THE THAI.LUS OF THE HIGHER ALGM. 2$ 



color overpowers the green and gives the plant a pink tinge. 

 In other red algae it is often present in greater quantity and 

 variety of hue, so that brilliant reds and purples, with shadings 

 of brown and green, mark the more striking species. 



EXERCISE VI. 



Folysiphonia. — Place a plant in a glass dish over a black or white back- 

 ground. Observe 



1. The form of the body and the mode of branching. (Fig. 24.) 



2. The mode of attachment at the base, if specimens are entire. 



3. Demons/ration. Mount the tip of one of the branches and shovf the 

 high, dome-shaped, apical cell, with segments cut off successively from its 

 base, to be later themselves divided longitudinally. (T 32, fig. 26.) 



4. Cut a transverse section of a medium-sized axis and observe the four 

 large peripheral cells, surrounding a central cell ; the latter to be seen only 

 under compound microscope. (^ 31, fig. 25.) 



Between the very simple body ol Polysiphonia and the much 

 larger and more complex body of the common bladder-wrack, 

 or Fucus vesicuiosus, there are all gradations, which cannot 

 be described here. 



Fucus. 



34. External form. — The body of Fucus (fig. 2 7) is large 

 as compared with the plants previously described. It is often 

 75-100 cm. long by 1-2 cm. broad, of greenish-brown color 

 and somewhat leathery texture. Near the base the thalliis is 

 contracted into a stalk whose extremity is broadened into a 

 sucker-like disk (often irregularly branched) which attaches 

 the plant firmly to the wave-washed rocks, on which it grows. 

 Above, the thallus is flattened, with a thicker rib in the mid- 

 dle (fig. 28), and branches abundantly by forking. These 

 branches, though often twisted, really lie in the same plane 

 as the flattening (fig. 27). Here and there the^ thallus has 



