34 



PLANT LIFE. 



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

 striking species. 



Fucus. 



l''rom the very simple Ijody 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- 



FlG, 43. — A transverse section of the thalkis of Fucus, showing midrib, 7- ; cortex, c ; 

 medulla, ;// ■ 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 alumdantly by 

 forking. These branches, though 

 often twisted, really lie in the same 

 place as the flattening. Here and 

 there the axis shows [lairs of oval 

 Fig. 44.-A longitudinal section swcllings, the bladders, which, by 



through tile apical meristem of ,, +„■„ i ■ . 



Fucus, at right angles to the the coiitainctl gases, give greater 



flattened sides of body, c, apical -i,„ 4.,.l i ^-.i 



cell; 3, 2, I, segments succes- buoyancy to the plants in the Water. 



sively cut off from c by its divi- An a.«;««1 „„n \ 



sion; 3, being the oldest, has "ti- ApiCai Ceil. An examuia- 



already become divided into ,■ c t-\ i ^ r .1 1 n 



three cells. Magnified 200 diam. tiOHOt the Structure of the thallus 



— After Rostaiinski. 1 j ■ j j i ■ rr ■ ■ r 



shows a decided dillcrcnlialion of 

 cells, which would be expected from the large and complex 



