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-Jike 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. 
