] 
Fic. 36.—Bryopsis Flana- 
gant natural size. (After B. 
8. Barton.) 
SEAWEEDS 
interwoven like so many other 
multinucleate Algze. 
In the thallus of Codiwm two 
layers may be distinguished, 
though their component elements 
are all branches of the same cell. 
In the middle there is a densely 
XB interwoven mass of filaments 
which end outwards in club- 
shaped apices arranged perpen- 
dicularly to the surface. These 
club-shaped ends lie parallel to 
each other, and form a kind of 
pallisade tissue (Fig. 35). The 
spongy thallus so formed is of 
varying habit, either elongate 
and dichotomously branched (C. 
tomentosum), or in globular cush- 
ions, or flat and encrusting, with- 
out definite stalk and with very 
slightly developed rhizoids. The 
lumen of the cell is sometimes 
interrupted (apart from the 
formation of reproductive bodies) 
by plug-like thickenings of the 
membrane. 
In Derbesia, the single fila- 
ments of the thallus show no 
differentiation of frond. They 
are dichotomously but sparingly 
branched, and are rarely, but 
with no regularity, septate in 
