20 GREEN SLIME. 



when they in turn divide into two, but usually by a par- 

 tition at right angles to the last one, and so on. The cells 

 thus formed either soon become separated, or remain 

 mechanically united. 



Another method of establishing new plants is by the 

 production of zoospores. The protoplasm, either as a 

 whole or divided into several parts, escapes from the cell- 

 wall. Each mass pushes out a pair of delicate filaments 

 or cilia, which, moving rapidly back and forth, propel the 

 naked protoplasm through the water. The motion and 

 form being animal-like suggested the name. After a 

 period of activity the zoospores come to rest, draw in or 

 drop off the cilia, secrete a cell- wall, and become ordinary 

 non-motile Pleurococcus cells. In some plants the proto- 

 plasm does not escape from the cell-wall, but contracts 

 somewhat, cilia are protruded through openings in the 

 wall, and the cell or colony is propelled about. The pro- 

 duction of zoospores at a specified time, as for a class 

 demonstration, is attended with so much uncertainty that 

 their study has been omitted from the laboratory work. 

 This method of asexual multiplication will be studied later 

 under more favorable conditions in other plants. 



