PH ZOPHYCEA 115 
on the British coasts; Sphacella in the Mediter- 
ranean; Phloiocaulon, Anisocladus, and Ptilopogon in 
the Southern Ocean. Sphacelaria is represented in 
all seas. 
CHORISTOCARPACES. 
General Characters.—The thallus is filamentous, 
consisting of a single row of cells, and possesses an 
apical cell by which it grows in length. The repro- 
ductive organs, both unilocular and plurilocular spor- 
angia, arise as lateral outgrowths of the filaments, 
as do also the vegetative gemme. 
The Thallus is in all cases filamentous and 
branched—never of more than one cell-row. The 
apical cell produces all the cells—ze, there is no 
intercalary growth whatever. 
The Reproductive Organs.—The plurilocular sporan- 
gia of Discosporangiwm form a remarkable rectangular 
plate one layer thick, arising laterally from a slight 
outward bulging of the wall of one of the cells of the 
thallus. The loculi open outwards. In Choristo- 
carpus the corresponding bodies more nearly approach 
those of Ectocarpacece. In Plewrocladia (a fresh-water 
form placed here) the plurilocular sporangia also 
resemble those of Hetocarpacec, and this genus further 
possesses unilocular sporangia (not known in Disco- 
sporangium and Choristocarpus) of similar type. 
The gemme are known only in Choristocarpus and 
are lateral outgrowths of two, rarely three, cells, the 
upper being the larger. After they are shed the 
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