DIV. I 



THALLOPHYTA 



397 



addition to the swarm -spores, gametes which conjugate isogamously in pairs have 

 been observed. 



The Heterocontae form part of the Marine plankton in which a number of 

 unicellular genera (Meringosphaera, Halasphaera) occur. 



At the base of the class may 

 be placed such Flagellate -like 

 forms as Chloramoeba hetero- 

 morpha (Fig. 330), which lives in 

 fresh water. The naked, amoeboid 

 cell contains a nucleus and 2-6 

 yellowish-green chloroplasts ; at 

 the anterior end, just outside a 

 vacuole, two cilia are situated 

 which are of very unequal length. 

 It is this last feature jvhich gives 

 the name to the group. Chlora- 

 inoeba is one of those low green 

 organisms which become colour- 

 less and lose the power of inde- 

 pendent nutrition when cultivated 

 in a nutritive solution in the dark. 

 Thick -walled resting cells also 

 occur. 



Among the higher Hetero- 



FIG. 330. Cliloramoeba heteromorpha : 1, 

 green form ; 2, colourless form ; 

 v, vacuole ; k, nucleus. 3, A resting 

 cell. (After BOHLIX, from OLT- 

 MAXXS' Algae.) 



FIG. 331. Conferva bombycina. 1, Filament ; 2, 3, forma- 

 tion of transverse wall (q) in cell division ; 5, forma- 

 tion of aplanospores by breaking down of the filament ; 

 10, Zoospores with cilia of unequal length. (After 

 GAY (1, 5), BOHLIX (2, 3), LUTHER (10). From 

 OLTMAXXS' Algae.) 



contae the genus Conferva (Tribonema), which is widely spread in fresh water, 

 must be mentioned (Fig. 331). The plant consists of simple unbranched fila- 

 ments the cells of which have peculiarly-constructed walls ; the wall consists of 

 two parts separated by an oblique annular split at the middle part of the cell. 

 On cell division a new portion, H -shaped in longitudinal section, is intercalated. 

 One or two zoospores are produced from a cell of the filament. In addition to 

 zoospores thick -walled aplanospores arise by the separation by the cells of the 

 filament. 



The majority of the Heterocontae have uninucleate, only occasionally binucleate 

 cells. But there are some genera with multinucleate cells in the class, e.g. 

 Ophiocytium and Sciadium. 



