THE ALG^E. Ill 



Fucacece. In the former the swarm spores are of the same 

 size and form, though it is believed that some are asexual 

 propagative cells and others are sexual cells or gametes, 

 which conjugate. In the Fucaceae the male elements are 

 minute antherozoids, each provided with a pair of cilia; 

 the female elements are comparatively large oospheres 

 not provided with cilia. 



In some cases there is a distinct alternation of genera- 

 tions ; in others there is none or it is doubtful. 



The Phaeosporeae. The Kelp and Laminaria of the 

 seashore are well-known plants, many of them showing a 

 considerable degree of differentiation. The differentia- 

 tion of structure is shown- in the stemlike stalk and in 

 rootlike appendages that enable it to cling to some fixed 

 support. In the Pacific and South Atlantic oceans, a 

 giant kelp is found, of 800 or 900 feet in length. 



Zoospores provided with two flagella each are known ta 

 be formed in some of the cells, but the union of the 

 zoospores to form zygospores from which new plants can 

 develop has been observed in only a few cases. 



The Fucaceae or Rockweeds. These plants are all 

 inhabitants of the salt water. The ordinary Rockweeds 

 are types. They grow attached to the rocks by a disk- 

 like expansion of the root ends, so to speak. The stem 

 divides and develops into expanded portions which resem- 

 ble leaves, being flat, and possessing an enlargement like 

 a midrib. The plants have at intervals air sacs, which are 

 evidently nature's provision for buoying them up. 



The only approach to asexual reproduction in Rock- 

 weeds is. the formation of little shoots on the edges of the 

 larger branches. It is possible that these separate from 

 the parent plant and grow into new plants ; this, however, 

 is not established, and asexual reproduction is not posi- 

 tively known to occur. The alternation of generations is 

 therefore unknown. 



