252 



PLANT STUDIES 



produced by oceanic currents and forming the so-called 

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



Fig. 220. 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. 



171. Reproduction. — The two main groups of Brown 

 Algae differ from each other in their reproduction. One, 

 represented by the Laminarias and a majority of the forms, 

 produces zoospores and is isogamous (Fig. 217). The zoo- 

 spores and gametes are peculiar in having the two cilia 

 attached at one side rather than at an end ; and they re- 

 semble each other very closely, except that the gametes 

 fuse in pairs and form zygotes. 



