THE ALG^E 



127 



there are the giant Kelps (Lessonia, Nereocystis, Macrocystis, etc.) 

 as well as other genera (e.g. Egregia [Fig. 97], Postelsia) which are 

 quite unrepresented in the Atlantic. 



The plant in all of these forms is very large and shows a high 

 degree of differentiation. In Laminaria it consists of a cylindrical 

 stalk expanding above into a leaflike lamina, and attached by a 

 large rootlike holdfast. Similar to Laminaria, in general structure, 

 are Egregia (Fig. 97) and Alaria, which have in addition to the 



FIG. 98. A, Nereocystis Liitkeana, young plant, reduced; r, holdfast. B, Macro- 

 cystis pyrifera, tip of branch, showing the growing-point (X s) ; v, air- vesicles. 



single leaf-like lamina, numerous small lateral leaves growing from 

 the stem. In Egregia some of these are sporophylls, and some are 

 modified into air-vesicles. 



Lessonia and Macrocystis branch extensively, and reach a very 

 large size. Nereocystis (Fig. 98), a very conspicuous Kelp of the 

 northern Pacific, has an enormously long stem, tapering to the 

 large holdfast, and having the hollow upper portion enlarged at its 

 upper end into a globular float as big as a croquet ball. To this are 

 attached large leaves, three or four metres long. 



