(amphiphloic siphonostele) A * siphonostele in which there is also a cylinder of phloem internal to the xylem. When an endodermis is present, there is also an endodermal layer internal to the internal phloem. Leaf gaps are present, but are sufficiently spaced longitudinally so that only one is visible in any one transverse section. This type of stele is found in certain ferns, e.g. Marsilea and Adiantum, and is often quoted as evidence for the hypothesis that siphonosteles originated through invasion of the xylem by other extrastelar tissues. Compare dictyostele. |
