154 Gibson. — Contributions towards a Knowledge 
protoxylems are arranged on the plan of those in S. Martensii , 
and the creeping and erect stems are both monostelic. There 
is externally a cuticle, a scarcely differentiated epidermis and 
a thick hypodermis, the thick cell-walls of these layers being 
of a bright red colour. The cortex is abundant and the walls 
of the cortical cells are also thick. The innermost layers are 
composed of tubular cells with thick sclerotic walls and are 
enclosed in a siliceous deposit (PI. IX, Fig. 9). Then follow 
two or more layers of loosely arranged thin-walled chloro- 
phyll-bearing parenchyma with silica, articulating with the 
endodermal cells. These latter are short and usually much 
constricted in the region of the cuticular band. 
There is a single ribbon-like stele with two marginal 
protoxylems. The pericycle is three layers deep dorsally and 
ventrally, but two-layered opposite the margin. Two layers 
of sieve-tubes occur dorsally and ventrally, and one imperfect 
(or occasionally perfect) layer opposite the marginal proto- 
xylems. There are a few protophloem-elements. The phloem- 
parenchyma is well developed and from three to four layers deep. 
5. Selaginella erythropus , Spr. Baker’s Handbook, No. 260. 
The stele is simple throughout and the arrangement of 
protoxylems typical. There is a cuticle, epidermis, and about 
twenty layers of stereome-cells. The inner layers of the 
cortex are thin-walled, and a small siliceous deposit occurs on 
their walls. The endodermal cells articulate with one or 
more swollen green cells lying loosely against the innermost 
layers of the cortex. The pericycle is from two to six layers 
deep in the fully developed erect shoot. There are two 
layers of sieve-tubes, absent however opposite the marginal 
protoxylems, and separated from the xylem by two to four 
layers of phloem-parenchyma. The cortex of the creeping 
stem is composed entirely of sclerenchyma, whose walls are 
deeply pitted, both lumina and pits being filled with a red 
colouring substance (PI. IX, Fig. 10). 
6. Selaginella Donglasii , Spr. Baker’s Handbook, No. 56. 
This species resembles in some respects X. Helvetica , Lk., 
but the dorsal cord soon fuses with the marginal protoxylem. 
