INTRODUCTION TO CRYPTOGAMIC BOTANY. 227 



place which systematists have agreed to assign them, com- 

 bining at once external perfection, with decided sexual dis- 

 tinctions, either in the same or in different individuals. In 

 some cases they attain the stature even of the more gigantic 

 of the seaweeds. They constitute a great portion of the shore- 

 weeds of our seas and estuaries, and in tropical climes form 

 floating beds many miles in extent. While, however, they are 

 so abundant on the European coasts, they are comparatively 

 rare on those of America, the only really common species 

 being Fucus vesiculosus and nodosus. 



212. A large portion are essentially plants of shallow waters, 

 either exposed at every tide, or uncovered only at spring tides. 

 Fucus ccmaliculatus occurs principally about high water- 

 mark and often becomes dry, reviving again and again on im- 

 mersion. A few CystoseircB belong to deeper water ; but the 

 common Halidrya is of similar habits with such species as 

 Fucus serratus. The gulf-weed by its floating habit is 

 intermediate between these and more essentially tropical 

 species. 



2] 3. The great bank of SargassuTn hacciferum, extending 

 between 20 and 25° N. lat., in 40 W. long., occupies the same 

 position as it did in the times of the earliest navigators, and 

 between this and the American shores are various detached 

 tracts, influenced as to situation by local currents. The same 

 individual continually produces new branches and leaves, and 

 thus multiplies the species. Such specimens never produce 

 fruit ; but whether they receive fresh accessories from plants 

 produced on rocks, is at present uncertain. The fact of these 

 floating masses being barren, is strictly analogous to that of 

 Macroeystis, producing fruit only on young attached speci- 

 mens. In both cases multiplication is so rapid .in the floating 

 beds as to render fruit needless ; and even the common 

 Fucus vesiculosus occurs in the Mediterranean under a 

 peculiar form, consisting entirely of specimens derived from 

 sea-bom weed, carried in by the current which sets in towards 

 the Mediterranean from the Atlantic. 



214. There is a curious fact, with respect to the geogra- 

 phical distribution of Gystoseirce, as remarked by Dr. Hooker, 

 15 * 



