the Anatomy of the Genus Selaginella. 459 
anomaly. In S. Helvetica^ Lk., the cortex is similar to that 
of S. involvens. The vascular cylinder of the stem is ribbon- 
shaped with two marginal protoxylems, one situated at each 
margin of the stele. At the point of origin of the vascular 
cylinder of the root the protoxylem becomes internally 
placed so that the stele shows on one side a perixylic, on the 
other a centroxylic structure (PL XX, Fig. 19). The same 
peculiarity is shown by S. denticulately Lk., a species which 
has otherwise a normal structure. 
Turning now to the homophyllous species, spinosa, P. B., 
vS. oreganay Eat., and 5 . rupestris, Spr., it will be found that 
in the case of the two last-mentioned species the root is 
normally monarch, save that, as in the case of the stem, 
the metaxylem consists chiefly of tracheae or vessels (i. e. 
cell-fusions). The root is covered externally by two layers 
of thin-walled cells with root-hairs, followed by four to eight 
layers of thick-walled cells with brown tannin-like contents, 
two to three layers of thin-walled cells, very liable to be torn 
through in the process of cutting, and a prominent and com- 
pletely cuticularized endodermis. The vascular system is 
poorly developed (PI. XX, Fig. 6). S. rupestrisy Spr., agrees with 
*S. oregana in all respects. The centroxylic condition of the 
creeping part of the stem of 5. spinosay P. B., has already been 
described by the present writer (10), and later by Bruchmann(8). 
It is worth while pointing out, however, that the stem, for 
some considerable distance before the point of origin of the 
roots, contains two vascular cylinders, both centroxylic. The 
root is normally monarch, as figured and described by Bruch- 
mann, to whose description I have nothing to add. 
With regard to the bistelic species it may be said generally 
that the root-structure is, in most respects, similar to that 
already described for the monostelic species. In 5. Galeottei , 
Spr., the aerial part of the root is very long, and one root 
arises at each fork of the stem on the upper side and bends 
over behind the lesser branch downwards to the soil. The 
vascular cylinder of the root arises just in front of the origin 
of the lateral branch and far behind the point of fusion of the 
