3(5 PLANT STRUCTURES 



produced by oceanic currents and forming the so-called 

 " Sargasso seas," as that of the Xorth Atlantic. 



Fio. 20. A portion of a brown alga (Sargassum), showing the thallus differentiated 

 into stem-like and leaf -like portions, and also the bladder-like floats. After BEN- 

 NETT and MURRAY. 



30. Reproduction. The two main groups of Brown Algae 

 differ from each other in their reproduction. One, repre- 

 sented by the Laminarias and a majority of the forms, pro- 

 duces zoospores and is isogamous (Fig. 18). The zoospores 

 and gametes are peculiar in having the two cilia attached 

 at one side rather than at an end ; and they resemble each 

 other very closely, except that the gametes fuse in pairs and 

 form zygotes. 



