. Fossil plants : for students of botany and geology . Paleobotany. 312 FILICALES [CH. be regarded as a stage in a series leading to another well-marked type, the solenostele. The solenostele\ a hollow cyclinder of xylem lined within and without by phloem, pericycle, and en- dodermis, occurs in several genera belonging to different families, Dipteris, species of Pteris, species of Lindsaya, Polypodium, Jamesonia, Loxsoma, Oleichenia and other genera. In a smaller number of ferns the stele consists of what may be called a meduUated protostele similar to the common form of stele in Lepidode
. Fossil plants : for students of botany and geology . Paleobotany. 312 FILICALES [CH. be regarded as a stage in a series leading to another well-marked type, the solenostele. The solenostele\ a hollow cyclinder of xylem lined within and without by phloem, pericycle, and en- dodermis, occurs in several genera belonging to different families, Dipteris, species of Pteris, species of Lindsaya, Polypodium, Jamesonia, Loxsoma, Oleichenia and other genera. In a smaller number of ferns the stele consists of what may be called a meduUated protostele similar to the common form of stele in Lepidodendron: this type is found in species of Schizaea and in Platyzoma (fig. 239). It is important to notice that in the. Fia. 239. Platyzoma microphylla. , leaf-trace; , internal endodermis. (After Tansley; modified from Boodle.) solenostele and as a rule in the medullated protostele when a leaf-trace passes out from the rhizome stele the vascular cylinder is interrupted by the formation of a foliar gap {Platyzoma^, fig. 239, is an exception). This fact has been emphasized by Jeffrey^ who draws a distinction between the Lycopodiaceous type of stele, which is not broken by the exit of leaf-traces, and the fern stele in which foliar gaps are produced: the former he speaks of as the cladosiphonic type (Lycopsida) and the latter as the phyllosiphonic (Pteropsida). The transition to a hollow cylinder of xylem from a protostele ' Gwjnne-Vaughan (01); (03). ^ Boodle (01) p. 73-5. » Jeffrey (00); (03).. 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 Seward, A. C. (Albert Charles), 1863-1941. Cambridge : University Press
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