INTRODUCTION. XVll 



frond on each side of the midrib. The Sargassum 

 bacciferiim derives its specific name lacciferum from 

 the abundance and form of the air-vessels, which 

 are currant-shaped and borne on short stalks ; and 

 takes its French popular appellation of JRaisin cles 

 Tropiques from the same cause. None of the 

 British species of the Laminariaceae bear air-vessels, 

 but exotic members of the order are often furnished 

 with them of large size. The Nereocystis, a spe- 

 cies vegetating" on the shores of the North Pacific, 

 with a slender stem upwards of 300 feet long-, bears 

 at its extremity a large air-vessel shaped like a 

 barrel, six or seven feet in length, crowned with a 

 tuft of upwards of fifty forked leaves, each thirty 

 to forty feet long : upon this. Dr. Henry Mertens 

 tells us, the sea-otter has its favourite lair — resting 

 himself on the vesicle, or hiding among the leaves 

 while he pursues his fishing. 



The geographical distribution of our marine 

 Flora, has been separated into distinct zones or 

 belts by writers on the subject. We have first the 

 Fucal or Littoral zone, comprising the space laid 



