the Anatomy of the Genus Selaginella. 509 
and its xylem is but little developed, being composed of seven tracheides, 
of which four belong to the protoxylem. 
The roots are very thin ; only a few cells of the epidermis are elongated 
into hair-roots. Then follow two layers of thin-walled cells, then the hypo- 
dermis cells composed of three layers which are but very slightly thick- 
walled. The vascular bundle is very small — the writer counted from two to 
three sieve-tubes in the phloem and but four to five tracheides in the xylem. 
Selaginella decora . 
The rhizophores have a length of 30 to 45 millimetres and a diameter of 
| to 1 millimetre. The cells of the epidermis are much smaller than those 
of the hypodermis ; the cell-walls of both are thick. The cortex is com- 
posed of to to 15 rows of cells. In comparison with the thickness of the 
aerial root, the vascular bundle is not as well developed as in other species. 
The protoxylem is composed of three to four tracheides and the metaxylem 
also of three to four. The phloem is, in comparison, better developed. 
The construction of the very thin roots is very much like that of the previous 
species. 
Selaginella Douglasi. 
The length of the rhizophores varies from 20 to about 28 millimetres; 
its diameter from | to •§ millimetre. The cells of epidermis, hypodermis, 
and mostly those of the cortex, are very thick-walled in plants which were 
developed in their native country (Oregon State, U.S.A.), where they have 
the habit of xerophytes growing upon stems of trees. Individuals which 
were grown in moist soil, and in the damp environment of a greenhouse, show 
considerably less thickened walls in the above-mentioned tissues. The xylem 
is well developed, and is composed of about five tracheides belonging to the 
protoxylem, and ten to sixteen belonging to the metaxylem. The phloem 
which surrounds the xylem is much like that of the stem. 
Selaginella molliceps. 
This species forms strong well-developed rhizophores, especially when 
twigs are growing close to one another. They attain a length of 6 to 15 
millimetres and a diameter of § to \ millimetre. The epidermis is com- 
posed of rather large cells, although somewhat smaller than those of the 
cortex. The cuticle is thin, even that of older rhizophores. The terrestrial 
root does not show marked differences, except that as usual the epidermis 
is followed by two thin-walled layers of cells. The development of the 
vascular bundle is like that of v$. decora. 
Selaginella Bakeriana. 
The rhizophores somewhat resemble in anatomical construction that of 
vS. rubella. They reach a length of 6 to 12 millimetres and a diameter of 
J to J millimetre. The cells of the epidermis and hypodermis remain 
