The origin of siphonostele in three species of Selaginella Spr.

Abstract

The observations recorded in the foregoing pages thus warrant the following general conclusion with regard to the origin of the amphiphloic siphonostele in Selaginella: The origin of the siphonostele in Selaginella is correlated with the polystelic condition and the amphiphloic siphonostele originated as a result of a fusion of a number of separate steles. The polystelic condition probably originated in response to the necessity of increasing the amount of conducting and mechanical tissues in the absence of provision for secondary growth. The pith is extrastelar in origin and the presence of internal phloem and internal endodermis is directly due to the origin of the siphonostele from the polystelic condition.