CRYPTOGAMS 



367 



The Fucaceae, although relatively large, do not compare with the Larninari- 

 aceae in size. As examples of well-known forms of this order may be cited Fucus 

 vesiculosus, which has a ribbon-shaped, dichotomously branching thallus with air- 



FIG. 302. Fucus serratus. To the left the end of an older branch bearing conceptacles. (J nat. size.) 



bladders, Fucus platycarpus without bladders, and Fucus serratus (Fig. 302). They 

 are fastened to the substratum by discoid holdfasts, and growing sometimes over 

 1 metre long, are found covering extended areas of the littoral region of the sea- 

 coast. Sargassum, a related genus chiefly inhabiting tropical oceans, surpasses 



