PHAZOPHYCEA 113 
of being able to renew the apical cell after the 
original one has perished. This property is akin 
to another exhibited by the branches which bear 
the gemme and sporangia. After the fall of a 
gemma, the remaining basal cells of the branch that 
bore it may proceed to grow and form another one. 
Similarly after the emptying of a sporangium, the 
branch may grow through the membrane and form 
a new sporangium. 
The branches are cither all of equal morphological 
value or there may be a distinction between 
long and short ones. The latter are alternate in 
Stypocaulon and Halopteris, opposite in Chetopteris, 
and in whorls in Cladostephus. They are either 
themselves unbranched (Stypocaulon and Chetopteris), 
or branched on one side (Cladostephus), or they re- 
semble in miniature the branching of the long 
branches (Halopteris). In Stypocaulon, Cladostephus, 
and not so markedly in Halopteris, the outermost 
cells of the filaments of the thallus undergo farther 
division and produce a cortical tissue of small cells 
which obscures the articulation of the original thallus. 
In Sphacelaria and Chetopteris this articulation of 
tiers of cells remains apparent throughout the life of 
the plants. A farther modification takes place in 
Cladostephus, Stypocaulon, Halopteris, and some 
species of Sphacelaria by the outgrowth of rhizoid 
filaments from the older parts of the shoots. These 
filaments grow downwards, creeping over the thallus, 
and form a kind of mantle over the lower parts of 
the shoots. 
Some of the Sphacelariacee are subject to the 
T 
