p, Pith; P, primary wood groups; W, secondary wood; l.t, leaf trace; s, sclerized bands in the cortex; S, longitudinal view of wood elements to show the rows of bordered pits.
The anatomy of the main stem is very suggestive of that of a Cycad. The zones of secondary wood are loosely built, the quantity of soft tissue between the radiating bands of wood, and the size of the pith being large, while from the main axis double strands of wood run out to the leaf base. The primary bundles, however, are not like those of a Cycad stem, but have groups of centripetal wood within the protoxylem, and thus resemble the primary bundles of Poroxylon (see [p. 97]), which are more primitive in this respect than those of the Cycads.
The roots of Lyginodendron, when young, were like those of the Marattiaceous ferns, their five-rayed mass of wood being characteristic of that family, and different from the type of root found in most other ferns (cf. [fig. 78B] with [fig. 35] on [p. 60]). Unlike fern roots of any kind, however, they have well-developed zones of secondary wood, in which they approach the Gymnospermic roots (see [fig. 78B], s).
Fig. 78B.—Transverse Section of Root of Lyginodendron
w, Five-rayed mass of primary wood; s, zone of secondary wood; c, cortical and other soft tissues.
A further mixture of characters is seen in the vascular bundles of the petioles. A double strand, like that in the lower Gymnosperms, goes off to the leaf base from the main axis, but in the petiole itself the bundle is like a normal fern stele, and shows no characters in transverse section which would separate it from the ferns. Such a petiole is illustrated in [fig. 79], with its V-shaped fernlike stele. On the petioles and stems were certain rough, spiny structures of the nature of complex hairs. In some cases they are glandular, as is seen in g in [fig. 79], and as they seem to be unique in their appearance they have been of great service in the identification of the various isolated organs of the plant.
As is seen from [fig. 77], the leaves were quite fern-like, but in structural specimens they have been found with the characteristic glandular hairs of the plant.
The seeds were so long known under the name of Lagenostoma that they are still called by it, though they have been identified as belonging to Lyginodendron. They were small (about ¼ in. in maximum length) when compared with those of most other plants of the group, or of the Cycads, with which they show considerable affinity. They are too complex to describe fully, and have been mentioned already (see [p. 76]), so that they will not be described in much detail here. The diagrammatic figure ([fig. 56]) shows the essential characters of their longitudinal section, and their transverse section, as illustrated in [fig. 80], shows the complex and elaborate mechanism of the apex.
