LOWER PLANTS 



153 



some Chlorophyta; stipes generally cylindrical, round 

 or flattened, solid or hollow, simple or branched, 

 erect structures; stipe branching and tree-like to 

 feather- or fern-like; blades generally thin, tongue- 

 like, leaf-like, disc-like, or membranous; blades nor- 

 mally arising all along stipe, sometimes only from the 

 top (one such form looks vaguely palm-like); hold- 

 fasts typically a mass of cylindrical, often partially 

 at least fused, structures that attach the plant to the 

 substrate; very simple tissues are present (Figure 9.3). 

 Cells: mostly complete and in contact with one 

 another, but often with some open spaces between 

 parts of adjacent cells; nucleus complex and com- 

 plete; cytoplasm pigments in plastids; nonreproduc- 



tive cells usually contain many small vacuoles, rarely 

 a single large one; cell walls generally present and of 

 two layers (outer gelatinous layer commonly of a 

 substance called algin, inner firm layer largely cellu- 

 lose); flagellae limited to motile reproductive cells, 

 regularly two and dissimilar. 



Tissues: one type, parenchyma, characterized by 

 the presence of relatively unspecialized cells; brown 

 algae parenchyma lacks the intercellular spaces and 

 central vacuoles of land plant parenchyma; paren- 

 chyma cells are found throughout the plant; in some 

 forms there are crudely organized phloem cells, the 

 basic units for one of the tissues, phloem, that forms 

 the vessels of vascular plants. 



\M:!yV. 



most green algae growth 

 Is duplicated 



hairy branched tubular 



flat blade; 

 rounded 

 stipe and 

 holdfast 



blades with floats 



rockweed segment 



Figure 9.3 Representative brown algae. Brown algae types include species that run the gamut of 

 green algae growth forms. Most brown algae grow very large. 



