STRUCTURE AND SUBSTANCE. 13 



digious length, instead of being spread along the bottom, as 

 otherwise they would be, are in part floated on the surface 

 by means of the numerous air-vessels they contain. A por- 

 tion of one of these gigantic sea-plants, said to be at times 

 1,500 feet in length, is now in my possession. A section of 

 it is so full of vesicles that it looks like a honeycomb, or 

 like a piece of wood perforated by that indefatigable borer, 

 Xylojiliaga dor sails. 



