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Type-COMMON BLADDER WRACK. 

 FUCUS VESICULOSUS. 



This Alga may be olive-green or brownish, in 

 ccilour ; it is flat, leaf-like, cartilaginous in texture, 

 traversed by a midrib which projects on both sides, 

 and bears bladder-like swellings in pairs (one on 

 either side of the midrib) as well as singly at the 

 base of the bifurcations ; it is attached to stones by 

 a branched attachment disc. The whole plant is 

 called a Thallus because there is no differentiation 

 into root, stem, and leaf. The branches of the 

 Thallus are all in one plane, and as a rule the branch- 

 ing is dichotomous, i.e., the apex ceases to grow in the 

 original direction, and its continuation is in two new 

 directions ; the two newly -formed branches are 

 termed bifurcations, and the member which j)roduces 

 them the hase of the bifurcation. Every base can 

 only bifurcate once, but every branch may become 

 the base of a new bifurcation. Dichotomous branch- 

 ing is common to all the Algse, but in some 

 Fucacese the branching is si/mpodial. This is the 

 case when one branch develops more strongly than the 

 other, and the weak one then appears to be laterally 

 developed ; the bases of the successive bifurcations 



