Class 3. CHLOROPHYCE^E. 



THIS group, which includes all the green Alga?, attains its 

 greatest development in fresh water, and the number of species 

 exceeds the combined total of the freshwater species of all other 

 Algae. 



The simpler forms of green Alga? are unicellular (e.g. some of 

 the Protococcoideae and Desmidiacese), some are coenocytic (e.g. 

 Yaucherfacea3, Sphasropleacese, Pediastrea?), some are incompletely 

 septate (e.g. Cladophoracea?), and others are multicellular or com- 

 pletely septate (e.g. CEdogoniales, Chtetophorales, Zygnemacese). 

 In other than the unicellular forms the thallus exhibits every 

 degree of development from simple rounded cells to long, simple 

 or branched filaments, flat expansions, or pulvinate masses of 

 tissue. As a rule there is no differentiation of the ordinary vegeta- 

 tive cells, but in some there is a marked distinction between the 

 vegetative and reproductive cells. 



The cell-protoplasm (or cytoplasm} of the green Alga 1 consists of 

 a lining layer or ' primordial utricle ' which adheres closely to the 

 cell- wall 1 , and, in many Alga?, of additional anastomosing strands and 

 threads traversing the interior of the cell. It contains numerous 

 granules of variable size which behave differently with staining 

 reagents. Evidence goes to prove that there is no definite proto- 

 plasmic continuity between the cells of multicellular green Algae. 

 A division of labour is rarely observed amongst this class of plants, 

 and in the Conjugata? the cells of most of the filamentous forms 

 arc under normal circumstances quite able to lead an independent 

 existence. The vacuoles are much as in other plant-cells and they 

 contain a fluid usually known as the cell-sap. In the Conjugate 

 the cell-sap is occasionally coloured violet or purple owing to the 



1 Cf. Chodat et Boubier, ' Sur la Plasmolyse et la membrane plasmique,' 

 Journ. Bot. de Morot, Paris, 1898. 



