SEA WEEDS. 
21 I 
club-mosses, cacti and other higher plants so nearly as to be 
named after them ; and in order that the one branching cell may 
sustain the strain on its walls entailed by this complexity of 
outward form, there is a mechanical support provided by “a 
system of trabeculae or narrow beams, branching and traversing 
the cell from wall to wall in all directions,” Even many expert 
botanists will make their first acquaintance with some of these 
multinucleate forms in this book. 
Among the green seaweeds we find an account given for the 
first time in any student’s manual of the microscopic floating 
algae which constitute so large a part of the marine flora. To 
the Peridimea belong the minute organisms called Ceratium, which 
cause the phosphorescent light on the surface of the sea off our 
own shores, and the species of Pyrocystis, which were observed 
during the “ Challenger ” expedition. Mr. Murray says of this : 
“ It is a tropical form, and to it was attributed the most brilliant 
displays of luminosity during the Challenger expedition.” Halo- 
sphara viridis {Protococcacecs) is a beautiful globular form, which 
floats in large quantities in the warm and temperate Atlantic and 
Mediterranean, Rhabdospheres and Coccospheres occur in 
temperate and tropical seas, and “ their broken-down parts . . . 
form a not inconsiderable part of deep-sea deposits, except 
those laid down in polar and sub-polar seas.” It is interesting 
to note the distribution of these plants. In tropical seas Rhab- 
dospheres prevail, Coccospheres are characteristic of the 
temperate seas, while round the coasts in temperate regions we 
have Peridiniecs, and these all give way to Diatomacea at the polar 
regions, where these organisms “ greatly outweigh all other 
pelagic plants.” Indeed the quantity of diatoms and of the 
minute animals that subsist on them in the polar seas is so great, 
that a distinguished traveller has declared them to be sufficient 
to sustain human life in cases of need, and that no polar expedi- 
HALOSPH.€RA VIRIDIS. 
