THE GKEAT Gli(.)UPS OF AUiM 



'2rA. 



feet long, M'liose stalk develops root-like holdfasts (Fig. 218). 

 The largest body is developed by tin Antarctic Lk miliaria 

 form, which rises to the surface from a sloping bottom with 

 a floating thallus six hundred to nine hundred feet long. 

 Other forms rise from the sea bottom like trees, with 

 thick trunks, numerous brandies, and leaf-like ai^peudages. 



The common Fiiriis, 

 or " rock weed," is rib- 

 bon-form and constantly 

 branches by forking at 

 the tip (Fig. 219). This 

 method of branching is 

 called dicliotoiiwus, as dis- 

 tinct from that in which 

 branches are put out 

 from the sides of the axis 

 {)i!ijjio])(idi(iI). The swol- 

 len air-bladders distrib- 

 uted throughout the body 

 are very conspicuous. 



The most dilfereuti- 

 ated thallus is that of 

 Sargas.sum (Fig. 220), or 

 " gulf weed," in which 

 there are slender branch- 

 ing stem-like axes bearing 

 lateral memlDcrs of various 

 kinds, some of them like 

 ordinary foliage leaves ; 

 others are floats or air- 

 bladders, which sometimes 



resemble clusters of berries ; and other branches bear the 

 sex organs. All of these structures are but different regions 

 of a branching thallus. Sargassian forms are often torn 

 from their anchorage by the waves and carried away from 

 the coast by currents, collecting in the great sea eddies 



Fig. :?10. Fragment of a common brown 

 aiga iFi'cusi, sliownig rho bodj- with 

 rlicbotomons branching and bladder-like 



air-bladders. — After Luerssen. 



