200 



FUCUS (THALLUS) 



The Seaweed Macrocystis, which is a close ally of Laminaria 

 and particularly common in the Southern Hemisphere, attains 

 to enormous dimensions, often measuring as much as 400 feet 

 from end to end. 



Another large Brown Alga is the common Bladder Wrack 

 (Fucus vesiculosus, Fig. 108), which, however, is found on rocks 

 between low and high tide-levels, so that it is uncovered for several 

 hours at a time (Fig. 107). An entire plant often attains a length 



FIG. 107. Photograph of Fucus vesiculosus on rocks between 

 tide-levels. [Photo : E. J. S.] 



of from one and a half to three feet, and exhibits three regions 

 similar to those of Laminaria, but the stalk is short and the frond 

 repeatedly forked (Fig. 108). Each portion possesses an obvious 

 midrib (m.), which is thicker and more pronounced in the older 

 parts where it gradually passes over into the stalk. The latter 

 is indeed nothing else than the persistent midrib of the first- 

 formed part of the thallus. The holdfast is similar to that of 

 Laminaria. 



rocks get carried out to sea. This may sometimes take place on a con- 

 siderable scale. 



