36 



PLANT STRUCTURES 



produced by oceanic currents and forming the so-called 

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



Fig. 20. A portion of a brown alga (Sargassum), showing the thalhis 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 iheir reproduction. One, repre- 

 sented by the Laminarias nd 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 a. an end ; and they resemble each 

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

 form zygotes. 



