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 dioecious 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- 



