34 



CHLOROPHYCEAE 



light green macroscopic colonies. These are most abundant in the 

 spring when they are attached at first, although later they become 

 free-floating. The cells are embedded in the mucilage in groups of 

 four, each group often being enclosed in a separate envelope. Two 

 or four pseudocilia proceed from each cell to the surface of the main 

 colonial envelope, each thread being surrounded by a sheath of 



&-e^ 



:o-^®}^e^%r^^- ®> 



©■.- " 







-A 





^ 



^:-- 





D 



(^'■■^■, 



Fig. 24. Tetraspora. A, T. cylindrica ( x |). B, portion of colony of T. cylindrica 

 showing outer envelope ( x 155). C, T. lubrica ( x ^). D, portion of colony of 

 T. lubrica ( x 500). (After Smith.) 



denser mucilage. These structures cannot be organs of locomotion 

 because they possess no power of movement, but they may repre- 

 sent such organs which have lost their function or they may be their 

 precursors. Reproduction is either by fragmentation of the parent 

 colony or else by means of biflagellate swarmers which may develop 

 into {a) a new colony, {b) the palmelloid state or (c) a thick- walled 

 resting spore. The resting spore gives rise to an amoeboid cell on 

 germination. Sexual reproduction is secured by means of bi- 

 flagellate isogametes, the colonies being either monoecious or 



