36 



PLANT b'i'RUCTUKES 



produced by oceanic currents and forming the so-called 

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



Fig. 20. A portion of a brown alga (Sargasmm), 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 isoganious (Fig. 18). The zoospores 

 and gametes are peculiarmTiaving 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. 



