CHAPTER FORTY-TWO 



THE ALG^ 



There is a large assemblage of chlorophyll-bearing plants 

 usually small and comparatively simple in structure, known as 

 algcB (singular, alga). Some species are unicellular and micro- 

 scopic, with cells so simple in structure that they are comparable 

 to those of bacteria ; other species are multicellular, filamentous 

 colonies, often branched and attaining lengths of several inches ; 

 a few species have thick, leathery, vegetative bodies, composed 

 of several distinct tissues and varying from a foot to many feet 

 in length. The algae are of peculiar interest in showing various 

 methods by which complex plants may be derived from simpler 

 forms. 



The algae include many diverse types of plants which are 

 grouped together because their vegetative and reproductive 

 structures are simple when compared with other groups of 

 chlorophyll-bearing plants. All algae reproduce by cell division, 

 and usually also by spores. 



Classification of algae. For convenience of description the 

 more important algae may be divided into five groups, four of 

 whose common names are suggested by the characteristic color 

 of the plants in each group. The classification, however, is 

 based upon more fundamental characters than color; namely, 

 (i) the structure of cells, or vegetative body; (2) the reproduc- 

 tive structures; and (3) the life history, or the series of events 

 that occur in the life of the plant, beginning with the germination 

 of a spore and ending with the formation of similar spores. 



THE BLUE- GREEN ALG^ OR MYXOPHYCE^ 



These are the simplest known autophytes. A majority of the 

 plants contain a water-soluble blue pigment in addition to the 

 chlorophyll. Both this pigment and the chlorophyll are dis- 

 persed in the protoplasm and are not in definitely organized 



441 



