The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.
a type of structure characteristic of the central cylinder of the stem of ferns; a siphonostele in which the xylem is surrounded on two sides by phloem. The interior phloem is the outer boundary of the parenchymal heartwood.
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.