UTILITY OF SEAWEEDS 77 



Altogether different from the microscopic flora of the 

 plankton is the noted Gulf Weed (Sargassum bacciferum), 

 which is found floating in great masses in the tropical 

 and subtropical seas of both hemispheres. It forms 

 ridges 30 to 60 feet wide, and of indefinite length. 

 Columbus mentioned this Alga as having delayed his 

 ships, and the celebrated Humboldt described it. The 

 thallus consists of a branched stem, bearing leaf-like 

 expansions, serrated on their margin. The plant is 

 buoyed up by a number of small, round air-vessels, 

 usually tipped with spine-like projections. It seems 

 that this Alga has for ages formed the " Sargasso Sea," 

 and it is probable that its increase is due entirely to 

 vegetative budding. 



Seaweeds have long been used by man as food and in 

 other connections. Irish Moss, or Carragheen (Chondrus 

 crisfus) and Dulse (Rhodymema falmata) are eaten. 

 Ceylon Moss (Gracilaria lichenoides), found in Eastern 

 seas, furnishes the well-known Agar-Agar used by 

 bacteriologists as a culture medium, and the Japanese 

 and Chinese in the manufacture of sweetmeats. Some 

 species of Seaweeds are cultivated for industrial purposes 

 in China and Japan. The Kelp industry was at one 

 time an important asset in Britain; it is still of some 

 small value in connection with the manufacture of 

 iodine, but I am led to understand that most of the 

 Kelp used in this direction is now imported. 



The structure and development of Green Algse have 

 received a fair share of attention in the previous chapter, 

 and in what follows in this connection we shall confine 

 ourselves to the Brown and Red Seaweeds. 



Within the ranks of the Ph^ophyce^, or Brown Sea- 



