128 SEAWEEDS 
multinucleate plants. The species occur not only in 
the sea, but even more plentifully in fresh water and 
in places that are merely damp. The description of 
the natural order below is based on its general 
characters, and is inclusive of those derived from 
fresh-water species. 
The Thallus is simply a multinucleate filament, 
irregularly or dichotomously branched, and without 
farther differentiation. It forms much-branched, 
colourless holdfasts. The cell-wall is thin and the 
nuclei abundant in the protoplasm lining the walls. 
Sometimes crystals of oxalate of lime occur in the 
cell-sap. The chromatophores are oval and without 
a pyrenoid. Cross-walls occur only in connection 
with reproductive processes. 
The Reproductive Organs——The oogonia and anthe- 
ridia are usually lateral outgrowths from a filament 
and occur side by side, though dicecious forms are 
known. The oogonia arise as round protuberances 
with a broad base, and gradually become more or less 
ovate and eventually cut off by a cross-wall at the 
base. The apex is generally papillate and the 
protoplasm becomes colourless here, and in this 
respect unlike the rest of the contents, which are 
coarsely granular and green, especially in the centre. 
The wall opens at the apex, and while the contents 
show a slight contraction, there is protruded a drop- 
like portion of a mucilaginous appearance. While 
this development is in progress the antheridium 
arises from the same filament as the oogonium and 
very near it. It is tubular in shape, and though 
sometimes straight is generally curved, and its cross- 
