the greatest variety of structure in the Filicales. The leaf, and particularly the root, offer little diversity of organization and may consequently be dismissed with relatively slight con- sideration. Anatomically the stem presents itself in the case of the Filicales under two main conditions: the protostelic, in which there is no medulla present in the fibrovascular system, and the siphonostelic, characterized by the existence of a central mass of parenchyma known as the medulla or pith. The first con- dition is represented in Fig. 199, portray- ing the transverse section of the stem of a species of Glei- chenia. The siphon- ostelic modification is delineated in Fig. 200, reproducing the transverse aspect of the stem of the maidenhair fern,. FIG. 199.—Transverse section of the stem Gleichenia species. Adiantum pedatum. In the second figure we find the fibrovascular tissues organized in the form of a tube, limited both internally and externally by an endodermal boundary which becomes continuous around the margins of the gaps caused by the exit of the traces of the lateral branches and leaves. Not only is the tubular central cylin- der bounded continuously by an endodermal layer, but it is likewise characterized in the particular case under discussion by an inner and outer lining of phloem. In the walls of the stelar tube so organized there are gaps formed in connection with the exit of the fibrovascular strands leading to both leaves and lateral branches. In addition to these there may be interruptions in the continuity of the fibrovascular hollow cylinder which are not related to. 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, Edwar
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