THE ALG^E. 71 



The principal classes are: 



CLASS I. THE GREEN ALG^E (Chlorophycece). 

 CLASS II. THE BROWN ALG^E (Phceophycece). 

 CLASS III. THE RED ALG^E (Rhodophycece or Floridece). 



CLASS I. The Green Algae (Chlorophycece). Simplicity 

 in the cell structure of the thallus is a characteristic of 

 the Green Algse. The position of the cilia at the ex- 

 treme tip of the zoospores is a further characteristic. The 

 plants are either single cells, filaments of cells, or super- 

 ficial cell surfaces, approaching the structure of solid cell 

 aggregates in the Stoneworts. The color is a pure green 

 except in some resting spores and in the reproductive 

 branches of the Stoneworts, which become red, brown, 

 or black by the formation of decomposition products in 

 the chlorophyl. 



There is in many cases an alternation of generations 

 from sporophyte to gametophyte. The asexual multipli- 

 cation is in some cases by the simple fission of cells; in 

 others by the formation of ciliated zoospores ; in some 

 cases no asexual multiplication is known to occur. The 

 sexual multiplication is in some plants by the union of two 

 cells that are apparently just alike. When union takes 

 place between cells of the same form, it is said to be isoga- 

 mous. This union is called conjugation ; the cell that 

 results is called a zygospore. In other plants the sexual 

 multiplication is by the union of one cell with another of 

 quite different appearance. The male gamete is called an 

 antherozoid or spermatozoid ; the female gamete, an oo sphere. 

 The cell which results from this union is called an oospore, 

 and the union is said to be heterogamous or oogamous. 



The subdivisions of the Green Algse are the Siphonece 

 or Cceloblastce, Volvocinew, Protococcacece, and Confervoi- 

 dece. The Conjugate and Characece are considered to be 

 forms collateral with the Confervoideae. 



