REVIEW OF THE GREEN ALGM 229 



REVIEW OF THE GREEN ALG^E. 



370 Importance of studying the green algae. There are 

 several important reasons for studying even a few members of the 

 green algae. First. They are generally of simple structure, either 

 single-celled or filamentous, and serve as excellent objects, easily 

 prepared, for microscopic study of the cell and its contents, the 

 processes of absorption, plasmolysis, etc. Second. The sexual 

 organs and methods of reproduction are simple and easily studied. 

 Third/ It is believed that some members of the green algae, exist- 

 ing perhaps ages ago, were the ancestors of the higher green plants. 

 It is therefore of interest to study a few types to see how the green 

 algae themselves are organized, and show among themselves dif- 

 ferent stages in this process of evolution from simple organisms 

 consisting of a single cell to the more complex ones where cells 

 are united into threads, cell plates and cell masses. 



371. Increase in the complexity of the plant body. The 

 simplest condition of the plant body is found in such plants as the 

 red snow plant (H&matococcus). The plant is a single cell. It 

 multiplies by division into two plants which are associated in the 

 parent envelope but a short while, when they escape and become 

 independent. In such a plant as Pleurococcus the cells are 

 united for a longer period during multiplication, while in the 

 colony algae like Pandorina, and the water-net, the individuals 

 are permanently united in a loose association. Most of the 

 desmids are single-celled plants, but other members of the 

 conjugating algae are filamentous. They are, however, really 

 colony algae, since each cell of the thread is identical in structure, 

 and potentially identical in function; each cell is capable of 

 division and growth, growth not yet being localized at any definite 

 growing point, or area. In the filamentous algae (Confervoideae), 

 however, while the cells are nearly all alike, growth is localized, 

 either at the tips of the threads and branches, as in Cladophora 

 and Chcztophora, or in definite cells at any point in the thread, 

 as in (Edogonium. Many of the filamentous forms are branched. 

 This produces a more complex plant body. In some forms the 



