Published online by Cambridge University Press: 06 July 2012
For over thirty years problems of stelar structure in the Ferns have claimed the attention of anatomists. By common consent protostely has been recognised as a primitive state. It is seen in all phyla of primitive vascular plants, except the semi-aquatic Equisetales, it figures universally in the juvenile plants of the Filicales, and is maintained in the adult stems of a number of their primitive genera.
But as to the origin of pith, inner phloëm, and inner endodermis, and the steps by which during descent the primitive protostely has in many instances been replaced in the adult by other more complex stelar states, there is no general agreement. On the one hand, the pith, inner phloëm, and inner endodermis have been regarded as purely intrastelar tissues directly referable in origin both in individual plants and descent to the procambial mass of the growing point of the stem.