Chap. II] 



MARINE VEGETATION 



805 



Each of the two zones is subdivided into a series of provinces, the differ- 

 ences in which only partially depend on conditions now prevailing (salinity, 

 temperature, light). Schlitt distinguishes the following more or less dis- 

 tinctly defined provinces of the seas explored by the Plankton Expedition : 



Fig. 496. Plankton-species of Ceratium (Peridinieae). a-f Warm-water forms, g-k Cold-water 

 forms, g Ceratium tripos tergestinum. h C. tripos balticum. Magnified 125. After F. Schiitt. 



Baltic (sharply defined), North Sea (less isolated), north-eastern Gulf Stream, 

 Irminger current, East Greenland current, West Greenland current, Labrador 

 current, Florida current, North-equatorial current, Guinea current, South- 

 equatorial current. All these provinces are characterized by predominant 

 forms (see Fig. 496). 



