. Studies in fossil botany . Paleobotany. 37° STUDIES IN FOSSIL BOTANY filled by a small-celled secretory tissue (Fig. 136). In certain conditions the glandular tissue has broken down and the head is left empty (Fig. 146). We haye so. far described the ordinary structure of the Lyginodendron stem, such as is common to the great majority of the specimens. Sometimes quite young stems are met with, with little or no second- ary growth ; one of these is represented, in transverse sec- tion, in Fig. 135, at a stage when the secondary wood (.t2) was still quite thin. Such specimens show very clearly
. Studies in fossil botany . Paleobotany. 37° STUDIES IN FOSSIL BOTANY filled by a small-celled secretory tissue (Fig. 136). In certain conditions the glandular tissue has broken down and the head is left empty (Fig. 146). We haye so. far described the ordinary structure of the Lyginodendron stem, such as is common to the great majority of the specimens. Sometimes quite young stems are met with, with little or no second- ary growth ; one of these is represented, in transverse sec- tion, in Fig. 135, at a stage when the secondary wood (.t2) was still quite thin. Such specimens show very clearly the identity of the leaf-traces (/./.) with the strands (.r) sur- rounding the pith. At this stage, the outer cortex con- tains only narrow bands of parenchyma ; evidently this tissue increased by dilatation as the stem enlarged in girth. In some cases small stems arc found which are not merely young, but really have a different structure from the usual kind. Some of these little stems have a very small pith, surrounded by a more or less continuous ring of primary xylem, instead of by separate bundles. These specimens may very likely be the stems of. ";. 136. — Lyginodetidi'on aldham- ium. Vegetative gland, showing well - preserved secretory tissue filling the head. The depression on the right of the stalk is a stoma. X about 60. S. Coll. 447. From a photograph hy Mr. L. A. Hoodie, (Phil. Trans. Oliver and Scott.). 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 Scott, Dukinfield Henry, 1854-1934. London, A. and C. Black
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