the Anatomy of the Genus Selaginella. 505 
thickness in which suberin can be demonstrated. The protoxylem is 
highly developed in the oldest part of the rhizophore, before it branches off 
for the first time ; it is composed of from twenty-five to even forty 
tracheides ; in young organs the secondary thickening of the walls takes place 
at the outer side of this group of tracheides, as is shown in Fig. VII ; 
Fig. VI. S. Wildenowi. i, cross-section of rhizophore; 2, longitudinal section of epidermis 
and hypodermis ; 3, longitudinal section of thick- and thin-walled cortex; 4, longitudinal section of 
cortex, endodermis, pericycle, protophloem, phloem, parenchyma, and metaxylem ; 5, cross-section 
of tracheides of xylem. 
when the rhizophore has branched off the protoxylem usually consists of 
six to ten tracheides. The metaxylem is always strongly developed, 
especially in the old primary rhizophore ; its tracheides are broad. The 
entire vascular bundle of the primary rhizophore is kidney-shaped (Fig. VII) ; 
when this organ has branched off the bundle is roundish (Fig. VI, 1). 
The terrestrial root possesses an epidermis with large cells which 
occasionally lengthen towards the periphery into root-hairs ; the epidermis 
