452 Harvey- Gibson, — Contributions to Knowledge of 
rhizophore contains two vascular cords. These authors com- 
pare the two cords with opposing protoxylems with the 
centroxylic condition of the rhizophore in S. Kraussiana. 
The planes of branching are always at right angles in 
S. Martensii. The root-cap is small, and is ultimately 
thrown off. 
In 5 . cuspidata , Lk., and S. laevigata , Spr., there are no 
rhizophores, and the roots arise directly from the bifurcations of 
the stem. They differ from rhizophores in not arising at every 
bifurcation. The vascular system is a monarch strand with one 
lateral protoxylem. Pfeffer, in his paper on the development 
of the embryo of Selaginella , draws attention to the occasional 
development of the upper rhizophore into a leafy branch in 
S. inaequalifolia ( 3 ). Van Tieghem ( 4 ) describes the vascular 
bundle of the rhizophore as triangular in section, and so 
orientated that the protoxylem faces the ground if the stem 
be placed in an erect position. He also draws attention to 
the change in orientation of the bundles at the forkings. The 
so-called rhizophore Van Tieghem considers as a case of 
exaggerated intercalary growth of the aerial part of the root, 
and dissents from the view held by Nageli and Leitgeb as to 
the cauline value of the organ. Russow ( 5 ) says that the so- 
called rhizophores and roots agree in anatomical structure, 
and holds the same view as Van Tieghem as to their morpho- 
logical value. Division of the monarch bundle takes place 
in the aerial part before any appearance of external division. 
The xylem first of all broadens, and division takes place in 
the protoxylem first. The xylems suffer torsion through 
90 degrees at the forkings both of the aerial and subterranean 
parts. In this relation it is interesting to note that Scott and 
Hill (10), in their paper on the anatomy of Isoetes Hystrix , 
remark that ‘ as the two strands (at the root-fork) separate 
from each other, they turn through an angle of 90 degrees so 
as to direct their protoxylems towards each other.’ 
Dangeard (6) describes and figures the central protoxylem 
of the rhizophore of S'. Kraussiana , and says that a similar 
centroxylic condition occurs between the spore and the first 
