156 Gibson. — Contributions towards a Knowledge 
formed, as in .S'. Martensii , out of the fused adjacent marginal 
protoxylems of branch and axis. The pericycle is two to 
three layers deep. The trabeculae are similar to those in 
6'. Martensii. The sieve-tubes are two layers deep save 
opposite the marginal protoxylems, where there is only one 
(occasionally interrupted) layer. The sieve-tubes are separated 
from the xylem by two to three layers of phloem-parenchyma 
(PI. IX, Fig. 11). 
9. Sclaginella Karsteniana , A. Br. Baker’s Handbook, 
No. 332. 
The anatomical and histological structure of the stem of 
this species is almost identical with that of X. haematodes , 
and does not therefore require special description. A deposit 
of silica occurs on the inner cortex. 
10. Selaginella plumosa, Bak. Baker’s Handbook, No. 65. 
The arrangement of the protoxylems is on the normal 
plan. The pericycle is two to three layers deep, enclosing 
one layer of sieve-tubes absent opposite the marginal proto- 
xylems. Two to four layers of parenchyma enclose the 
xylem. The endodermal cells arise from single cells of the 
pericycle, and end in clusters of cells lying against the inner 
cortex. 
Dangeard figures the course of the protoxylem strands in 
X. monospora. X. monospora is, according to Baker, a variety 
of X. plumosa. Dangeard makes the inner marginal proto- 
xylem of the branch unite with the outer marginal protoxylem, 
the adjacent marginal protoxylem of the chief axis alone 
forming the dorsal protoxylem-cord of the stele. I have not 
had an opportunity of examining X. plumosa , var. monospora , 
and so can only say that in S. plumosa itself the arrange- 
ment of the protoxylems is on the Martensii plan. 
11. Selaginella suberosa , Spr. Baker’s Handbook, No. 318. 
The protoxylems are arranged on the X. Martensii plan. 
There is a distinct epidermis followed by two or more layers 
of stereome. The cortex consists of large cells, and there is 
a deposit of silica on the innermost layer. The endodermal 
cells are short and articulate with several swollen cells which 
