54 



PLANT LIFE. 



purples, with shadings of brown and green, mark the more 

 striking species. 



Fucus. 



From the very simple body of Polysiphonia to the common 

 bladder-wrack, or Fucus vesiculosus, there are all stages of 

 complexity, which cannot be traced here. 



41. External form. — The body of Fucus (fig. 42), is 

 large as compared with the plants previously described. It 

 is often 75-100 cm. long by 1-2 cm. broad, of greenish - 



Fig. 43. — A transverse section of the thallus of Fucus, showing midrib, r ; cortex, c ; 

 medulla, m ; and a hair-pit,/. Magnified 10 diam. — From a drawing by Mr. C. E. 

 Allen. 



brown color and cartilaginous consistency. Near the base 

 the thallus is contracted into a stalk whose extremity is 

 broadened into a sucker-like disk (often lobed) which at- 

 taches the plant firmly to the wave- 

 washed rocks on which it grows. 

 Above, the thallus is flattened, with 

 a thicker rib in the middle (fig. 

 43), and branches abundantly by 

 forking. These branches, though 

 often twisted, really lie in the same 

 place as the flattening. Here and 

 there the axis shows pairs of oval 

 f.g 44 -a longitudinal section swellings, the bladders, which, by 

 $Zl?£ e nt?lp S T*l the contained gases, give greater 



flattened sides oJ e body t/ ,ap,cal buoyancy tQ the pl ant s in the Water. 



SWrfiSW&WE 42 - A P ical cell.-An examina- 

 toiiii^ifiESdiSS! tion of the structure of the thallus 

 -After Rostafinsk,. shows a decided differentiation of 



cells, which would be expected from the large and complex 



