THE ALG.E. 



89 



The asexual reproduction is by the successive division 

 and redivision of the cells in particular directions. In 

 outward appearance the plant resembles the higher Flower- 

 ing Plants, but a more minute examination reveals only 

 the simplest structure of aggregations of cells produced by 

 cell division. There is wanting entirely anything like 

 differentiation of the cells to form tissues of different 

 kinds. The cells are held in posi- 

 tion by an investing membrane, but 

 this membrane bears little resem- 

 blance to the epidermis of the higher 

 plants. Again, the different parts 

 of the plant differ as little in func- 

 tion as in form, any part being capa- 

 ble of reproducing the plant. 



The sexual reproduction begins 

 by the division of the endochrome, 

 or colored contents, of some of the 

 cells into many portions. These 

 portions become motile, the cell wall breaks down, and 

 zoospores, which are provided with two or four flagella, 

 swim out into the water. The zoospores are of two sizes. 

 The larger ones, those having four flagella, are called mega- 

 zoospores ; the smaller ones are microzoospores. These 

 spores resemble very closely the motile forms of Proto- 

 coccus. 



The megazoospores cling to some supporting object and 

 develop asexually by cell division into plants; the micro- 

 zoospores unite in pairs and form zygospores. The 

 zygospores grow into new plants. The zygospore repre- 

 sents the sporophyte; the ordinary form is the gameto- 

 phyte ; the megaspores are gonidia. 1 



1 These spores are easily obtained by allowing some of the Sea Lettuce 

 to go to decay in a jar of sea water. Arrange Practical Studies of Sea 

 Lettuce. 



FIG. 47. Sea Lettuce. 

 The individual cells are 

 shown held together 

 hy the investing mem- 

 brane. 



