36 



PLANT STEDCTUEES 



produced by oceanic currents and forming the so-called 

 isso seas," as that of the IS'orth Atlantic. 



Fig. 20. A portion of p brown alga {Sargassum), showing the thallus differentiated 

 into .stem-like and leaf -like portion.^, and also the bladder-like floats.— After Ben- 

 nett and iWuRKAx. 



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. 



