507 
the Anatomy of the Genus Selaginella. 
hypodermis cells belonging to the inner row are sometimes larger. The 
outer layer of the cortex also may be slightly thick-walled, although the 
remainder are thin-walled, and are composed of eight to ten rows of cells. 
The cells of the endodermis are much smaller than those of the inner cortex, 
and therefore easily visible. The phloem is much like that of the stem, and 
therefore does not need any further description. The xylem is composed of 
thirty-two to forty tracheides ; the members of the protoxylem, although 
visible, are not much smaller than those of the metaxylem. 
All cells contain a red pigment which is dissolved in the vacuole. The 
cells of the hypodermis, cortex, and sometimes of the epidermis contain 
mycelia, which suggests the presence of mycorrhiza (Fig. IX, i and 2). No 
further study of this mycorrhiza has been made, as it would require a special 
treatise. 
The terrestrial root (Fig. VIII) has a large-celled epidermis, and cells of 
the two following layers also have the same appearance. The hypodermis 
