Anatomy of the Genus Selaginella , Spr. 31 
This is due to the development of secondary tracheides round the base 
of the ligule (cf. 14 ). Transverse sections of the cone (whether these be 
homophyllous, or dorsiventral, as in 6'. molliceps) show that radial symmetry 
obtains here. The stele is circular and lies in a circular lacuna. The only 
exception to this rule is S.Lyallii (PI. IV, Fig. 3). Here there are two dis¬ 
tinct steles, in a somewhat elongated lacuna. Each is provided with one 
protoxylem which points to the outside, and the two may be sometimes 
united by their pericycles. Figs. 5 and 8, PI. IV, illustrate the method 
of fusion of the several bundles of the stem into the simpler type of struc¬ 
ture of the cone as seen in .S. inaequalifolia and V. Lyallii respectively. 
The vascular system of the cone is again differentiated into (1) a cen¬ 
tral cone of metaxylem with marginal protoxylems, (2) a region of phloem 
parenchyma, (3) one layer of sieve-tubes, frequently absent opposite the 
marginal protoxylems, (4) a large-celled pericycle, ranging from one 
to five cells in thickness, and (5) the endodermal trabeculae. Apart from 
the fact that radial symmetry is characteristic of the cone, there is naturally 
a great resemblance between the vascular system of the cone and that 
of the stem, which soon becomes evident on comparing the cases given 
below with the corresponding figures and descriptions given by Professor 
Harvey-Gibson in his paper on the stem of Selaginella ( 13 ). 
a. S. Lyallii (PL IV, Fig. 3). 
There are two circular steles, occasionally joined by their pericycles, 
each bearing an outwardly placed protoxylem, and surrounded by a common 
lacuna. The pericyclic cells, which are one or two layers deep, are large, 
and contain starch, &c., and surround a layer of sieve-tubes which are 
separated from the central cone of xylem by two or three layers of phloem 
parenchyma. A few isolated protophloem patches may occur. 
b. S. spinosa (PI. IV, Fig. 9). 
The metaxylem consists of small elements, which are frequently not 
thickened towards the centre, and carries eight protoxylems (as in the 
tip of the vegetative shoot) which are partially sunk in the metaxylem. 
The phloem parenchyma is one to three layers thick, and is followed by one 
layer of sieve-tubes, which, however, may be about opposite the proto¬ 
xylems. The pericycle is one to two cells in thickness. 
c. S . oregana (cf. 13 ). 
The pericycle is two to five layers deep, and there are no protophloem 
elements. The one layer of sieve-tubes is absent opposite the two marginal 
protoxylems, the phloem parenchyma (of which there are two or three 
layers) abutting directly on the pericycle. 
d. S. inaequalifolia (cf. structure of central stele in stem). 
The procambial area extends down to the base of the cone. The 
pericycle is generally one layer thick, and encloses a layer of sieve-tubes 
(whose continuity may be broken opposite the marginal protoxylems). 
