. The anatomy of woody plants. Botany -- Anatomy. THE LYCOPODIALES 255 polystelic. In still another modification, presented by S. laemgata from Madagascar (Fig. 181), a true siphonostele is exemplified which is complicated by the presence of medullary strands joining up with the walls of the tube in the regions where branches are given off. In the species under discussion the traces of the leaves illustrate the condition typical for the Lycopsida and pass off from the cylinder without causing any gaps in its continuity. Isoetes has a protostelic stem which is remarkable among ex- isting Lycops
. The anatomy of woody plants. Botany -- Anatomy. THE LYCOPODIALES 255 polystelic. In still another modification, presented by S. laemgata from Madagascar (Fig. 181), a true siphonostele is exemplified which is complicated by the presence of medullary strands joining up with the walls of the tube in the regions where branches are given off. In the species under discussion the traces of the leaves illustrate the condition typical for the Lycopsida and pass off from the cylinder without causing any gaps in its continuity. Isoetes has a protostelic stem which is remarkable among ex- isting Lycopsida in manifesting well-marked secondary growth (Fig. 182). The external prod- uct of cambial activity is a radially disposed storage paren- chyma, while internally the di- viding layer originates additions to the fibrovascular tissues which are most commonly inter- preted as consisting of alternate zones of xylem and phloem. The situation here, however, is disputed, and uncertainty per- sists as a result of the indifferent development of the tissues re- sulting from the characteristic- ally aquatic habit of the plant. The roots in Isoetes are distin- guished, in common with the smaller radical organs of a number of the lower Lycopsida, by the fact that they develop a single mass of xylem in proximity to a single strand of phloem. The leaf is not worthy of special note. In the Lepidodendraceae the stem manifests great diversity of structure, as would naturally be expected in a group which in Paleozoic times displayed numerous types with generally marked secondary growth. The primary structures of the stem were either protostelic or siphonostelic. In the former condition a considerable amount of parenchymatous tissue was developed. FIG. 182.—Cambial activity in Isoetes. 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 origi
Size: 1310px × 1906px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookpublisherchicagoilltheuniversityo, booksubjectbotanyanatomy
